JP7718548B2 - Diester Compounds - Google Patents

Description

The present invention relates to a diester compound. It also relates to a resin crosslinking agent, a resin composition, a resin sheet, a prepreg, a cured product, a semiconductor chip package, a printed wiring board, and a semiconductor device obtained using the diester compound.

Resin compositions containing cross-linkable resins such as epoxy resins and their cross-linking agents (curing agents) produce cured products with excellent insulation, heat resistance, and adhesion, and have therefore been widely used as materials for electronic components such as semiconductor packages and printed wiring boards.

On the other hand, with high-speed communications such as fifth-generation mobile communications systems (5G), transmission loss becomes an issue when operating in high-frequency environments. This necessitates insulating materials with excellent dielectric properties (low dielectric constant, low dielectric dissipation factor). Furthermore, as electronic devices become increasingly smaller, more highly integrated, and more multifunctional, the number of pins is increasing, leading to smaller bump diameters, narrower pitches, and narrower gaps. This makes the flow path of the encapsulant during encapsulation molding more complex, requiring semiconductor encapsulants to have even better fluidity, and lower viscosity crosslinkers are also required.

As an example of a resin material with excellent dielectric properties, Patent Document 1 discloses an active ester resin, which is a reaction product of aromatic diacid chlorides and aromatic hydroxy compounds, as a crosslinking agent for epoxy resins.

International Publication No. 2018/235424

The active ester resin described in Patent Document 1 has superior dielectric properties compared to conventional phenolic crosslinking agents, but there is room for improvement in terms of lowering viscosity, and the fluidity of resin compositions containing the active ester resin and a crosslinkable resin is not at a satisfactory level.

In addition, resin compositions with a high inorganic filler content may be used to obtain a cured product with a low dielectric loss tangent, to improve heat resistance and moisture resistance after encapsulation molding, to achieve low warpage when encapsulating large areas such as wafer-level packaging (WLP), and to achieve good heat dissipation in high-heat-generating devices such as power semiconductors. However, in such cases, the fluidity at molding temperatures deteriorates, and problems such as the occurrence of flow marks and unfilled areas are likely to occur.

The objective of the present invention is to provide a low-viscosity diester compound that, when combined with a crosslinkable resin, produces a resin composition exhibiting excellent fluidity.

Conventionally, when an ester compound is used as a crosslinking agent for a crosslinkable resin, it has been thought that in order to exhibit crosslinking properties, the ester compound must have an ester bond with an aromatic carbon-ester bond-aromatic carbon structure, as described in Patent Document 1. However, after extensive research, the inventors discovered that even in an aliphatic carbon-ester bond-aromatic carbon structure, crosslinking properties can be exhibited for ester bonds with an aliphatic carbon-C(=O)-O-aromatic carbon structure. In the course of further research into diester compounds with such an aliphatic carbon-C(=O)-O-aromatic carbon structure, they discovered that a diester compound with the following structure could solve the above-mentioned problems, leading to the completion of the present invention.

That is, the present invention includes the following.
[1] A diester compound represented by the following formula (X):
(In the formula,
X _core represents a divalent aliphatic group;
X ¹ _end and X ² _end each independently represent an aromatic ring which may have a substituent, and at least one of X ¹ _end and X ² _end is an aromatic ring having one or more substituents selected from an unsaturated aliphatic hydrocarbon group, a halogen atom, an alkyl group, and an aryl group.
[2] The diester compound according to [1], wherein the divalent aliphatic group in X _core has 6 or more carbon atoms.
[3] The diester compound according to [1] or [2], wherein in X _core , the divalent aliphatic group is an alkylene group.
[4] The diester compound according to any one of [1] to [3], wherein both X ¹ _end and X ² _end are aromatic rings having an unsaturated aliphatic hydrocarbon group as a substituent.
[5] The diester compound according to any one of [1] to [4], wherein the unsaturated aliphatic hydrocarbon group in X ¹ _end and X ² _end is an allyl group.
[6] The diester compound according to any one of [1] to [5], wherein the aromatic ring in X ¹ _end and X ² _end is an aromatic carbocyclic ring having 6 to 14 carbon atoms.
[7] The diester compound according to any one of [1] to [6], which is liquid at 25°C.
[8] The diester compound according to any one of [1] to [7], which has a viscosity at 25°C of 300 mPa·s or less.
[9] A resin crosslinking agent containing a diester compound represented by the following formula (X):
(In the formula,
X _core represents a divalent aliphatic group;
X ¹ _end and X ² _end each independently represent an aromatic ring which may have a substituent.
[10] The resin crosslinking agent according to [9], wherein the diester compound is the diester compound according to any one of [1] to [8].
[11] A resin composition comprising a diester compound (X) and a crosslinkable resin (Y),
A resin composition, wherein the diester compound (X) is represented by the following formula (X):
(In the formula,
X _core represents a divalent aliphatic group;
X ¹ _end and X ² _end each independently represent an aromatic ring which may have a substituent.
[12] The resin composition according to [11], wherein the diester compound (X) is the diester compound according to any one of [1] to [8].
[13] The resin composition according to [11] or [12], wherein the crosslinkable resin (Y) is at least one selected from the group consisting of a thermosetting resin and a radical polymerizable resin.
[14] The resin composition according to any one of [11] to [13], further comprising an inorganic filler.
[15] The resin composition according to any one of [11] to [14], further comprising an organic solvent.
[16] The resin composition according to any one of [11] to [15], which is for semiconductor encapsulation.
[17] The resin composition according to any one of [11] to [15], which is for use in an insulating layer of a printed wiring board.
[18] A resin sheet comprising a support and a layer of the resin composition according to any one of [11] to [17] provided on the support.
[19] A prepreg obtained by impregnating a sheet-like fiber substrate with the resin composition according to any one of [11] to [17].
[20] A cured product of the resin composition according to any one of [11] to [17].
[21] A semiconductor chip package comprising an encapsulating layer made of a cured product of the resin composition according to any one of [11] to [16].
[22] The semiconductor chip package according to [21], which is a fan-out type package.
[23] A printed wiring board comprising an insulating layer made of a cured product of the resin composition according to any one of [11] to [15] and [17].
[24] A semiconductor device comprising the semiconductor chip package according to [21] or [22] or the printed wiring board according to [23].

The present invention provides a low-viscosity diester compound that, when combined with a crosslinkable resin, produces a resin composition exhibiting excellent fluidity.

The diester compound of the present invention can produce a resin composition that exhibits good fluidity at molding temperatures, even when the inorganic filler content is high.

FIG. 1a shows a GPC chart of the diester compound (A) in Example 1. FIG. 1b shows an IR chart of the diester compound (A) in Example 1. FIG. 2a shows a GPC chart of the diester compound (B) in Example 2. FIG. 2b shows an IR chart of the diester compound (B) in Example 2. FIG. 3a shows a GPC chart of the diester compound (C) in Example 3. FIG. 3b shows an IR chart of the diester compound (C) in Example 3. FIG. 4a shows a GPC chart of the diester compound (D) in Example 4. FIG. 4b shows an IR chart of the diester compound (D) in Example 4. FIG. 5a shows a GPC chart of the diester compound (E) in Example 5. FIG. 5b shows an IR chart of the diester compound (E) in Example 5. FIG. 6a shows a GPC chart of the diester compound (F) in Comparative Example 1. FIG. 6b shows an IR chart of the diester compound (F) in Comparative Example 1.

<Terminology>
As used herein, the term "optionally substituted" in reference to a compound or group means both a case where the hydrogen atoms of the compound or group are not substituted with substituents, and a case where some or all of the hydrogen atoms of the compound or group are substituted with substituents.

Unless otherwise specified, the term "substituent" used herein means a halogen atom, alkyl group, alkenyl group, alkynyl group, alkapolyenyl group, cycloalkyl group, cycloalkenyl group, alkoxy group, cycloalkyloxy group, aryl group, aryloxy group, arylalkyl group, arylalkoxy group, monovalent heterocyclic group, alkylidene group, amino group, silyl group, acyl group, acyloxy group, carboxy group, sulfo group, cyano group, nitro group, hydroxy group, mercapto group, or oxo group. Aliphatic hydrocarbon groups having unsaturated bonds, such as alkenyl groups, alkynyl groups, alkapolyenyl groups, and cycloalkenyl groups, are also collectively referred to as "unsaturated aliphatic hydrocarbon groups."

Halogen atoms used as substituents include, for example, fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.

The alkyl group used as a substituent may be either linear or branched. The alkyl group preferably has 1 to 20 carbon atoms, more preferably 1 to 14, even more preferably 1 to 12, even more preferably 1 to 6, and particularly preferably 1 to 3. Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, and decyl.

The alkenyl group used as a substituent may be either linear or branched. The alkenyl group preferably has 2 to 20 carbon atoms, more preferably 2 to 14, even more preferably 2 to 12, even more preferably 2 to 6, and particularly preferably 2 or 3. Examples of the alkenyl group include vinyl, allyl, 1-propenyl, butenyl, sec-butenyl, isobutenyl, tert-butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl, and decenyl.

The alkynyl group used as a substituent may be either linear or branched. The alkynyl group preferably has 2 to 20 carbon atoms, more preferably 2 to 14, even more preferably 2 to 12, even more preferably 2 to 6, and particularly preferably 2 or 3. Examples of the alkynyl group include ethynyl, propynyl, butynyl, sec-butynyl, isobutynyl, tert-butynyl, pentynyl, hexynyl, heptynyl, octynyl, nonynyl, and decynyl.

The alkapolyenyl group used as a substituent may be either linear or branched, and the number of double bonds is preferably 2 to 10, more preferably 2 to 6, even more preferably 2 to 4, and even more preferably 2. The number of carbon atoms in the alkapolyenyl group is preferably 3 to 20, more preferably 3 to 14, even more preferably 3 to 12, and even more preferably 3 to 6.

The number of carbon atoms in the cycloalkyl group used as a substituent is preferably 3 to 20, more preferably 3 to 12, and even more preferably 3 to 6. Examples of the cycloalkyl group include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group.

The number of carbon atoms in the cycloalkenyl group used as a substituent is preferably 3 to 20, more preferably 3 to 12, and even more preferably 3 to 6. Examples of such cycloalkenyl groups include cyclopropenyl groups, cyclobutenyl groups, cyclopentenyl groups, and cyclohexenyl groups.

The alkoxy group used as a substituent may be either linear or branched. The alkoxy group preferably has 1 to 20 carbon atoms, more preferably 1 to 12, and even more preferably 1 to 6. Examples of the alkoxy group include methoxy, ethoxy, propyloxy, isopropyloxy, butoxy, sec-butoxy, isobutoxy, tert-butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, nonyloxy, and decyloxy.

The number of carbon atoms in the cycloalkyloxy group used as a substituent is preferably 3 to 20, more preferably 3 to 12, and even more preferably 3 to 6. Examples of such cycloalkyloxy groups include cyclopropyloxy, cyclobutyloxy, cyclopentyloxy, and cyclohexyloxy groups.

The aryl group used as a substituent is a group in which one hydrogen atom on the aromatic ring has been removed from an aromatic hydrocarbon. The number of carbon atoms in the aryl group used as a substituent is preferably 6 to 24, more preferably 6 to 18, even more preferably 6 to 14, and even more preferably 6 to 10. Examples of such aryl groups include phenyl, naphthyl, and anthracenyl groups.

The number of carbon atoms in the aryloxy group used as a substituent is preferably 6 to 24, more preferably 6 to 18, even more preferably 6 to 14, and even more preferably 6 to 10. Examples of aryloxy groups used as substituents include a phenoxy group, a 1-naphthyloxy group, and a 2-naphthyloxy group.

The number of carbon atoms in the arylalkyl group used as a substituent is preferably 7 to 25, more preferably 7 to 19, even more preferably 7 to 15, and even more preferably 7 to 11. Examples of the arylalkyl group include a phenyl-C ₁ to C ₁₂ alkyl group, a naphthyl-C ₁ to C ₁₂ alkyl group, and an anthracenyl-C ₁ to C ₁₂ alkyl group.

The number of carbon atoms in the arylalkoxy group used as a substituent is preferably 7 to 25, more preferably 7 to 19, even more preferably 7 to 15, and even more preferably 7 to 11. Examples of the arylalkoxy group include a phenyl-C ₁ to C ₁₂ alkoxy group and a naphthyl-C ₁ to C ₁₂ alkoxy group.

A monovalent heterocyclic group used as a substituent refers to a group in which one hydrogen atom has been removed from the heterocycle of a heterocyclic compound. The monovalent heterocyclic group preferably has 3 to 21 carbon atoms, more preferably 3 to 15 carbon atoms, and even more preferably 3 to 9 carbon atoms. Monovalent heterocyclic groups also include monovalent aromatic heterocyclic groups (heteroaryl groups). Examples of monovalent heterocyclic rings include thienyl, pyrrolyl, furanyl, furyl, pyridyl, pyridazinyl, pyrimidyl, pyrazinyl, triazinyl, pyrrolidyl, piperidyl, quinolyl, and isoquinolyl groups.

The alkylidene group used as a substituent refers to a group in which two hydrogen atoms have been removed from the same carbon atom of an alkane. The number of carbon atoms in the alkylidene group is preferably 1 to 20, more preferably 1 to 14, even more preferably 1 to 12, even more preferably 1 to 6, and particularly preferably 1 to 3. Examples of the alkylidene group include a methylidene group, an ethylidene group, a propylidene group, an isopropylidene group, a butylidene group, a sec-butylidene group, an isobutylidene group, a tert-butylidene group, a pentylidene group, a hexylidene group, a heptylidene group, an octylidene group, a nonylidene group, and a decylidene group.

The acyl group used as a substituent is a group represented by the formula: -C(=O)-R (wherein R is an alkyl group or an aryl group). The alkyl group represented by R may be either linear or branched. Examples of aryl groups represented by R include phenyl, naphthyl, and anthracenyl groups. The number of carbon atoms in the acyl group is preferably 2 to 20, more preferably 2 to 13, and even more preferably 2 to 7. Examples of such acyl groups include acetyl, propionyl, butyryl, isobutyryl, pivaloyl, and benzoyl groups.

The acyloxy group used as a substituent is a group represented by the formula: -O-C(=O)-R (wherein R is an alkyl group or an aryl group). The alkyl group represented by R may be either linear or branched. Examples of aryl groups represented by R include phenyl, naphthyl, and anthracenyl groups. The acyloxy group preferably contains 2 to 20 carbon atoms, more preferably 2 to 13, and even more preferably 2 to 7. Examples of acyloxy groups include acetoxy, propionyloxy, butyryloxy, isobutyryloxy, pivaloyloxy, and benzoyloxy groups.

The above-mentioned substituents may further have a substituent (hereinafter sometimes referred to as a "secondary substituent"). Unless otherwise specified, the secondary substituent may be the same as the above-mentioned substituent.

As used herein, the term "aliphatic group" refers to a group in which one or more hydrogen atoms bonded to an aliphatic carbon of an aliphatic compound have been removed. Specifically, a monovalent aliphatic group refers to a group in which one hydrogen atom bonded to an aliphatic carbon of an aliphatic compound has been removed, and a divalent aliphatic group refers to a group in which two hydrogen atoms bonded to an aliphatic carbon of an aliphatic compound have been removed. Examples of divalent aliphatic groups include optionally substituted alkylene groups, optionally substituted cycloalkylene groups, optionally substituted alkenylene groups, and optionally substituted cycloalkenylene groups. Unless otherwise specified, the number of carbon atoms in an aliphatic group is preferably 1 or more, more preferably 2 or more, even more preferably 3 or more, 4 or more, 5 or more, or 6 or more; and is preferably 50 or less, more preferably 40 or less, even more preferably 30 or less, 20 or less, 18 or less, 16 or less, 14 or less, or 12 or less. The number of carbon atoms in the substituents is not included in this number of carbon atoms.

As used herein, the term "aromatic ring" refers to a ring conforming to Hückel's rule, in which the number of electrons in the π-electron system of the ring is 4p + 2 (where p is a natural number). This includes monocyclic aromatic rings and fused aromatic rings formed by condensing two or more monocyclic aromatic rings. An aromatic ring may be an aromatic carbocyclic ring containing only carbon atoms as ring-constituting atoms, or an aromatic heterocyclic ring containing, in addition to carbon atoms, heteroatoms such as oxygen, nitrogen, or sulfur atoms. Unless otherwise specified, the number of carbon atoms in an aromatic ring is preferably 3 or more, more preferably 4 or more or 5 or more, and even more preferably 6 or more. The upper limit is preferably 24 or less, more preferably 18 or less or 14 or less, and even more preferably 10 or less. This number of carbon atoms does not include the number of carbon atoms of substituents. Examples of aromatic rings include monocyclic aromatic rings such as a benzene ring, a furan ring, a thiophene ring, a pyrrole ring, a pyrazole ring, an oxazole ring, an isoxazole ring, a thiazole ring, an imidazole ring, a pyridine ring, a pyridazine ring, a pyrimidine ring, and a pyrazine ring; and fused aromatic rings formed by condensing two or more monocyclic aromatic rings, such as a naphthalene ring, an anthracene ring, a phenanthrene ring, a benzofuran ring, an isobenzofuran ring, an indole ring, an isoindole ring, a benzothiophene ring, a benzimidazole ring, an indazole ring, a benzoxazole ring, a benzisoxazole ring, a benzothiazole ring, a quinoline ring, an isoquinoline ring, a quinoxaline ring, an acridine ring, a quinazoline ring, a cinnoline ring, and a phthalazine ring.

The present invention will now be described in detail with reference to preferred embodiments. However, the present invention is not limited to the following embodiments and examples, and can be modified and implemented as desired without departing from the scope of the claims of the present invention and their equivalents.

[Diester Compound]
The diester compound of the present invention is
a core unit comprising a divalent aliphatic group;
The polymer comprises a first and a second blocking unit bonded to the core unit via an ester bond, and the first and second blocking units are each independently an aromatic ring which may have a substituent.

In the diester compound of the present invention, the core unit and the blocking unit are bonded via an ester bond (-C(=O)-O-). Specifically, the core unit and the blocking unit are bonded via an ester bond such that the carbonyl group (-C(=O)-) is bonded to the core unit and the oxy group (-O-) is bonded to the blocking unit. As a result, the diester compound of the present invention has an aliphatic carbon-C(=O)-O-aromatic carbon structure as the ester bond. As described below, the present invention is based on the discovery that ester bonds having such an aliphatic carbon-C(=O)-O-aromatic carbon structure exhibit crosslinking properties, and originates from findings that were unpredictable based on conventional technical knowledge.

Therefore, when the core unit is X _core and the first and second blocking units are X ¹ _end and X ² _end , respectively, the diester compound of the present invention can be represented by the following formula (X).

(In the formula,
X _core represents a divalent aliphatic group;
X ¹ _end and X ² _end each independently represent an aromatic ring which may have a substituent.

-Core unit (X _core )-
The core unit X _core is composed of a divalent aliphatic group.

By having a core unit consisting of a divalent aliphatic group, the diester compound of the present invention is able to exhibit low viscosity characteristics. Furthermore, when combined with a crosslinkable resin, it is possible to obtain a cured product that is highly tough and flexible.

When an ester compound is used as a crosslinking agent for a crosslinkable resin, it has been thought that in order to exhibit crosslinking properties, the ester bond must have an aromatic carbon-C(=O)-O-aromatic carbon structure to form an active ester bond. In contrast, the diester compound of the present invention, which contains a core unit consisting of a divalent aliphatic group, has an aliphatic carbon-C(=O)-O-aromatic carbon structure. The inventors have discovered that diester compounds having this specific ester bond structure exhibit favorable low viscosity properties and function as crosslinking agents for crosslinkable resins.

In the core unit X _core , the number of carbon atoms in the divalent aliphatic group is preferably 4 or more, more preferably 6 or more or 8 or more, from the viewpoint of realizing a diester compound with a lower viscosity. Therefore, in a preferred embodiment, the number of carbon atoms in the divalent aliphatic group in the core unit X _core is 6 or more. The upper limit of the number of carbon atoms in the divalent aliphatic group is not particularly limited and may be determined appropriately from the above-mentioned range. Note that this number of carbon atoms does not include the number of carbon atoms of the substituent.

In the core unit X _core , the divalent aliphatic group is preferably an alkylene group which may have a substituent or an alkenylene group which may have a substituent, from the viewpoint of realizing a diester compound with a lower viscosity, and an alkylene group which may have a substituent is particularly preferred. The alkylene group in the core unit may be either linear or branched. Therefore, in a preferred embodiment, the divalent aliphatic group in the core unit X _core is an alkylene group.

The substituents that the alkylene group or alkenylene group in the core unit may have are as described above. Among these, the substituent is preferably one or more selected from a halogen atom, an alkyl group, and an alkenyl group, and more preferably one or more selected from a fluorine atom and an alkyl group having 1 to 6 carbon atoms.

- First and second blocking units (X ¹ _end and X ² _end ) -
The first and second blocking units X ¹ _end and X ² _end are each independently an aromatic ring which may have a substituent.

By having aromatic rings, which may have substituents, as the first and second blocking units, the diester compound of the present invention can be incorporated into a resin composition and used as a crosslinking agent for a crosslinkable resin.

In the blocking units X ¹ _end and X ² _end , the aromatic ring is preferably an aromatic carbon ring from the viewpoint of obtaining the effects of the present invention more effectively. The number of carbon atoms in the aromatic carbon ring is preferably 6 to 14, more preferably 6 to 10. Therefore, in a preferred embodiment, the aromatic ring in the blocking unit is an aromatic carbon ring having 6 to 14 carbon atoms.

The substituents that the aromatic ring in the blocking unit may have are as described above. Among these, from the viewpoint of realizing a diester compound with a lower viscosity, one or more selected from unsaturated aliphatic hydrocarbon groups, halogen atoms, alkyl groups, and aryl groups are preferred, and one or more selected from unsaturated aliphatic hydrocarbon groups having 2 to 20 carbon atoms, fluorine atoms, alkyl groups having 1 to 6 carbon atoms, and aryl groups having 6 to 10 carbon atoms are more preferred. When the aromatic ring in the blocking unit has a substituent, only one of the first and second blocking units X ¹ _end and X ² _end may have a substituent, or both of them may have a substituent. In one embodiment, at least one of the first and second blocking units X ¹ _end and X ² _end is an aromatic ring having a substituent, and in a preferred embodiment, at least one of the first and second blocking units X ¹ _end and X ² _end is an aromatic ring having one or more substituents selected from unsaturated aliphatic hydrocarbon groups, halogen atoms, alkyl groups, and aryl groups. When X ¹ _end and X ² _end are aromatic rings having no substituents, the crystallinity is strong and they tend not to liquefy at room temperature, whereas when X ¹ _end and X ² _end are aromatic rings having substituents, the crystallinity is weak, they tend to liquefy at room temperature, and they have excellent fluidity and workability.

In particular, when at least one of the first and second blocking units X ¹ _end and X ² _end is an aromatic ring having an unsaturated aliphatic hydrocarbon group as a substituent, a diester compound with particularly low viscosity can be realized, which is preferred. Therefore, in a preferred embodiment, at least one of the first and second blocking units X ¹ _end and X ² _end is an aromatic ring having an unsaturated aliphatic hydrocarbon group as a substituent. When both the first and second blocking units are aromatic rings having an unsaturated aliphatic hydrocarbon group as a substituent, a diester compound with particularly low viscosity, for example, a liquid at room temperature (25°C), can be realized. Here, in this specification, "liquid at room temperature (25°C)" in relation to a diester compound means that the viscosity of the diester compound at 25°C is 3,000 mPa·s or less. Therefore, in a preferred embodiment, both the first and second blocking units X ¹ _end and X ² _end are aromatic rings having an unsaturated aliphatic hydrocarbon group as a substituent.

From the viewpoint of realizing a diester compound with an even lower viscosity, the unsaturated aliphatic hydrocarbon group that the aromatic ring in the blocking unit may have as a substituent preferably has 2 to 20 carbon atoms, more preferably 2 to 14, 2 to 12, 2 to 10, or 2 to 6 carbon atoms. From the viewpoint of realizing a diester compound with an even lower viscosity, the unsaturated aliphatic hydrocarbon group is preferably an alkenyl group or an alkynyl group, more preferably an alkenyl group. Among these, the unsaturated aliphatic hydrocarbon group that the aromatic ring in the blocking unit may have as a substituent is preferably an alkenyl group having 2 to 10 carbon atoms, more preferably an alkenyl group having 2 to 6 carbon atoms, and even more preferably an allyl group. Therefore, in a preferred embodiment, the unsaturated aliphatic hydrocarbon group that the aromatic ring in the blocking units X ¹ _end and X ² _end may have as a substituent is an allyl group.

In one embodiment, the diester compound of the present invention is represented by the following formula (X1):

(In the formula,
X _core represents a core unit composed of a divalent aliphatic group,
each ring Ar independently represents an aromatic ring;
Each ^R1 independently represents an unsaturated aliphatic hydrocarbon group;
^R2 each independently represents a substituent;
n11 and n12 each independently represent an integer of 0 to 2,
m11 and m12 represent integers that satisfy 0≦m11≦(p-n11) and 0≦m12≦(p-n12), where p is the number of substitutable hydrogen atoms in the ring Ar.

In formula (X1), X _core represents a core unit consisting of a divalent aliphatic group. The core unit, including preferred examples thereof, is as described above. In a preferred embodiment, X _core is a divalent aliphatic group having 6 or more carbon atoms, more preferably an alkylene group having 6 or more carbon atoms which may have a substituent. Preferred examples of the substituent are also as described above.

In formula (X1), each ring Ar independently represents an aromatic ring. The aromatic ring corresponds to the aromatic ring in the first and second blocking units, and preferred examples thereof are as described above. In a preferred embodiment, each ring Ar independently represents an aromatic carbocyclic ring having 6 to 14 carbon atoms, more preferably a benzene ring or a naphthalene ring.

In formula (X1), each R ¹ independently represents an unsaturated aliphatic hydrocarbon group. R ¹ corresponds to the unsaturated aliphatic hydrocarbon group that the aromatic rings in the first and second blocking units may have as a substituent, and preferred examples thereof are as described above. In a preferred embodiment, each R ¹ independently represents an unsaturated aliphatic hydrocarbon group having 2 to 20 carbon atoms, more preferably an alkenyl group having 2 to 20 carbon atoms (preferably 2 to 10 or 2 to 6) or an alkynyl group having 2 to 20 carbon atoms (preferably 2 to 10 or 2 to 6), and even more preferably an allyl group.

In formula (X1), ^R2 each independently represents a substituent. ^R2 corresponds to the substituent that the aromatic ring in the first and second blocking units may have, and preferred examples thereof are as described above. In a preferred embodiment, ^R2 is each independently selected from a halogen atom, an alkyl group, and an aryl group, and more preferably selected from a fluorine atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 10 carbon atoms.

In formula (X1), n11 and n12 each independently represent an integer from 0 to 2. As explained for the first and second blocking units, it is preferable that at least one of n11 and n12 is 1 or greater, particularly from the viewpoint of achieving a diester compound with a low viscosity. In a preferred embodiment, n11 and n12 each independently represent 1 or 2, and more preferably, both n11 and n12 are 1.

When n11 or n12 is 1 or more, the bonding position of ^R1 to the ring Ar is not particularly limited, but from the viewpoint of realizing a diester compound with a lower viscosity, it is preferably the ortho-position or meta-position relative to the bonding position of the oxy group of the ester bond, and more preferably the ortho-position.

In formula (X1), m11 and m12 represent integers that satisfy 0≦m11≦(p-n11) and 0≦m12≦(p-n12), where p is the number of substitutable hydrogen atoms in ring Ar. The number p of substitutable hydrogen atoms in ring Ar does not include the bonding site with the oxy group in the ester bond. For example, when ring Ar is a benzene ring, the number p of substitutable hydrogen atoms is 5, and when ring Ar is a naphthalene ring, the number p of substitutable hydrogen atoms is 7.

In a preferred embodiment, the diester compound of the present invention is represented by the following formula (X2) or the following formula (X3):

(In the formula,
X _core , R ¹ and R ² are as defined above;
n21 and n22 each independently represent an integer of 0 to 2,
m21 and m22 represent integers that satisfy 0≦m21≦(5−n21) and 0≦m22≦(5−n22).

(In the formula,
X _core , R ¹ and R ² are as defined above;
n31 and n32 each independently represent an integer of 0 to 2,
m31 and m32 represent integers that satisfy 0≦m31≦(7-n31) and 0≦m32≦(7-n32).

Regardless of whether it is formula (X2) or formula (X3), X _core , R ¹ and R ² are as described above, and preferred examples thereof are also as described above.

In formula (X2), n21 and n22 each independently represent an integer from 0 to 2. From the perspective of achieving a particularly low-viscosity diester compound, it is preferable that at least one of n21 and n22 is 1 or greater. In a preferred embodiment, n21 and n22 each independently represent 1 or 2, and more preferably, both n21 and n22 are 1.

When n21 or n22 is 1 or more, the bonding position of ^R1 to the benzene ring is not particularly limited, but from the viewpoint of realizing a diester compound with a lower viscosity, it is preferably the ortho-position or meta-position relative to the bonding position of the oxy group of the ester bond, and more preferably the ortho-position.

In formula (X2), m21 and m22 represent integers that satisfy the conditions 0≦m21≦(5-n21) and 0≦m22≦(5-n22).

In formula (X3), n31 and n32 each independently represent an integer from 0 to 2. From the perspective of achieving a particularly low-viscosity diester compound, it is preferable that at least one of n31 and n32 is 1 or greater. In a preferred embodiment, n31 and n32 each independently represent 1 or 2, and more preferably, both n31 and n32 are 1.

When n31 or n32 is 1 or more, the bonding position of ^R1 to the naphthalene ring is not particularly limited, but from the viewpoint of realizing a diester compound with a lower viscosity, it is preferably the ortho-position or meta-position relative to the bonding position of the oxy group of the ester bond, and more preferably the ortho-position.

In formula (X3), m31 and m32 represent integers that satisfy 0≦m31≦(7-n31) and 0≦m32≦(7-n32).

In one preferred embodiment, in formula (X2),
i) X _core is an alkylene group having 6 or more carbon atoms which may have a substituent,
ii) (a) at least one of n21 and n22 is 1 or 2, ^R1 's are each independently an alkenyl group having 2 to 20 carbon atoms or an alkynyl group having 2 to 20 carbon atoms, m21 and m22 are each independently an integer of 0 to 2, and ^R2 's are each independently selected from a halogen atom, an alkyl group, and an aryl group, or (b) n21 and n22 are 0, m21 and m22 are each independently an integer of 0 to 5, and R2 ^'s are each independently selected from a halogen atom, an alkyl group, and an aryl group.

In a more preferred embodiment, in formula (X2),
i) X _core is an alkylene group having 6 or more carbon atoms which may have one or more substituents selected from a halogen atom, an alkyl group, and an alkenyl group;
ii) (a) at least one of n21 and n22 is 1 or 2, ^R1 's are each independently an alkenyl group having 2 to 10 carbon atoms, m21 and m22 are each independently an integer of 0 to 2, and ^R2 's are each independently selected from a halogen atom, an alkyl group, and an aryl group, or (b) n21 and n22 are 0, m21 and m22 are each independently an integer of 0 to 5, and R2 ^'s are each independently selected from a halogen atom, an alkyl group, and an aryl group.

In one preferred embodiment, in formula (X3),
i) X _core is an alkylene group having 6 or more carbon atoms which may have a substituent,
ii) (a) at least one of n31 and n32 is 1 or 2, R ¹ 's are each independently an alkenyl group having 2 to 20 carbon atoms or an alkynyl group having 2 to 20 carbon atoms, m31 and m32 are each independently an integer of 0 to 2, and R ² 's are each independently selected from a halogen atom, an alkyl group, and an aryl group, or (b) n31 and n32 are 0, m31 and m32 are each independently an integer of 0 to 7, and R ² 's are each independently selected from a halogen atom, an alkyl group, and an aryl group.

In a more preferred embodiment, in formula (X3),
i) X _core is an alkylene group having 6 or more carbon atoms which may have one or more substituents selected from a halogen atom, an alkyl group, and an alkenyl group;
ii) (a) at least one of n31 and n32 is 1 or 2, R ¹ 's are each independently an alkenyl group having 2 to 10 carbon atoms, m31 and m32 are each independently an integer of 0 to 2, and R ² 's are each independently selected from a halogen atom, an alkyl group, and an aryl group, or (b) n31 and n32 are 0, m31 and m32 are each independently an integer of 0 to 7, and R ² 's are each independently selected from a halogen atom, an alkyl group, and an aryl group.

In the diester compound of the present invention, the oxycarbonyl group equivalent (active ester equivalent) is preferably 150 g/eq. or more, more preferably 160 g/eq. or more, even more preferably 180 g/eq. or more, or 200 g/eq. or more. The upper limit of the oxycarbonyl group equivalent can be, for example, 1000 g/eq. or less, 750 g/eq. or less, 700 g/eq. or less, 600 g/eq. or less, or 500 g/eq. or less.

From the perspective of using the diester compound of the present invention as a crosslinking agent for a crosslinkable resin in a resin composition, the molecular weight (number average molecular weight Mn, if it has a molecular weight distribution) is preferably 2000 or less, more preferably 1500 or less, and even more preferably 1400 or less, 1200 or less, or 1000 or less. The lower limit of the molecular weight is not particularly limited and can be, for example, 300 or more, 320 or more, etc. The molecular weight can be measured as a polystyrene-equivalent value by gel permeation chromatography (GPC).

An example of the synthesis procedure for the diester compound of the present invention is shown below.

In one embodiment, the diester compound of the present invention is
(A) a divalent aliphatic carboxylic acid compound or a divalent aliphatic carboxylic acid halide compound,
(B) It is obtained by a condensation reaction with a monovalent aromatic hydroxy compound which may have a substituent.

-(A) Divalent Aliphatic Carboxylic Acid (Halide) Compound-
The component (A) is a divalent aliphatic carboxylic acid compound or a divalent aliphatic carboxylic acid halide compound, and is represented by the following formula (X4).

(In the formula, X _core is as defined above, and Z represents a hydroxy group or a halogen atom.)

As the component (A), any divalent aliphatic carboxylic acid (halide) compound may be used depending on the desired core unit X _core . Suitable examples of X _core are as described above. For example, when the desired core unit X _core is a linear alkylene group having 6 carbon atoms, suberic acid (chloride) may be used, and when the desired core unit X core is a linear alkylene group having 8 carbon atoms, sebacic acid (chloride) may be used.

-(B) Optionally substituted monovalent aromatic hydroxy compound-
The component (B) is a monovalent aromatic hydroxy compound which may have a substituent and is represented by the following formula (X5).

(In the formula,
Ring Ar, ^R1 and ^R2 are as defined above;
n represents an integer of 0 to 2;
m represents an integer satisfying 0≦m≦(p−n), where p is the number of substitutable hydrogen atoms in the ring Ar.

Any aromatic monool may be used as component (B) depending on the desired blocking unit. The ring Ar, ^R1 , and ^R2 are as described above. For example, when the desired blocking unit is a benzene ring having one alkenyl group of 2 to 6 carbon atoms as a substituent, a phenol compound in which n is 1 and ^R1 is an alkenyl group of 2 to 6 carbon atoms, such as vinylphenol, allylphenol, 1-propenylphenol, butenylphenol, pentenylphenol, or hexenylphenol, may be used as the aromatic monool. When the desired blocking unit is a benzene ring having a fluorine atom as a substituent, a phenol compound in which m is 1 to 5 and ^R2 is a fluorine atom, such as pentafluorophenol, tetrafluorophenol, or trifluorophenol, may be used.

The condensation reaction may be carried out in a solvent-free system without using a solvent, or in an organic solvent system using an organic solvent. Examples of organic solvents that can be used in the condensation reaction include ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; acetate-based solvents such as ethyl acetate, butyl acetate, cellosolve acetate, propylene glycol monomethyl ether acetate, and carbitol acetate; carbitol-based solvents such as cellosolve and butyl carbitol; aromatic hydrocarbon solvents such as toluene and xylene; and amide-based solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone. These organic solvents may be used alone or in combination.

A base may be used in the condensation reaction. Examples of bases include alkali metal hydroxides such as sodium hydroxide (caustic soda) and potassium hydroxide; and tertiary amines such as triethylamine, pyridine, and N,N-dimethyl-4-aminopyridine (DMAP). A single base may be used, or two or more bases may be used in combination.

The condensation reaction may also use a condensing agent or phase transfer catalyst. Any conventionally known condensing agent or phase transfer catalyst that can be used in an esterification reaction may be used.

The reaction temperature for the condensation reaction is not particularly limited as long as the condensation reaction proceeds, and may be, for example, in the range of 0 to 80°C. The reaction time for the condensation reaction is also not particularly limited as long as the desired diester compound structure is achieved, and may be, for example, in the range of 30 minutes to 8 hours.

The diester compound may be purified after the condensation reaction. For example, after the condensation reaction, a purification step such as water washing or microfiltration may be performed to remove by-product salts and excess starting materials from the system. Specifically, after the condensation reaction, an amount of water necessary to dissolve the by-product salts is added, and the mixture is allowed to stand and separated, with the aqueous layer discarded. If necessary, an acid is added to neutralize the mixture, and water washing is repeated. The mixture is then purified by microfiltration after a dehydration step using a chemical or azeotropic method, and the organic solvent is then removed by distillation, if necessary, to obtain the diester compound. The organic solvent may also be used directly as a solvent for the resin composition without completely removing it.

The diester compound of the present invention is characterized by its low viscosity. For example, when measured using a vibration viscometer as described in the section (Viscosity Measurement Conditions During Heating) below, the viscosity of the diester compound of the present invention at 75°C is preferably 1000 mPa·s or less, more preferably 500 mPa·s or less, and even more preferably 300 mPa·s or less, 200 mPa·s or less, 150 mPa·s or less, 100 mPa·s or less, 80 mPa·s or less, 60 mPa·s or less, or 50 mPa·s or less.

In a preferred embodiment in which at least one (preferably both) of the first and second blocking units is an aromatic ring having an unsaturated aliphatic hydrocarbon group as a substituent, a particularly low viscosity can be exhibited. In such a preferred embodiment, the diester compound of the present invention is liquid at room temperature (25°C). For example, when measured using an E-type viscometer (100 rpm) as described in the "Viscosity Measurement Conditions" section below, the viscosity of the diester compound of the present invention at 25°C can be preferably 2000 mPa·s or less, more preferably 1500 mPa·s or less, and even more preferably 1000 mPa·s or less, 800 mPa·s or less, 600 mPa·s or less, 500 mPa·s or less, or 400 mPa·s or less. In a particularly preferred embodiment in which both the first and second blocking units are aromatic rings having unsaturated aliphatic hydrocarbon groups as substituents, the diester compound of the present invention can exhibit a lower viscosity, and the viscosity at 25°C can be reduced to, for example, 300 mPa·s or less, 250 mPa·s or less, 200 mPa·s or less, 150 mPa·s or less, or 100 mPa·s or less. Thus, in a preferred embodiment, the viscosity of the diester compound of the present invention at 25°C is 300 mPa·s or less.

The diester compound of the present invention retains the advantage of ester compounds, namely, that when combined with a crosslinkable resin, it produces a cured product exhibiting excellent dielectric properties. However, it also has low viscosity, and when combined with a crosslinkable resin, it can produce a resin composition with good fluidity, thereby preventing the occurrence of flow marks and unfilled areas during molding, such as encapsulation molding. Furthermore, when combined with a crosslinkable resin, the diester compound of the present invention can produce a cured product with excellent toughness and flexibility. Furthermore, even when the inorganic filler content is high, it can produce a resin composition that exhibits good fluidity at molding temperatures, and it can produce a cured product with excellent heat resistance and moisture resistance, a lower dielectric dissipation factor, low warpage, and good heat dissipation properties. Therefore, in a preferred embodiment, the diester compound of the present invention can be used as a resin crosslinking agent.

[Resin composition]
The diester compound of the present invention can be used to produce a resin composition, and the present invention also provides such a resin composition.

The resin composition of the present invention comprises a diester compound (X) and a crosslinkable resin (Y), and is characterized in that the diester compound (X) is the diester compound of the present invention, i.e., the diester compound represented by the above formula (X).

Details of the diester compound (X), including suitable examples of the core unit and the first and second blocking units, and suitable embodiments of the general formula, are as explained in the "Diester Compound" section above.

In the resin composition of the present invention, the type of crosslinkable resin (Y) is not particularly limited, as long as it is capable of crosslinking in combination with the diester compound (X). From the viewpoint of being able to produce a cured product that exhibits excellent dielectric properties and good fluidity during molding in combination with the diester compound (X), the crosslinkable resin (Y) is preferably one or more types selected from the group consisting of thermosetting resins and radically polymerizable resins.

Thermosetting resins and radically polymerizable resins may be known resins used to form insulating layers for printed wiring boards and semiconductor chip packages. Below, we will explain the thermosetting resins and radically polymerizable resins that can be used as the crosslinkable resin (Y).

Examples of thermosetting resins include epoxy resins, benzocyclobutene resins, epoxy acrylate resins, urethane acrylate resins, urethane resins, cyanate resins, polyimide resins, benzoxazine resins, unsaturated polyester resins, phenolic resins, melamine resins, silicone resins, and phenoxy resins. Thermosetting resins may be used alone or in combination with two or more. In particular, it is preferable for the crosslinkable resin (Y) to contain an epoxy resin, as this provides good fluidity during molding and excellent dielectric properties after curing when combined with the diester compound (X).

The type of epoxy resin is not particularly limited, as long as it contains one or more (preferably two or more) epoxy groups per molecule. Examples of epoxy resins include bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol S epoxy resins, bisphenol AF epoxy resins, phenol novolac epoxy resins, tert-butyl-catechol epoxy resins, naphthol epoxy resins, naphthalene epoxy resins, naphthylene ether epoxy resins, glycidylamine epoxy resins, glycidyl ester epoxy resins, cresol novolac epoxy resins, biphenyl epoxy resins, phenol aralkyl epoxy resins, biphenyl aralkyl epoxy resins, fluorene skeleton epoxy resins, dicyclopentadiene epoxy resins, anthracene epoxy resins, linear aliphatic epoxy resins, epoxy resins with a butadiene structure, alicyclic epoxy resins, heterocyclic epoxy resins, spiro ring-containing epoxy resins, cyclohexanedimethanol epoxy resins, trimethylol epoxy resins, and halogenated epoxy resins. The resin composition of the present invention containing diester compound (X) exhibits good fluidity during molding and provides excellent dielectric properties after curing, regardless of the type of epoxy resin used.

Epoxy resins can be classified into those that are liquid at a temperature of 20°C (hereinafter referred to as "liquid epoxy resins") and those that are solid at a temperature of 20°C (hereinafter referred to as "solid epoxy resins"). The resin composition of the present invention may contain, as the crosslinkable resin (Y), only a liquid epoxy resin, only a solid epoxy resin, or a combination of a liquid epoxy resin and a solid epoxy resin. When a combination of a liquid epoxy resin and a solid epoxy resin is contained, the blending ratio (liquid:solid) may be in the range of 20:1 to 1:20 by mass (preferably 10:1 to 1:10, more preferably 3:1 to 1:3).

The epoxy group equivalent of the epoxy resin is preferably 50 g/eq. to 2000 g/eq., more preferably 60 g/eq. to 1000 g/eq., and even more preferably 80 g/eq. to 500 g/eq. The epoxy group equivalent is the mass of the epoxy resin containing one equivalent of epoxy groups, and can be measured in accordance with JIS K7236.

The weight-average molecular weight (Mw) of the epoxy resin is preferably 100 to 5,000, more preferably 250 to 3,000, and even more preferably 400 to 1,500. The Mw of the epoxy resin can be measured as a polystyrene-equivalent value using the GPC method.

The type of radically polymerizable resin is not particularly limited, as long as it has one or more (preferably two or more) radically polymerizable unsaturated groups per molecule. Examples of radically polymerizable resins include resins having one or more radically polymerizable unsaturated groups selected from maleimide groups, vinyl groups, allyl groups, styryl groups, vinylphenyl groups, acryloyl groups, methacryloyl groups, fumaroyl groups, and maleoyl groups. In particular, from the viewpoint of exhibiting good fluidity during molding and excellent dielectric properties after curing in combination with diester compound (X), it is preferable that crosslinkable resin (Y) contain one or more resins selected from maleimide resins, (meth)acrylic resins, and styryl resins.

There is no particular limitation on the type of maleimide resin, as long as it contains one or more (preferably two or more) maleimide groups (2,5-dihydro-2,5-dioxo-1H-pyrrol-1-yl groups) per molecule. Examples of maleimide resins include maleimide resins containing an aliphatic skeleton with 36 carbon atoms derived from dimer diamine, such as "BMI-3000J," "BMI-5000," "BMI-1400," "BMI-1500," "BMI-1700," and "BMI-689" (all manufactured by DigiCner Molecules); maleimide resins containing an indane skeleton, as described in the Japan Institute of Invention and Innovation Disclosure Technical Bulletin No. 2020-500211; and maleimide resins containing an aromatic ring skeleton directly bonded to the nitrogen atom of the maleimide group, such as "MIR-3000-70MT" (manufactured by Nippon Kayaku Co., Ltd.), "BMI-4000" (manufactured by Daiwa Kasei Co., Ltd.), and "BMI-80" (manufactured by Keiai Kasei Co., Ltd.).

There are no particular restrictions on the type of (meth)acrylic resin, as long as it contains one or more (preferably two or more) (meth)acryloyl groups per molecule. Here, the term "(meth)acryloyl group" is a general term for acryloyl groups and methacryloyl groups. Examples of methacrylic resins include "A-DOG" (manufactured by Shin-Nakamura Chemical Co., Ltd.), "DCP-A" (manufactured by Kyoeisha Chemical Co., Ltd.), "NPDGA," "FM-400," "R-687," "THE-330," "PET-30," and "DPHA" (all manufactured by Nippon Kayaku Co., Ltd.).

The type of styryl resin is not particularly limited, as long as it contains one or more (preferably two or more) styryl groups or vinylphenyl groups per molecule. Examples of styryl resins include "OPE-2St," "OPE-2St 1200," and "OPE-2St 2200" (all manufactured by Mitsubishi Gas Chemical Company, Inc.).

The resin composition of the present invention may contain only a thermosetting resin as the crosslinkable resin (Y), only a radically polymerizable resin, or a combination of a thermosetting resin and a radically polymerizable resin.

In the resin composition of the present invention, the mass ratio ((X)/(Y)) of the diester compound (X) to the crosslinkable resin (Y) may preferably be 0.8 or greater, and more preferably 0.9 or greater, 1 or greater, 1.1 or greater, or 1.2 or greater. The upper limit of the mass ratio ((X)/(Y)) may be, for example, 2 or less, 1.9 or less, or 1.8 or less. Therefore, in one embodiment, the mass ratio ((X)/(Y)) of the diester compound (X) to the crosslinkable resin (Y) is 0.8 to 2.0.

The resin composition of the present invention may further contain an inorganic filler. By including an inorganic filler, the linear thermal expansion coefficient and dielectric loss tangent can be further reduced. Furthermore, by including an inorganic filler with high thermal conductivity, a cured product with excellent heat dissipation properties can be achieved.

Inorganic fillers include, for example, silica, alumina, barium sulfate, talc, clay, mica powder, aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, magnesium oxide, boron nitride, aluminum borate, barium titanate, strontium titanate, calcium titanate, magnesium titanate, bismuth titanate, titanium oxide, barium zirconate, and calcium zirconate, and may be selected according to the specific application. Inorganic fillers may be used alone or in combination of two or more. Commercially available inorganic fillers include, for example, "UFP-30" (manufactured by Denka Chemical Industry Co., Ltd.); "YC100C," "YA050C," "YA050C-MJE," "YA010C," "SC2500SQ," "SC4050-SX," "SO-C4," "SO-C2," "SO-C1," and "SC-C2" (all manufactured by Admatechs Co., Ltd.); "Silfil NSS-3N," "Silfil NSS-4N," and "Silfil NSS-5N" (manufactured by Tokuyama Corporation), and "DAW-0525" (manufactured by Denka Company Limited).

The average particle size of the inorganic filler may be determined within a suitable range depending on the specific application. For example, when forming an interlayer insulating layer for a printed wiring board or a rewiring formation layer for a semiconductor chip package, the average particle size of the inorganic filler is preferably 5 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less, to ensure a low surface roughness of the cured product (insulating layer) and facilitate the formation of fine wiring. Furthermore, when forming an encapsulating layer for a semiconductor chip package, the average particle size of the inorganic filler is preferably 15 μm or less, more preferably 14 μm or less, even more preferably 12 μm or less, 10 μm or less, or 8 μm or less, to improve fluidity during encapsulation molding. The lower limit of the average particle size is not particularly limited and may be determined depending on the specific application, and may be, for example, 0.01 μm or more, 0.02 μm or more, 0.03 μm or more, 0.05 μm or more, or 0.1 μm or more. The average particle size of the inorganic filler can be measured using a laser diffraction/scattering method based on Mie scattering theory. Specifically, a particle size distribution of the inorganic filler is created on a volume basis using a laser diffraction scattering particle size distribution analyzer, and the median diameter is used as the average particle size. A preferred measurement sample is one in which the inorganic filler is dispersed in water using ultrasonic waves. An example of a laser diffraction scattering particle size distribution analyzer that can be used is the LA-950 manufactured by Horiba, Ltd.

It is preferable that the inorganic filler be surface-treated with a surface treatment agent such as an aminosilane coupling agent, a ureidosilane coupling agent, an epoxysilane coupling agent, a mercaptosilane coupling agent, a vinylsilane coupling agent, a styrylsilane coupling agent, an acrylatesilane coupling agent, an isocyanatesilane coupling agent, a sulfidesilane coupling agent, an organosilazane compound, or a titanate coupling agent to improve its moisture resistance and dispersibility.

When the resin composition of the present invention contains an inorganic filler, the content of the inorganic filler in the resin composition may be determined depending on the properties required of the resin composition. Taking the total nonvolatile components in the resin composition as 100% by mass, the content is, for example, 5% by mass or more, 10% by mass or more, preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more. The resin composition of the present invention, which contains a diester compound (X) having a core unit consisting of a divalent aliphatic group, can further increase the content of the inorganic filler while ensuring good fluidity during molding. The content of the inorganic filler in the resin composition may be increased, for example, to 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, or 80% by mass or more. This allows the resin composition of the present invention to achieve a cured product that exhibits exceptionally low dielectric tangent, excellent heat resistance, moisture resistance, and low warpage, while still satisfying narrow gap filling properties. Furthermore, depending on the type of inorganic filler, it can also produce a cured product with excellent heat dissipation properties. The upper limit of the inorganic filler content in the resin composition is not particularly limited, but can be, for example, 95% by mass or less, or 90% by mass or less.

The resin composition of the present invention may further contain a resin crosslinking agent other than the diester compound (X).

Resin crosslinking agents other than diester compound (X) include "TD2090", "TD2131" (manufactured by DIC Corporation), "MEH-7600", "MEH-7851", "MEH-8000H" (manufactured by Meiwa Kasei Co., Ltd.), "NHN", "CBN", "GPH-65", "GPH-103" (manufactured by Nippon Kayaku Co., Ltd.), "SN170", "SN180", "SN190", "SN475", "SN485", "SN495", "SN375", "SN395" (manufactured by Nippon Steel Chemical & Material Co., Ltd.), "LA7052", Examples include phenol-based curing agents such as LA7054, LA3018, and LA1356 (manufactured by DIC Corporation); benzoxazine-based crosslinking agents such as Fa and Pd (manufactured by Shikoku Kasei Corporation) and HFB2006M (manufactured by Showa Polymer Co., Ltd.); acid anhydride-based crosslinking agents such as methylhexahydrophthalic anhydride, methyl nadic anhydride, and hydrogenated methyl nadic anhydride; cyanate ester-based crosslinking agents such as PT30, PT60, and BA230S75 (manufactured by Lonza Japan); and benzoxazine-based crosslinking agents.

When the resin composition of the present invention contains a resin crosslinking agent other than diester compound (X), the content of the resin crosslinking agent in the resin composition may be determined depending on the properties required of the resin composition. Given that the non-volatile components in the resin composition are 100% by mass, the content is preferably 40% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. The lower limit may be 0.01% by mass or more, 0.05% by mass or more, 0.1% by mass or more, etc.

The resin composition of the present invention may further contain a crosslinking accelerator. By including a crosslinking accelerator, the crosslinking time and crosslinking temperature can be efficiently adjusted.

Examples of crosslinking accelerators include organic phosphine compounds such as "TPP," "TPP-K," "TPP-S," and "TPTP-S" (manufactured by Hokko Chemical Industry Co., Ltd.); imidazole compounds such as "Curesol 2MZ," "2E4MZ," "Cl1Z," "Cl1Z-CN," "Cl1Z-CNS," "Cl1Z-A," "2MZ-OK," "2MA-OK," and "2PHZ" (manufactured by Shikoku Chemical Industry Co., Ltd.); amine adduct compounds such as Novacure (manufactured by Asahi Chemical Industry Co., Ltd.) and Fujicure (manufactured by Fuji Chemical Industry Co., Ltd.); amine compounds such as 1,8-diazabicyclo[5,4,0]undecene-7,4-dimethylaminopyridine, benzyldimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol, and 4-dimethylaminopyridine; and organometallic complexes or organometallic salts of cobalt, copper, zinc, iron, nickel, manganese, tin, etc.

When the resin composition of the present invention contains a crosslinking accelerator, the content of the crosslinking accelerator in the resin composition may be determined depending on the properties required of the resin composition. Given that the non-volatile components in the resin composition are 100% by mass, the content is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less. The lower limit may be 0.001% by mass or more, 0.01% by mass or more, 0.05% by mass or more, etc.

The resin composition of the present invention may further contain optional additives. Examples of such additives include organic fillers such as rubber particles; radical polymerization initiators such as peroxide-based radical polymerization initiators and azo-based radical polymerization initiators; thermoplastic resins such as phenoxy resin, polyvinyl acetal resin, polysulfone resin, polyethersulfone resin, polyphenylene ether resin, polyetheretherketone resin, and polyester resin; organometallic compounds such as organocopper compounds, organozinc compounds, and organocobalt compounds; colorants such as phthalocyanine blue, phthalocyanine green, iodine green, diazo yellow, crystal violet, titanium oxide, and carbon black; polymerization inhibitors such as hydroquinone, catechol, pyrogallol, and phenothiazine; leveling agents such as silicone-based leveling agents and acrylic polymer-based leveling agents; thickeners such as bentone and montmorillonite; defoamers such as silicone-based defoamers, acrylic defoamers, fluorine-based defoamers, and vinyl resin-based defoamers; and benzotriazole. surfactants such as fluorine-based surfactants and silicone-based surfactants; flame retardants such as phosphorus-based flame retardants (e.g., phosphate ester compounds, phosphazene compounds, phosphinic acid compounds, red phosphorus), nitrogen-based flame retardants (e.g., melamine sulfate), halogen-based flame retardants, and inorganic flame retardants (e.g., antimony trioxide); dispersants such as phosphate ester-based dispersants, polyoxyalkylene-based dispersants, acetylene-based dispersants, silicone-based dispersants, anionic dispersants, and cationic dispersants; and stabilizers such as borate-based stabilizers, titanate-based stabilizers, aluminate-based stabilizers, zirconate-based stabilizers, isocyanate-based stabilizers, carboxylic acid-based stabilizers, and carboxylic acid anhydride-based stabilizers. The content of such additives may be determined depending on the properties required of the resin composition.

The resin composition of the present invention may further contain an organic solvent as a volatile component. Examples of organic solvents include ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone; ether-based solvents such as tetrahydropyran, tetrahydrofuran, 1,4-dioxane, diethyl ether, diisopropyl ether, dibutyl ether, and diphenyl ether; alcohol-based solvents such as methanol, ethanol, propanol, butanol, and ethylene glycol; 2-ethoxyethyl acetate, propylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, ethyl diglycol acetate, γ-butyrolactone, and methyl methoxypropionate. ether alcohol solvents such as 2-methoxypropanol, 2-methoxyethanol, 2-ethoxyethanol, propylene glycol monomethyl ether, and diethylene glycol monobutyl ether (butyl carbitol); amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; sulfoxide solvents such as dimethyl sulfoxide; nitrile solvents such as acetonitrile and propionitrile; aliphatic hydrocarbon solvents such as hexane, cyclopentane, cyclohexane, and methylcyclohexane; and aromatic hydrocarbon solvents such as benzene, toluene, xylene, ethylbenzene, and trimethylbenzene. These organic solvents may be used alone or in combination of two or more.

When the resin composition of the present invention contains an organic solvent, the content of the organic solvent in the resin composition may be determined depending on the properties required of the resin composition, but when all components in the resin composition are taken as 100% by mass, it may be, for example, 60% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 15% by mass or less, 10% by mass or less, etc.

To reduce the viscosity of resin compositions, organic solvents have been added as diluents to the resin compositions. When such resin compositions are used to form insulating layers for semiconductor chip packages or printed wiring boards, problems arise, such as the generation of voids during the film-forming and encapsulation molding processes, the need for large-scale disposal facilities for the organic solvent, and residual organic solvents remaining in the resulting insulating layer. In contrast, the resin composition of the present invention, which contains a diester compound (X) having a core unit composed of a divalent aliphatic group, is preferred because it exhibits good fluidity during molding, even when the organic solvent content is low or even when no organic solvent is present. The organic solvent content in the resin composition of the present invention may be, for example, less than 10% by mass, 8% by mass or less, 6% by mass or less, 5% by mass or less, 4% by mass or less, 2% by mass or less, 1% by mass or less, or 0.5% by mass or less, or even 0% by mass (solvent-free system).

The resin composition of the present invention can be prepared by appropriately mixing the necessary components from among the above ingredients, and, if necessary, kneading or mixing them using kneading means such as a triple roll mill, ball mill, bead mill, or sand mill, or stirring means such as a super mixer or planetary mixer.

The resin composition of the present invention, which contains a combination of diester compound (X) and crosslinkable resin (Y), exhibits good fluidity during molding and can provide excellent dielectric properties after curing.

In one embodiment, the cured product of the resin composition of the present invention is characterized by a low dielectric constant (Dk). For example, when measured at 5.8 GHz and 23°C as described in the "Dielectric Properties" section below, the dielectric constant (Dk) of the cured product of the resin composition of the present invention may preferably be 3.3 or less, 3.2 or less, 3.1 or less, 3.0 or less, 2.9 or less, or 2.8 or less.

In one embodiment, the cured product of the resin composition of the present invention is characterized by a low dielectric dissipation factor (Df). For example, when measured at 5.8 GHz and 23°C as described in the "Dielectric Properties" section below, the dielectric dissipation factor (Df) of the cured product of the resin composition of the present invention may preferably be 0.01 or less, 0.008 or less, 0.007 or less, 0.006 or less, 0.005 or less, or 0.004 or less.

In one embodiment, the cured product of the resin composition of the present invention is characterized by high thermal conductivity. For example, when measured by the hot disc method as described in the "Thermal Conductivity" section below, the thermal conductivity of the cured product of the resin composition of the present invention may preferably be 2.5 W/mK or more, 2.6 W/mK or more, 2.8 W/mK or more, 3 W/mK or more, 3.1 W/mK or more, or 3.2 W/mK or more.

The resin composition of the present invention can be suitably used as a resin composition for encapsulating semiconductor chips (semiconductor encapsulation resin composition). The resin composition of the present invention can also be suitably used as a resin composition for forming a rewiring layer (resin composition for rewiring layer) as an insulating layer for forming a rewiring layer in a semiconductor chip package. The resin composition of the present invention can also be suitably used as a resin composition for forming an insulating layer of a printed wiring board (resin composition for insulating layer of printed wiring board), and more suitably as a resin composition for forming an interlayer insulating layer of a printed wiring board (resin composition for insulating interlayer of printed wiring board). The resin composition of the present invention can also be suitably used when the printed wiring board is a circuit board with built-in components. The resin composition of the present invention can also be used in a wide range of applications requiring a resin composition, such as sheet-like laminate materials such as resin sheets and prepregs, solder resists, underfill materials, die bonding materials, hole-filling resins, and component-embedding resins.

[Sheet-like laminated materials (resin sheets, prepregs)]
The resin composition of the present invention can be used as it is, but may also be used in the form of a sheet-like laminate material containing the resin composition.

The following resin sheets and prepregs are preferred as sheet-like laminate materials.

In one embodiment, the resin sheet includes a support and a layer of a resin composition (hereinafter simply referred to as a "resin composition layer") provided on the support, and is characterized in that the resin composition layer is formed from the resin composition of the present invention.

The optimum thickness of the resin composition layer varies depending on the application, and may be determined appropriately depending on the application. For example, from the perspective of reducing the thickness of printed wiring boards and semiconductor chip packages, the thickness of the resin composition layer is preferably 200 μm or less, and more preferably 150 μm or less, 120 μm or less, 100 μm or less, 80 μm or less, 60 μm or less, or 50 μm or less. There is no particular lower limit to the thickness of the resin composition layer, but it can typically be 1 μm or more, 5 μm or more, etc.

Examples of the support include films made of plastic materials, metal foils, and release paper, with films made of plastic materials and metal foils being preferred.

When a film made of a plastic material is used as the support, examples of the plastic material include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), acrylics such as polycarbonate (PC) and polymethyl methacrylate (PMMA), cyclic polyolefins, triacetyl cellulose (TAC), polyether sulfide (PES), polyether ketone, and polyimides. Among these, polyethylene terephthalate and polyethylene naphthalate are preferred, with inexpensive polyethylene terephthalate being particularly preferred.

When a metal foil is used as the support, examples of the metal foil include copper foil and aluminum foil, with copper foil being preferred. The copper foil may be a foil made of the single metal copper, or a foil made of an alloy of copper and another metal (e.g., tin, chromium, silver, magnesium, nickel, zirconium, silicon, titanium, etc.).

The surface of the support that will be bonded to the resin composition layer may be matte-treated, corona-treated, or antistatic-treated. Alternatively, a support with a release layer, which has a release layer on the surface that will be bonded to the resin composition layer, may be used. Examples of release agents used in the release layer of the support with a release layer include one or more release agents selected from the group consisting of alkyd resins, polyolefin resins, urethane resins, and silicone resins. Commercially available support with a release layer may be used, including PET films with a release layer primarily composed of alkyd resin-based release agents, such as "SK-1," "AL-5," and "AL-7" manufactured by Lintec Corporation, "Lumirror T60" manufactured by Toray Industries, Inc., "Purex" manufactured by Teijin Limited, and "Uni-Peel" manufactured by Unitika Limited.

The thickness of the support is not particularly limited, but is preferably in the range of 5 μm to 75 μm, and more preferably in the range of 10 μm to 60 μm. When using a support with a release layer, it is preferable that the overall thickness of the support with a release layer be in the above range.

The support may also be a metal foil with a support substrate, which is a thin metal foil with a peelable support substrate laminated thereto. In one embodiment, the metal foil with a support substrate includes a support substrate, a release layer provided on the support substrate, and metal foil provided on the release layer. When a metal foil with a support substrate is used as the support, the resin composition layer is provided on the metal foil.

In metal foil with a supporting substrate, the material of the supporting substrate is not particularly limited, but examples include copper foil, aluminum foil, stainless steel foil, titanium foil, copper alloy foil, etc. When copper foil is used as the supporting substrate, it may be electrolytic copper foil or rolled copper foil. In addition, the release layer is not particularly limited as long as it allows the metal foil to be released from the supporting substrate, and examples include an alloy layer of an element selected from the group consisting of Cr, Ni, Co, Fe, Mo, Ti, W, and P; an organic coating, etc.

For metal foil with a supporting substrate, the material of the metal foil is preferably, for example, copper foil or copper alloy foil.

In metal foil with a supporting substrate, the thickness of the supporting substrate is not particularly limited, but is preferably in the range of 10 μm to 150 μm, and more preferably in the range of 10 μm to 100 μm. The thickness of the metal foil may be, for example, in the range of 0.1 μm to 10 μm.

In one embodiment, the resin sheet may further include an optional layer, as needed. Examples of such optional layers include a protective film provided on the surface of the resin composition layer that is not bonded to the support (i.e., the surface opposite the support). The thickness of the protective film is not particularly limited, but is, for example, 1 μm to 40 μm. By laminating a protective film, it is possible to prevent the adhesion of dust and other particles to the surface of the resin composition layer and to prevent scratches.

The resin sheet can be produced, for example, by preparing a resin varnish by dissolving the resin composition in a liquid form in an organic solvent, applying the resin varnish to a support using a die coater or the like, and then drying the applied resin varnish to form a resin composition layer.

The organic solvent may be the same as the organic solvents described as components of the resin composition. One organic solvent may be used alone, or two or more organic solvents may be used in combination.

Drying may be carried out by known methods such as heating or hot air blowing. Drying conditions are not particularly limited, but drying is carried out so that the organic solvent content in the resin composition layer is 10% by mass or less, preferably 5% by mass or less. While this varies depending on the boiling point of the organic solvent in the resin composition or resin varnish, for example, when using a resin composition or resin varnish containing 30% to 60% by mass of organic solvent, a resin composition layer can be formed by drying at 50°C to 150°C for 3 to 10 minutes.

The resin sheet can be stored rolled up. If the resin sheet has a protective film, it can be used by peeling off the protective film.

In one embodiment, the prepreg is formed by impregnating a sheet-like fiber substrate with the resin composition of the present invention.

The sheet-like fiber substrate used for the prepreg is not particularly limited, and commonly used prepreg substrates such as glass cloth, aramid nonwoven fabric, and liquid crystal polymer nonwoven fabric can be used. From the perspective of thinning printed wiring boards and semiconductor chip packages, the thickness of the sheet-like fiber substrate is preferably 50 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, and particularly preferably 20 μm or less. There is no particular lower limit to the thickness of the sheet-like fiber substrate. It is usually 10 μm or more.

Prepregs can be manufactured using known methods such as the hot melt method and the solvent method.

The thickness of the prepreg can be in the same range as the resin composition layer in the resin sheet described above.

The sheet-like laminate material of the present invention can be suitably used for encapsulating semiconductor chips (for semiconductor encapsulation) and can be suitably used as a rewiring formation layer, serving as an insulating layer for forming a rewiring layer. The sheet-like laminate material of the present invention can also be suitably used for forming an insulating layer of a printed wiring board (for an insulating layer of a printed wiring board), and can be even more suitably used for forming an interlayer insulating layer of a printed wiring board (for an insulating interlayer of a printed wiring board).

[Semiconductor chip package]
The semiconductor chip package of the present invention includes a sealing layer made of a cured product of the resin composition of the present invention. As described above, the semiconductor chip package of the present invention may also include an insulating layer (rewiring formation layer) for forming a rewiring layer made of a cured product of the resin composition of the present invention.

A semiconductor chip package can be manufactured, for example, by a method including the following steps (1) to (6) using the resin composition and resin sheet of the present invention. The resin composition and resin sheet of the present invention can be used to form the sealing layer in step (3) or the rewiring formation layer in step (5). An example of forming a sealing layer or a rewiring formation layer using a resin composition or a resin sheet will be shown below. However, techniques for forming sealing layers and rewiring formation layers for semiconductor chip packages are known, and a person skilled in the art can manufacture a semiconductor package using the resin composition and resin sheet of the present invention according to known techniques.
(1) A step of laminating a temporary fixing film on a substrate;
(2) A step of temporarily fixing a semiconductor chip on a temporary fixing film;
(3) forming an encapsulation layer on the semiconductor chip;
(4) peeling the substrate and the temporary fixing film from the semiconductor chip;
(5) forming a rewiring formation layer as an insulating layer on the surface of the semiconductor chip from which the base material and the temporary fixing film have been peeled off; and (6) forming a rewiring layer as a conductor layer on the rewiring formation layer.

-Process (1)-
The material used for the substrate is not particularly limited, and examples of the substrate include a silicon wafer, a glass wafer, a glass substrate, a metal substrate such as copper, titanium, stainless steel, or cold-rolled steel plate (SPCC), a substrate in which glass fiber is impregnated with epoxy resin or the like and subjected to a thermosetting treatment (e.g., an FR-4 substrate), and a substrate made of bismaleimide triazine resin (BT resin).

The material of the temporary fixing film is not particularly limited as long as it can be peeled off from the semiconductor chip in step (4) and can temporarily fix the semiconductor chip. Commercially available temporary fixing films can be used. Examples of commercially available products include Riva Alpha manufactured by Nitto Denko Corporation.

-Process (2)-
The semiconductor chip is temporarily fixed on the temporary fixing film so that its electrode pad surface is bonded to the temporary fixing film. The temporary fixing of the semiconductor chip can be performed using a known device such as a flip chip bonder or a die bonder. The layout and number of semiconductor chips to be arranged can be appropriately set depending on the shape and size of the temporary fixing film, the number of semiconductor packages to be produced, etc., and for example, the semiconductor chips can be temporarily fixed by arranging them in a matrix of multiple rows and multiple columns.

-Process (3)-
The resin composition of the present invention is applied onto a semiconductor chip, or a resin composition layer of the resin sheet of the present invention is laminated onto a semiconductor chip and cured (for example, thermally cured) to form an encapsulating layer.

By using the resin composition of the present invention, which contains a diester compound (X) having a core unit composed of a divalent aliphatic group, good fluidity can be exhibited during encapsulation molding, whether the resin composition is applied as is or a resin composition layer is laminated in the form of a resin sheet.

For example, when used in the form of a resin sheet, the semiconductor chip and resin sheet can be laminated by removing the protective film from the resin sheet and then thermocompressing the resin sheet to the semiconductor chip from the support side. Examples of the member that thermocompresses the resin sheet to the semiconductor chip (hereinafter also referred to as the "thermocompression member") include a heated metal plate (such as a stainless steel plate) or a metal roll (such as a stainless steel roll). It is preferable to press the thermocompression member not directly onto the resin sheet, but rather via an elastic material such as heat-resistant rubber, so that the resin sheet can adequately conform to the surface irregularities of the semiconductor chip. The semiconductor chip and resin sheet can also be laminated using a vacuum lamination method. The lamination conditions and preferred ranges are the same as those described below in connection with the method for manufacturing a printed wiring board.

After lamination, the resin composition is thermally cured to form the sealing layer. The thermal curing conditions are the same as those described below in connection with the method for manufacturing a printed wiring board.

The support for the resin sheet may be peeled off after the resin sheet is laminated on the semiconductor chip and thermally cured, or the support may be peeled off before the resin sheet is laminated on the semiconductor chip.

When forming a sealing layer by applying the resin composition of the present invention, the application conditions may be the same as those used to form the resin composition layer described in connection with the resin sheet of the present invention. By using the resin composition of the present invention, good fluidity can be achieved at application and molding temperatures.

-Process (4)-
The method for peeling off the substrate and the temporary fixing film can be changed as appropriate depending on the material of the temporary fixing film, etc., and examples include a method in which the temporary fixing film is heated and foamed (or expanded) to peel it off, and a method in which ultraviolet light is irradiated from the substrate side to reduce the adhesive strength of the temporary fixing film and peel it off.

In the method of peeling off the temporary fixing film by heating and foaming (or expanding) it, the heating conditions are usually 100 to 250° C. for 1 to 90 seconds or 5 to 15 minutes. In the method of peeling off the temporary fixing film by irradiating it with ultraviolet light from the substrate side to reduce the adhesive strength of the temporary fixing film, the irradiation dose of ultraviolet light is usually 10 mJ/cm ² to 1000 mJ/cm ² .

-Process (5)-
The material for forming the rewiring formation layer (insulating layer) is not particularly limited as long as it has insulating properties when the rewiring formation layer (insulating layer) is formed, and from the viewpoint of ease of manufacturing a semiconductor chip package, a photosensitive resin or a thermosetting resin is preferred. The rewiring formation layer may be formed using the resin composition or resin sheet of the present invention.

After forming the redistribution layer, via holes may be formed in the redistribution layer to establish interlayer connections between the semiconductor chip and the conductor layer described below. The via holes may be formed using known methods depending on the material of the redistribution layer.

-Process (6)-
The material of the conductor layer formed on the redistribution layer is not particularly limited. In a preferred embodiment, the conductor layer contains one or more metals selected from the group consisting of gold, platinum, palladium, silver, copper, aluminum, cobalt, chromium, zinc, nickel, titanium, tungsten, iron, tin, and indium. The conductor layer may be a single metal layer or an alloy layer. Examples of the alloy layer include a layer formed from an alloy of two or more metals selected from the above group (e.g., a nickel-chromium alloy, a copper-nickel alloy, and a copper-titanium alloy). Among these, from the viewpoints of versatility, cost, ease of patterning, etc., of the conductor layer formation, a single metal layer of chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or an alloy layer of a nickel-chromium alloy, a copper-nickel alloy, or a copper-titanium alloy is preferred. A single metal layer of chromium, nickel, titanium, aluminum, zinc, gold, palladium, silver, or copper, or an alloy layer of a nickel-chromium alloy is more preferred, and a single metal layer of copper is even more preferred.

The conductor layer may have a single-layer structure, or a multi-layer structure consisting of two or more single-metal or alloy layers made of different types of metals or alloys. If the conductor layer has a multi-layer structure, the layer in contact with the insulating layer is preferably a single-metal layer of chromium, zinc, or titanium, or an alloy layer of nickel-chromium alloy.

The thickness of the conductor layer depends on the desired semiconductor chip package design, but is generally between 1 μm and 35 μm, preferably between 1 μm and 20 μm.

In one embodiment, the conductor layer may be formed by plating. For example, a conductor layer having the desired wiring pattern can be formed by plating the surface of the rewiring formation layer using conventional techniques such as semi-additive and full-additive methods. From the perspective of ease of manufacturing, formation by a semi-additive method is preferred. Below is an example of forming a conductor layer by a semi-additive method.

First, a plating seed layer is formed on the surface of the rewiring formation layer by electroless plating. Next, a mask pattern is formed on the formed plating seed layer, exposing a portion of the plating seed layer corresponding to the desired wiring pattern. A metal layer is formed on the exposed plating seed layer by electrolytic plating, and the mask pattern is then removed. Unnecessary plating seed layer is then removed by etching or other methods, forming a conductor layer (rewiring layer) with the desired wiring pattern.

In addition, steps (5) and (6) may be repeated to alternately stack (build up) conductor layers (rewiring layers) and rewiring formation layers (insulating layers).

When manufacturing a semiconductor chip package, the following steps may be further performed: (7) forming a solder resist layer on the conductor layer (rewiring layer), (8) forming bumps, and (9) dicing multiple semiconductor chip packages into individual semiconductor chip packages. These steps may be performed according to various methods known to those skilled in the art that are used in the manufacture of semiconductor chip packages.

The above is an example of a method for manufacturing a semiconductor chip by first providing a semiconductor chip and then forming a rewiring layer on its electrode pad surface, i.e., the Chip- ^1st method. In addition to the Chip-1st method, the semiconductor chip package of the present invention may also be manufactured by a method for first providing a rewiring layer, then providing a semiconductor chip on the rewiring layer in a state where the electrode pad surface can be electrically connected to the rewiring layer, and then sealing the semiconductor chip, i.e., the Rewiring Layer-1st (RDL- ^1st ) method. The resin composition and resin sheet of the present invention, which have excellent narrow gap filling properties, can realize a semiconductor chip package with extremely low transmission loss, which is required for 5G applications, regardless of whether the Chip- ^1st method or the RDL- ^1st method is used.

By forming an encapsulating layer and a rewiring formation layer using the resin composition and resin sheet of the present invention, which exhibit good fluidity during molding and provide excellent dielectric properties after curing, it is possible to realize a semiconductor chip package with extremely low transmission loss while suppressing the occurrence of flow marks, unfilled areas, and warpage, regardless of whether the semiconductor package is a fan-in package or a fan-out package. In one embodiment, the semiconductor chip package of the present invention is a fan-out package. The resin composition and resin sheet of the present invention can be applied to both fan-out panel level packages (FOPLPs) and fan-out wafer level packages (FOWLPs). In one embodiment, the semiconductor package of the present invention is a fan-out panel level package (FOPLP). In another embodiment, the semiconductor package of the present invention is a fan-out wafer level package (FOWLP).

[Printed wiring board]
The printed wiring board of the present invention includes an insulating layer made of a cured product of the resin composition of the present invention.

The printed wiring board can be produced, for example, by using the above-mentioned resin sheet by a method including the following steps (I) and (II).
(I) a step of laminating a resin sheet on an inner layer substrate so that the resin composition layer of the resin sheet is bonded to the inner layer substrate; and (II) a step of curing (e.g., thermally curing) the resin composition layer to form an insulating layer.

The "inner layer substrate" used in step (I) refers to a component that will become the substrate of a printed wiring board, and examples include glass epoxy substrates, metal substrates, polyester substrates, polyimide substrates, BT resin substrates, and thermosetting polyphenylene ether substrates. The substrate may also have a conductor layer on one or both sides, and this conductor layer may be patterned. An inner layer substrate with a conductor layer (circuit) formed on one or both sides of the substrate is sometimes referred to as an "inner layer circuit board." Furthermore, the term "inner layer substrate" used in this invention also includes intermediate products on which insulating layers and/or conductor layers are to be further formed during the manufacture of a printed wiring board. When the printed wiring board is a component-embedded circuit board, an inner layer substrate with embedded components may be used.

The inner layer substrate and resin sheet can be laminated, for example, by thermocompression bonding the resin sheet to the inner layer substrate from the support side. Examples of the member that thermocompresses the resin sheet to the inner layer substrate (hereinafter also referred to as the "thermocompression member") include a heated metal plate (such as a SUS panel) or a metal roll (SUS roll). The thermocompression member may be pressed directly onto the resin sheet, or it may be pressed via an elastic material such as heat-resistant rubber so that the resin sheet can adequately conform to the surface irregularities of the inner layer substrate.

The lamination of the inner layer substrate and the resin sheet may be carried out by vacuum lamination. In vacuum lamination, the thermocompression temperature is preferably in the range of 60°C to 160°C, more preferably 80°C to 140°C, the thermocompression pressure is preferably in the range of 0.098 MPa to 1.77 MPa, more preferably 0.29 MPa to 1.47 MPa, and the thermocompression time is preferably in the range of 20 seconds to 400 seconds, more preferably 30 seconds to 300 seconds. Lamination is preferably carried out under reduced pressure conditions of 26.7 hPa or less.

Lamination can be performed using a commercially available vacuum laminator. Examples of commercially available vacuum laminators include the vacuum pressure laminator manufactured by Meiki Seisakusho Co., Ltd., the vacuum applicator manufactured by Nikko Materials Co., Ltd., and the batch vacuum pressure laminator.

After lamination, the laminated resin sheets may be smoothed under normal pressure (atmospheric pressure), for example, by pressing a thermocompression member from the support side. The pressing conditions for the smoothing process may be the same as the thermocompression conditions for lamination described above. The smoothing process may be performed using a commercially available laminator. Note that lamination and smoothing may also be performed consecutively using the commercially available vacuum laminator described above.

The support may be removed between step (I) and step (II), or after step (II). When a metal foil is used as the support, the conductor layer may be formed using the metal foil without peeling off the support. When a metal foil with a supporting substrate is used as the support, the supporting substrate (and release layer) may be peeled off. Then, the conductor layer may be formed using the metal foil.

In step (II), the resin composition layer is cured (e.g., thermally cured) to form an insulating layer made of the cured resin composition. The curing conditions for the resin composition layer are not particularly limited, and conditions typically used for forming insulating layers for printed wiring boards may be used.

For example, the thermal curing conditions for the resin composition layer vary depending on the type of resin composition, but in one embodiment, the curing temperature is preferably 120°C to 250°C, more preferably 150°C to 240°C, and even more preferably 180°C to 230°C. The curing time is preferably 5 minutes to 240 minutes, more preferably 10 minutes to 150 minutes, and even more preferably 15 minutes to 120 minutes.

Before thermally curing the resin composition layer, the resin composition layer may be preheated at a temperature lower than the curing temperature. For example, prior to thermally curing the resin composition layer, the resin composition layer may be preheated at a temperature of 50°C to 120°C, preferably 60°C to 115°C, and more preferably 70°C to 110°C for 5 minutes or more, preferably 5 minutes to 150 minutes, more preferably 15 minutes to 120 minutes, and even more preferably 15 minutes to 100 minutes.

When manufacturing a printed wiring board, the following steps may be further carried out: (III) drilling holes in the insulating layer; (IV) roughening the insulating layer; and (V) forming a conductor layer. These steps (III) through (V) may be carried out according to various methods known to those skilled in the art and used in the manufacture of printed wiring boards. If the support is removed after step (II), the removal of the support may be carried out between steps (II) and (III), between steps (III) and (IV), or between steps (IV) and (V). Furthermore, if necessary, the formation of the insulating layer and conductor layer in steps (I) through (V) may be repeated to form a multilayer wiring board.

In another embodiment, the printed wiring board of the present invention can be manufactured using the prepreg described above. The manufacturing method is basically the same as when a resin sheet is used.

Step (III) is a step of drilling holes in the insulating layer, thereby forming holes such as via holes and through holes in the insulating layer. Step (III) may be performed using, for example, a drill, laser, plasma, etc., depending on the composition of the resin composition used to form the insulating layer. The dimensions and shape of the holes may be determined appropriately depending on the design of the printed wiring board.

Step (IV) is a step in which the insulating layer is roughened. Typically, smear removal (desmearing) is also performed in this step (IV). The roughening treatment procedures and conditions are not particularly limited, and known procedures and conditions commonly used in forming insulating layers for printed wiring boards can be used. For example, the insulating layer can be roughened by performing a swelling treatment using a swelling liquid, a roughening treatment using an oxidizing agent, and a neutralization treatment using a neutralizing liquid, in that order.

The swelling liquid used in the roughening treatment is not particularly limited, but examples include alkaline solutions and surfactant solutions. Alkaline solutions are preferred, with sodium hydroxide and potassium hydroxide solutions being more preferred. Commercially available swelling liquids include "Swelling Dip Securigans P" and "Swelling Dip Securigans SBU" manufactured by Atotech Japan. The swelling treatment using a swelling liquid is not particularly limited, but can be carried out by immersing the insulating layer in a swelling liquid at 30°C to 90°C for 1 to 20 minutes, for example. To keep swelling of the resin in the insulating layer to an appropriate level, it is preferable to immerse the insulating layer in a swelling liquid at 40°C to 80°C for 5 to 15 minutes.

The oxidizing agent used in the roughening treatment is not particularly limited, but examples include alkaline permanganate solutions prepared by dissolving potassium permanganate or sodium permanganate in an aqueous solution of sodium hydroxide. Roughening treatment using an oxidizing agent such as alkaline permanganate solution is preferably carried out by immersing the insulating layer in an oxidizing agent solution heated to 60°C to 100°C for 10 to 30 minutes. The concentration of permanganate in the alkaline permanganate solution is preferably 5% to 10% by mass. Commercially available oxidizing agents include alkaline permanganate solutions such as "Concentrate Compact CP" and "Dosing Solution Securigance P" manufactured by Atotech Japan.

The neutralizing solution used in the roughening treatment is preferably an acidic aqueous solution, and a commercially available product such as "Reduction Solution Securigant P" manufactured by Atotech Japan is one example.

Treatment with a neutralizing solution can be carried out by immersing the surface that has been roughened with an oxidizing agent in a neutralizing solution at 30°C to 80°C for 5 to 30 minutes. From the standpoint of workability, etc., it is preferable to immerse the object that has been roughened with an oxidizing agent in a neutralizing solution at 40°C to 70°C for 5 to 20 minutes.

Step (V) is a step of forming a conductor layer on an insulating layer. Step (V) may be performed in the same manner as step (6) described in relation to the method for manufacturing a semiconductor chip package.

The thickness of the conductor layer depends on the desired printed wiring board design, but is generally between 3 μm and 35 μm, preferably between 5 μm and 30 μm.

The conductor layer may also be formed using metal foil. When forming the conductor layer using metal foil, it is preferable to perform step (V) between steps (I) and (II). For example, after step (I), the support is removed and metal foil is laminated on the exposed surface of the resin composition layer. The resin composition layer and metal foil may be laminated using a vacuum lamination method. The lamination conditions may be the same as those described for step (I). Next, step (II) is performed to form an insulating layer. Thereafter, a conductor layer having the desired wiring pattern can be formed using the metal foil on the insulating layer using conventional techniques such as a subtractive method or a modified semi-additive method.

Metal foil can be manufactured by known methods such as electrolysis and rolling. Commercially available metal foils include HLP foil and JXUT-III foil manufactured by JX Nippon Mining & Metals Corporation, and 3EC-III foil and TP-III foil manufactured by Mitsui Mining & Smelting Co., Ltd.

Alternatively, as mentioned above, if a metal foil or a metal foil with a supporting substrate is used as the support for the resin sheet, the conductor layer may be formed using the metal foil.

[Semiconductor device]
The semiconductor device of the present invention includes a layer made of a cured product of the resin composition of the present invention. The semiconductor device of the present invention can be produced using the semiconductor chip package or printed wiring board of the present invention.

Semiconductor devices include various semiconductor devices used in electrical appliances (e.g., computers, mobile phones, digital cameras, and televisions) and vehicles (e.g., motorcycles, automobiles, trains, ships, and aircraft).

Example 1 Synthesis of Diester Compound (A) 268 g (2.00 mol) of allylphenol, 239 g (1.00 mol) of sebacoyl chloride, and 500 g of methyl isobutyl ketone were weighed into a 2-liter four-necked round flask equipped with a stirrer, thermometer, dropping funnel, and nitrogen gas inlet. The contents were heated to 30°C with stirring to dissolve uniformly. 231 g (2.20 mol) of triethylamine was added dropwise to the flask. Triethylamine was added dropwise over a period of 1 hour, starting when the contents reached 30°C. While taking care to avoid heat buildup, the mixture was added dropwise over a period of 1 hour in a temperature-raising curve so that the liquid temperature reached 60-70°C after the completion of the addition. After further stirring at 60-70°C for 1 hour, 200 g of distilled water was added to completely dissolve the by-product organic salt. The resulting liquid was then transferred to a separatory funnel, and the lower layer (aqueous layer) was allowed to stand and separated. Next, 200 g of distilled water and 10 g of disodium phosphate were added, and the mixture was vigorously permeated. The mixture was then allowed to stand and separated, and the lower layer (aqueous layer) was discarded. The mixture was then washed three times with 200 g of distilled water. An appropriate amount of magnesium sulfate (dehydrating agent) was added to the washed reaction solution, and the mixture was vigorously shaken to dehydrate it. The dehydrated reaction solution was then microfiltered. Finally, the reaction solvent was recovered from the filtrate by distillation under high vacuum (maximum temperature 120°C) using a rotary evaporator or the like, to obtain 405 g of diester compound (A) as a liquid compound.

The viscosity of the resulting diester compound (A) was measured using an E-type viscometer (for viscosity at 25°C) and a vibration viscometer (for viscosity at 75°C) under the following measurement conditions. The viscosity of the diester compound (A) at 25°C was 72 mPa·s, and the viscosity at 75°C was 12 mPa·s.

(Viscosity measurement conditions)
Measuring device: E-type viscometer ("RE-80U" manufactured by Toki Sangyo Co., Ltd.)
Cone plate: radius 24 mm, angle 1.34°
Rotation speed: 100 rpm
Temperature: 25℃

(Viscosity measurement conditions when heated)
Measuring device: Vibration viscometer ("VM-10A-L" manufactured by Sekonic Corporation)
Temperature: 75℃

The resulting diester compound (A) was also analyzed by gel permeation chromatography (GPC) and infrared spectroscopy (IR). Figure 1a shows the GPC chart for the compound, and Figure 1b shows the IR chart. Furthermore, a mass spectrum was observed at m/z = 434, which corresponds to the molecular weight of the target substance. As a result, it was confirmed that the resulting diester compound (A) has the desired molecular structure shown below.

Example 2 Synthesis of diester compound (B) 325 g of a solid diester compound (B) was obtained in the same manner as in Example 1, except that 188 g (2.00 mol) of phenol was used instead of allylphenol.

The melting point of the resulting diester compound (B) was 60°C. Furthermore, when the viscosity was measured using a vibration viscometer in the same manner as in Example 1, the viscosity of the compound at 75°C was found to be 17 mPa·s. Figure 2a shows the GPC chart of the compound, and Figure 2b shows its IR chart. Furthermore, a mass spectrum at m/z = 354, corresponding to the molecular weight of the target substance, was observed. As a result, it was confirmed that the resulting diester compound (B) had the desired molecular structure shown below.

Example 3 Synthesis of Diester Compound (C) 370 g of a liquid diester compound (C) was obtained in the same manner as in Example 1, except that 211 g (1.00 mol) of suberic acid dichloride was used instead of sebacoyl chloride.

The viscosity of the resulting diester compound (C) was measured using an E-type viscometer and a vibration viscometer in the same manner as in Example 1. The viscosity was 68 mPa·s at 25°C and 12 mPa·s at 75°C. The GPC chart of this compound is shown in Figure 3a, and the IR chart is shown in Figure 3b. In addition, a mass spectrum was observed at m/z = 406, which corresponds to the molecular weight of the target substance. As a result, it was confirmed that the resulting diester compound (C) had the desired molecular structure shown below.

Example 4 Synthesis of diester compound (D) 418 g of diester compound (D) was obtained as a solid compound in the same manner as in Example 1, except that 288 g (2.00 mol) of 1-naphthol was used instead of allylphenol.

The melting point of the resulting diester compound (D) was 68°C. Furthermore, when the viscosity was measured using a vibration viscometer in the same manner as in Example 1, the viscosity of the compound at 75°C was found to be 76 mPa·s. Figure 4a shows the GPC chart of the compound, and Figure 4b shows its IR chart. Furthermore, a mass spectrum at m/z = 454, corresponding to the molecular weight of the target substance, was observed. As a result, the resulting diester compound (D) was confirmed to have the desired molecular structure shown below.

Example 5 Synthesis of diester compound (E) 505 g of diester compound (E) was obtained as a solid compound in the same manner as in Example 1, except that 368 g (2.00 mol) of pentafluorophenol was used instead of allylphenol.

The melting point of the obtained diester compound (E) was 61°C. Furthermore, when the viscosity was measured using a vibration viscometer in the same manner as in Example 1, the viscosity at 75°C was 19 mPa·s. The GPC chart of this compound is shown in Figure 5a, and the IR chart is shown in Figure 5b. Furthermore, a mass spectrum was observed at m/z = 534, which corresponds to the molecular weight of the target substance. As a result, it was confirmed that the obtained diester compound (E) has the desired molecular structure shown below.

Comparative Example 1 Synthesis of Diester Compound (F) 240 g of a liquid diester compound (F) was obtained in the same manner as in Example 1, except that 203 g (1.00 mol) of isophthalic acid dichloride was used instead of sebacoyl chloride.

The viscosity of the resulting diester compound (F) was measured using an E-type viscometer and a vibration viscometer in the same manner as in Example 1. The viscosity was 6,000 mPa·s at 25°C and 85 mPa·s at 75°C. Figure 6a shows the GPC chart of the compound, and Figure 6b shows the IR chart. In addition, a mass spectrum at m/z = 398, corresponding to the molecular weight of the target substance, was observed. As a result, it was confirmed that the resulting diester compound (F) had the molecular structure shown below.

<Examples 6 to 20 and Comparative Examples 2 to 4>
(1) Preparation of Resin Compositions The synthesized diester compounds (A) to (F) were stirred and mixed while heating to 80°C in the compositions shown in Tables 1 to 3 below to prepare resin compositions.

(2) Production of cured product The prepared resin composition was poured into the gap between two glass plates and cured by heating at 180°C for 90 minutes using a heat circulation oven, to obtain a cured product with a thickness of approximately 1 mm.

Evaluation tests were conducted using the resulting cured products and resin compositions as described below. The results are shown in Tables 1 to 3.

[Dielectric properties]
The cured product was cut into test pieces measuring 2 mm wide and 80 mm long, and the relative permittivity and dielectric loss tangent were measured by the cavity resonance method using a cavity resonator perturbation dielectric constant measuring device ("CP521" manufactured by Kanto Applied Electronics Development Co., Ltd.) and a network analyzer ("E8362B" manufactured by Agilent Technologies) at a measurement frequency of 5.8 GHz and 23°C. For each cured product, measurements were taken on two test pieces (n=2), and the average value was calculated.

[Toughness evaluation]
The cured product was cut into a test piece 30 mm wide and 80 mm long, and the condition of the test piece when bent in half by 180° along the long side was visually inspected.
◯: No cracks or damage observed in the cured product ×: Cracks or damage observed in the cured product

[Thermal conductivity]
Each resin composition was placed in a designated container and cured by heating at 180°C for 90 minutes in a heat circulation oven to produce a cylindrical cured product having a thickness of 10 mm and a diameter of φ36 mm. The thermal conductivity of the obtained cylindrical cured product was measured by the hot disk method using a thermal property measuring device (Kyoto Electronics Manufacturing Co., Ltd., "TPS-2500") in a constant temperature environment of 25°C and 40% RH.

Claims (36)

A resin composition comprising a diester compound (X) and a thermosetting resin,
A resin composition, wherein the diester compound (X) is represented by the following formula (X):
(In the formula,
X _core represents an alkylene group having 6 to 50 carbon atoms;
X ¹ _end and X ² _end each independently represent an aromatic ring which may have a substituent selected from an unsaturated aliphatic hydrocarbon group having 2 to 20 carbon atoms, a halogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 10 carbon atoms. A resin composition comprising a diester compound (X) and a thermosetting resin,
A resin composition, wherein the diester compound (X) is represented by the following formula (X):
(In the formula,
X _core represents an alkylene group having 1 to 50 carbon atoms;
X ¹ _end and X ² _end each independently represent an aromatic ring having an unsaturated aliphatic hydrocarbon group having 2 to 20 carbon atoms as a substituent. A resin composition comprising a diester compound (X) and a thermosetting resin,
A resin composition, wherein the diester compound (X) is represented by the following formula (X):
(In the formula,
X _core represents an alkylene group having 1 to 50 carbon atoms;
X ¹ _end and X ² _end each independently represent an aromatic ring optionally having a substituent selected from an unsaturated aliphatic hydrocarbon group having 2 to 20 carbon atoms, a halogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 10 carbon atoms, and at least one of X ¹ _end and X ² _end is a naphthalene ring optionally having a substituent selected from an unsaturated aliphatic hydrocarbon group having 2 to 20 carbon atoms, a halogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 10 carbon atoms . A resin composition comprising a diester compound (X) and a thermosetting resin,
A resin composition, wherein the diester compound (X) is a diester compound that is liquid at 25°C and is represented by the following formula (X):
(In the formula,
X _core represents an alkylene group having 1 to 50 carbon atoms;
X ¹ _end and X ² _end each independently represent an aromatic ring which may have a substituent selected from an unsaturated aliphatic hydrocarbon group having 2 to 20 carbon atoms, a halogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 10 carbon atoms. A resin composition for an insulating layer of a printed wiring board, comprising a diester compound (X) and a thermosetting resin,
A resin composition for an insulating layer of a printed wiring board , wherein the diester compound (X) is represented by the following formula (X):
(In the formula,
X _core represents an alkylene group having 1 to 50 carbon atoms;
X ¹ _end and X ² _end each independently represent an aromatic ring which may have a substituent selected from an unsaturated aliphatic hydrocarbon group having 2 to 20 carbon atoms, a halogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 10 carbon atoms. A resin composition for semiconductor encapsulation , comprising a diester compound (X) and a thermosetting resin,
A resin composition for semiconductor encapsulation , wherein the diester compound (X) is represented by the following formula (X):
(In the formula,
X _core represents an alkylene group having 1 to 50 carbon atoms;
X ¹ _end and X ² _end each independently represent an aromatic ring which may have a substituent selected from an unsaturated aliphatic hydrocarbon group having 2 to 20 carbon atoms, a halogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 10 carbon atoms. A resin composition comprising a diester compound (X) and a thermosetting resin,
A resin composition, wherein the diester compound (X) is represented by the following formula (X):
(In the formula,
X _core represents an alkylene group having 1 to 50 carbon atoms;
X ¹ _end and X ² _end are the same and represent an aromatic ring having a fluorine atom as a substituent . The resin composition according to any one of claims 2 to 7 , wherein X _core is an alkylene group having 6 to 50 carbon atoms. The resin composition according to any one of claims 1 to 8 , wherein X _core is an alkylene group having 8 to 50 carbon atoms. The resin composition according to any one of claims 1, 4 to 6, 8 and 9, wherein X ¹ _end and X ² _end are each independently an aromatic carbon ring optionally having a substituent selected from an unsaturated aliphatic hydrocarbon group having 2 to 20 carbon atoms, a halogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 10 carbon atoms. The resin composition according to any one of claims 1, 4 to 6, and 8 to 10, wherein X ¹ _end and X ² _end are each independently an aromatic carbon ring optionally having a substituent selected from an unsaturated aliphatic hydrocarbon group having 2 to 20 carbon atoms, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 10 carbon atoms. 12. The resin composition according to claim 1, wherein the aromatic ring in X ¹ _end and X ² _end is an aromatic carbon ring having 6 to 14 carbon atoms. The resin composition according to any one of claims 1 , 3 to 6, 8 to 10 and 12 , wherein X ¹ _end and X ² _end are the same and are aromatic rings having a fluorine atom as a substituent. The resin composition according to any one of claims 1, 4 to 6, and 8 to 13, wherein at least one of X ¹ _end and X ² _end is a naphthalene ring optionally having a substituent selected from an unsaturated aliphatic hydrocarbon group having 2 to 20 carbon atoms, a halogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 10 carbon atoms. The resin composition according to any one of claims 1 , 3 to 6, 8 to 12 and 14 , wherein at least one of X ¹ _end and X ² _end is an aromatic ring selected from a 1-naphthyl group and a phenyl group. The resin composition according to any one of claims 1 , 3 to 6, 8 to 12 , 14 and 15 , wherein at least one of X ¹ _end and X ² _end is a 1-naphthyl group. The resin composition according to any one of claims 1 , 4 to 6, and 8 to 14 , wherein both X ¹ _end and X ² _end are aromatic rings having an unsaturated aliphatic hydrocarbon group having 2 to 20 carbon atoms as a substituent. 18. The resin composition according to claim 1, wherein the unsaturated aliphatic hydrocarbon group in X ¹ _end and X ² _end is an allyl group. The resin composition according to any one of claims 1 to 3 and 5 to 18 , wherein the diester compound (X) is liquid at 25°C. The resin composition according to any one of claims 1 to 19 , wherein the diester compound (X) has a viscosity at 25°C of 300 mPa·s or less. The resin composition according to any one of claims 1 , 5, 6, 8 to 12 , and 15 , wherein the diester compound (X) is a compound represented by the following formula (B):
The resin composition according to any one of claims 1 , 3, 5, 6, 8 to 12 , and 14 to 16 , wherein the diester compound (X) is a compound represented by the following formula (D):
The resin composition according to any one of claims 1 and 5 to 13 , wherein the diester compound (X) is a compound represented by the following formula (E):
The resin composition according to any one of claims 1 to 23 , wherein the thermosetting resin is an epoxy resin. The resin composition according to any one of claims 1 to 24 , further comprising an inorganic filler. The resin composition according to claim 25, wherein the content of the inorganic filler is 50% by mass or more, based on 100% by mass of nonvolatile components in the resin composition. The resin composition according to any one of claims 1 to 26 , further comprising an organic solvent. The resin composition according to any one of claims 1 to 4 and 7 to 27 , which is used for semiconductor encapsulation. The resin composition according to any one of claims 1 to 4 and 7 to 27 , which is used for an insulating layer of a printed wiring board. A resin sheet comprising a support and a layer of the resin composition according to any one of claims 1 to 29 provided on the support. A prepreg obtained by impregnating a sheet-like fiber substrate with the resin composition according to any one of claims 1 to 29 . A cured product of the resin composition according to any one of claims 1 to 29 . A semiconductor chip package comprising an encapsulating layer made of a cured product of the resin composition according to any one of claims 1 to 4 and 6 to 28 . 34. The semiconductor chip package of claim 33 , which is a fan-out type package. A printed wiring board comprising an insulating layer made of a cured product of the resin composition according to any one of claims 1 to 5, 7 to 27 , and 29 . A semiconductor device comprising the semiconductor chip package according to claim 33 or 34 or the printed wiring board according to claim 35 .