JP7541809B2 - Method for manufacturing sacrificial substrate and coreless substrate - Google Patents

Description

The present invention relates to a sacrificial substrate used in the manufacture of a coreless substrate, and a method for manufacturing a coreless substrate using the sacrificial substrate.

In the manufacturing methods of printed circuit boards (package boards), the demand for higher density and thinner printed circuit boards is ever increasing. In conventional manufacturing methods for printed circuit boards, a core has been used when creating a printed circuit board. However, there is a limit to how much higher density and thinner a printed wiring board can be achieved by simply thinning the core. Therefore, in order to meet the demand for higher density and thinner printed circuit boards, coreless boards using coreless manufacturing methods are being investigated.

In general, the coreless method involves, for example, forming a thermosetting resin layer on a sacrificial substrate, then heating and pressurizing the thermosetting resin layer and cooling it to harden it to create a build-up layer, and then peeling the sacrificial substrate from the build-up layer to obtain a coreless substrate.
In addition, when manufacturing a coreless substrate having two or more build-up layers, a first thermosetting resin is laminated on a sacrificial core, and hardened by heating, pressurizing, and cooling to form a first build-up layer, and a second thermosetting resin layer is laminated on the first build-up layer, and hardened by heating, pressurizing, and cooling to form a second build-up layer. Next, the sacrificial substrate is peeled off from the build-up layer to obtain a coreless substrate having two build-up layers.
Patent Document 1 discloses a starting material for manufacturing a coreless substrate, which is configured by laminating a resin substrate, a resin sheet, and copper foil. In Patent Document 1, a starting material is used in which, for reinforcement during the manufacture of a coreless substrate, resin sheets are formed on both sides of a reinforcing plate such as a heat-resistant resin plate or a fiber-reinforced resin plate by vacuum lamination, and two peelable copper foils are further arranged on the resin sheets.
Furthermore, Patent Document 2 discloses an invention relating to a plate-shaped carrier made of synthetic resin used in manufacturing coreless substrates, and describes that in order to suppress misalignment of the circuits, the thermal expansion coefficient of the plate-shaped carrier is within +10% to -30% of the thermal expansion coefficient of the metal foil.

JP 2006-332115 A JP 2014-159175 A

However, the method described in Patent Document 1 has a problem that raw material costs and manufacturing costs are increased and a decrease in production efficiency is unavoidable because a plurality of raw materials are used as starting materials, starting from a plurality of different materials. In addition, the existing technology has a problem that the obtained coreless substrate is warped, which is one of the causes of a decrease in yield.
Furthermore, in the coreless method, for example, a coreless substrate having a second buildup layer on a first buildup layer, or a coreless substrate having two or more buildup layers, such as a coreless substrate having a second buildup layer and a third buildup layer in addition to the second buildup layer, can also be manufactured. However, the problem of warping has been particularly pronounced in such coreless substrates having multiple buildup layers, such as two or more layers.

The present invention has been made in consideration of the above circumstances, and provides a sacrificial substrate that can suppress warping that occurs in the build-up layer after peeling off the sacrificial substrate from two or more build-up layers in a coreless method, and a method for manufacturing a coreless substrate using the sacrificial substrate that can suppress warping that occurs in the build-up layer after peeling off the sacrificial substrate.

As described above, when manufacturing a coreless substrate having two or more build-up layers, the process of laminating a thermosetting resin on a sacrificial substrate and heating, pressurizing, and cooling is performed multiple times, so the sacrificial substrate and the lower build-up layers undergo multiple thermal histories. In addition, the sacrificial substrate, the first build-up layer, the second build-up layer, and the nth build-up layer each shrink due to the hardening and cooling of the thermosetting resin during the heating, pressurizing, and cooling process, so that internal stress accumulates between the sacrificial substrate and the first build-up layer, between the first build-up layer and the second build-up layer, and between the n-1th build-up layer and the nth build-up layer. In particular, in manufacturing a coreless substrate having two or more build-up layers, it was very difficult to design the materials for the sacrificial substrate and the build-up layers while taking into account the shrinkage and deformation of the materials that make up each layer.

The inventors have investigated the causes of warping in coreless substrates having multiple build-up layers and have found that warping in coreless substrates having multiple build-up layers can occur when the sacrificial substrate is peeled off, and that by using a sacrificial substrate that meets certain requirements, it is easier to control the warping of the resulting coreless substrate.
That is, as described above, in the manufacturing process of a coreless substrate having multiple build-up layers, the sacrificial substrate used in manufacturing the coreless substrate undergoes heating, pressurizing, and cooling processes the same number of times as the number of build-up layers to be formed. In this case, if the amount of shrinkage of the sacrificial substrate varies during each heating, pressurizing, and cooling process, it becomes difficult to design the build-up layers taking into account the shrinkage of the sacrificial substrate.

The present inventors have newly discovered that, among the many factors that affect warping during the manufacture of a coreless substrate, the linear expansion coefficient _α1 measured during the temperature rise process of the sacrificial substrate from 50°C to 100°C and the difference in the amount of shrinkage of the sacrificial substrate under specific measurement conditions are set within specific numerical ranges, and a coreless substrate is manufactured using the sacrificial substrate, thereby making it possible to control warping of a coreless substrate having multiple build-up layers, and have thus achieved the present invention.
That is, the present invention provides:
A sacrificial substrate used to form a coreless substrate, comprising:
The sacrificial substrate is a sacrificial substrate for forming a coreless substrate having two or more build-up layers formed by a process involving a heat treatment on at least one surface of the sacrificial substrate,
The sacrificial substrate is composed of a cured prepreg obtained by impregnating a fiber base material with a thermosetting resin composition,
The linear expansion coefficient α ₁ of the sacrificial substrate measured using a thermomechanical analyzer during a temperature rise process from 50° C. to 100° C. is 10 ppm/° C. or less,
The sacrificial substrate has a shrinkage difference Y-X% of -0.0230% or more and 0% or less, as measured by the following measurement method.
(Measurement method)
Shrinkage amount of the first hot press X%: The sacrificial substrate is heated and pressurized using a hot press at a temperature of 200°C and a pressure of 8 kgf/ ^mm2 for 2 hours. The sacrificial substrate at room temperature before the first hot press is used as a reference, and the shrinkage amount of the sacrificial substrate cooled to room temperature after the first hot press is X%.
Second hot-press shrinkage amount Y%: After the first hot-press, the sacrificial substrate is cooled to room temperature and then heated and pressurized using a hot press at a temperature of 200°C and a pressure of 8 kgf/mm2 for ² hours. The sacrificial substrate at room temperature before the first hot-press is used as a reference, and the shrinkage amount of the sacrificial substrate cooled to room temperature after the second hot-press is defined as Y%.
The difference between the amount of shrinkage X% in the first hot-press and the amount of shrinkage Y% in the second hot-press, calculated by the above method, is defined as Y-X%, which is the shrinkage difference Y-X%.

The present invention also provides a method for manufacturing a semiconductor device comprising the steps of: forming a first thermosetting resin layer on at least one surface of the sacrificial substrate;
Next, a first curing step of curing the first thermosetting resin layer to form a first build-up layer;
Then, a second lamination step of forming a second thermosetting resin layer on the first build-up layer;
Then, a second curing step of curing the second thermosetting resin layer to form a second build-up layer;
Next, a peeling step of peeling the sacrificial substrate from a first buildup layer and a second buildup layer is provided.

The sacrificial substrate according to this embodiment can reduce warping of the coreless substrate after peeling off the sacrificial substrate from the multiple build-up layers, reducing the occurrence of defective products and improving yields.

5A to 5C show an example of a manufacturing process for the coreless substrate according to the present embodiment. 1 shows an example of a sacrificial substrate with a hole for measuring the amount of shrinkage. 1 is a cross-sectional view showing an example of a semiconductor device using a coreless substrate according to an embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described. In addition, unless otherwise specified, "-" between numbers in the text indicates "above" or "below."
In this specification, the term "electronic device" is used to include elements, devices, final products, etc. to which electronic engineering technology is applied, such as semiconductor chips, semiconductor elements, printed wiring boards, electric circuit display devices, information and communication terminals, light-emitting diodes, physical batteries, and chemical batteries.
In addition, in all the drawings, the same components are denoted by the same reference numerals, and the description thereof will be omitted as appropriate. Also, the drawings are schematic diagrams and do not correspond to the actual dimensional ratio.

The sacrificial substrate according to this embodiment is a sacrificial substrate for forming a coreless substrate having two or more build-up layers formed on at least one surface of the sacrificial substrate by a process involving a heat treatment.
In the coreless method for manufacturing a coreless substrate, a thermosetting resin layer is formed on a sacrificial substrate, and then the thermosetting resin layer is hardened by heating, pressurizing, and cooling to create a build-up layer. The sacrificial substrate is then peeled off from the build-up layer to obtain the coreless substrate.
A typical method for manufacturing a coreless substrate having two or more build-up layers is to first laminate a first thermosetting resin on a sacrificial core, and then heat, pressurize, and cool the resin to harden it to form a first build-up layer. A second thermosetting resin layer is then laminated on the first build-up layer, and then heat, pressurize, and cool the resin to harden it to form a second build-up layer. The nth build-up layer can also be formed by repeating the lamination of the thermosetting resin layer, and the heating, pressurizing, and cooling. The sacrificial substrate is then peeled off from the build-up layer to obtain a coreless substrate having two or more build-up layers.
The sacrificial substrate of this embodiment is a sacrificial substrate for forming a coreless substrate having two or more build-up layers by a coreless method in which a thermosetting resin layer is formed on a sacrificial substrate, the formed thermosetting resin layer is then hardened by heating, pressurizing, and cooling to create at least two or more build-up layers, and the sacrificial substrate is then peeled off from the build-up layers.

The sacrificial substrate according to this embodiment has a linear expansion coefficient _α1 of 10 ppm/°C or less, more preferably 7 ppm/°C or less, and particularly preferably 5 ppm/°C or less, as measured using a thermomechanical analyzer during a temperature rise process from 50°C to 100°C.
By setting the linear expansion coefficient _α1 to a specific value or less, it is possible to reduce the internal stress occurring at the interface between the sacrificial substrate and the first buildup layer, and to suppress warping of the obtained coreless substrate. The lower limit of the average linear expansion coefficient is not particularly limited, but may be, for example, 0.1 ppm/°C or more, or 1 ppm/°C or more.

The upper limit of the average linear expansion coefficient of the sacrificial substrate according to this embodiment, calculated in the range of 50°C to 250°C, is, for example, 20 ppm/°C or less, preferably 10 ppm/°C or less, and more preferably 8 ppm/°C or less. This makes it possible to reduce warping of the sacrificial substrate and the coreless substrate during the manufacturing process. On the other hand, the lower limit of the average linear expansion coefficient is not particularly limited, but may be, for example, 1 ppm/°C or more, or 3 ppm/°C or more.

The linear expansion coefficient can be measured, for example, using a thermomechanical analyzer TMA. Specifically, the linear expansion coefficient is measured for two cycles of thermomechanical analysis (TMA) using a thermomechanical analyzer TMA (Q400, manufactured by TA Instruments) under conditions of a temperature range of 30 to 260°C, a heating rate of 10°C/min, a load of 10 g, and tension mode. The average linear expansion coefficient in the planar direction (XY direction) in the range of 50 to 100°C or 50°C to 250°C is calculated. The linear expansion coefficient used is the value from the second cycle.

Furthermore, the sacrificial substrate according to this embodiment has a shrinkage difference Y-X of the sacrificial substrate measured by the following measurement method, which is preferably -0.0230% or more and 0% or less, more preferably -0.0200% or more and 0% or less, and particularly preferably -0.0150% or more and 0% or less.
(Measurement method)
Shrinkage amount of the first hot press X%: The sacrificial substrate is heated and pressurized using a hot press at a temperature of 200°C and a pressure of 8 kgf/ ^mm2 for 2 hours. The sacrificial substrate at room temperature before the first hot press is used as a reference, and the shrinkage amount of the sacrificial substrate cooled to room temperature after the first hot press is X%.
Second hot-press shrinkage amount Y%: After the first hot-press, the sacrificial substrate is cooled to room temperature and then heated and pressurized using a hot press at a temperature of 200°C and a pressure of 8 kgf/mm2 for ² hours. The sacrificial substrate at room temperature before the first hot-press is used as a reference, and the shrinkage amount of the sacrificial substrate cooled to room temperature after the second hot-press is defined as Y%.
The difference between the amount of shrinkage X% in the first hot-press and the amount of shrinkage Y% in the second hot-press, calculated by the above method, is defined as Y-X%, which is the shrinkage difference Y-X%.

The present invention is characterized in that, among the various factors involved in the warping that occurs during the manufacture of a coreless substrate, the shrinkage difference Y-X%, which is the difference between the amount of shrinkage of the sacrificial substrate in the second heat press and the amount of shrinkage of the first heat press, is set to a specific value. If the shrinkage difference Y-X%, which is the difference between the amount of shrinkage of the sacrificial substrate in the second heat press and the amount of shrinkage of the first heat press, is set within the above-mentioned range, the difference in the amount of shrinkage between the first heat press and the second heat press will be equal to or less than a certain value. For example, in the design of the thermosetting resin layer for the first buildup layer and the thermosetting resin layer for the second buildup layer, it becomes easier to design materials that take the shrinkage of the sacrificial substrate into consideration, and to design a coreless substrate with less warping overall, and the warping of the resulting coreless substrate can be reduced.

The sacrificial substrate according to this embodiment is made of a cured prepreg obtained by impregnating a fiber base material with a thermosetting resin composition.
Here, in order to set the linear expansion coefficient _α1 and the shrinkage difference to the specific numerical ranges described above, it is important to appropriately select the type, amount, and characteristics of the thermosetting resin composition impregnated into the prepreg. The thermosetting resin composition impregnated into the prepreg is not particularly limited as long as the cured product of the prepreg can have the linear expansion coefficient _α1 and the shrinkage difference to be within the specific numerical ranges described above, but may contain a thermosetting resin, a curing agent, and an inorganic filler.
Each component constituting the thermosetting resin composition according to this embodiment will be described in detail below.

(Thermosetting resin)
The thermosetting resin is not particularly limited as long as the sacrificial substrate, which is a cured product of a prepreg obtained by impregnating a fiber base material with a thermosetting resin composition, can have the linear expansion coefficient _α1 and the shrinkage amount within the specific numerical ranges described above.
The thermosetting resin is preferably at least one selected from the group consisting of an epoxy resin, a maleimide resin, a phenolic resin, and a cyanate resin. The thermosetting resin may contain at least an epoxy resin or a maleimide compound, or may contain at least an epoxy resin.
In addition, the thermosetting resin is preferably liquid at room temperature of 25° C. This can improve the dispersibility of each component in the thermosetting resin composition and can increase the amount of inorganic filler filled.

The lower limit of the viscosity of the thermosetting resin of this embodiment at 25°C is, for example, 0.1 Pa·s or more, more preferably 0.5 Pa·s or more, and even more preferably 1 Pa·s or more. This can improve the film-forming properties of the thermosetting resin composition. On the other hand, the upper limit of the viscosity at 25°C is, for example, 200 Pa·s or less, preferably 100 Pa·s or less, and more preferably 50 Pa·s or less. This can improve the dispersibility of the thermosetting resin composition.

The lower limit of the epoxy equivalent of the epoxy resin of this embodiment is, for example, 300 g/eq or more, preferably 330 g/eq or more, and more preferably 350 g/eq or more. This allows the molecular weight of the crosslinking point to be appropriately controlled, so that a cured product of the thermosetting resin composition with an optimal crosslinking density can be realized. In addition, the breaking elongation of the cured product of the thermosetting resin composition can be improved. On the other hand, the upper limit of the epoxy equivalent is not particularly limited, but may be, for example, 700 g/eq or less, 600 g/eq or less, or 500 g/eq or less. This allows the strength of the cured product of the thermosetting resin composition to be improved.

The lower limit of the weight average molecular weight (Mw) of the epoxy resin of this embodiment is not particularly limited, but may be Mw 300 or more, and preferably Mw 800 or more. When Mw is equal to or greater than the above lower limit, it is possible to suppress the occurrence of tack in the cured resin film. The upper limit of Mw is not particularly limited, but may be Mw 20,000 or less, and preferably Mw 15,000 or less. When Mw is equal to or less than the above upper limit, handling properties are improved and it is easy to form a resin film. The Mw of the epoxy resin can be measured, for example, by GPC.

The epoxy resin of the present embodiment is liquid at room temperature of 25° C. and preferably contains at least one first epoxy resin whose epoxy equivalent is within the above range.
The type of the first epoxy resin is not particularly limited, and examples thereof include bisphenol type epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol E type epoxy resin, bisphenol S type epoxy resin, bisphenol M type epoxy resin, bisphenol P type epoxy resin, and bisphenol Z type epoxy resin; novolac type epoxy resins such as phenol novolac type epoxy resin, cresol novolac type epoxy resin, tetraphenol group ethane type novolac type epoxy resin, and novolac type epoxy resin having a condensed ring aromatic hydrocarbon structure; biphenyl type epoxy resins; Examples of the first epoxy resin include alkoxy resins; aralkyl epoxy resins such as xylylene epoxy resins and biphenyl aralkyl epoxy resins; naphthalene epoxy resins such as naphthylene ether epoxy resins, naphthol epoxy resins, naphthalene diol epoxy resins, bifunctional to tetrafunctional naphthalene epoxy resins, binaphthyl epoxy resins, and naphthalene aralkyl epoxy resins; anthracene epoxy resins; phenoxy epoxy resins; dicyclopentadiene epoxy resins; norbornene epoxy resins; adamantane epoxy resins; fluorene epoxy resins; and polyether epoxy resins. The first epoxy resin may be used alone or in combination of two or more. Among the first epoxy resins, from the viewpoint of viscosity, one or more selected from the group consisting of bisphenol A epoxy resins, fluorene epoxy resins, bifunctional naphthalene epoxy resins, and polyether epoxy resins may be used.

In addition, as the epoxy resin of this embodiment, in addition to the first epoxy resin, another second epoxy resin may be used in combination. This second epoxy resin can be selected from the types of epoxy resins listed as the first epoxy resin.

Among the epoxy resins, from the viewpoint of the heat resistance of the resulting sacrificial substrate, one or more selected from the group consisting of bisphenol type epoxy resins, novolac type epoxy resins, biphenyl type epoxy resins, aralkyl type epoxy resins, naphthalene type epoxy resins, anthracene type epoxy resins, and dicyclopentadiene type epoxy resins are preferred, and one or more selected from the group consisting of aralkyl type epoxy resins, novolac type epoxy resins having a condensed ring aromatic hydrocarbon structure, and naphthalene type epoxy resins are more preferred.

The lower limit of the content of the epoxy resin is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more, based on 100% by mass of the entire thermosetting resin composition (total solid content excluding the solvent). When the content of the epoxy resin is equal to or more than the above lower limit, the handling property is improved and it becomes easier to form a resin film. On the other hand, the upper limit of the content of the epoxy resin is not particularly limited to the entire thermosetting resin composition, but is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 25% by mass or less. When the content of the epoxy resin is equal to or less than the above upper limit, the strength and heat resistance of the obtained sacrificial substrate may be improved, or the linear expansion coefficient of the sacrificial substrate may be reduced, improving the effect of reducing warpage.
The total solid content of the thermosetting resin composition refers to all components excluding the solvent contained in the thermosetting resin composition. The same applies hereinafter in this specification.

(Maleimide Compound)
The thermosetting resin composition of the present embodiment may contain a maleimide compound.
In this embodiment, the maleimide group of the maleimide compound has a planar structure of a five-membered ring, and the double bond of the maleimide group is highly polar and easily interacts with molecules, so that it exhibits strong intermolecular interactions with the maleimide group, benzene ring, other compounds having planar structures, etc., and can suppress molecular motion. Therefore, by including the maleimide compound in the thermosetting resin composition, the linear expansion coefficient of the obtained sacrificial substrate can be reduced, the glass transition temperature can be improved, and further, the heat resistance can be improved.

The maleimide compound is preferably a maleimide compound having at least two maleimide groups in the molecule.
Examples of the imide-extended bismaleimide include a maleimide compound represented by the following formula (a1), a maleimide compound represented by the following formula (a2), and a maleimide compound represented by the following formula (a3). Specific examples of the maleimide compound represented by formula (a1) include BMI-1500 (manufactured by Designer Molecules, molecular weight 1500). Specific examples of the maleimide compound represented by formula (a2) include BMI-1700 (manufactured by Designer Molecules, molecular weight 1700), BMI-1400 (manufactured by Designer Molecules, molecular weight 1400), and the like. Specific examples of the maleimide compound represented by formula (a3) include BMI-3000 (manufactured by Designer Molecules, molecular weight 3000), and the like.

上記式（ａ１）において、ｎは１以上１０以下の整数を示す。

In the above formula (a1), n represents an integer of 1 or more and 10 or less.

上記式（ａ２）において、ｎは１以上１０以下の整数を示す。

In the above formula (a2), n represents an integer of 1 or more and 10 or less.

上記式（ａ３）において、ｎは１以上１０以下の整数を示す。

In the above formula (a3), n represents an integer of 1 or more and 10 or less.

The lower limit of the weight average molecular weight (Mw) of the maleimide compound is not particularly limited, but is preferably Mw400 or more, particularly preferably Mw800 or more. When Mw is equal to or more than the lower limit, it is possible to suppress the occurrence of tack in the insulating layer. The upper limit of Mw is not particularly limited, but is preferably Mw4000 or less, more preferably Mw2500 or less. When Mw is equal to or less than the upper limit, the handling property is improved during the preparation of the sacrificial substrate, and it is easy to form the sacrificial substrate. The Mw of the maleimide compound can be measured, for example, by GPC (gel permeation chromatography, standard substance: polystyrene equivalent).
Moreover, the Mw of the imide-extended bismaleimide having maleimides at both ends can be regarded as the molecular weight between crosslinking points.

The content of the maleimide compound contained in the thermosetting resin composition is not particularly limited, but is preferably 1.0% by mass or more and 25.0% by mass or less, and more preferably 3.0% by mass or more and 20.0% by mass or less, when the total solid content of the thermosetting resin composition (i.e., components excluding the solvent) is taken as 100% by mass. When the content of the maleimide compound is within the above range, the balance between low thermal shrinkage and chemical resistance of the resulting sacrificial substrate can be further improved.

(Hardening agent)
The thermosetting resin composition of the present embodiment may contain a curing agent.
The curing agent is not particularly limited, but examples thereof include tertiary amine compounds such as benzyldimethylamine (BDMA) and 2,4,6-trisdimethylaminomethylphenol (DMP-30); imidazole compounds such as 2-methylimidazole, 2-ethyl-4-methylimidazole (EMI24), 2-phenyl-4-methylimidazole (2P4MZ), 2-phenylimidazole (2PZ), 2-phenyl-4-methyl-5-hydroxyimidazole (2P4MHZ), and 1-benzyl-2-phenylimidazole (1B2PZ); and catalyst-type curing agents such as Lewis acids such as BF3 complexes.
Further, for example, aliphatic polyamines such as diethylenetriamine (DETA), triethylenetetramine (TETA), and metaxylylenediamine (MXDA), m-phenylenediamine, p-phenylenediamine, o-xylylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 1,5-diaminonaphthalene, 4,4'-(p-phenylenediisopropane), aromatic polyamines such as 4,4'-diamino-3,3'-dimethyldiphenylmethane, 4,4'-diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane, and 3,3'-diethyl-4,4'-diaminodiphenylmethane; polyamine compounds including dicyandiamide (DICY) and organic acid dihydralazide; alicyclic polyamines such as hexahydrophthalic anhydride (HHPA) and methyltetrahydrophthalic anhydride (MTHPA); Acid anhydrides, including aromatic acid anhydrides such as trimellitic anhydride (TMA), pyromellitic anhydride (PMDA), and benzophenonetetracarboxylic acid (BTDA); polymercaptan compounds such as polysulfides, thioesters, and thioethers; isocyanate compounds such as isocyanate prepolymers and blocked isocyanates; polyaddition-type curing agents such as organic acids such as carboxylic acid-containing polyester resins; 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 2,2'-methylenebis Phenol compounds such as bis(4-methyl-6-tert-butylphenol), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), 4,4'-thiobis(3-methyl-6-tert-butylphenol), 2,6-di-tert-butyl-4-methylphenol, 2,5-di-tert-butylhydroquinone, and 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)trione can also be used.
Furthermore, as the second curing agent, for example, a phenolic resin-based curing agent such as a novolac-type phenolic resin or a resol-type phenolic resin, a urea resin such as a methylol group-containing urea resin, or a melamine resin such as a methylol group-containing melamine resin may be used as a condensation type curing agent. These may be used alone or in combination of two or more kinds.

The phenolic resin-based curing agent is a monomer, oligomer, or polymer having two or more phenolic hydroxyl groups in one molecule, and the molecular weight and molecular structure are not particularly limited. Examples of the curing agent include novolac-type phenolic resins such as phenol novolac resin, cresol novolac resin, and naphthol novolac resin; multifunctional phenolic resins such as triphenolmethane-type phenolic resin; modified phenolic resins such as terpene-modified phenolic resin and dicyclopentadiene-modified phenolic resin; aralkyl-type resins such as phenol aralkyl resins having a phenylene skeleton and/or biphenylene skeleton, and naphthol aralkyl resins having a phenylene skeleton and/or biphenylene skeleton; and bisphenol compounds such as bisphenol A and bisphenol F. These may be used alone or in combination of two or more. Among these, those having a hydroxyl equivalent of 90 g/eq or more and 250 g/eq or less may be used from the viewpoint of curability.
The weight average molecular weight of the phenol resin is not particularly limited, and may be 4×10 ² or more and 1.8×10 ³ or less, and preferably 5×10 ² or more and 1.5×10 ³ or less. By setting the weight average molecular weight to be equal to or more than the above lower limit, problems such as tackiness of the prepreg are less likely to occur, and by setting it to be equal to or less than the above upper limit, impregnation into the fiber base material is improved during preparation of the prepreg, and a more uniform sacrificial substrate can be obtained.

The lower limit of the content of the curing agent is not particularly limited, but is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.2% by mass or more, based on 100% by mass of the total solid content of the thermosetting resin composition. By setting the content of the curing agent to the above lower limit or more, the effect of promoting curing can be fully exhibited. On the other hand, the upper limit of the content of the curing agent is not particularly limited, but is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less, based on 100% by mass of the total solid content of the thermosetting resin composition. When the content of the curing agent is equal to or less than the above upper limit, the prepreg can be further improved in storage stability.

(Inorganic filler)
The thermosetting resin composition of the present embodiment may contain an inorganic filler.
Examples of inorganic fillers include silicates such as talc, calcined clay, uncalcined clay, mica, and glass; oxides such as titanium oxide, alumina, boehmite, silica, and fused silica; carbonates such as calcium carbonate, magnesium carbonate, and hydrotalcite; hydroxides such as aluminum hydroxide, magnesium hydroxide, and calcium hydroxide; sulfates or sulfites such as barium sulfate, calcium sulfate, and calcium sulfite; borates such as zinc borate, barium metaborate, aluminum borate, calcium borate, and sodium borate; nitrides such as aluminum nitride, boron nitride, silicon nitride, and carbon nitride; and titanates such as strontium titanate and barium titanate.
Among these, talc, alumina, glass, silica, mica, aluminum hydroxide, and magnesium hydroxide are preferred, and silica is particularly preferred. As the inorganic filler, one of these may be used alone, or two or more of them may be used in combination.

The lower limit of the average particle size of the inorganic filler is not particularly limited, but may be, for example, 0.01 μm or more, or 0.05 μm or more.
This can prevent the viscosity of the thermosetting resin varnish from increasing, and improve the workability when preparing the insulating layer. The upper limit of the average particle size of the inorganic filler is not particularly limited, but is preferably 5.0 μm or less, more preferably 2.0 μm or less, and even more preferably 1.5 μm or less. This can prevent the phenomenon of sedimentation of the inorganic filler in the thermosetting resin varnish, and can obtain a more uniform resin film.
In this embodiment, the average particle diameter of the inorganic filler can be determined by, for example, measuring the particle size distribution of the particles on a volume basis using a laser diffraction particle size distribution measuring device (LA-500, manufactured by HORIBA), and the median diameter (D50) can be regarded as the average particle diameter.

In addition, in this embodiment, when the content of the inorganic filler is 60 mass% or more, the lower limit of the average particle diameter of the inorganic filler is, for example, 0.5 μm or more, preferably 0.6 μm or more, and more preferably 0.8 μm or more. On the other hand, the upper limit of the average particle diameter of the inorganic filler is, for example, 2 μm or less, preferably 1.9 μm or less, and more preferably 1.8 μm or less. By setting the content of the inorganic filler within the above range, it is possible to further increase the strength while reducing warping of the cured product of the thermosetting resin composition.

The inorganic filler is not particularly limited, but may be an inorganic filler having a monodisperse average particle size, or an inorganic filler having a polydisperse average particle size. Furthermore, one or more types of inorganic fillers having monodisperse and/or polydisperse average particle sizes may be used in combination.

The inorganic filler preferably contains silica particles. The average particle size of the silica particles is not particularly limited, but may be, for example, 5.0 μm or less, 0.01 μm or more and 4.0 μm or less, or 0.02 μm or more and 2.0 μm or less. This can further improve the filling property of the inorganic filler.

The lower limit of the content of the inorganic filler is not particularly limited, but is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on 100% by mass of the total solid content of the thermosetting resin composition. This allows the cured resin film to have particularly low thermal expansion and low water absorption. This allows the sacrificial substrate and the resulting coreless substrate to be suppressed from warping. In addition, the cured prepreg of this embodiment can increase the content of the inorganic filler while maintaining a high elongation rate, thereby improving the stress relaxation properties. On the other hand, the upper limit of the content of the inorganic filler is not particularly limited, but may be, for example, 98% by mass or less, 95% by mass or less, or 90% by mass or less, based on 100% by mass of the total solid content of the thermosetting resin composition. This allows the processability of the cured prepreg to be improved.

(Cyanate resin)
The thermosetting resin composition of the present embodiment may further contain a cyanate resin.
The cyanate resin is a resin having a cyanate group (-O-CN) in the molecule, and a resin having two or more cyanate groups in the molecule can be used. There are no particular limitations on such cyanate resin, but it can be obtained, for example, by reacting a halogenated cyanide compound with a phenol or naphthol, and prepolymerizing it by a method such as heating as necessary. In addition, a commercially available product prepared in this manner can also be used.
By using a cyanate resin, it is possible to reduce the linear expansion coefficient of the cured prepreg and to increase the mechanical strength of the cured prepreg.

Examples of cyanate resins include novolac cyanate resins; bisphenol cyanate resins such as bisphenol A cyanate resin, bisphenol E cyanate resin, and tetramethylbisphenol F cyanate resin; naphthol aralkyl cyanate resins obtained by reacting naphthol aralkyl phenol resin with a cyanogen halide; dicyclopentadiene cyanate resin; and biphenyl alkyl cyanate resin. Among these, novolac cyanate resins and naphthol aralkyl cyanate resins are preferred, and novolac cyanate resins are more preferred. By using novolac cyanate resins, the crosslink density of the cured product of the prepreg is increased, improving heat resistance.

The reason for this is that novolac cyanate resin forms a triazine ring after the curing reaction. Furthermore, it is thought that novolac cyanate resin has a high proportion of benzene rings due to its structure, making it prone to carbonization. In addition, the cured resin film containing novolac cyanate resin has excellent rigidity. This further improves the heat resistance of the cured prepreg.

As the novolac-type cyanate resin, for example, one represented by the following general formula (I) can be used.

The average repeating unit n of the novolac cyanate resin represented by general formula (I) is any integer. The average repeating unit n is not particularly limited, but is preferably 1 or more, and more preferably 2 or more. When the average repeating unit n is equal to or greater than the above lower limit, the heat resistance of the novolac cyanate resin is improved, and the elimination and volatilization of low molecular weight molecules during heating can be suppressed. The average repeating unit n is not particularly limited, but is preferably 10 or less, and more preferably 7 or less. When n is equal to or less than the above upper limit, the melt viscosity can be suppressed from increasing, and the moldability of the prepreg can be improved.

As the cyanate resin, naphthol aralkyl type cyanate resin represented by the following general formula (II) is also preferably used. The naphthol aralkyl type cyanate resin represented by the following general formula (II) is obtained by condensing a naphthol aralkyl type phenol resin obtained by reacting naphthols such as α-naphthol or β-naphthol with p-xylylene glycol, α,α'-dimethoxy-p-xylene, 1,4-di(2-hydroxy-2-propyl)benzene, etc., with a cyanogen halide. The repeating unit n in general formula (II) is preferably an integer of 10 or less. When the repeating unit n is 10 or less, a more uniform prepreg can be obtained. In addition, intramolecular polymerization is less likely to occur during synthesis, liquid separation during washing with water is improved, and a decrease in yield tends to be prevented.

（式中、Ｒはそれぞれ独立に水素原子またはメチル基を示し、ｎは１以上１０以下の整数を示す。）

(In the formula, each R independently represents a hydrogen atom or a methyl group, and n represents an integer of 1 to 10.)

In addition, one type of cyanate resin may be used alone, or two or more types may be used in combination, or one or more types may be used in combination with their prepolymers.

The lower limit of the cyanate resin content is, for example, preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, based on 100% by mass of the total solid content of the thermosetting resin composition. The cured prepreg can have a low linear expansion and a high elastic modulus. On the other hand, the upper limit of the cyanate resin content is not particularly limited, based on 100% by mass of the total solid content of the thermosetting resin composition, but is, for example, preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. The heat resistance and moisture resistance can be improved. In addition, when the cyanate resin content is within the above range, the storage modulus E' of the cured prepreg can be further improved.

(Cure Accelerator)
The thermosetting resin composition of the present embodiment may contain, for example, a curing accelerator. This can improve the curing property of the thermosetting resin composition. As the curing accelerator, one that accelerates the curing reaction of the thermosetting resin can be used, and the type is not particularly limited. In the present embodiment, examples of the curing accelerator include organic metal salts such as zinc naphthenate, cobalt naphthenate, tin octylate, cobalt octylate, zinc octylate, bisacetylacetonate cobalt (II), and trisacetylacetonate cobalt (III), tertiary amines such as triethylamine, tributylamine, and diazabicyclo[2,2,2]octane, 2-phenylimidazole, 2-phenyl-4-methylimidazole, and 2-ethyl-4-ethylimidazole. The curing agent may contain one or more selected from imidazoles such as 2-phenyl-4-ethylimidazole, 2-phenyl-4-methyl-5-hydroxyimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, and 2-phenyl-4,5-dihydroxyimidazole, phenolic compounds such as phenol, bisphenol A, and nonylphenol, organic acids such as acetic acid, benzoic acid, salicylic acid, and paratoluenesulfonic acid, and onium salt compounds. Among these, it is more preferable to contain an onium salt compound from the viewpoint of more effectively improving the curing property.

The onium salt compound used as the curing accelerator is not particularly limited, but for example, a compound represented by the following general formula (2) can be used.

（式（２）中、Ｐはリン原子、Ｒ_３、Ｒ_４、Ｒ_５およびＲ_６は、それぞれ、置換もしくは無置換の芳香環または複素環を有する有機基、あるいは置換もしくは無置換の脂肪族基を示し、互いに同一であっても異なっていてもよい。Ａ－は分子外に放出しうるプロトンを少なくとも１個以上分子内に有するｎ（ｎ≧１）価のプロトン供与体のアニオン、またはその錯アニオンを示す）

(In formula (2), P represents a phosphorus atom, R ₃ , R ₄ , R ₅ and R ₆ each represent a substituted or unsubstituted organic group having an aromatic ring or heterocycle, or a substituted or unsubstituted aliphatic group, and may be the same or different from one another. A- represents an anion of a proton donor having a valence of n (n≧1) and having at least one proton capable of being released to the outside of the molecule, or a complex anion thereof.)

The lower limit of the content of the curing accelerator may be, for example, 0.01% by mass or more, preferably 0.05% by mass or more, based on 100% by mass of the total solid content of the thermosetting resin composition. By setting the content of the curing accelerator to the above lower limit or more, the curability of the thermosetting resin composition can be more effectively improved. On the other hand, the upper limit of the content of the curing accelerator may be, for example, 2.5% by mass or less, preferably 1% by mass or less, based on 100% by mass of the total solid content of the thermosetting resin composition. By setting the content of the curing accelerator to the above upper limit or less, the storage stability of the thermosetting resin composition can be improved.

(Coupling Agent)
The thermosetting resin composition of the present embodiment may contain a coupling agent. The coupling agent may be added directly during preparation of the thermosetting resin composition, or may be added in advance to the inorganic filler. The use of the coupling agent can improve the wettability of the interface between the inorganic filler and each resin. Therefore, it is preferable to use a coupling agent, and the heat resistance of the cured product of the prepreg can be improved. In addition, as described later, a metal foil is adhered to the sacrificial substrate of the present embodiment, and the use of a coupling agent can improve the adhesion with the metal foil. Furthermore, since the moisture absorption resistance can be improved, the adhesion with the copper foil can be maintained even after being placed in a humid environment.

Examples of the coupling agent include silane coupling agents such as epoxy silane coupling agents, cationic silane coupling agents, and amino silane coupling agents, titanate coupling agents, and silicone oil coupling agents. The coupling agent may be used alone or in combination of two or more. In this embodiment, the coupling agent may contain a silane coupling agent.
This makes it possible to increase the wettability at the interface between the inorganic filler and each resin, and further improve the heat resistance of the cured product of the prepreg.

Various types of silane coupling agents can be used, including, for example, epoxy silane, amino silane, alkyl silane, ureido silane, mercapto silane, vinyl silane, etc.

Specific examples of compounds include γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane, N-phenylγ-aminopropyltriethoxysilane, N-phenylγ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltriethoxysilane, N-6-(aminohexyl)3-aminopropyltrimethoxysilane, N-(3-(trimethoxysilylpropyl)-1,3-benzenedimethanane, γ-glycidoxy Examples of the silane include cyclopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, methyltrimethoxysilane, γ-ureidopropyltriethoxysilane, vinyltriethoxysilane, etc., and one or more of these can be used in combination. Among these, epoxysilane, mercaptosilane, and aminosilane are preferred, and as the aminosilane, primary aminosilane or anilinosilane is more preferred.

The amount of the coupling agent added can be appropriately adjusted based on the specific surface area of the inorganic filler. The lower limit of the amount of the coupling agent added can be, for example, 0.05% by mass or more, preferably 0.1% by mass or more, based on 100% by mass of the total solid content of the thermosetting resin composition. When the content of the coupling agent is equal to or more than the above lower limit, the inorganic filler can be sufficiently coated, and the heat resistance of the cured resin film can be improved. On the other hand, the upper limit of the amount of the coupling agent added can be, for example, 3% by mass or less, preferably 1.5% by mass or less, based on 100% by mass of the total solid content of the thermosetting resin composition. When the content of the coupling agent is equal to or less than the above upper limit, the reaction can be suppressed from being affected, and the bending strength of the cured prepreg can be suppressed from being reduced.

(Additives)
The thermosetting resin composition of the present embodiment may contain additives other than the above components, such as a colorant containing one or more selected from the group consisting of dyes such as green, red, blue, yellow, and black, pigments such as black pigments, and coloring agents, a stress reducing agent, an antifoaming agent, a leveling agent, an ultraviolet absorbing agent, a foaming agent, an antioxidant, a flame retardant, an ion trapping agent, and rubber particles, within the scope of the present invention. These may be used alone or in combination of two or more.

Examples of pigments include inorganic pigments such as kaolin, synthetic iron oxide red, cadmium yellow, nickel titanium yellow, strontium yellow, hydrous chromium oxide, chromium oxide, cobalt aluminate, and synthetic ultramarine blue, polycyclic pigments such as phthalocyanine, and azo pigments.

Dyes include isoindolinone, isoindoline, quinophthalone, xanthene, diketopyrrolopyrrole, perylene, perinone, anthraquinone, indigoid, oxazine, quinacridone, benzimidazolone, violanthrone, phthalocyanine, azomethine, etc.

Examples of rubber particles include core-shell type rubber particles, cross-linked acrylonitrile butadiene rubber particles, cross-linked styrene butadiene rubber particles, acrylic rubber particles, silicone particles, etc.

(Prepreg manufacturing method)
The prepreg constituting the sacrificial substrate in this embodiment is a prepreg containing a fiber base material inside and impregnated with a thermosetting resin composition into the fiber base material. The prepreg according to this embodiment is obtained, for example, by impregnating a fiber base material with a resin composition containing one or more thermosetting resins and a filler, and then semi-curing the resin composition.
In this embodiment, the method of impregnating the resin composition into the fiber substrate is not particularly limited, but examples include a method of dissolving the resin composition in a solvent to prepare a resin varnish and applying the resin varnish to the fiber substrate.

In this embodiment, the varnish-like thermosetting resin composition may contain a solvent.
Examples of the solvent include organic solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, toluene, ethyl acetate, cyclohexane, heptane, cyclohexane, cyclohexanone, tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethylsulfoxide, ethylene glycol, cellosolves, carbitols, anisole, and N-methylpyrrolidone. These may be used alone or in combination of two or more.

When the thermosetting resin composition is in the form of a varnish, the solid content of the thermosetting resin composition may be, for example, 30% by mass or more and 80% by mass or less, and more preferably 40% by mass or more and 70% by mass or less. This results in a thermosetting resin composition that is extremely excellent in workability and film-forming properties.

The varnish-like thermosetting resin composition can be prepared by dissolving, mixing, and stirring the above-mentioned components in a solvent using various mixers such as ultrasonic dispersion, high-pressure collision dispersion, high-speed rotation dispersion, bead mill, high-speed shear dispersion, and rotation-revolution dispersion. In this embodiment, the method of impregnating the thermosetting resin composition into the fiber substrate is not particularly limited, but examples include a method of dissolving the thermosetting resin composition in a solvent to prepare a resin varnish and immersing the fiber substrate in the resin varnish, a method of applying the resin varnish to the fiber substrate using various coaters, a method of spraying the resin varnish onto the fiber substrate, and a method of laminating both sides of the fiber substrate with the resin film made of the thermosetting resin composition.

The glass transition temperature of the cured product of the thermosetting resin composition is preferably 150° C. or higher and 350° C. or lower, and more preferably 200° C. or higher and 290° C. or lower.
The higher the glass transition temperature Tg of the cured product of the thermosetting resin composition, the higher the linear expansion coefficient _α1 tends to be, while the shrinkage amount tends to be smaller. Therefore, in order to set the linear expansion coefficient _α1 and the shrinkage amount in the desired numerical range, it is preferable to set the glass transition temperature Tg of the cured product of the thermosetting resin composition within a specific numerical range.

The glass transition temperature can be measured using a dynamic viscoelasticity analyzer (DMA). The glass transition temperature is the temperature at which the loss tangent tan δ is maximum in the curve obtained by dynamic viscoelasticity measurement at a heating rate of 5°C/min and a frequency of 1 Hz.

In this embodiment, the glass transition temperature of the cured product of the thermosetting resin composition can be calculated from the measurement results obtained by performing a dynamic viscoelasticity test on the cured product of the resin film obtained by heat treatment at 200°C for 2 hours using, for example, a dynamic viscoelasticity measuring device under conditions of a frequency of 1 Hz and a temperature increase rate of 5°C/min. The dynamic viscoelasticity measuring device is not particularly limited, but for example, a DMA device (Q800, manufactured by TA Instruments) can be used.

(Fiber base material)
Examples of the fiber substrate include glass fiber substrates such as woven glass cloth and nonwoven glass cloth, inorganic fiber substrates such as woven or nonwoven cloth containing inorganic compounds other than glass as components, and organic fiber substrates composed of organic fibers such as aromatic polyamideimide resin, polyamide resin, aromatic polyester resin, polyester resin, polyimide resin, and fluororesin, etc. Among these substrates, the use of a glass fiber substrate typified by glass woven cloth in terms of strength can improve the mechanical strength and heat resistance of the printed wiring board.
The thickness of the fiber base material is not particularly limited, but is preferably 10 μm or more and 200 μm or less, more preferably 15 μm or more and 180 μm or less, and even more preferably 20 μm or more and 150 μm or less. By using a fiber base material having such a thickness, the handling property during the production of the prepreg is improved, and it becomes easy to control the thermal expansion and thermal contraction of the obtained sacrificial substrate.
When the thickness of the fiber substrate is equal to or less than the upper limit, the impregnation of the thermosetting resin composition in the fiber substrate is improved, and the generation of voids can be suppressed. When the thickness of the fiber substrate is equal to or more than the lower limit, the strength of the fiber substrate and the prepreg can be improved. As a result, the handling property can be improved, the preparation of the prepreg can be facilitated, and the warping of the resulting sacrificial substrate can be suppressed.

As the glass fiber substrate, for example, a glass fiber substrate formed from one or more types of glass selected from E glass, S glass, D glass, T glass, NE glass, UT glass, L glass, HP glass, and quartz glass is preferably used.

(Method of manufacturing a sacrificial substrate using prepreg)
The prepreg obtained by the above method is cured to obtain the sacrificial substrate according to the present embodiment. The sacrificial substrate according to the present embodiment can also be obtained by stacking one or more prepregs and curing them. The number of prepregs stacked is, for example, 1 to 4.
The thickness of the sacrificial substrate made of the cured prepreg is preferably 20 μm to 300 μm, more preferably 25 μm to 250 μm, and even more preferably 30 μm to 200 μm. By using a sacrificial substrate having such a thickness, the amount of warping during the coreless method and the internal stress with the build-up layer can be controlled, and the amount of warping of the coreless substrate when the sacrificial substrate is peeled off can be further reduced.

The sacrificial substrate according to this embodiment can also have metal foil adhered to one or both surfaces. The prepreg curing and the metal foil adhesion can be performed at the same time or at different times, but it is preferable to perform the prepreg curing and the metal foil adhesion simultaneously.

(Metal foil to be attached to sacrificial substrate)
Examples of metals constituting the metal foil include copper, copper-based alloys, aluminum, aluminum-based alloys, silver, silver-based alloys, gold, gold-based alloys, zinc, zinc-based alloys, nickel, nickel-based alloys, tin, tin-based alloys, iron, iron-based alloys, Fe-Ni-based alloys such as Kovar (trade name), 42 alloy, Invar, and Super Invar, W, and Mo. Among these, the metal constituting the metal foil is preferably copper or a copper alloy, because it has excellent conductivity, is easy to form a circuit by etching, and is inexpensive. That is, the metal foil is preferably copper foil.
The metal foil to be adhered to the sacrificial substrate is preferably a peelable metal foil. When two or more desired build-up layers are laminated on the sacrificial substrate, the peelable metal foil is sandwiched between the sacrificial substrate and the first build-up layer. In this state, it is preferable to detach the sacrificial substrate from the build-up layer by peeling the peelable copper foil. After peeling, one side of the peelable metal foil remains on the build-up layer side, and the other side of the peelable metal foil remains on the sacrificial substrate side. As the peelable metal foil, for example, model number MT18Ex-S manufactured by Mitsui Mining & Smelting Co., Ltd. can be used. In addition, the peelable metal foil is preferably a foil having a total thickness before peeling of 15 μm to 30 μm, and more preferably a foil having a thickness of 18 μm to 25 μm. The peelable metal foil is preferably one having a thin film thickness of 1 μm to 6 μm after peeling, more preferably one having a thickness of 2 μm to 5 μm, and the peelable metal foil is preferably one having a thick film thickness of 14 μm to 24 μm after peeling, more preferably one having a thickness of 16 μm to 20 μm. The peelable metal foil is preferably bonded so that the thin film side remains on the build-up layer side and the thick film side remains on the sacrificial substrate side.
Additionally, the metal foil can be adhered to one or both sides of the sacrificial substrate, and more preferably to both sides.

The method for producing the sacrificial substrate with metal foil is as follows.
A metal foil is placed on both the upper and lower surfaces or one side of the outer surface of a prepreg or a laminate of two or more prepregs, and these are bonded under high vacuum conditions using a laminator or Becquerel device, or a metal foil is placed on both the upper and lower surfaces or one side of the outer surface of the prepreg as is. When two or more prepregs are laminated, a metal foil is placed on both the upper and lower surfaces or one side of the outermost surface of the laminated prepregs. Next, a sacrificial substrate with metal foil can be obtained by heating and pressurizing the laminate of the prepreg and the metal foil. Here, it is preferable to continue pressing until the end of cooling during the heating and pressurizing.
The heating temperature during the above hot and pressure molding is preferably 100° C. or higher and 250° C. or lower, and more preferably 150° C. or higher and 240° C. or lower.
The pressure applied during the above-mentioned hot-press molding is preferably 0.5 MPa or more and 5 MPa or less, and more preferably a high pressure of 1.5 MPa or more and 5.0 MPa or less.

(Method of manufacturing coreless substrate)
Next, a method for manufacturing a coreless substrate using a sacrificial substrate according to this embodiment will be described.
In general, the coreless method involves, for example, forming a thermosetting resin layer on a sacrificial substrate, then heating and pressurizing the thermosetting resin layer and cooling it to harden it to create a build-up layer, and then peeling the sacrificial substrate from the build-up layer to obtain a coreless substrate.
The manufacturing method according to the present embodiment includes a first lamination step of forming a first thermosetting resin layer on at least one surface of a sacrificial substrate;
Next, a first curing step of curing the thermosetting resin layer to form a first build-up layer;
Then, a second lamination step of forming a second thermosetting resin layer on the first build-up layer;
Then, a second curing step of curing the second thermosetting resin layer to form a second build-up layer;
Then, a peeling step is included of peeling the sacrificial substrate from the first buildup layer and the second buildup layer.
The present invention is a method for producing a coreless substrate having two or more build-up layers, and includes a coreless substrate having three, four, or more build-up layers.
In other words, the sacrificial substrate of this embodiment is particularly effective when the total number of stacked build-up layers is large, a large thermal history is required for manufacturing, and internal stress accumulates between the sacrificial substrate and the first build-up layer and between each build-up layer, making it difficult to design the sacrificial substrate and each build-up layer.
Furthermore, the coreless substrate according to the present invention preferably has a thickness of 50 μm or more and 500 μm or less, more preferably 150 μm or more and 450 μm or less, and particularly preferably 200 μm or more and 400 μm or less.

In the manufacturing method of the coreless substrate according to this embodiment, in the first lamination step, a three-layer laminate structure is formed in which the sacrificial substrate, the first thermosetting resin layer, and a metal layer are laminated in this order,
It is preferable to include an etching step of etching the metal layer prior to the peeling step.

Hereinafter, a specific manufacturing process of the coreless substrate produced using the sacrificial substrate of the present invention as a support will be described. FIG. 1 is an example of a manufacturing process of the coreless substrate according to this embodiment. The manufacturing method of the coreless substrate according to this embodiment can be obtained, for example, by sequentially performing (A) a process of forming a circuit on a sacrificial substrate with a metal foil, (B-1) a process of laminating a first thermosetting resin layer, hot pressing and pressing, and forming a circuit, (B-2) a process of laminating a second thermosetting resin layer, hot pressing and pressing, and forming a circuit, (B-N) a process of laminating an Nth thermosetting resin layer, hot pressing and pressing, and forming a circuit, (C) peeling from the sacrificial substrate, and (D) flash etching.

(A) Step of forming a circuit on a sacrificial substrate with metal foil In the manufacturing method according to the present embodiment, it is preferable to first form a circuit on a sacrificial substrate with metal foil, which is obtained by bonding a peelable copper foil 20 to a sacrificial substrate 10. When forming a circuit pattern 21 on a sacrificial substrate with metal foil, a known method can be used for forming the circuit, and for example, the circuit can be formed by the following method. A plating resist having a predetermined opening pattern is formed on the metal foil. This opening pattern corresponds to, for example, a circuit pattern. The plating resist is not particularly limited and known materials can be used, but liquid and dry films can be used. In the case of forming fine wiring, it is preferable to use a photosensitive dry film or the like as the plating resist. An example using a photosensitive dry film will be described. For example, a photosensitive dry film is laminated on a metal foil, and a non-circuit forming area is exposed to light to harden it, and an unexposed area is dissolved and removed with a developer. The hardened photosensitive dry film is left to form a plating resist.

Then, an electrolytic metal plating layer is formed at least on the opening pattern of the plating resist by electroplating. As the electroplating, a known method used in ordinary printed wiring boards can be used, for example, a method of passing an electric current through a plating solution such as copper sulfate while immersed in the plating solution can be used. The electrolytic metal plating layer may be a single layer or may have a multi-layer structure. As the material of the electrolytic metal plating layer, for example, one or more of copper, copper alloy, 42 alloy, nickel, iron, chromium, tungsten, gold, and solder can be used.
Next, the plating resist is removed using an alkaline stripping solution, sulfuric acid, or a commercially available resist stripping solution, etc., to obtain the circuit pattern 21 on the sacrificial substrate.

(B) Step of Laminating Thermosetting Resin Layers, Heating and Pressing to Form a Circuit Next, a first thermosetting resin layer 41 is laminated on the resulting sacrificial substrate with metal foil after the circuit has been formed.
The first thermosetting resin layer 41 to be laminated may be made of the same thermosetting resin composition as the thermosetting resin composition used in the prepreg for producing the sacrificial substrate described above, or may be made of a different thermosetting resin composition.
The thermosetting resin composition to be laminated is not particularly limited, but may have a thickness of, for example, 10 to 200 μm, or 15 to 150 μm.

The thermal expansion coefficient of the cured product of the laminated thermosetting resin layer is preferably 20 ppm/°C or less, more preferably 15 ppm/°C or less, and particularly preferably 10 ppm/°C or less, in terms of linear expansion coefficient _α1 of the cured product of the thermosetting resin layer, measured using a thermomechanical analyzer during a temperature rise process from 50°C to 100°C.
Furthermore, the cured product of the laminated thermosetting resin layer preferably has a shrinkage difference Y-X of -1% or more and 1% or less, more preferably -0.5% or more and 0.5% or less, and particularly preferably -0.2% or more and 0% or less, as measured under the following measurement conditions.
The glass transition temperature of the cured product of the thermosetting resin layer is preferably 150° C. or higher and 400° C. or lower, and more preferably 180° C. or higher and 320° C. or lower.

The thermosetting resin layer to be laminated can be formed by impregnating a fiber substrate with a thermosetting resin composition, semi-curing the composition to obtain a sheet-like prepreg, and then laminating the layer. The method for impregnating a fiber substrate with a thermosetting resin composition is not particularly limited, but examples include a method of dissolving a thermosetting resin composition in a solvent to prepare a resin varnish and immersing a fiber substrate in the resin varnish, a method of applying the resin varnish to a fiber substrate using various coaters, a method of spraying the resin varnish onto a fiber substrate using a sprayer, and a method of laminating a fiber substrate with a resin layer made of a thermosetting resin composition from both sides of the fiber substrate.

When the prepreg that will become the first thermosetting resin layer 41 is laminated onto a sacrificial substrate (or the lower build-up layer) and heated and pressurized, a metal foil can be placed on top of the laminated thermosetting resin layer and the metal foil can be laminated at the same time.
A metal foil is placed on the top surface of a prepreg or a laminate of two or more prepregs, and then these are bonded under high vacuum conditions using a laminator or Becquerel device, or the metal foil is placed directly on the prepreg. When two or more prepregs are laminated, the metal foil is placed on the outermost surface of the laminated prepregs.
Next, the laminate of the prepreg and the metal foil is molded under heat and pressure. During the heat and pressure molding, it is preferable to continue pressing until the end of cooling.
The conditions of the hot pressing when curing the thermosetting resin layer are preferably 100° C. or higher and 250° C. or lower, and more preferably 150° C. or higher and 240° C. or lower.
The pressure applied during the above-mentioned hot-press molding is preferably 0.5 MPa or more and 5 MPa or less, and more preferably a high pressure of 1.5 MPa or more and 5.0 MPa or less.
When forming a circuit on the laminated build-up layers, a known method can be used for forming the circuit, and for example, the circuit pattern 42 can be formed by a semi-additive process (SAP) or the same method as the circuit formation method on the sacrificial substrate described above. By the above method, a first build-up layer 40 in which a circuit pattern 42 is laminated on a first thermosetting resin layer 41 can be obtained. In addition, a second build-up layer 50 in which a circuit pattern 52 is laminated on a second thermosetting resin layer 51 can be obtained by repeating the same process as that for obtaining the first build-up layer 40.
The steps of laminating the thermosetting resin layer and metal foil, curing, and forming the circuit can be repeated as many times as necessary to obtain the desired multi-layer build-up layer.

(C) Peeling from Sacrificial Substrate After obtaining the desired build-up layer, the sacrificial substrate is peeled off from the multiple build-up layers. After obtaining the desired build-up layer, the metal foil is sandwiched between the sacrificial substrate and the first build-up layer. In this state, it is preferable to peel off the peelable copper foil to detach the sacrificial substrate from the build-up layer. After peeling, it is preferable that the thinner side of the peelable metal foil remains on the build-up layer side and the thicker side remains on the sacrificial substrate side.
In this case, after peeling, the peelable copper foil (remaining portion after peeling) 22, which is all or a part of the peelable metal foil having a thickness of 1 to 6 μm, remains on the build-up layer side.

(D) Flash Etching Next, after peeling off the sacrificial substrate, the peelable copper foil (remaining portion after peeling) 22 remaining on the build-up layer can be removed by, for example, soft etching (flash etching) or the like to obtain the coreless substrate 100. Here, the soft etching process can be performed by, for example, etching using an etching solution containing sulfuric acid and hydrogen peroxide. By the above method, the coreless substrate 100 having two or more build-up layers can be obtained.
The coreless substrate 100 manufactured using the sacrificial substrate according to this embodiment has a structure in which circuits are embedded on the sacrificial substrate side, and metal residues are less likely to remain, making it easier to form circuits with a narrow pitch, which has the effect of enabling greater density.

The above describes embodiments of the present invention, but these are merely examples of the present invention, and various configurations other than those described above can also be adopted.

(Printed wiring board)
This embodiment can be used for a normal printed wiring board, and can mount one or more semiconductor elements. In addition, after the multiple semiconductor elements mounted on the printed wiring board are encapsulated together, they can be divided into individual pieces to obtain multiple semiconductor packages.

An example of the printed wiring board of this embodiment will be described below. Figure 3 is a cross-sectional view showing steps in an example of a manufacturing process for the printed wiring board 500. Figure 3(c) shows the printed wiring board 500 that does not have a core layer.
The printed wiring board 500 of this embodiment does not include a core layer having a fiber base material, and can be a coreless board composed of, for example, a build-up layer or a solder resist layer. For example, the printed wiring board 500 shown in FIG. 3(c) includes two build-up layers (insulating layers 540, 550) and a solder resist layer (insulating layer 560). The printed wiring board can be obtained, for example, by forming a build-up layer and a solder resist layer on a sacrificial substrate 510, and then peeling off the sacrificial substrate 510. Specifically, as shown in FIG. 3, peelable metal foils 520, 530 (for example, copper foil) are placed on a large-area sacrificial substrate 510. The peelable metal foils 520, 530 can later be peeled off into the peelable metal foil 520 (upper surface) and the peelable metal foil 530 (lower surface). Next, a metal layer 542 is formed on the peelable metal foil 530. This metal layer 542 is patterned by a normal method such as a SAP (semi-additive process) method. Next, a desired number of thermosetting resin layers and metal foils are laminated by a hot press molding method or the like, and then the build-up layer is peeled off from the sacrificial substrate by peeling off the peelable metal foils 520 and 530. Then, the peelable metal foil 530 is removed by etching or the like.
In this manner, the printed wiring board 500 shown in FIG. 3 is obtained.

In the printed wiring board of this embodiment, the coreless substrate is composed of multiple interlayer insulating layers. In such an interlayer insulating layer, via wiring and a metal layer may be formed as interlayer connection wiring. In this embodiment, the via wiring, the metal layer, or the metal layer may be composed of a metal such as copper. The upper and lower surfaces of the coreless resin substrate may be covered with a solder resist layer (insulating layer).

The present invention will be described in detail below with reference to examples, but the present invention is not limited to the description of these examples.

(1) Preparation of Resin Varnish First, each component was dissolved or dispersed at the solid content shown in Table 1, and the non-volatile content was adjusted to 70% with methyl ethyl ketone. The mixture was then stirred using a high-speed stirrer to prepare resin varnishes P1, P2, and P3.
The numerical values showing the blending ratio of each component in Table 1 indicate the blending ratio (mass %) of each component relative to the total solid content of the thermosetting resin composition.

Details of each component in Table 1 are as follows.
In the examples and comparative examples, the following raw materials were used.

(Thermosetting resin)
Thermosetting resin 1: Multifunctional maleimide (BMI-2300, manufactured by Daiwa Chemical Industry Co., Ltd.)
Thermosetting resin 2: Diaminodiphenylmethane type benzoxazine (P-d type benzoxazine, manufactured by Shikoku Chemical Industry Co., Ltd.)
Thermosetting resin 3: Bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical, jER828EL)
Thermosetting resin 4: Naphthalene aralkyl type epoxy resin (manufactured by DIC Corporation, HP-5000)
Thermosetting resin 5: Cyanate resin (PT-30, weight average molecular weight 700, manufactured by Lonza Japan Co., Ltd.)

(Hardening agent)
Hardener 1: 2-phenylimidazole (Shikoku Kasei Corporation, 2PZ-PW)
Hardener 2: Tetraphenylphosphonium bis(naphthalene-2,3-dioxy)phenylsilicate adduct

(Inorganic filler)
Inorganic filler 1: Silica particles (manufactured by Admatechs Co., Ltd., SC4050, average particle size 1.1 μm)
Inorganic filler 2: Silica nanoparticles (Admatechs, Admanano, average particle size 50 nm)

The fiber base materials used in each of the Examples and Comparative Examples are shown below.
(Fiber base material)
Fiber substrate 1: Glass cloth (manufactured by Nitto Boseki Co., Ltd., WEA-116E)
Fiber base material 2: Glass cloth (Unitika Glass Fiber Co., Ltd., E10T)

(2) Manufacturing of Coreless Substrate <Example 1>
(Prepreg Production)
The obtained resin varnish P1 was impregnated into glass fibers having a thickness of 90 μm, and the resin varnish was applied to a fiber substrate 1, and then the solvent was removed at 160° C. for 5 minutes to form a prepreg 1 having a thickness of 105 μm.

(Sacrificial substrate with metal foil)
One sheet of the obtained prepreg 1 was prepared, and peelable copper foil (manufacturer: Mitsui Mining & Smelting Co., Ltd., model number MT18Ex, thickness 5 μm) was bonded to both sides of the prepreg 1 to obtain a sacrificial substrate with metal foil. The bonding conditions were a pressure of 2 MPa, a temperature of 220° C., and 2 hours. The thickness of the obtained sacrificial substrate with metal foil was 151 μm.

(Formation of build-up layer)
A build-up prepreg and a metal foil (manufacturer: Mitsui Mining & Smelting Co., Ltd., model number MT18Ex, thickness 5 μm) were laminated on both sides of the sacrificial substrate with metal foil obtained as described above, and the resulting substrate was heated and pressurized for 2 hours at a pressure of 2 MPa and a temperature of 220° C. to form a first build-up layer on both sides of the sacrificial substrate with metal foil. The same process was then repeated to form a second build-up layer.

(Removal of sacrificial substrate)
The peelable copper foil was peeled off from the obtained sacrificial substrate, thereby peeling off the build-up layer from the sacrificial substrate, and a coreless substrate 1 was obtained.

(etching)
The metal foil on the sacrificial substrate side of the obtained coreless substrate was removed by flash etching. After etching and peeling off the sacrificial substrate, the thickness of the obtained coreless substrate was 60 μm.

Example 2
The obtained resin varnish P2 was impregnated into glass fibers having a thickness of 90 μm, and the resin varnish was applied to a fiber base material 2, after which the solvent was removed at 160° C. for 5 minutes to form a prepreg 2 having a thickness of 105 μm.
Using the obtained prepreg 2, a coreless substrate 2 was produced in the same manner as in Example 1. In Example 2, the thickness of the sacrificial substrate with metal foil was 150 μm, and the thickness of the obtained coreless substrate 2 was 60 μm.

(Comparative Example 1)
The resin varnish P3 thus obtained was impregnated into glass fibers having a thickness of 90 μm, and the resin varnish was then applied to a fiber substrate 2, after which the solvent was removed at 160° C. for 5 minutes to form a prepreg having a thickness of 105 μm.
The obtained prepreg was used to produce a coreless substrate in the same manner as in Example 1. In Comparative Example 1, the thickness of the sacrificial substrate with metal foil was 150 μm, and the thickness of the obtained coreless substrate was 60 μm.

(Linear expansion coefficient)
A test piece of 4 mm x 15 mm was cut out from the metal foil-attached sacrificial substrate before laminating the build-up layer, and the copper foil was removed with an etching solution (ferric chloride solution, 35°C) to obtain a test piece for evaluating the linear expansion coefficient. Next, the obtained test piece was subjected to two cycles of thermomechanical analysis (TMA) using a thermomechanical analyzer TMA (manufactured by TA Instruments, Q400) under the conditions of a temperature range of 30 to 260°C, a heating rate of 10°C/min, a load of 10 g, and compression mode. The average value α ₁ of the linear expansion coefficient in the planar direction (XY direction) in the range of 50°C to 100°C was calculated.
The linear expansion coefficient was the value at the second cycle.

(Shrinkage amount)
The shrinkage difference Y-X was calculated by measuring the distance between the centers of the holes in the punched sacrificial substrate (FIG. 2). The measurement method, heating conditions, and calculation method are as follows:
(1) Sacrificial substrate with holes for measuring shrinkage A test piece of 250 mm x 250 mm was cut out from the metal foil-attached sacrificial substrate of each Example and Comparative Example. A hole with a diameter of 1 mm was drilled at each of the four corners of the test piece. The holes were located at four points, centered on the intersection of straight lines 10 mm away from the plate end of each test piece.

(2) Measurement of dimensions of sacrificial substrate before hot pressing For four holes with a diameter of 1 mm, the length from the center of one hole to the center of another hole, excluding the diagonal line, was measured at four points (A, B, C, and D in the figure). The measured values were designated _D0A , _D0B , _D0C , and _D0D , and the average was designated _D0 .

(3) Dimensional measurement after the first hot pressing The sacrificial substrate was heated and pressed for 2 hours using a hot press under conditions of a temperature of 200°C and a pressure of 8 kgf/ ^mm2 . Pressurization was continued until the sacrificial substrate was cooled to 50°C after the 2-hour heating and pressing period was completed. After the sacrificial substrate was cooled to 25°C, the length from the center of a hole to the center of another hole was measured at four points (A, B, C, and D in the figure) at 25°C, and the respective measured values were designated _D1A , _D1B , _D1C , and _D1D , with the average being designated _D1 .

(4) Dimensional measurement after the second hot pressing After the first hot pressing, the sacrificial substrate was cooled to 25°C and then heated and pressed using a hot press at a temperature of 200°C and a pressure of 8 kgf/ ^mm2 for 2 hours. Pressurization was continued until the sacrificial substrate was cooled to 50°C after the 2-hour heating and pressing period was completed. After the sacrificial substrate was cooled to 25°C, the length from the center of a hole to the center of another hole was measured at four points (A, B, C, and D in the figure) at 25°C, and the measured values were designated _D2A , _D2B , _D2C , and _D2D , with the average being designated _D2 .

(5) Calculation method: The shrinkage amount X of the first heat press is
X=(D ₀ - D ₁ )/D ₀ ×100 [%]
It was decided.
The shrinkage amount Y of the second heat press is
Y=(D ₀ - D ₂ )/D ₀ ×100[%]
It was decided.
The difference Y-X% between the amount of shrinkage X% in the first hot-press and the amount of shrinkage Y% in the second hot-press calculated by the above method was defined as the shrinkage difference Y-X%.

(warp)
The warpage of the obtained coreless substrates of each of the Examples and Comparative Examples was measured with a vernier caliper at 25° C. Specifically, each coreless substrate was placed on a horizontal plane, and the largest displacement difference was taken as the amount of warpage. The evaluation criteria were as follows:
◎: Warpage is less than 10 mm. ◯: Warpage is 10 mm or more but less than 20 mm. ×: Warpage is 20 mm or more.

10 Sacrificial substrate 20 Peelable metal foil 21 Circuit pattern 22 Peelable copper foil (remaining part after peeling)
40 First buildup layer 41 First thermosetting resin layer 42 Circuit pattern 50 Second buildup layer 51 Second thermosetting resin layer Name of member 52 Circuit pattern 100 Coreless substrate 500 Printed wiring substrate 510 Support substrate 520 Peelable metal foil 530 Peelable metal foil 540 Insulating layer 542 Metal layer 550 Insulating layer 552 Metal layer 560 Insulating layer 562 Metal layer

Claims (6)

A sacrificial substrate used to form a coreless substrate, comprising:
The sacrificial substrate is a sacrificial substrate for forming a coreless substrate having two or more build-up layers formed by a process involving a heat treatment on at least one surface of the sacrificial substrate,
The sacrificial substrate is composed of a cured prepreg obtained by impregnating a fiber base material with a thermosetting resin composition,
The linear expansion coefficient α1 of the sacrificial substrate is 10 ppm/° C. or less, as measured by the following measurement method 1 using a thermomechanical analyzer during a temperature rise process from 50° C. to 100° C.,
A sacrificial substrate having a shrinkage difference Y-X% of the sacrificial substrate, which is measured by the following measurement method 2 , is -0.0230% or more and 0% or less;
The thermosetting resin composition contains an inorganic filler,
A sacrificial substrate, wherein the content of the inorganic filler in the thermosetting resin composition is 60% by mass or more and 98% by mass or less, relative to 100% by mass of a total solid content of the thermosetting resin composition.
(Measurement Method 1)
The cured prepreg is subjected to two cycles of thermomechanical analysis using a thermomechanical analyzer under conditions of a temperature range of 30 to 260°C, a heating rate of 10°C/min, a load of 10 g, and compression mode. The average value of the linear expansion coefficient in the planar direction (XY direction) in the range of 50°C to 100°C is defined as the linear expansion coefficient α1. The value of the linear expansion coefficient in the second cycle is used.
(Measurement Method 2 )
Shrinkage amount by X% due to first hot pressing: The sacrificial substrate is heated and pressurized for 2 hours using a hot press under conditions of a temperature of 200°C and a pressure of 8 kgf/ ^mm2 . The amount of shrinkage of the sacrificial substrate cooled to room temperature after the first hot pressing is taken as X%, based on the sacrificial substrate at room temperature before the first hot pressing.
Shrinkage amount by second hot pressing Y%: After the first hot pressing, the sacrificial substrate is cooled to room temperature and then heated and pressurized using a hot press at a temperature of 200°C and a pressure of 8 kgf/ ^mm2 for 2 hours. The sacrificial substrate at room temperature before the first hot pressing is used as a reference, and the shrinkage amount of the sacrificial substrate cooled to room temperature after the second hot pressing is defined as Y%.
The difference between the amount of shrinkage X% in the first hot-press and the amount of shrinkage Y% in the second hot-press, calculated by the above method, is defined as Y-X%, which is the shrinkage difference Y-X%. 2. The sacrificial substrate of claim 1,
The thermosetting resin composition includes a thermosetting resin,
The thermosetting resin is at least one selected from the group consisting of an epoxy resin, a maleimide resin, a phenolic resin, and a cyanate resin. 3. A sacrificial substrate according to claim 1 or 2 ,
The thickness of the coreless substrate is 50 μm or more and 500 μm or less. A first lamination step of forming a first thermosetting resin layer on at least one surface of the sacrificial substrate according to any one of claims 1 to 3 ;
Next, a first curing step of curing the first thermosetting resin layer to form a first build-up layer;
Then, a second lamination step of forming a second thermosetting resin layer on the first build-up layer;
Then, a second curing step of curing the second thermosetting resin layer to form a second build-up layer;
and then a peeling step of peeling the sacrificial substrate from a first buildup layer and a second buildup layer. A method for producing a coreless substrate according to claim 4 ,
In the first lamination step, a three-layer laminate structure is formed by laminating the sacrificial substrate, the first thermosetting resin layer, and a metal layer in this order;
The method for producing a coreless substrate includes, before the peeling step, an etching step of etching the metal layer. A method for producing a coreless substrate according to claim 4 or 5 ,
The sacrificial substrate is a sacrificial substrate with a metal foil, the sacrificial substrate having a metal foil bonded thereto,
A method for producing a coreless substrate, comprising the steps of: flash etching the metal foil on the sacrificial substrate after the peeling step.

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