JP7647828B2 - Release film and method for manufacturing semiconductor package - Google Patents

Description

The present invention relates to a method for manufacturing a release film and a semiconductor package.

In recent years, as electronic devices, especially mobile phones, have become thinner, there is a demand for semiconductor packages that incorporate electronic components such as semiconductor elements to be even thinner. Also, from the perspective of improving heat dissipation, there are an increasing number of cases where exposed die molding, which exposes part of the surface of an electronic component, is adopted instead of over molding, which covers the entire electronic component with sealing resin.

When sealing electronic components so that a portion of the electronic component is exposed, it is necessary to prevent leakage of the sealing material to the exposed portion of the electronic component (flash burrs). Therefore, sealing is performed with a film having releasability (release film) attached to the exposed portion of the electronic component, and then the release film is peeled off to expose the surface of the electronic component. For example, Patent Document 1 describes a laminated film in which a film made of a fluororesin is laminated on at least one side of a base film made of a stretched polyester resin film.

Patent Application No. 2005-186740

As described above, the release film is peeled off from the surface of the electronic component after the sealing process. If the release film is charged at this time, discharge may occur during the peeling process, which may cause electrostatic damage to the electronic component.
Furthermore, a technology for sealing a plurality of packages together after mounting them on a substrate has been considered in recent years, and the use of a release film for exposing the terminals has been considered. In this case, since various types of packages exist on the substrate, the release film is required to have excellent extensibility (mold followability). In addition, since some types of packages are sensitive to heat, the release film is required to have excellent extensibility even at low temperatures (for example, 150°C or less).

In view of the above circumstances, one aspect of the present invention aims to provide a release film that suppresses electrostatic damage to electronic components and has excellent elongation at low temperatures. Another aspect of the present invention aims to provide a method for manufacturing a semiconductor package using this release film.

Means for solving the above problems include the following embodiments.
<1> A release film comprising: a base layer; an adhesive layer; and a conductive layer disposed between the base layer and the adhesive layer, wherein the base layer contains a polyester copolymer having a butylene structure and an alkylene oxide structure.
<2> A release film comprising a base layer, an adhesive layer, and a conductive layer disposed between the base layer and the adhesive layer, the release film having an elongation rate of 1000% or more at 150°C.
<3> The release film according to <1> or <2>, for use in the production of a semiconductor package by exposure molding.
<4> A method for manufacturing a semiconductor package, comprising: a step of sealing the periphery of an electronic component with the adhesive layer of the release film according to any one of <1> to <3> in contact with at least a portion of a surface of the electronic component; and a step of peeling the release film from the electronic component.

According to one aspect of the present invention, a release film is provided that suppresses electrostatic damage to electronic components and has excellent elongation at low temperatures. According to another aspect of the present invention, a method for manufacturing a semiconductor package using this release film is provided.

FIG. 2 is a diagram illustrating a schematic configuration of a release film. FIG. 2 is a diagram showing the shape of a test specimen used for measuring the elongation and elastic modulus of a release film.

The following describes in detail the form for carrying out the present invention. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including element steps, etc.) are not essential unless specifically stated otherwise. The same applies to numerical values and their ranges, and they do not limit the present invention.

In this specification, the term "step" includes not only a step that is independent of other steps, but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved.
In the present specification, the numerical range indicated using "to" includes the numerical values before and after "to" as the minimum and maximum values, respectively.
In the numerical ranges described in this specification, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in another stepwise manner. In addition, in the numerical ranges described in this specification, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.
In this specification, the content or amount of each component in a composition means, when multiple substances corresponding to each component are present in the composition, the total content or amount of those multiple substances present in the composition, unless otherwise specified.
In this specification, the particle size of each component in a composition means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified, when multiple types of particles corresponding to each component are present in the composition.
In this specification, the term "layer" includes cases where the layer is formed over the entire area when the area in which the layer exists is observed, as well as cases where the layer is formed over only a portion of the area.
In this specification, the thickness of the release film or each layer constituting the release film can be measured by a known method. For example, it may be measured using a dial gauge or the like, or it may be measured from a cross-sectional image of the release film. Alternatively, the material constituting the layer may be removed using a solvent or the like, and the thickness may be calculated from the mass before and after removal, the density of the material, the area of the layer, etc. If the thickness of the layer is not constant, the arithmetic average value of the values measured at any five points is taken as the thickness of the layer.
In this specification, "(meth)acrylic" means either or both of acrylic and methacrylic, and "(meth)acrylate" means either or both of acrylate and methacrylate.

<Release film>
The release film of the present disclosure comprises a base layer, an adhesive layer, and a conductive layer disposed between the base layer and the adhesive layer, and satisfies at least one of the following (1) or (2):
(1) The substrate layer contains a polyester copolymer containing a butylene structure and an alkylene oxide structure (hereinafter, also simply referred to as a polyester copolymer).
(2) The elongation at 150°C is 1000% or more.

The release film described above suppresses electrostatic damage to electronic components. The reason for this is not entirely clear, but it is thought that the provision of a conductive layer suppresses the buildup of static electricity in the release film, making it less likely that discharge will occur when the release film is peeled off from the electronic components.

The structure of the release film is shown in FIG. 1. As shown in FIG. 1, the release film 40 includes a base layer 10, an adhesive layer 20, and a conductive layer 30 disposed between the base layer 10 and the adhesive layer 20.

As shown in FIG. 1, in the release film of the present disclosure, the conductive layer 30 is disposed between the base layer 10 and the adhesive layer 20 (the adhesive layer 20 is disposed on the surface of the release film) rather than on the surface of the release film 40. This allows the release film to be sufficiently adhered to the surface of the electronic component via the adhesive layer, effectively preventing the intrusion of the sealant.

Furthermore, since the release film satisfies at least one of the above (1) or (2), it has excellent elongation at low temperatures.

The release film of the present disclosure is attached with the adhesive layer side to the surface of an adherend such as an electronic component, and then peeled off after a sealing process or other process. The release film of the present disclosure is less likely to generate discharge when peeled off from the adherend. For this reason, it is suitable for use, for example, in the manufacture of semiconductor packages by exposed molding.

In the present disclosure, the elongation (%) of a release film at 150° C. is measured as follows.
First, a test piece having a shape as shown in FIG. 2 is prepared using a release film. Both ends of this test piece are gripped by a tester to carry out a tensile test. The measurement is carried out under conditions of 150° C., and the tensile speed is 500 mm/min. The elongation is calculated from the gauge length A of the sample before the test (length of the part of the test piece with a width of 10 mm shown in FIG. 2: 40 mm) and the gauge length B when the sample is cut, according to the following formula.

To measure the elongation of the release film, use, for example, the "Tensilon Tensile Tester RTA-100" manufactured by Orientec Co., Ltd. or a similar tester equipped with a gripper and a 180-degree peeling device.

The release film preferably has an elongation rate of 1200% or more at 150°C, and more preferably 1400% or more. For example, when the base layer contains a polyester copolymer, the elongation rate of the release film at 150°C can be adjusted by the composition ratio of butylene structures and alkylene oxide structures in the polyester copolymer.

The release film preferably has an elastic modulus of 10 MPa to 50 MPa, more preferably 20 MPa to 40 MPa, at 150° C. When the elastic modulus at 150° C. is 10 MPa or more, good mold conformability tends to be obtained, and when it is 50 MPa or less, good extensibility tends to be obtained.
When the base layer contains a polyester copolymer, for example, the elastic modulus of the release film at 150° C. can be adjusted by the composition ratio of butylene structures and alkylene oxide structures in the polyester copolymer.

(Elastic modulus at 150° C.)
The elastic modulus (MPa) of the release film at 150° C. is calculated from the slope of the tangent in the stress-strain diagram by pulling the test piece in the same manner as in the measurement of the elongation at 150° C. It is calculated from the force (MPa) per unit cross-sectional area (mm2) applied to the test piece, the gauge length L0 (40 mm) before the test, and the gauge length L according to the following formula.

(Base layer)
From the viewpoint of extensibility at low temperatures, the base layer preferably contains a polyester copolymer containing a butylene structure and an alkylene oxide structure.
The alkylene oxide structure contained in the polyester copolymer is a structure in which an alkylene group is bonded to an oxygen atom, and the alkylene group preferably has 1 to 6 carbon atoms, more preferably 4 carbon atoms.

The polyester copolymer can be synthesized, for example, by copolymerizing an aromatic dicarboxylic acid such as terephthalic acid or a derivative thereof, 1,4-butanediol, and a poly(alkylene oxide) glycol.

A preferred polyester copolymer is a copolymer containing a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2). This copolymer is an elastomer in which the structural unit represented by formula (1) constitutes a hard segment (PBT), and the structural unit represented by formula (2) constitutes a soft segment (PTMG).

The mass ratio (PBT:PTMG) of the hard segment (PBT) and the soft segment (PTMG) constituting the above copolymer is not particularly limited. For example, it may be selected from the range of 1:9 to 9:1, from the range of 2:8 to 8:2, or from the range of 3:7 to 7:3.

The substrate layer may contain components other than the polyester copolymer. Examples include polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polyimide, polyamide, polyester ether, polyamideimide, and fluorine-containing resins. When the substrate layer contains components other than the polyester copolymer, the proportion of the polyester copolymer in the entire substrate layer is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

The thickness of the substrate layer is not particularly limited, and is preferably 10 μm to 300 μm, and more preferably 20 μm to 100 μm. If the thickness of the substrate layer is 10 μm or more, the release sheet is less likely to tear and has excellent handleability. If the thickness of the substrate layer is 300 μm or less, it has excellent conformability to the mold, and therefore tends to suppress the occurrence of poor appearance due to wrinkles in the molded semiconductor package.

The substrate layer may be composed of only one layer, or may be composed of two or more layers. Methods for obtaining a substrate layer composed of two or more layers include a method in which the materials for each layer are extruded by a co-extrusion method, a method in which two or more films are laminated, etc.

If necessary, the surface of the base layer on which the conductive layer is to be provided may be treated to improve adhesion to the conductive layer. Treatment methods include surface treatments such as corona treatment and plasma treatment, and application of a primer.

If necessary, a back treatment agent may be applied to the back surface of the base layer (the surface opposite to the side on which the conductive layer is disposed) to adjust the unwinding property of the release film from the roll. Examples of back treatment agents include silicone resins, fluorine-containing resins, polyvinyl alcohol, and resins having alkyl groups. If necessary, these back treatment agents may be modified. Only one type of back treatment agent may be used, or two or more types may be used in combination.

(Adhesive layer)
The adhesive layer preferably contains an adhesive from the viewpoint of adhesion to the surface of the electronic component. The type of adhesive is not particularly limited and can be selected in consideration of adhesion, releasability, heat resistance, etc. Specifically, acrylic adhesives, silicone adhesives, and urethane adhesives are preferred, and acrylic adhesives are more preferred. The adhesive layer may contain only one type or two or more types of adhesives.

The acrylic adhesive is preferably a copolymer (hereinafter also referred to as an acrylic copolymer) obtained by copolymerizing a monomer with a low glass transition temperature (Tg) (e.g., -20°C or lower) such as butyl acrylate, ethyl acrylate, or 2-ethylhexyl acrylate as the main monomer with a monomer having a functional group such as (meth)acrylic acid, hydroxyethyl (meth)acrylate, hydroxyethyl (meth)acrylate, (meth)acrylamide, or (meth)acrylonitrile. The above "glass transition temperature" is the glass transition temperature of a homopolymer obtained using the corresponding monomer.

The acrylic copolymer may be a cross-linked acrylic copolymer. The cross-linked acrylic copolymer can be synthesized by cross-linking the monomers that are the raw materials of the acrylic copolymer using a cross-linking agent. Examples of cross-linking agents used in the synthesis of the cross-linked acrylic copolymer include known cross-linking agents such as isocyanate compounds, melamine compounds, and epoxy compounds. In order to form a network structure that spreads gently in the acrylic adhesive, it is more preferable that the cross-linking agent is a multifunctional cross-linking agent such as a trifunctional or tetrafunctional cross-linking agent.

The adhesive layer may contain an anchoring enhancer, a crosslinking promoter, a filler, a colorant, etc., as necessary. For example, by including a filler in the adhesive layer, the outer surface of the adhesive layer (the side opposite the conductive layer) is roughened, thereby improving the peelability from the electronic component.

The material of the filler is not particularly limited, and may be an organic material such as a resin, an inorganic material such as a metal or a metal oxide, or a combination of an organic material and an inorganic material. The adhesive layer may contain only one type of filler or two or more types of fillers. The volume average particle size of the filler is not particularly limited. For example, it may be selected from the range of 1 μm to 20 μm. In this specification, the volume average particle size of the filler is the particle size (D50) at which the cumulative amount from the small diameter side in the volume-based particle size distribution measured by a laser diffraction method is 50%.

From the viewpoint of affinity with the adhesive contained in the adhesive layer, the filler is preferably resin particles. Examples of resins constituting the resin particles include acrylic resin, olefin resin, styrene resin, acrylonitrile resin, silicone resin, etc. From the viewpoint of suppressing residues on the surface of the semiconductor package after molding, acrylic resin is preferred.

The thickness of the adhesive layer is not particularly limited, and is preferably 0.1 μm to 100 μm, and more preferably 1 μm to 100 μm. When the thickness of the adhesive layer is 0.1 μm or more, sufficient adhesion to electronic components is obtained, and the intrusion of the sealing material is effectively suppressed. When the thickness of the adhesive layer is 100 μm or less, the distance from the conductive layer to the surface of the adhesive layer is not too far, the surface resistivity is maintained low, and electrostatic damage to electronic components is effectively suppressed. In addition, heat shrinkage stress is unlikely to occur during thermal curing of the adhesive layer, and the flatness of the release film is easily maintained.
Taking into consideration the ease of forming the adhesive layer (coatability, etc.), ensuring adhesive strength, ensuring antistatic function, etc., the thickness of the adhesive layer is more preferably 3 μm to 50 μm.

(Conductive Layer)
The conductive layer is not particularly limited in structure as long as it can increase the conductivity of the release film and suppress charging. For example, it may be a layer containing a conductive material such as an antistatic agent, a conductive polymer material, or a metal.

Examples of the antistatic agent contained in the conductive layer include cationic antistatic agents having a cationic group such as a quaternary ammonium salt, a pyridinium salt, or a primary to tertiary amino group, an anionic antistatic agent having an anionic group such as a sulfonate group, a sulfate group, or a phosphate group, an amphoteric antistatic agent such as an amino acid or amino acid sulfate group, a nonionic antistatic agent having a nonionic group such as an amino alcohol group, a glycerin group, or a polyethylene glycol group, and a polymeric antistatic agent obtained by increasing the molecular weight of these antistatic agents, etc. The antistatic agent may be a combination of a main agent and an auxiliary (such as a curing agent).
Examples of the conductive polymer material contained in the conductive layer include polymer compounds having polythiophene, polyaniline, polypyrrole, polyacetylene, or the like in the skeleton.
Examples of metals include aluminum, copper, gold, chromium, and tin, with aluminum being preferred from the viewpoint of availability.

There are no particular limitations on the method for forming the conductive layer. For example, there is a method of laminating a metal foil or the like on one side of the film that will be the base layer, or a method of applying the material for the conductive layer by coating, vapor deposition, or the like on one side of the film that will be the base layer.

The thickness of the conductive layer is not particularly limited as long as it provides a sufficient antistatic effect for the release film. For example, it may be in the range of 0.01 μm to 1 μm.

<Method of manufacturing semiconductor package>
The method for manufacturing a semiconductor package according to the present disclosure includes a step of sealing the periphery of an electronic component with the adhesive layer of the above-mentioned release film in contact with at least a portion of the surface of the electronic component, and a step of peeling the release film from the electronic component.

As described above, the release film of the present disclosure is less likely to cause discharge when peeled off, and electrostatic damage to electronic components is suppressed. Therefore, according to the above method, a semiconductor package with excellent reliability can be manufactured.
Furthermore, the release film of the present disclosure has excellent adhesion to electronic components, and therefore the sealant is less likely to penetrate into the exposed portion after the release film is peeled off from the electronic component.

The type of electronic component used in the above method is not particularly limited, and examples thereof include semiconductor elements, capacitors, terminals, etc.
In the above method, the type of material (sealant) used to seal the periphery of the electronic component is not particularly limited, and examples thereof include resin compositions containing epoxy resins, acrylic resins, etc.

The release film of the present disclosure will be described below based on examples. However, the present disclosure is not limited to the following examples.

Example 1
As the material for the substrate layer, a polyester copolymer having a mass ratio (PBT:PTMG) of a hard segment (PBT) having a structure represented by general formula (1) and a soft segment (PTMG) having a structure represented by general formula (2) of 3:7 was used to prepare a substrate film having a thickness of 100 μm, and one side of the substrate film was subjected to a corona treatment.
An antistatic agent diluted to 2.5% by mass with a solvent was applied to the corona-treated surface of the substrate film, and the coated film was heated at 100° C. for 1 minute to form a conductive layer (thickness: 0.3 μm). A mixture of water and isopropyl alcohol (mass ratio 1:1) was used as the solvent.
As a material for the adhesive layer, an adhesive layer-forming composition was prepared by mixing an adhesive (100 parts by mass), a crosslinking agent (20 parts by mass), a mixed solvent (34 parts by mass) of toluene:methyl ethyl ketone in a mass ratio of 8:2, and a filler (5 parts by mass). This adhesive layer-forming composition was applied onto the conductive layer so that the adhesive layer had a thickness of 5 μm, and heated at 100° C. for 1 minute to form an adhesive layer, and a release film was produced.

Example 2
A release film was produced in the same manner as in Example 1, except that the mass ratio (PBT:PTMG) of the hard segment (PBT) and the soft segment (PTMG) of the polyester copolymer was 5:5.

Example 3
A release film was produced in the same manner as in Example 1, except that the mass ratio (PBT:PTMG) of the hard segment (PBT) and the soft segment (PTMG) of the polyester copolymer was 7:3.

Example 4
A release film was produced in the same manner as in Example 1, except that the mass ratio (PBT:PTMG) of the hard segment (PBT) and the soft segment (PTMG) of the polyester copolymer was 8:2.

Example 5
A substrate film (thickness 100 μm) was prepared by coextrusion in which a layer A made of polybutylene terephthalate and a layer B made of a polyester copolymer having a mass ratio (PBT:PTMG) of hard segment (PBT) and soft segment (PTMG) of 2:8 were laminated. The thickness ratio of the layer A to the layer B was 1:1.
A release film was produced in the same manner as in Example 1, except that the obtained base film was used.

<Comparative Example 1>
A release film was prepared in the same manner as in Example 1, except that a polybutylene terephthalate film having a thickness of 100 μm and having been subjected to a corona treatment on one side was used as the base film.

<Comparative Example 2>
A release film was produced in the same manner as in Example 3, except that an adhesive layer was formed on the base film without forming a conductive layer.

Details of each material used in the preparation of the release film are as follows.
Antistatic agent: A mixture of the following Component A (100 parts by mass) and Component B (25 parts by mass). Component A: A cationic antistatic agent which is an acrylic copolymer having a quaternary ammonium salt, product name "Bondip PA-100 base agent", Konishi Co., Ltd. Component B: An epoxy resin, product name "Bondip PA-100 hardener", Konishi Co., Ltd.

Adhesive: Acrylic adhesive, product name "FS-1208", Lion Specialty Chemicals Co., Ltd., composed of a mixture of multiple types of methacrylic acid ester monomers. Crosslinking agent: Polyisocyanate crosslinking agent (hexamethylene diisocyanate crosslinking agent (HMDI)), product name "Duranate E405-80T", Asahi Kasei Chemicals Corporation. Filler: Crosslinked acrylic particles, product name "MX-500", Soken Chemical Co., Ltd., volume average particle size 5 μm.

<Evaluation test>
The prepared release films were subjected to the following evaluation tests.

(Elongation and Elastic Modulus at 150°C)
The elongation and elastic modulus of the release film at 150° C. were measured by the above-mentioned method. For the measurement, a Tensilon tensile tester RTA-100 type manufactured by Orientec Co., Ltd. was used. The results are shown in Table 1.

(Mold conformity and molded product appearance)
A release film was attached to the upper part of a transfer mold having a depth of 3 mm, and the upper part was fixed in a vacuum, and then the mold was clamped and transfer molded with a sealant. The mold temperature was 150° C., the molding pressure was 6.86 MPa (70 kgf/cm ² ), and the molding time was 300 seconds.
The mold conformability was evaluated as follows: ○ if the release sheet could conform to the mold without any tearing, △ if only a few tears occurred but no practical problem occurred, × if tears occurred.
The appearance of the molded product was evaluated as follows: ◯: no wrinkles, flow marks, etc. on the release film and good appearance; △: slight wrinkles, flow marks, etc. on the release film but no practical problem; ×: poor appearance due to wrinkles, flow marks, etc. on the release film.

(Electrostatic destruction test for electronic components)
The adhesive layer side of the release film was attached to a circuit board on which an electronic component (semiconductor element) was mounted, and the circuit board was left for 60 seconds in an atmosphere with a temperature of 23±2°C and a humidity of 60±10% RH. The release film was then forcefully peeled off. This procedure was repeated five times, and the circuit board was checked by VI (voltage-current characteristics) measurement. If electricity was able to flow, it was evaluated as "good", and if electricity could not be flowed, it was evaluated as "bad".

As shown in the results in Table 1, the release films of the examples in which the base layer contained a polyester copolymer and the elongation at 150° C. was 1000% or more were superior in elongation at low temperatures to the release film of Comparative Example 1 in which the base layer did not contain a polyester copolymer and the elongation at 150° C. was less than 1000%, and the evaluations of the mold followability and the appearance of the molded product were also favorable.
Furthermore, in the release films of the examples in which a conductive layer was formed between the base layer and the adhesive layer, no electrostatic damage occurred to electronic components in the electrostatic damage test.

10: Base material layer 20: Adhesive layer 30: Conductive layer 40: Release film

Claims (4)

A release film comprising a base layer, an adhesive layer, and a conductive layer disposed between the base layer and the adhesive layer, wherein the base layer contains a structural unit (PBT) represented by the following formula (1) and a structural unit (PTMG) represented by the following formula (2), and the mass ratio of PBT to PTMG (PBT:PMTG) is 2.8 to 8.2 .

2. The release film according to claim 1, comprising a base layer, an adhesive layer, and a conductive layer disposed between the base layer and the adhesive layer, and having an elongation at 150°C of 1000% or more. The release film according to claim 1 or 2, for use in manufacturing semiconductor packages by exposure molding. A method for manufacturing a semiconductor package comprising the steps of: sealing the periphery of an electronic component with the adhesive layer of the release film according to any one of claims 1 to 3 in contact with at least a portion of the surface of the electronic component; and peeling the release film from the electronic component.