JP7593326B2 - Release film and method for manufacturing semiconductor package - Google Patents

Description

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

Semiconductor chips are usually sealed with resin to protect them from the outside air, and are mounted on a board as a molded product called a package. Conventionally, molded products are molded as individual packages with each chip connected via a runner, which is a flow path for the sealing resin. The releasability of the molded product from the mold is ensured by the structure of the mold and the addition of a release agent to the sealing resin, etc.

In recent years, due to the demand for smaller packages and more pins, there has been an increase in packages such as Ball Grid Array (BGA), Quad Flat Non-leaded (QFN), and Wafer Level-Chip Size Package (WL-CSP). In the QFN format, a resin release film is used to ensure standoff and prevent burrs from forming on the terminals, while in the BGA and WL-CSP formats, a resin release film is used to improve the releasability of the package from the mold (see, for example, Patent Document 1). The molding method that uses a release film is called "film-assisted molding."

JP 2002-158242 A

In film-assisted molding, the release properties of the release film make it relatively easy to release the encapsulated semiconductor package from the mold. However, in the BGA and WL-CSP methods, when the molding method is changed from the conventional transfer molding method to the compression molding method, the release film may not be able to conform to the mold. If the release film does not conform to the mold, wrinkles or slack may occur in the release film during molding, which may damage the semiconductor package when the release film is peeled off. In addition, wrinkles or slack in the release film may cause a defective appearance of the semiconductor package. In addition, wrinkles or slack in the release film may cause defects in the encapsulation of the semiconductor package, which may cause poor performance of the semiconductor package. It is expected that semiconductor packages will become even smaller, thinner, and more highly integrated in the future, and there is a demand for improved conformity of the release film.

The embodiments of the present disclosure have been made in light of the above circumstances.
An object of an embodiment of the present disclosure is to provide a release film that has excellent conformability to a mold during resin molding of a semiconductor package, can be easily peeled off from the sealing resin after molding, and is less likely to cause poor appearance of the semiconductor package, and a manufacturing method for a semiconductor package using the same.

Specific means for solving the above problems include the following aspects:

<1> A release film for use in manufacturing a semiconductor package, comprising: a base layer having a tensile modulus of elasticity of 150 MPa or less at a temperature of 170°C and a recovery rate of 70% or more at a temperature of 170°C; and a release layer disposed on one side of the base layer and containing resin particles.
<2> The release film according to <1>, wherein a volume ratio of the resin particles in the release layer is 5 volume % to 65 volume %.
<3> The release film according to <1> or <2>, wherein the base layer is a polyester film.
<4> A release film for use in manufacturing a semiconductor package, comprising: a base layer; and a release layer disposed on one side of the base layer and containing resin particles, the release film having a tensile modulus of elasticity of 150 MPa or less at a temperature of 170°C and a recovery rate of 70% or more at a temperature of 170°C.
<5> The release film according to <4>, wherein a volume ratio of the resin particles in the release layer is 5 volume % to 65 volume %.
<6> The release film according to <4> or <5>, wherein the base layer is a polyester film.
<7> The release film according to any one of <1> to <6>, which is used in compression molding of a semiconductor package.
<8> A method for producing a semiconductor package, comprising the steps of: sealing a semiconductor chip with a sealing material using a mold on which the release film according to any one of <1> to <7> is arranged, to form a semiconductor package.

According to an embodiment of the present disclosure, there is provided a release film that has excellent conformability to a mold during resin molding of a semiconductor package, can be easily peeled off from the sealing resin after molding, and is less likely to cause defects in the appearance of the semiconductor package, and a method for manufacturing a semiconductor package using the same.

FIG. 2 is a diagram illustrating an example of a layer structure of the release film of the present disclosure.

In the present disclosure, 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 disclosure, the numerical ranges indicated using "to" include the numerical values before and after "to" as the minimum and maximum values, respectively.
In the numerical ranges described in the present disclosure in stages, 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 stages. In addition, in the numerical ranges described in the present disclosure, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.
In the present disclosure, each component may contain multiple types of the corresponding substance. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified.
In the present disclosure, the particles corresponding to each component may include multiple types. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.
In this disclosure, 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 part of the area.
In the present disclosure, "(meth)acrylic" means at least one of acrylic and methacrylic, and "(meth)acrylate" means at least one of acrylate and methacrylate.
When an embodiment of the present disclosure is described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. In addition, the size of the members in each drawing is conceptual, and the relative relationship between the sizes of the members is not limited to this.

In the present disclosure, the average thickness of a layer of a release film is a value obtained by measuring the thickness of the target layer at five points and calculating the arithmetic mean value. The thickness of a layer can be measured using a micrometer. When measuring the thickness of one layer of a laminate or the total thickness of multiple layers, the thickness can be measured by observing the cross section of the release film using an electron microscope.

In this disclosure, "MD direction" refers to the longitudinal direction of a film manufactured in a long shape, and "TD direction" refers to the direction perpendicular to the "MD direction." In this disclosure, "MD direction" is also called "machine direction" and "TD direction" is also called "width direction."

<Release film>
The release film of the first embodiment of the present disclosure has a base layer having a tensile modulus of elasticity of 150 MPa or less at a temperature of 170°C and a recovery rate of 70% or more at a temperature of 170°C, and a release layer containing resin particles arranged on one side of the base layer.
The release film of the second embodiment of the present disclosure has a base layer and a release layer containing resin particles arranged on one side of the base layer, and has a tensile modulus of elasticity of 150 MPa or less at a temperature of 170°C and a recovery rate of 70% or more at a temperature of 170°C.
Hereinafter, matters common to the release film of the first embodiment and the release film of the second embodiment will be collectively referred to as the "release film of the present disclosure."

An example of the layer structure of the release film of the present disclosure is shown generally in Fig. 1. The release film 10 shown in Fig. 1 includes a base layer 20 and a release layer 30 disposed on the base layer 20. The release layer 30 contains resin particles therein.
The release film of the present disclosure is not limited to the configuration shown in Fig. 1. The release film of the present disclosure may have, for example, a second release layer on the surface of the base layer 20 opposite to the surface on which the release layer 30 is provided, or may have another layer (for example, an antistatic layer, a colored layer, etc.) between the base layer 20 and the release layer 30.

In the release film of the present disclosure, the release layer containing resin particles comes into contact with the sealing resin when a semiconductor package is produced.
The release film of the present disclosure has excellent conformability to a mold during resin molding of a semiconductor package, can be easily peeled off from a sealing resin (e.g., epoxy resin) after molding, and is unlikely to cause defects in the appearance of the semiconductor package. The reason why the release film of the present disclosure exhibits the above-mentioned performance is not necessarily clear, but is presumed to be as follows.

The base material layer of the release film of the first embodiment has a tensile modulus of elasticity of 150 MPa or less at a temperature of 170°C and a recovery rate of 70% or more at a temperature of 170°C. Therefore, when heat and external force are applied, the base material layer exhibits a property of maintaining its shape while deforming moderately. As a result, it is presumed that wrinkles or sagging are less likely to occur when the film is attached to a mold or when the sealing resin flows during molding, and the film has excellent conformability to the mold.
The release film of the second embodiment has a tensile modulus of elasticity of 150 MPa or less at a temperature of 170°C and a recovery rate of 70% or more at a temperature of 170°C, and therefore exhibits the property of maintaining its shape while deforming moderately when heat and external force are applied. As a result, it is presumed that the release film has excellent conformability to the mold, being less likely to wrinkle or slacken when attached to the mold or when the sealing resin flows during molding.

The release layer of the release film of the present disclosure contains resin particles. The resin particles form fine irregularities on the outer surface of the release layer, and it is presumed that the fine irregularities of the resin particles enhance the slipperiness of the outer surface of the release layer and contribute to improving the release properties. In addition, it is presumed that the fine irregularities suppress the occurrence of flow marks of the sealing resin, so that the semiconductor package is less likely to have a defective appearance. Furthermore, combined with the tensile modulus and recovery rate being within the above ranges, the resin particles are less likely to fall off the release layer than inorganic particles, so that the release layer containing resin particles is less likely to contaminate the surface of the semiconductor package and the surface of the mold than a release layer containing inorganic particles but not resin particles.

The release film of the present disclosure has excellent conformability to a molding die, and is therefore unlikely to wrinkle or slacken during molding. Therefore, with the release film of the present disclosure, (a) there is a low possibility that the semiconductor package will be damaged when the release film is peeled off, (b) appearance defects caused by wrinkles or slackness of the release film are unlikely to occur in the semiconductor package, and (c) sealing defects in the semiconductor package are unlikely to occur due to wrinkles or slackness of the release film.
The release film of the present disclosure has excellent releasability from the encapsulating resin after molding, and therefore requires less force to peel off the release film, and therefore the release film of the present disclosure is less likely to damage the semiconductor package when peeled off.

The release film of the present disclosure has excellent conformability to the mold during molding and excellent releasability from the encapsulating resin after molding, so it can be used with molds having complex shapes or molds having relatively deep grooves. In addition, the release film of the present disclosure is suitable for compression molding in which the release film is placed on the mold by vacuum suction or the like.

Below, we will explain the characteristics of each layer of the release film disclosed herein, the components contained in each layer, etc.

[Base layer]
The release film of the present disclosure has a base material layer. The base material layer is not particularly limited, and it is preferable to select a resin film having a tensile modulus of elasticity of 150 MPa or less at a temperature of 170° C. and a recovery rate of 70% or more at a temperature of 170° C. from resin films used in the present technical field.

(Tensile Modulus)
In the release film of the first embodiment, the base material layer has a tensile modulus of elasticity of 150 MPa or less at a temperature of 170° C. In the release film of the second embodiment, the base material layer preferably has a tensile modulus of elasticity of 150 MPa or less at a temperature of 170° C.

The tensile modulus of elasticity of the substrate layer is determined by the following test method.
A substrate layer, which is a material for producing a release film, is prepared, or a layer other than the substrate layer is peeled off from a release film to prepare a substrate layer. The substrate layer is cut into the shape of a dumbbell-shaped No. 1 test piece as specified in JIS K6251:2010. Two parallel marks are drawn 40 mm apart at the center of the test piece. A tensile test is performed using a tensile tester (e.g., model RTC-1210 manufactured by A&D Co., Ltd.) at a temperature of 170°C in accordance with the test method as specified in JIS K6251:2010 to determine the tensile modulus.
Specifically, the test piece is placed in a tensile tester (e.g., model RTC-1210 manufactured by A&D Co., Ltd.) and stretched 100% at a temperature of 170° C. and a tensile speed of 500 mm/min (i.e., stretched until the distance between the two benchmark lines is 80 mm). From the stress-strain curve measured at this time, the stress σ1 (MPa) at strain ε1=0.0005 (0.05%) and the stress σ2 (MPa) at strain ε2=0.0025 (0.25%) are obtained, and the tensile modulus is calculated from the following formula.
(Formula) ... Tensile modulus (MPa) = (σ2 - σ1) ÷ (ε2 - ε1)
Here, when the base layer is a resin film manufactured in a long shape, a test piece is prepared in which the length direction of the test piece coincides with the MD direction of the resin film, and a test piece in which the length direction of the test piece coincides with the TD direction of the resin film. The tensile modulus of the base layer is determined by averaging the tensile modulus of the test piece in the MD direction and the tensile modulus of the test piece in the TD direction.

In the release film of the first embodiment, the tensile modulus of the base layer at a temperature of 170°C is 150 MPa or less from the viewpoint of improving the followability of the release film to the mold. In the release film of the second embodiment, the tensile modulus of the base layer at a temperature of 170°C is preferably 150 MPa or less from the viewpoint of improving the followability of the release film to the mold. In the release film of the present disclosure, the tensile modulus of the base layer at a temperature of 170°C is more preferably 130 MPa or less, even more preferably 110 MPa or less, and even more preferably 100 MPa or less from the above viewpoint. In the release film of the present disclosure, the lower limit of the tensile modulus of the base layer at a temperature of 170°C is, for example, 1 MPa or more, 2 MPa or more, or 3 MPa or more from the viewpoint of ensuring the strength required of the base layer.

The release film of the first embodiment preferably has a tensile modulus of 150 MPa or less at a temperature of 170 ° C. as a whole release film. The release film of the second embodiment has a tensile modulus of 150 MPa or less at a temperature of 170 ° C. as a whole release film. The release film of the present disclosure more preferably has a tensile modulus of 130 MPa or less at a temperature of 170 ° C. as a whole release film, even more preferably has a tensile modulus of 110 MPa or less, even more preferably has a tensile modulus of 100 MPa or less, and particularly preferably has a tensile modulus of 80 MPa or less at a temperature of 170 ° C. as a whole release film. The lower limit of the tensile modulus of the release film of the present disclosure at a temperature of 170 ° C. is, for example, 1 MPa or more, 2 MPa or more, or 3 MPa or more from the viewpoint of ensuring the strength required for the release film.
The method of determining the tensile modulus of the release film is the same as that of the base layer, and the release film is used as a test piece. When the release film is manufactured in a long shape, a test piece whose length direction coincides with the MD direction of the release film and a test piece whose length direction coincides with the TD direction of the release film are prepared. The average value of the tensile modulus of the test piece in the MD direction and the tensile modulus of the test piece in the TD direction is taken as the tensile modulus of the release film.

(Recovery rate)
In the release film of the first embodiment, the base material layer has a restoration rate of 70% or more at a temperature of 170° C. In the release film of the second embodiment, the base material layer preferably has a restoration rate of 70% or more at a temperature of 170° C.

The recovery rate of the base material layer is determined by the following test method.
A base layer, which is a material for producing a release film, is prepared, or a layer other than the base layer is peeled off from a release film to prepare a base layer. The base layer is cut into the shape of a dumbbell-shaped No. 1 test piece as specified in JIS K6251:2010. Two parallel marks are placed 40 mm apart in the center of the test piece. The test piece is placed in a tensile tester (e.g., A&D Co., Ltd., model number RTC-1210), and the test piece is stretched 100% at a temperature of 170°C and a tensile speed of 500 mm/min (i.e., stretched until the distance between the two marks is 80 mm), and then the test piece grip of the tensile tester is returned to its original position. After leaving it for 1 minute, the test piece is removed from the tester, the distance L (mm) between the two marks is measured, and the recovery rate is calculated from the following formula.
(Formula) ... restoration rate (%) = (80 - L) ÷ 40 x 100
Here, when the base layer is a resin film manufactured in a long shape, a test piece is prepared in which the length direction of the test piece coincides with the MD direction of the resin film, and a test piece in which the length direction of the test piece coincides with the TD direction of the resin film. The average value of the restoration rate of the test piece in the MD direction and the restoration rate of the test piece in the TD direction is defined as the restoration rate of the base layer.

In the release film of the first embodiment, the restoration rate of the base layer at a temperature of 170°C is 70% or more from the viewpoint of improving the followability of the release film to the mold. In the release film of the second embodiment, the restoration rate of the base layer at a temperature of 170°C is preferably 70% or more from the viewpoint of improving the followability of the release film to the mold. In the release film of the present disclosure, the restoration rate of the base layer at a temperature of 170°C is more preferably 75% to 100%, even more preferably 80% to 100%, and even more preferably 90% to 100%, from the above viewpoints.

The release film of the first embodiment preferably has a restoration rate of 70% or more as a whole at a temperature of 170° C. The release film of the second embodiment preferably has a restoration rate of 70% or more as a whole at a temperature of 170° C. The release film of the present disclosure more preferably has a restoration rate of 75% to 100%, even more preferably 80% to 100%, and even more preferably 90% to 100% as a whole at a temperature of 170° C.
The method of determining the restoration rate of the release film is the same as that of the base material layer, and the release film is used as the test piece. When the release film is manufactured in a long shape, a test piece whose length direction coincides with the MD direction of the release film and a test piece whose length direction coincides with the TD direction of the release film are prepared. The average value of the restoration rate of the test piece in the MD direction and the restoration rate of the test piece in the TD direction is taken as the restoration rate of the release film.

(Components of Base Material Layer)
Considering that resin molding of semiconductor packages is carried out at high temperatures (approximately 100° C. to 200° C.), it is desirable for the base material layer to have heat resistance at or above this temperature.

From the viewpoints of heat resistance and tensile modulus at high temperatures, it is preferable that the base layer contains a polyester resin. Examples of polyester resins include polyethylene terephthalate resin, polyethylene naphthalate resin, polybutylene terephthalate resin, and copolymers or modified resins thereof.

As the base layer, a polyester film molded from polyester resin is preferred, and from the viewpoint of conformability to the mold, a biaxially oriented polyester film is more preferred.

When a polyester film is used as the base layer, the tensile modulus and recovery rate of the base layer can be controlled by the stretching ratio or stretching temperature when producing the polyester film.

(Average thickness of substrate layer)
The average thickness of the base layer is not particularly limited, and is preferably 5 μm to 200 μm, and more preferably 10 μm to 100 μm. When the average thickness of the base layer is 5 μm or more, the handleability is excellent and wrinkles tend not to occur. When the average thickness of the base layer is 200 μm or less, the conformability to the mold during molding is excellent, and the occurrence of wrinkles and the like in the semiconductor package is further suppressed.

The outer surface of the substrate layer (the surface that comes into contact with the mold) may be surface treated to facilitate peeling from the mold.

[Release layer]
The release film of the present disclosure has a release layer containing resin particles on one side of a substrate layer. The release layer contains at least the resin particles, and may further contain a binder resin and other components.

(Resin particles)
The resin particles preferably contain at least one selected from the group consisting of acrylic resin, polyolefin resin, polystyrene resin, polyacrylonitrile resin, and silicone resin. From the viewpoint of the releasability of the release layer, the resin particles more preferably contain at least one selected from acrylic resin, polystyrene resin, and polyacrylonitrile resin.

The acrylic resin contained in the resin particles may be a homopolymer or copolymer of a (meth)acrylic monomer, such as a (meth)acrylic acid resin or a (meth)acrylic acid ester resin (e.g., an alkyl (meth)acrylate resin or a dimethylaminoethyl (meth)acrylate resin). Examples of the (meth)acrylic monomer include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, tetradecyl (meth)acrylate, butyl ... Examples thereof include hexadecyl acrylate, octadecyl (meth)acrylate, eicosyl (meth)acrylate, docosyl (meth)acrylate, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, benzyl (meth)acrylate, phenyl (meth)acrylate, methoxyethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, 2-chloroethyl (meth)acrylate, 2-fluoroethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, etc. These may be used alone or in combination of two or more.
The polyolefin resin contained in the resin particles is not particularly limited as long as it is a homopolymer or copolymer of an olefin monomer or an alkene monomer, and specific examples thereof include polyethylene, polypropylene, polymethylpentene, and the like.
The polystyrene resin contained in the resin particles may be a homopolymer or copolymer of styrene or a styrene derivative. Examples of the styrene derivative include alkyl-substituted styrenes having an alkyl chain, such as α-methylstyrene, 4-methylstyrene, 2-methylstyrene, 3-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene; halogen-substituted styrenes, such as 2-chlorostyrene, 3-chlorostyrene, and 4-chlorostyrene; fluorine-substituted styrenes, such as 4-fluorostyrene and 2,5-difluorostyrene; and vinylnaphthalene.
The polyacrylonitrile resin contained in the resin particles may be a homopolymer or copolymer of an acrylonitrile monomer.

From the viewpoint of uniformity of the appearance of the semiconductor package, the resin particles are preferably insoluble or poorly soluble in organic solvents (e.g., toluene, methyl ethyl ketone, ethyl acetate) that can be used to prepare the composition for forming the release layer. Here, insoluble or poorly soluble in organic solvents means that in a gel fraction test conforming to JIS K6769:2013, the resin particles are dispersed in an organic solvent such as toluene and the gel fraction after being kept at 50°C for 24 hours is 97% or more. From the viewpoint of suppressing the solubility of the resin particles in organic solvents, it is preferable that the resin contained in the resin particles is a crosslinked resin.

The average particle diameter of the resin particles is preferably 1 μm to 55 μm. If the average particle diameter of the resin particles is 1 μm or more, it is possible to form sufficient unevenness on the outer surface of the release layer, and the release properties of the release layer are better. From this viewpoint, the average particle diameter of the resin particles is more preferably 3 μm or more, and even more preferably 5 μm or more. If the average particle diameter of the resin particles is 55 μm or less, it is not necessary to make the thickness of the release layer excessively large in order to retain the resin particles in the release layer. From this viewpoint, the average particle diameter of the resin particles is more preferably 45 μm or less, and even more preferably 35 μm or less.

The average particle size of the resin particles is determined by the following measurement method.
A part of the release film is cut out, embedded in resin, and then cut in the thickness direction of the release film to prepare a thin sample. This thin sample is imaged with a scanning electron microscope (SEM). In the SEM image, 100 resin particles contained in the release layer are randomly selected, and the major axis of 100 particles is measured. The arithmetic average of the major axis of 100 particles is taken as the average particle diameter of the resin particles.

The shape of the resin particles contained in the release layer is not particularly limited and may be spherical, plate-like, or amorphous.

Specific examples of resin particles include the Tuftic series, such as Tuftic FH-S010 (Toyobo Co., Ltd.), which is an acrylic resin particle.

The volume ratio of the resin particles in the release layer is preferably 5% to 65% by volume from the viewpoint of improving the releasability of the release layer and suppressing contamination of the semiconductor package surface. If the volume ratio of the resin particles is 5% by volume or more, it is possible to form sufficient unevenness on the outer surface of the release layer, and the release property of the release layer is more excellent. From this viewpoint, the volume ratio of the resin particles is more preferably 10% by volume or more, and even more preferably 20% by volume or more. If the volume ratio of the resin particles is 65% by volume or less, the resin particles are less likely to fall off from the release layer, and contamination of the semiconductor package surface can be suppressed. From this viewpoint, the volume ratio of the resin particles is more preferably 60% by volume or less, and even more preferably 50% by volume or less.

The volume ratio of the resin particles in the release layer can be determined by observing a cut surface of the release layer with a SEM and by the following method.
In the SEM image of the thin sample prepared by the above-mentioned method, an arbitrary area S of the release layer is specified, and the total area A of the resin particles contained in the area S is calculated. Assuming that the release layer is homogeneous, the total area A of the resin particles is divided by the area S, and the value is converted into a percentage (%), which is the volume ratio of the resin particles in the release layer.
The area S is set to be sufficiently large with respect to the size of the resin particles, for example, a size that includes 100 or more resin particles. The area S may be the total area of a plurality of cut surfaces.

(Binder resin)
The release layer may contain a binder resin, which helps hold the resin particles in the release layer.

The binder resin of the release layer is not particularly limited. From the viewpoints of releasability from the semiconductor package and heat resistance of the release layer, the binder resin is preferably an acrylic resin or a silicone resin, and more preferably a cross-linked acrylic resin (hereinafter also referred to as a "cross-linked acrylic copolymer").

The acrylic resin is preferably an acrylic copolymer obtained by copolymerizing a low glass transition temperature (Tg) monomer such as butyl acrylate, ethyl acrylate, or 2-ethylhexyl acrylate as the main monomer with a functional group monomer such as acrylic acid, methacrylic acid, hydroxyethyl methacrylate, hydroxyethyl acrylate, acrylamide, or acrylonitrile. Crosslinked acrylic copolymers can be produced by crosslinking the above monomers using a crosslinking agent.

Examples of crosslinking agents used in the production of crosslinked acrylic copolymers include known crosslinking agents such as isocyanate compounds, melamine compounds, and epoxy compounds. In order to form a gently spreading network structure in the acrylic resin, the crosslinking agent is preferably a multifunctional crosslinking agent such as a trifunctional or tetrafunctional crosslinking agent. Since the crosslinked acrylic copolymer produced using a multifunctional crosslinking agent has a gently spreading network structure, the release layer containing this crosslinked acrylic polymer easily follows the stretching of the base layer, improving the followability of the release film to the mold.

The amount of crosslinking agent used in the production of the crosslinked acrylic copolymer is preferably 3 to 100 parts by weight, more preferably 5 to 70 parts by weight, per 100 parts by weight of the acrylic copolymer. When the amount of crosslinking agent is 3 parts by weight or more per 100 parts by weight of the acrylic copolymer, the strength of the release layer is ensured, making it difficult for resin particles to fall off and suppressing contamination of the semiconductor package surface. When the amount of crosslinking agent is 100 parts by weight or less per 100 parts by weight of the acrylic copolymer, the flexibility of the crosslinked acrylic copolymer is improved and the extensibility of the release layer is improved.

(Other ingredients)
The release layer may contain, as necessary, a solvent, an anchoring enhancer, a crosslinking promoter, an antistatic agent, a colorant, and the like, so long as the effects of the release film of the present disclosure are exhibited.

(Average thickness of release layer)
The average thickness of the release layer is not particularly limited, and may be set in consideration of the particle diameter of the resin particles contained in the release layer. From the viewpoint of improving the releasability of the release layer by forming unevenness on the outer surface of the release layer, it is preferable that the thickness of the release layer is not too thick. On the other hand, if the resin particles contained in the release layer fall off from the release layer, the surface of the semiconductor package will be contaminated, so the thickness of the release layer is preferably a thickness that can hold the resin particles in the release layer. Specifically, the average thickness of the release layer is preferably 0.1 μm to 100 μm, more preferably 1 μm to 50 μm.

(Surface roughness of release layer)
The outer surface of the release layer preferably has fine irregularities. The fine irregularities of the outer surface of the release layer can be evaluated by the arithmetic mean roughness (Ra) or the ten-point mean roughness (Rz). From the viewpoint of improving the releasability of the release layer, the arithmetic mean roughness (Ra) of the outer surface of the release layer is preferably 0.5 μm to 5 μm, and the ten-point mean roughness (Rz) of the outer surface of the release layer is preferably 5 μm to 50 μm. The surface roughness of the outer surface of the release layer can be adjusted by adjusting the average particle diameter of the resin particles and the thickness of the release layer.

The arithmetic mean roughness (Ra) and ten-point mean roughness (Rz) of the outer surface of the release layer are determined by analyzing the results measured using a surface roughness measuring device (e.g., Kosaka Laboratory Co., Ltd., model number SE-3500) under conditions of a stylus tip diameter of 2 μm, a scanning speed of 0.5 mm/s, and a scanning distance of 8 mm in accordance with JIS B0601:2013 or ISO 4287 (1997).

[Other layers]
The release film of the present disclosure may have an antistatic layer, a colored layer, or the like between the substrate layer and the release layer.

The release film of the present disclosure may have a second release layer on one side of the base layer opposite to the side on which the release layer (first release layer) containing resin particles is provided, for the purpose of facilitating release of the release film from the mold. It is desirable to select a material for the second release layer from the binder resins described above, taking into consideration releasability from the mold, heat resistance, and the like. The thickness of the second release layer is not particularly limited, but is preferably 0.1 μm to 100 μm.

<Method of producing release film>
The release film of the present disclosure can be manufactured by a known method. For example, a release layer forming composition containing resin particles is prepared, and the release layer forming composition is applied to one side of a substrate layer and dried to manufacture the release film of the present disclosure. The release film of the present disclosure may be provided with the other layers described above as necessary.

[Preparation of Release Layer Forming Composition]
The method for preparing the composition for forming the release layer is not particularly limited, and may be, for example, a method of dispersing resin particles in a solvent. The composition for forming the release layer may contain a binder resin and other components in addition to the resin particles.

The solvent used to prepare the composition for forming the release layer is not particularly limited. As the solvent used to prepare the composition for forming the release layer, an organic solvent capable of dispersing resin particles and dissolving binder resin is preferable. Examples of the organic solvent include toluene, methyl ethyl ketone, and ethyl acetate.

[Application and drying of release layer forming composition]
The method for applying the release layer-forming composition to one side of the base layer is not particularly limited, and any known application method such as roll coating, bar coating, kiss coating, etc. can be used. When applying the release layer-forming composition to one side of the base layer, it is desirable to apply it so that the thickness of the composition layer (release layer) after drying is 0.1 μm to 100 μm.

There are no particular limitations on the method for drying the release layer-forming composition applied to one side of the substrate layer, and any known drying method can be used. For example, a drying method in which the composition is placed in an atmosphere at a temperature of 50°C to 150°C for 0.1 to 60 minutes can be used.

<Method of manufacturing semiconductor package>
The release film of the present disclosure is used in the manufacture of a semiconductor package. That is, a mold having the release film of the present disclosure disposed thereon is used to encapsulate a semiconductor chip with an encapsulant to mold a semiconductor package.

The release film of the present disclosure can be suitably used for compression molding. A typical compression molding process is as follows.
A release film is placed on the mold of a compression molding device, and the release film is made to conform to the shape of the mold by vacuum suction or the like. Next, an encapsulant (e.g., epoxy resin, etc.) for the semiconductor package is placed in the mold, a semiconductor chip is placed on it, and the encapsulant is hardened by compressing the mold while heating, thereby molding the semiconductor package. Next, the mold is opened, and the molded semiconductor package is removed.

In compression molding, a release film is usually placed on a mold by vacuum suction or the like, so the release film is required to have excellent conformability to the shape of the mold. The release film of the present disclosure has excellent conformability to the mold and is suitable for compression molding.

A semiconductor package molded using the release film of the present disclosure has a good appearance. In addition, a semiconductor package molded using the release film of the present disclosure has reduced sealing defects of the semiconductor package caused by wrinkles or sagging of the release film, and reduced damage that may occur when the release film is peeled off.

Below, embodiments of the present disclosure are explained in detail using examples, but the embodiments of the present disclosure are not limited to these examples.

Example 1
[Preparation of release film]
A release layer-forming composition was prepared by adding 100 parts by mass of an acrylic resin (Teikoku Chemical Industries Co., Ltd., product name WS-023), 10 parts by mass of a crosslinking agent (Nippon Polyurethane Industry Co., Ltd., product name Coronate L), and 10 parts by mass of acrylic resin particles (Toyobo Co., Ltd., product name Tuftic FH-S010, average particle size 10 μm) to toluene to prepare a toluene solution with a solid content of 15% by mass.
A biaxially stretched polyethylene terephthalate film (Teijin Film Solutions Co., Ltd., product name FT3, thickness 25 μm) was prepared as a substrate layer, and the tensile modulus and recovery rate of this biaxially stretched polyethylene terephthalate film were determined by the above-mentioned test methods.
After subjecting the biaxially oriented polyethylene terephthalate film to corona treatment, a release layer forming composition was applied to one side using a roll coater so that the average thickness after drying would be 10 μm, and the composition was dried to form a release layer, thereby obtaining a release film.
The average particle size and volume ratio of the resin particles contained in the release layer of the obtained release film were determined by the previously described test method using SEM. The tensile modulus and recovery rate of the obtained release film were also determined by the previously described test method. The measurement results are shown in Table 1.

[Performance evaluation of release film]
A bare semiconductor chip was set on the lower die of the compression molding die. A release film was placed on the upper die of the compression molding die, and the die was then clamped. An encapsulant (Hitachi Chemical Co., Ltd., product name CEL-9750ZHF10) was compression molded to obtain a semiconductor package. The die temperature was 180° C., the molding pressure was 6.86 MPa (70 kgf/cm ² ), and the molding time was 180 seconds. The performance of the release film was evaluated in the following items (1) to (3). The evaluation results are shown in Table 1.

(1) Adherence to Mold During Molding The adherence of the release film to the mold was visually observed during compression molding and classified as follows.
A ⁺ (A): No wrinkles, sagging or tenting was observed, and the mold conformance was sufficient.
A (◯): Wrinkles, sagging or tenting are observed, but they are minor and do not pose a problem in practical use.
B (Δ): Wrinkles, sagging or tenting are observed, but are within the practically acceptable range.
C (x): Wrinkles, sagging and tenting were all observed, and the mold conformity was insufficient.
"Tenting" refers to a state in which the release film does not conform sufficiently to the mold and the release film floats over the corners of the mold, giving the appearance of a tent at the corners.

(2) Releasability from Molded Encapsulating Resin A peel test was carried out in which the release film was peeled from the molded encapsulating resin at a peel angle of 180° and a peel speed of 300 mm/min. The force required for peeling was measured and classified as follows:
A (○): Less than 0.5N/50mm B (△): 0.5N/50mm or more and less than 5.0N/50mm C (×): 5.0N/50mm or more

(3) Appearance of Semiconductor Package The appearance of the semiconductor package after molding was visually observed, and the presence or absence of appearance defects due to wrinkles or slackness of the release film was classified as follows.
A (◯): Neither poor appearance due to wrinkles nor poor appearance due to slackness is observed.
B (Δ): Poor appearance due to wrinkles or poor appearance due to slackness is observed.
C(x): Both poor appearance due to wrinkles and poor appearance due to slackness are observed.

<Examples 2 to 3>
A release film was produced and its performance was evaluated in the same manner as in Example 1, except that the base layer was changed to another biaxially oriented polyethylene terephthalate film. The evaluation results are shown in Table 1.

<Examples 4 to 7>
Release films were produced and their performance was evaluated in the same manner as in Example 1, except that the amount of acrylic resin particles (Tuftic FH-S010) added to the composition for forming the release layer was changed to change the volume ratio of the resin particles in the release layer as shown in Table 1. The evaluation results are shown in Table 1.

<Comparative Example 1>
The biaxially stretched polyethylene terephthalate film (Teijin Film Solutions Co., Ltd., product name FT3, thickness 25 μm) used in Example 1 was used as a release film without providing a release layer, and the performance was evaluated. The evaluation results are shown in Table 1.

<Comparative Example 2>
Except for preparing the composition for forming the release layer without using the acrylic resin particles (Tuftic FH-S010), a release film was produced and its performance was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

<Comparative Example 3>
A release film was produced and its performance was evaluated in the same manner as in Example 1, except that a composition for forming a release layer was prepared using silica particles (Toagosei Co., Ltd., product name HPS-3500, average particle size 3.5 μm) instead of acrylic resin particles (Tuftic FH-S010). The evaluation results are shown in Table 1.

<Comparative Example 4>
A release film was produced and its performance was evaluated in the same manner as in Example 1, except that the base layer was changed to another biaxially oriented polyethylene terephthalate film. The evaluation results are shown in Table 1.

<Comparative Example 5>
A release film was produced and its performance was evaluated in the same manner as in Example 1, except that the base layer was changed to an unstretched polybutylene terephthalate film. The evaluation results are shown in Table 1.

The release films of Examples 1 to 7 had excellent conformability to the mold during molding, good releasability from the encapsulating resin after molding, and the appearance of the semiconductor package was also good. However, in Example 7, in which the volume ratio of the resin particles in the release layer exceeded 65 volume %, the resin particles were observed to fall off from the release layer.
By using the release film of this embodiment for compression molding of a semiconductor package, it is possible to easily release the sealing material from the mold without damaging the semiconductor package, and it is possible to provide a semiconductor package with a good appearance.

The release film of Comparative Example 1 (a release film without a release layer) could not be peeled off from the sealing resin after molding.

The release film of Comparative Example 2 (a release film that does not contain resin particles in the release layer) could not be easily peeled off from the encapsulating resin after molding. In addition, the appearance of the semiconductor package surface was uneven, and traces of flow of the encapsulating material were visible.

The release film of Comparative Example 3 (a release film containing silica particles instead of resin particles in the release layer) could not be easily peeled off from the encapsulating resin after molding. In addition, the silica particles were observed to have fallen off from the release layer both visually and under a microscope.

The disclosure of Japanese Patent Application No. 2019-193307 is incorporated herein by reference in its entirety.
All publications, patent applications, and standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or standard was specifically and individually indicated to be incorporated by reference.

10 Release film 20 Base layer 30 Release layer

Claims (8)

A base layer having a tensile modulus of elasticity of 150 MPa or less at a temperature of 170°C and a recovery rate of 70% or more at a temperature of 170°C;
a release layer disposed on one surface of the base layer and containing resin particles;
having
The recovery rate is calculated by cutting the base layer into the shape of a dumbbell-shaped No. 1 test piece specified in JIS K6251:2010, marking two parallel benchmark lines 40 mm apart in the center of the test piece, placing the test piece in a tensile tester, stretching the test piece 100% at a temperature of 170°C and a tensile speed of 500 mm/min, returning the test piece gripper of the tensile tester to its original position, leaving the test piece stationary for 1 minute, removing the test piece from the tester, measuring the distance L (mm) between the two benchmark lines, and calculating from the following formula :
(Formula) ... restoration rate (%) = (80 - L) ÷ 40 x 100 The release film according to claim 1, wherein the volume ratio of the resin particles in the release layer is 5 volume % to 65 volume %. The release film according to claim 1 or 2, wherein the base layer is a polyester film. A base layer;
A release layer is disposed on one surface of the base layer and contains resin particles,
The tensile modulus at a temperature of 170° C. is 150 MPa or less and the recovery rate at a temperature of 170° C. is 70% or more,
The restoration rate is calculated by cutting a release film into the shape of a dumbbell-shaped No. 1 test piece specified in JIS K6251:2010, marking two parallel lines 40 mm apart in the center of the test piece, placing the test piece in a tensile tester, stretching the test piece by 100% at a temperature of 170°C and a tensile speed of 500 mm/min, returning the test piece gripper of the tensile tester to its original position, leaving the test piece still for 1 minute, removing the test piece from the tester, measuring the distance L (mm) between the two marks, and calculating from the following formula: Release film for use in manufacturing semiconductor packages.
(Formula) ... restoration rate (%) = (80 - L) ÷ 40 x 100 The release film according to claim 4, wherein the volume ratio of the resin particles in the release layer is 5 volume % to 65 volume %. The release film according to claim 4 or claim 5, wherein the base layer is a polyester film. The release film according to any one of claims 1 to 6, for use in compression molding of semiconductor packages. A method for manufacturing a semiconductor package, comprising: using a mold on which the release film according to any one of claims 1 to 7 is placed, sealing a semiconductor chip with a sealing material to form a semiconductor package.