Release film, base material for release film, method for producing release film, and method for producing semiconductor package

Abstract

This release film has (1) a base material and a release layer that are uniaxially stretched in the MD direction or the TD direction, and (2) the elongation in the MD direction is 250% to 3000%, and the length change rate M170 at 170°C in a tensile measurement in the MD direction according to thermomechanical analysis (TMA) is 2.0% or less.

Description

Release film, substrate for release film, method for producing release film, and method for producing semiconductor package

[0001] The present invention relates to a release film, a substrate for a release film, a method for producing a release film, and a method for producing a semiconductor package.

[0002] Semiconductor chips are typically sealed with resin to shield and protect them from the outside air, and are mounted on a substrate as a molded product called a package. Molded products are produced by injecting a resin-containing encapsulant into a mold. The mold has multiple cavities that are connected via runners that act as flow paths for the encapsulant. To facilitate release of the molded product from the mold, various measures are taken, such as the mold structure and the addition of a mold release agent to the encapsulating resin.

[0003] On the other hand, due to demands for smaller packages and higher pin counts, packaging methods such as the Ball Grid Array (BGA) method, Quad Flat Non-leaded (QFN) method, and Wafer Level Chip Size Package (WL-CSP) method are on the rise. In the QFN method, in order to ensure standoff and prevent burrs from forming on the terminals due to the encapsulant, and in the BGA and WL-CSP methods, in order to improve the releasability of the package from the mold, a resin release film is placed inside the mold along the mold, and the encapsulant is injected into the film for molding (see, for example, Patent Document 1). The molding method using a release film is called a "film-assisted molding method."

[0004] As a release film used for such applications, a release film having a base material of biaxially oriented polyethylene terephthalate (PET) film, which has excellent dimensional stability, is widely used (see, for example, Patent Document 2).

[0005] JP 2002-158242 A JP 2019-73022 A

[0006] However, current release films are rigid and have little elongation, which means that they have poor conformability to molds. For example, when sealing a package in which multiple semiconductor chips are stacked, it is desirable for the film to conform to the mold, which becomes deeper depending on the height of the package.

[0007] On the other hand, if the flexibility of the release film is increased, wrinkles tend to occur in the release film during the production of a molded article, and these wrinkles may be transferred to the molded article, deteriorating the appearance of the molded article.

[0008] In view of these circumstances, an object of the present disclosure is to provide a release film that has excellent mold conformability and suppresses the occurrence of wrinkles when producing a molded body, a substrate for a release film, a method for manufacturing a release film, and a method for manufacturing a semiconductor package.

[0009] The present disclosure includes the following embodiments. <1> A release film having a substrate uniaxially stretched in the MD direction or the TD direction and a release layer. <2> The release film according to <1>, wherein the substrate is uniaxially stretched in the MD direction. <3> The release film has an MD elongation of 250% to 3000% at 170°C, and a length change rate M at 170°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) is 250% to 3000%. １７０ <4> A release film having an MD elongation of 250% to 3000% at 170°C, and a length change rate M at 170°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) of 2.0% or less. １７０ <5> The release film according to <2>, wherein the length change rate M at 150°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) is 2.0% or less. １５０ <6> The release film according to <3> or <4>, wherein the length change rate T at 170°C in tensile measurement in the TD direction by thermomechanical analysis (TMA) is 1.5% or less. １７０ <7> The release film according to any one of <3> to <5>, wherein the length change rate T at 150°C in tensile measurement in the TD direction by thermomechanical analysis (TMA) is 4.5% or more. １５０ <8> The release film according to any one of <3> to <6>, wherein the length change rate M１７０ and the length change rate T １７０ <9> The release film according to <6> or <7>, wherein the absolute value of the difference between the length change rate M at 150°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) and the length change rate M at 150°C is 2.5% or more. １５０ and the length change rate T at 150 ° C. in tensile measurement in the TD direction by thermomechanical analysis (TMA). １５０ <10> The release film according to any one of <2> to <9>, wherein the absolute value of the difference between the modulus of elasticity and the modulus of elasticity in the MD direction at 170°C is 30 MPa to 500 MPa. <11> The release film according to any one of <2> to <10>, wherein the modulus of elasticity in the MD direction at 150°C is 60 MPa to 600 MPa. <12> The release film according to any one of <1> to <11>, wherein the thickness is 38 μm to 300 μm. <13> The release film according to any one of <1> to <12>, wherein the thickness comprises a polyester copolymer having a butylene structure. <14> The release film according to <1> or <2>, wherein the thickness of the substrate is 50 μm or more. <15> The release film according to any one of <3> to <13>, which has a substrate and a release layer, and the thickness of the substrate is 50 μm or more. <16> The release film according to any one of <1> to <15>, wherein a value obtained by dividing the total thickness by the larger of the modulus of elasticity in the MD direction and the modulus of elasticity in the TD direction at 170°C is 0.4 or more. <17> The release film according to any one of <1> to <16>, wherein a value obtained by dividing the total thickness by the larger of the modulus of elasticity in the MD direction and the modulus of elasticity in the TD direction at 150°C is 0.4 or more. <18> The substrate for a release film is uniaxially stretched in the MD direction or the TD direction. <19> The substrate for a release film according to <18>, which is uniaxially stretched in the MD direction. <20> The elongation in the MD direction at 170 ° C is 250% to 3000%, and the length change rate M at 170 ° C in tensile measurement in the MD direction by thermomechanical analysis (TMA) is １７０<21> A substrate for a release film, having an MD elongation of 250% to 3000% at 170°C, and a length change rate M at 170°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) of 2.0% or less. １７０ <22> The substrate for a release film according to <19>, wherein the length change rate M at 150°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) is 2.0% or less. １５０ <23> The substrate for a release film according to <20> or <21>, wherein the length change rate T at 170°C in tensile measurement in the TD direction by thermomechanical analysis (TMA) is 1.5% or less. １７０ <24> The substrate for a release film according to any one of <20> to <22>, wherein the length change rate T at 150°C in tensile measurement in the TD direction by thermomechanical analysis (TMA) is 4.5% or more. １５０ <25> The substrate for a release film according to any one of <20> to <23>, wherein the length change rate M １７０ and the length change rate T １７０ <26> The substrate for a release film according to <23> or <24>, wherein the absolute value of the difference between the length change rate M at 150°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) and the length change rate M at 150°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) is 2.5% or more. １５０ and the length change rate T at 150 ° C. in tensile measurement in the TD direction by thermomechanical analysis (TMA). １５０<27> The substrate for release films according to any one of <19> to <26>, having an MD modulus of elasticity of 30 MPa to 500 MPa at 170°C. <28> The substrate for release films according to any one of <19> to <27>, having an MD modulus of elasticity of 60 MPa to 600 MPa at 150°C. <29> The substrate for release films according to any one of <18> to <28>, comprising a polyester copolymer containing a butylene structure. <30> The substrate for release films according to any one of <18> to <29>, having a thickness of 50 μm or more. <31> The substrate for release films according to any one of <18> to <30>, wherein a value obtained by dividing the thickness by the larger of the modulus of elasticity in the MD direction and the modulus of elasticity in the TD direction at 170°C is 0.4 or more. <32> The substrate for release films according to any one of <18> to <31>, wherein a value obtained by dividing the thickness by the larger of the modulus of elasticity in the MD direction and the modulus of elasticity in the TD direction at 150°C is 0.4 or more. <33> A method for producing a release film, comprising: a step of uniaxially stretching an unstretched substrate in the MD direction or the TD direction; and a step of applying a release layer-forming composition to the stretched substrate to form a release layer. <34> A method for producing a semiconductor package, wherein a transfer molding step or a compression molding step is carried out using the release film according to any one of <1> to <17>. <35> The method for manufacturing a semiconductor package according to <34>, wherein the transfer molding step or the compression molding step is performed in a state where the release film is placed in a plurality of recesses of a mold.

[0010] According to the present disclosure, there are provided a release film that has excellent conformability to a mold and suppresses the occurrence of wrinkles when a molded body is produced, a substrate for a release film, a method for manufacturing a release film, and a method for manufacturing a semiconductor package.

[0011] 1 is a diagram illustrating a schematic configuration of a release film, a diagram illustrating the shape of a test piece used to measure the elongation and elastic modulus of a release film, and a diagram illustrating an outline of a method for producing a semiconductor package using the release film of the present disclosure in transfer molding.

[0012] Hereinafter, embodiments for carrying out the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure.

[0013] In the present disclosure, the term "process" includes not only processes that are independent of other processes, but also processes that cannot be clearly distinguished from other processes as long as the purpose of the process is achieved. In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another staged numerical range. Furthermore, in numerical ranges described in the present disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the Examples. In the present disclosure, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in a 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 term "layer" includes cases where the layer is formed over the entire region when the region in which the layer is present is observed, as well as cases where the layer is formed only in a portion of the region.

[0014] In the present disclosure, the thickness of the release film or each layer constituting the release film can be measured by known methods. 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 release film or layer is not constant, the arithmetic mean value of values ​​measured at any five points is taken as the thickness of the release film or layer.

[0015] When describing embodiments with reference to the drawings in this disclosure, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of components in each drawing are conceptual, and the relative size relationships between components are not limited to these.

[0016] In the present disclosure, the term "MD direction" refers to the longitudinal direction of a release film or a substrate for a release film, and the term "TD direction" refers to the width direction.

[0017] <Release Film> A first release film of the present disclosure has a substrate that is uniaxially stretched in the MD direction or the TD direction, and a release layer. The first release film is preferably uniaxially stretched in the MD direction. A second release film of the present disclosure has an MD elongation of 200% to 3000% at 170°C, and a length change rate M at 170°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) is 200% to 3000%. １７０ Hereinafter, the first release film and the second release film will also be collectively referred to as release films.

[0018] The release film has excellent conformability to a mold and suppresses the occurrence of wrinkles when a molded article is produced. The reason for this is not entirely clear, but is presumed to be as follows. In the first release film, a uniaxially stretched substrate is used, which results in high elongation and excellent conformability to a mold. Furthermore, in a uniaxially stretched substrate, the occurrence of wrinkles in the stretching direction is suppressed. In particular, when the film is uniaxially stretched in the MD direction, the occurrence of wrinkles in the MD direction, which is longer than the TD direction, is suppressed, and it is thought that the occurrence of wrinkles in the release film as a whole when a molded article is produced is more likely to be suppressed. Furthermore, in the second release film, since the elongation in the MD direction at 170°C is 250% to 3000%, the length change M at 170°C in tensile measurement in the MD direction by TMA is 250% to 3000%. １７０ It is believed that the occurrence of wrinkles during the production of a molded body can be suppressed by keeping the content of the film at 2.0% or less. Generally, molded bodies are produced by heating at a temperature of around 170°C, and therefore the release film is also heated at a temperature of around 170°C.

[0019] In addition, it is preferable that the first release film also has an MD elongation of 250% to 3000% at 170°C, and a length change rate M １７０ is preferably 2.0% or less. The uniaxially stretched substrate of the first release film is stretched in the MD direction. The second release film preferably has a substrate and a release layer, and the substrate of the second release film is preferably a substrate that is uniaxially stretched in the MD direction.

[0020] The elongation M of the release film in the MD direction at 170° C. is preferably 300% to 2000%, and more preferably 600% to 1500%. When the elongation M is 300% or more, the film tends to have excellent conformability to the mold, and when it is 2000% or less, the film tends to have excellent transportability when being moved to the mold.

[0021] The elongation T of the release film in the TD direction at 170° C. is preferably 200% to 3000%, more preferably 300% to 2000%, and even more preferably 600% to 1500%. When the elongation T is 200% or more, the film tends to have excellent conformability to the mold, and when it is 3000% or less, the film tends to have excellent transportability when being moved to the mold.

[0022] The absolute value of the difference between the elongation M and the elongation T is preferably 3.0% to 5.0%, and more preferably 4.0% to 5.0%. When the absolute value of the difference between the elongation M and the elongation T is 3.0% or more, the wrinkle prevention properties tend to be excellent, and when it is 4.0% or less, the dimensional stability against a mold tends to be excellent.

[0023] The elongation in the MD and TD directions at 170°C can be adjusted by the stretch ratio of the substrate. Furthermore, the elongation in the MD and TD directions at 170°C can be adjusted by the material of the substrate. For example, when the substrate contains a polyester copolymer, the elongation can be adjusted by selecting an acid-derived structure (e.g., terephthalic acid) and an alcohol-derived structure (e.g., butanediol) in the polyester copolymer, or in the case of a polyester copolymer containing a butylene structure and an alkylene oxide structure as described below, by the composition ratio of the butylene structure and the alkylene oxide structure.

[0024] The elongation of a release film in the MD or TD direction at 170°C is measured by the following method. First, a test piece having a shape as shown in Figure 2 is prepared using the release film. Both ends of this test piece are gripped with a testing machine and a tensile test is performed. The measurement is performed under conditions of 170°C and a tensile speed of 500 mm / min. The elongation is calculated using the following formula from the gauge length A of the sample before the test (the length of the 10 mm wide portion of the test piece shown in Figure 2: 40 mm) and the gauge length B when the sample is cut.

[0025]

[0026] The elongation of the release film is measured using a tensile tester (for example, Tensilon tensile tester "RTA-100" manufactured by Orientec Co., Ltd.).

[0027] Release film length change rate M １７０ is preferably 1.5% or less, more preferably 1.0% or less, even more preferably 0.0% or less, and particularly preferably -1.0% or less. １７０ When the length change rate in the TMA tensile measurement is a positive value, it means that the release film has expanded compared to before the measurement, and when the length change rate is a negative value, it means that the release film has shrunk.

[0028] Length change rate M １７０ is preferably −4.0% or more, more preferably −3.0% or more, even more preferably −2.0% or more, and particularly preferably −1.5% or more. １７０ When the thickness is within the above range, the occurrence of wrinkles in the release film tends to be further suppressed during the production of a molded article.

[0029] The length change rate M at 150°C in tensile measurement in the MD direction by TMA １５０is preferably 1.5% or less, more preferably 1.0% or less, even more preferably 0.5% or less, and particularly preferably 0.0% or less. １５０ When the thickness is within the above range, the occurrence of wrinkles in the release film tends to be further suppressed during the production of a molded article.

[0030] Length change rate M １５０ is preferably −2.5% or more, more preferably −2.0% or more, even more preferably −1.5% or more, and particularly preferably −1.0% or more. １５０ When the thickness is within the above range, the occurrence of wrinkles in the release film tends to be further suppressed during the production of a molded article.

[0031] The length change rate T at 170°C in tensile measurement in the TD direction by TMA １７０ is preferably 4.3% or more, more preferably 5.0% or more, and even more preferably 6.0% or more. １７０ When the thickness is within the above range, the occurrence of wrinkles in the release film tends to be further suppressed during the production of a molded article.

[0032] Length change rate T １７０ is preferably 11% or less, more preferably 9% or less, even more preferably 7% or less, and particularly preferably 5% or less. １７０ When the amount is within the above range, the dimensional stability to the mold tends to be excellent.

[0033] The rate of change in length T at 150°C in tensile measurement in the TD direction by TMA １５０ is preferably 3.8% or more, more preferably 4.5% or more, and even more preferably 5.0% or more. １５０ When the thickness is within the above range, the occurrence of wrinkles in the release film tends to be further suppressed during the production of a molded article.

[0034] Length change rate T １５０is preferably 10% or less, more preferably 8% or less, even more preferably 6% or less, and particularly preferably 4% or less. １５０ When the amount is within the above range, the dimensional stability to the mold tends to be excellent.

[0035] Length change rate M １７０ and the rate of change of length T １７０ Difference ΔMT １７０ The absolute value of the difference ΔMT is preferably 2.5% or more, more preferably 3.0% or more, and even more preferably 4.0% or more. １７０ When the absolute value of is within the above range, the occurrence of wrinkles in the release film tends to be further suppressed during the production of a molded article.

[0036] Difference ΔMT １７０ The absolute value of the difference ΔMT is preferably 15% or less, more preferably 10% or less, and even more preferably 6% or less. １７０ When the absolute value of is within the above range, the dimensional stability to the mold tends to be excellent.

[0037] Length change rate M １５０ and the rate of change of length T １５０ Difference ΔMT １５０ The absolute value of the difference ΔMT is preferably 2.5% or more, more preferably 3.0% or more, and even more preferably 4.0% or more. １５０ When the absolute value of is within the above range, the occurrence of wrinkles in the release film tends to be further suppressed during the production of a molded article.

[0038] Difference ΔMT １５０ The absolute value of the difference ΔMT is preferably 10% or less, more preferably 8% or less, and even more preferably 6% or less. １５０ When the absolute value of is within the above range, the dimensional stability to the mold tends to be excellent.

[0039] Length change rate M １７０ , M １５０ , T １７０ , and T １５０ can be adjusted by the stretching ratio of the substrate. １７０ , M１５０ , T １７０ , and T １５０ For example, when the substrate contains a polyester copolymer, the length change rate can be adjusted by selecting an acid-derived structure (e.g., terephthalic acid) and an alcohol-derived structure (e.g., dibutanol) in the polyester copolymer, or in the case of a polyester copolymer containing a butylene structure and an alkylene oxide structure as described below, by adjusting the composition ratio of the butylene structure and the alkylene oxide structure.

[0040] Length change rate M １７０ , M １５０ , T １７０ , and T １５０ is measured using a thermomechanical analyzer (for example, Seiko Instruments Inc. "SS6000") under the following measurement conditions: (Measurement conditions) Temperature range: 30°C to 220°C Heating rate: 10°C / min Load: 50mN Test piece: 4mm (width) x 10mm (length) Test mode: Tensile

[0041] The release film has an elastic modulus E in the MD direction at 170°C. Ｍ１７０ is preferably 30 MPa to 500 MPa, more preferably 40 MPa to 400 MPa, and even more preferably 50 MPa to 300 MPa. Ｍ１７０ When the compressive strength is 30 MPa or more, the moldability tends to be excellent, and when the compressive strength is 500 MPa or less, the elongation tends to be excellent.

[0042] The release film has an elastic modulus E in the MD direction at 150°C. Ｍ１５０ is preferably 60 MPa to 600 MPa, more preferably 80 MPa to 500 MPa, and even more preferably 100 MPa to 400 MPa. Ｍ１５０ When the compressive strength is 60 MPa or more, the moldability tends to be excellent, and when the compressive strength is 600 MPa or less, the elongation tends to be excellent.

[0043] The release film has a TD modulus of elasticity E Ｔ１７０is preferably 350 MPa to 10 MPa, more preferably 150 MPa to 30 MPa, and even more preferably 150 MPa to 50 MPa. Ｔ１７０ When the compressive strength is 350 MPa or more, the film tends to be less likely to tear during handling, and when the compressive strength is 350 MPa or less, the film tends to have excellent conformability to a mold.

[0044] The release film has a TD modulus of elasticity E Ｔ１５０ is preferably 400 MPa to 30 MPa, more preferably 200 MPa to 50 MPa, and even more preferably 150 MPa to 70 MPa. Ｔ１５０ When the compressive strength is 70 MPa or more, the film tends to be less likely to tear during handling, and when the compressive strength is 400 MPa or less, the film tends to have excellent conformability to a mold.

[0045] Elastic modulus E Ｍ１７０ , E Ｔ１７０ , E Ｍ１５０ , and E Ｔ１５０ The elastic modulus E can be adjusted by the stretching ratio of the substrate. Ｍ１７０ , E Ｔ１７０ , E Ｍ１５０ , and E Ｔ１５０ For example, when the substrate contains a polyester copolymer, the elastic modulus can be adjusted by selecting an acid-derived structure (e.g., terephthalic acid) and an alcohol-derived structure (e.g., dibutanol) in the polyester copolymer, or by adjusting the composition ratio of the butylene structure and the alkylene oxide structure in the case of a polyester copolymer containing a butylene structure and an alkylene oxide structure as described below.

[0046] The elastic modulus in the MD or TD direction at each temperature is measured using a dynamic viscoelasticity measuring device (for example, UBM's "E4000") under the following measurement conditions: (Measurement conditions) Temperature range: -20°C to 220°C Heating rate: 10°C / min Frequency: 10 Hz Test piece: 5 mm (width) x 10 mm (length) Test mode: Tension

[0047] The thickness of the release film is preferably 38 μm to 300 μm, more preferably 50 μm to 250 μm, and even more preferably 75 μm to 200 μm. When sealing a tall package (for example, a package in which multiple semiconductor chips are stacked), the mold depth is deep, so the thickness of the release film is preferably thin, with emphasis on conformability to the mold; for example, preferably 250 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less. Furthermore, when there is variation in the height of the semiconductor chips, it is preferable to make the thickness of the release film thick to a certain extent so that the height variation can be absorbed by the thickness of the release film (cushioning properties); for example, preferably 50 μm or more, more preferably 75 μm or more, and even more preferably 100 μm or more.

[0048] The total thickness of the release film is defined as the elastic modulus E Ｍ１７０ and E Ｔ１７０ C divided by the larger value of Ｔ１７０ is preferably 0.4 or more, more preferably 0.6 or more, and even more preferably 0.8 or more. Ｔ１７０ When C is equal to or greater than the lower limit, the cushioning properties are excellent and the height variations of the semiconductor chips tend to be easily absorbed. Ｔ１７０ is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.2 or less. Ｔ１７０ When the thickness of the molded surface is equal to or greater than the lower limit, the thickness variation of the molded surface tends to be suppressed.

[0049] The total thickness of the release film is defined as the elastic modulus E Ｍ１５０ and E Ｔ１５０ C divided by the larger value of Ｔ１５０ is preferably 0.4 or more, more preferably 0.6 or more, and even more preferably 0.8 or more. Ｔ１５０ When C is equal to or greater than the lower limit, the cushioning properties are excellent and the height variations of the semiconductor chips tend to be easily absorbed. Ｔ１５０is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.2 or less. Ｔ１５０ When the thickness is equal to or less than the upper limit, the thickness variation of the molding surface tends to be suppressed.

[0050] The release film preferably contains a polyester copolymer containing a butylene structure, which will be described in detail in the section on the substrate.

[0051] As an example of the release film of the present disclosure, the cross-sectional structure of the release film is shown schematically in Figure 1. As shown in Figure 1, the release film 10 has a substrate 12 and a release layer 14. A conductive layer 16 may be provided between the substrate 12 and the release layer 14. The release film 10 may further have other layers. Examples of the other layers include a second release layer, an anchoring improving layer, and a colored layer.

[0052] (Base Material) From the viewpoint of elongation, the base material preferably contains a polyester copolymer containing a butylene structure, more preferably 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 and an oxygen atom are bonded, and the number of carbon atoms in the alkylene group is preferably 1 to 6, more preferably 4.

[0053] 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.

[0054] A preferred example of the polyester copolymer is a copolymer (hereinafter also referred to as a specific polyester copolymer) containing a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2): The specific polyester 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).

[0055]

[0056]

[0057] The mass ratio (PBT:PTMG) of the hard segment (PBT) to the soft segment (PTMG) constituting the specific polyester copolymer is not particularly limited and may be selected from the range of 1:9 to 9:1, 2:8 to 8:2, or 3:7 to 7:3, for example.

[0058] The substrate may contain components other than the specific 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 contains components other than the specific polyester copolymer, the proportion of the specific polyester copolymer in the entire substrate is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0059] The thickness of the substrate is not particularly limited, and is preferably 10 μm to 300 μm, and more preferably 20 μm to 200 μm. When the thickness of the substrate is 10 μm or more, the release sheet is less likely to tear and has excellent handleability. When the thickness of the substrate is 300 μm or less, it has excellent mold conformability. Furthermore, when emphasis is placed on mold conformability, the thickness of the substrate is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less. Furthermore, from the viewpoint of cushioning properties, the thickness of the substrate is preferably 50 μm or more, more preferably 75 μm or more, and even more preferably 100 μm or more.

[0060] The substrate may be composed of only one layer or two or more layers. Methods for obtaining a substrate composed of two or more layers include a method of extruding the materials of each layer by a co-extrusion method, a method of laminating two or more films, and the like.

[0061] If necessary, the substrate may be subjected to a surface treatment, such as corona treatment, plasma treatment, or application of a primer.

[0062] If necessary, a backside treatment agent may be applied to the backside of the substrate (the side opposite to the side on which the release layer is disposed) to adjust the unwinding property of the release film from the roll. Examples of backside treatment agents include silicone resins, fluorine-containing resins, polyvinyl alcohol, and resins having an alkyl group. If necessary, these backside treatment agents may be modified. One type of backside treatment agent may be used alone, or two or more types may be used in combination.

[0063] (Release Layer) The release layer is responsible for releasing the semiconductor package during molding. The release layer contains at least a resin. The 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 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").

[0064] 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. A crosslinked acrylic copolymer can be produced by crosslinking the above-mentioned monomers using a crosslinking agent.

[0065] Examples of crosslinking agents used in producing the crosslinked acrylic copolymer include known crosslinking agents such as isocyanate compounds, melamine compounds, epoxy compounds, etc. In order to form a network structure that spreads gently in the acrylic resin, the crosslinking agent is preferably a multifunctional crosslinking agent such as a trifunctional or tetrafunctional crosslinking agent.

[0066] The release layer may contain, as needed, a solvent, an anchoring improver, a crosslinking accelerator, an antistatic agent, a filler, a colorant, and the like, as long as the effects of the release film of the present disclosure are exhibited.

[0067] The filler material is not particularly limited, and may be an organic substance such as a resin, an inorganic substance such as a metal or a metal oxide, or a combination of an organic substance and an inorganic substance. The release layer may contain one or more types of filler. The volume average particle diameter 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 diameter of the filler is the particle diameter (D50) at which the cumulative total from the small diameter side reaches 50% in the volume-based particle size distribution measured by laser diffraction.

[0068] From the viewpoint of affinity with the resin contained in the release layer, the filler is preferably resin particles. Examples of resins constituting the resin particles include acrylic resin, olefin resin, styrene resin, acrylonitrile resin, and silicone resin. From the viewpoint of suppressing residues on the surface of the semiconductor package after molding, acrylic resin is preferred.

[0069] The thickness of the release layer is not particularly limited, and is preferably 0.1 μm to 100 μm. When the thickness of the release layer is 0.1 μm or more, it can contain a resin sufficient to exhibit flexibility or extensibility to conform to the mold, and peeling or chipping of the release layer from the substrate is unlikely to occur. When the thickness of the release layer is 100 μm or less, when the release layer is formed using a thermosetting resin, thermal shrinkage during heat curing is suppressed, and the flatness of the release film is maintained. From the above-mentioned viewpoints, the thickness of the release layer is more preferably 1 μm to 100 μm, and even more preferably 10 μm to 50 μm. When comprehensively considering the ease of forming the release layer (e.g., coatability), ensuring antistatic function by shortening the distance from the surface of the release film to the conductive layer that is optionally provided, and the like, the thickness of the release layer is more preferably 3 μm to 50 μm.

[0070] (Conductive Layer) The release film of the present disclosure may include a conductive layer between the substrate and the release layer. The conductive layer has an antistatic function. The configuration of the conductive layer is not particularly limited as long as it can increase the conductivity of the release film and suppress static buildup. For example, the conductive layer may be a layer containing a conductive material such as an antistatic agent, a conductive polymer material, or a metal.

[0071] Examples of antistatic agents contained in the conductive layer include cationic antistatic agents having cationic groups such as quaternary ammonium salts, pyridinium salts, and primary to tertiary amino groups; anionic antistatic agents having anionic groups such as sulfonate groups, sulfate groups, and phosphate groups; amphoteric antistatic agents such as amino acid-based and amino acid sulfate-based; nonionic antistatic agents having nonionic groups such as amino alcohol-based, glycerin-based, and polyethylene glycol-based; and polymeric antistatic agents obtained by increasing the molecular weight of these antistatic agents. The antistatic agent may be a combination of a main component and an auxiliary (such as a curing agent). Examples of conductive polymer materials contained in the conductive layer include polymeric compounds having a skeleton such as polythiophene, polyaniline, polypyrrole, or polyacetylene. Examples of metals include aluminum, copper, gold, chromium, and tin, with aluminum being preferred from the standpoint of availability.

[0072] The method for forming the conductive layer is not particularly limited, and examples thereof include a method of laminating a metal foil or the like on one side of a film serving as a substrate, and a method of applying a material for the conductive layer to one side of a film serving as a substrate by coating, vapor deposition, or the like.

[0073] The thickness of the conductive layer is not particularly limited as long as it provides a sufficient antistatic effect for the release film, and may be, for example, within the range of 0.01 μm to 1 μm.

[0074] <Method for Producing Release Film> The release film of the present disclosure can be obtained by forming a release layer on a substrate. When a conductive layer is provided between the substrate and the release layer, the conductive layer can be formed on the substrate, and then a release layer can be formed on the conductive layer. The conductive layer can be formed on the substrate by, for example, a vapor deposition method, a lamination method, or a coating method.

[0075] The release layer can be formed, for example, by applying a composition containing the above-mentioned resin, a solvent, and optionally other components (hereinafter also referred to as a "release layer-forming composition") to a substrate and thermally curing the composition. The solvent used in the release layer-forming composition is not particularly limited.

[0076] The method for producing a release film of the present disclosure may include a step of uniaxially stretching an unstretched substrate in the MD direction or the TD direction, and a step of applying a release layer-forming composition to the stretched substrate to form a release layer. The method for producing a release film of the present disclosure preferably includes a step of uniaxially stretching an unstretched substrate in the MD direction, and a step of applying a release layer-forming composition to the stretched substrate to form a release layer.

[0077] In the production of the release film of the present disclosure, the release layer-forming composition may be applied to an unstretched substrate, and the substrate may be uniaxially stretched in the MD direction when heated and dried. Alternatively, the release layer-forming composition may be applied using a substrate that is uniaxially stretched in the MD direction, but the substrate may shrink to its original shape due to heating during drying after application of the release layer-forming composition. In such cases, it is preferable to use an unstretched substrate as described above, and uniaxially stretch the substrate in the MD direction during heat drying after application of the release layer-forming composition.

[0078] It is preferable to appropriately adjust the force used to stretch the substrate in the MD direction during heating and drying after application of the release layer-forming composition so that the elongation, length change rate, elastic modulus, etc. of the release film fall within the above-mentioned ranges.

[0079] The width shrinkage ratio calculated from the following formula before and after the formation of the release layer is preferably 1.8% to 10.0%, more preferably 2.0% to 8.0%, and even more preferably 2.2% to 6.0%. When the width shrinkage ratio is 1.8% or more, the force stretching the substrate in the MD direction during heat drying after application of the release layer-forming composition is sufficient, and a suitable uniaxially stretched substrate tends to be obtained. When the width shrinkage ratio is 10.0% or less, the transportability in the release layer-forming step tends to be excellent.

[0080] Width shrinkage rate (%)=(width of substrate before forming release layer−width of substrate after forming release layer) / width of substrate before forming release layer×100

[0081] In the above formula, the width of the obtained release film may be substituted for the width of the substrate after the release layer is formed.

[0082] The method of applying the composition onto the substrate is not particularly limited, and can be a general application method.When the composition applied to the substrate is dried while stretching the substrate in the MD direction, a general application method can be used, and examples thereof include spray coating, inkjet coating, bar coating, knife coating, roll coating, blade coating, die coating, gravure coating, microgravure coating, comma coating, slot die coating, and lip coating.

[0083] <Substrate for release film> The first substrate for release film of the present disclosure is uniaxially stretched in the MD direction or the TD direction. The second substrate for release film of the present disclosure has an elongation in the MD direction of 250% to 3000% at 170°C, and a length change rate M at 170°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) is 250% to 3000%. １７０ Hereinafter, the first release film substrate and the second release film substrate are also collectively referred to as release film substrates.

[0084] A release film using the above-mentioned substrate for a release film has excellent conformability to a mold, and the occurrence of wrinkles during the production of a molded article is suppressed.

[0085] Elongation M, elongation T, length change rate M in the substrate for release film １７０ , M １５０ , T １７０ , and T １５０ , and the elastic modulus E Ｍ１７０ , E Ｔ１７０ , E Ｍ１５０ , and E Ｔ１５０ The preferred ranges of the elongation M, elongation T, and length change rate M １７０ , M １５０ , T １７０ , and T １５０ , and the elastic modulus E Ｍ１７０ , E Ｔ１７０ , E Ｍ１５０ , and E Ｔ１５０ In addition, the absolute value of the difference between the elongation M and the elongation T, the ratio (elongation M / elongation T), and the difference ΔMT １７０Absolute value, difference ΔMT １５０ The absolute value of the ratio (M １７０ / T １７０ ), ratio (M １５０ / T １５０ ), difference ΔE １７０ Absolute value of difference ΔE １５０ The absolute value of the ratio (E Ｍ１７０ / E Ｔ１７０ ), ratio (E Ｍ１５０ / E Ｔ１５０ ), C Ｔ１７０ , and C Ｔ１５０ The preferred range of the difference between the elongation M and the elongation T in the release film is also determined by the absolute value of the difference, the ratio (elongation M / elongation T), and the difference ΔMT １７０ Absolute value, difference ΔMT １５０ The absolute value of the ratio (M １７０ / T １７０ ), ratio (M １５０ / T １５０ ), difference ΔE １７０ Absolute value of difference ΔE １５０ The absolute value of the ratio (E Ｍ１７０ / E Ｔ１７０ ), ratio (E Ｍ１５０ / E Ｔ１５０ ), C Ｔ１７０ , and C Ｔ１５０ The preferred range is the same as that of the above.

[0086] The description of the substrate given in the section on release films also applies to substrates for release films.

[0087] <Method for manufacturing a semiconductor package> In the method for manufacturing a semiconductor package of the present disclosure, a transfer molding process or a compression molding process is performed using the release film of the present disclosure. The release film is placed in multiple recesses of a mold, and in this state, the transfer molding process or the compression molding process is performed. As an example, Figure 3 shows an outline of a method for manufacturing a semiconductor package using the release film 10 of the present disclosure in transfer molding.

[0088] As shown in Figure 3 (A), the release film 10 of the present disclosure, which is stretched over a pair of rolls 20, 21, is placed along the shape of the upper die 30 of the molding machine. The upper die 30 has a plurality of recesses. When placing the release film 10, care must be taken not to wrinkle it. The release film 10 may be made to conform to the upper die 30 by vacuum suction or the like.

[0089] The semiconductor chip 42 mounted on the substrate 40 is placed in the lower mold 32 of the mold so that the semiconductor chip 42 faces upward. Examples of the semiconductor chip include a semiconductor element, a capacitor, and a terminal.

[0090] Then, as shown in FIG. 3(B), the upper mold 30 and the lower mold 32 are closed. The semiconductor chip 42 is placed in the recess of the upper mold 30. In this state, the release film 10 and the semiconductor chip 42 are in contact with each other. After the mold is closed, molten encapsulant 50 is injected into the space within the mold, and the semiconductor chip is encapsulated with the encapsulant. There are no particular limitations on the type of encapsulant, and examples include resin compositions containing epoxy resin, acrylic resin, etc. After the semiconductor chip is encapsulated, the mold is opened as shown in FIG. 3(C), and the semiconductor package in which the semiconductor chip is encapsulated with the encapsulant is removed. When the mold is opened, the release film 10 is peeled off the semiconductor chip 42.

[0091] The mold is heated to about 170°C to prevent the molten encapsulant 50 from cooling and solidifying, and to ensure sufficient curing when the encapsulant 50 is a thermosetting resin composition. The release film is also heated to about 170°C to fit the release film to the heated mold. If the release film swells to a certain extent due to this heating, wrinkles will form. However, in the method for manufacturing a semiconductor package according to the present disclosure, the release film 10 according to the present disclosure is used, and thus the occurrence of wrinkles in the release film 10 within the mold is suppressed.

[0092] After the semiconductor chips are sealed, the release film 10 is wound up in a roll-to-roll manner, and a new surface is placed on the upper mold 30. In this way, in the case of the roll-to-roll method, the release film 10 is used continuously.

[0093] The release film of the present disclosure will be described below based on examples, although the present disclosure is not limited to the following examples.

[0094] Example 1 (Preparation of Substrate) A substrate film having a thickness of 100 μm was prepared using a polyester copolymer having 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) in a mass ratio (PBT:PTMG) of 3:7. In Tables 1 and 2, this is referred to as PBT.

[0095] (Preparation of release layer-forming composition) A release layer-forming composition was prepared by mixing a resin (100 parts by mass), a crosslinking agent (20 parts by mass), and toluene (34 parts by mass).

[0096] Details of the materials used are as follows: Resin: Acrylic resin, trade 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 (tolylene isocyanate crosslinking agent (TDI)), trade name "Coronate L (TOSOH Corporation), trade name)";

[0097] (Preparation of Release Film) This release layer-forming composition was applied to a substrate so that the thickness of the release layer would be 25 μm, and a release film was prepared by stretching in the MD direction while heating and drying for 1 minute at 100° C. The width of the substrate film before the release layer was formed and the width of the resulting release film were measured, and the width shrinkage rate (%) was calculated using the above formula.

[0098] Examples 2 to 5 Release films were produced in the same manner as in Example 1, except that the stretching force in the MD direction during production of the release film was changed.

[0099] Comparative Example 1: A biaxially stretched PET film having a thickness of 38 μm was used as a substrate. The same release layer-forming composition as in Example 1 was applied onto this substrate so that the thickness of the release layer became 3 μm, and the substrate was dried without being stretched to produce a release film.

[0100] Comparative Example 2 A release film was prepared in the same manner as in Comparative Example 1, except that the release layer-forming composition was applied so that the thickness of the release layer became 25 μm.

[0101] Comparative Example 3 The release film was the same as the PET film used in Comparative Example 1. That is, the release film of Comparative Example 3 did not have a release layer on the PET film.

[0102] Comparative Example 4 The same procedure as in Comparative Example 3 was carried out, except that the thickness of the PET film was set to 50 μm.

[0103] Comparative Example 5 Comparative Example 5 was carried out in the same manner as in Comparative Example 3, except that the thickness of the PET film was set to 75 μm.

[0104] Comparative Example 6 A substrate film having a thickness of 50 μm was prepared using the polyester copolymer of Example 1. That is, the film of Comparative Example 6 did not have a release layer on the substrate film and was unstretched.

[0105] Comparative Example 7 The same procedure as in Comparative Example 6 was carried out, except that the thickness was set to 75 μm.

[0106] Comparative Example 8 The same procedure as in Comparative Example 6 was carried out, except that the thickness was set to 100 μm.

[0107] Comparative Example 9 A Boblet (biaxially stretched PBT film, thickness 25 μm) manufactured by Kohjin Film & Chemicals Co., Ltd. was used.

[0108] Comparative Example 10 A release film was produced in the same manner as in Example 1, except that the film was not stretched during production. The tension during transport of the base film when the release layer-forming composition was applied was adjusted so that the width shrinkage rate was 0%.

[0109] Comparative Example 11 A release film was produced in the same manner as in Comparative Example 10, except that the release layer was coated with the composition for forming a release layer so that the thickness of the release layer was 20 μm. The tension during transport of the base film when the composition for forming a release layer was coated was adjusted so that the width shrinkage rate was 1.5%.

[0110] [Evaluation Tests] The following evaluation tests were carried out using the prepared release films.

[0111] (Elongation and Elastic Modulus) The elongation and elastic modulus of the release film were measured by the above-mentioned method using a Tensilon tensile tester RTA-100 manufactured by Orientec Co., Ltd.

[0112] (Rate of Length Change) The rate of length change of the release film was measured by TMA measurement using the method described above. Seiko Instruments Inc. "SS6000" was used for the measurement.

[0113] (Mold followability, wrinkle occurrence, cushioning) A release film was attached to the upper mold of a 3 mm deep transfer mold, and the mold was then clamped and transfer molded with a sealing material. The mold temperature was 150°C and the molding pressure was 6.86 MPa (70 kgf / cm ２ ), and the molding time was 300 seconds.

[0114] The mold followability was evaluated as A if the release sheet could follow the mold without any breakage, B if slight breakage occurred but no practical problem, and C if breakage occurred. The occurrence of wrinkles was checked by visual inspection of the release film adsorbed to the mold. If no wrinkles occurred, it was evaluated as A; if slight wrinkles occurred but no practical problem, it was evaluated as B; if wrinkles occurred in the release film and the appearance of the molded article was impaired, it was evaluated as C. The cushioning property was evaluated as A if the value obtained by dividing the thickness by the elastic modulus was 1.0 or more, B if it was 0.4 or more but less than 1.0, and C if it was less than 0.4. The elastic modulus used for cushioning property was the MD or TD value (E Ｍ１５０、 E Ｍ１７０、 E Ｔ１５０、 E Ｔ１５０ ) was used.

[0115]

[0116]

[0117] As shown in the results of Tables 1 and 2, the release film (1) has a substrate and a release layer that are uniaxially stretched in the MD or TD direction, or (2) has an elongation in the MD direction of 200% to 3000% and a length change rate M at 170°C in tensile measurement in the MD direction by thermomechanical analysis (TMA).１７０ The release films of the examples in which the elongation ratio was 2.0% or less were excellent in conformity to the mold and cushioning property, and the occurrence of wrinkles was suppressed when the encapsulating material was molded. In contrast, the release films of the examples in which (1) a substrate uniaxially stretched in the MD direction or the TD direction was not used, or (2) the elongation in the MD direction was outside the range of 200% to 3000%, or the length change ratio M １７０ In the comparative examples where the length change rate M was more than 2.0%, the mold conformability, cushioning properties, and wrinkle formation were poor. Specifically, in the comparative examples 1 to 5 and 9 using a biaxially stretched substrate, the mold conformability was poor. １７０ In Comparative Examples 6 to 8 and 10 to 11, where the content was more than 2.0%, wrinkles were observed.

[0118] In addition, in Example 1, a uniaxially stretched substrate without a release layer was prepared by stretching in the MD direction during dry heating in the same manner as in Example 1 except that a release layer was not formed. This was used as the film of Example 0, and the elongation in the MD direction and the length change rate M １７０ The values ​​were almost the same as those of the release film with a release layer.

[0119] REFERENCE SIGNS LIST 10 Release film 12 Base material 14 Release layer 16 Conductive layer 20, 21 Roll 30 Upper die 32 Lower die 40 Substrate 42 Semiconductor chip 50 Encapsulating material

Claims

1. A release film having a substrate uniaxially stretched in the MD or TD direction and a release layer.

2. The release film according to claim 1, wherein the substrate is uniaxially stretched in the machine direction.

3. The elongation in the MD direction at 170°C is 250% to 3000%, and the length change rate M at 170°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) is １７０ A release film having a modulus of elasticity of 2.0% or less.

4. The elongation in the MD direction at 170°C is 250% to 3000%, and the length change rate M at 170°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) is １７０ The release film according to claim 2, wherein the modulus of elasticity is 2.0% or less.

5. Length change rate M at 150°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) １５０ The release film according to claim 3 or claim 4, wherein the modulus of elasticity is 1.5% or less.

6. Length change rate T at 170°C in tensile measurement in the TD direction by thermomechanical analysis (TMA) １７０ The release film according to claim 3 or claim 4, wherein the modulus of elasticity is 4.5% or more.

7. Length change rate T at 150°C in tensile measurement in the TD direction by thermomechanical analysis (TMA) １５０ The release film according to claim 3 or claim 4, wherein the modulus of elasticity is 3.8% or more.

8. The length change rate M １７０ and the length change rate T １７０ The release film according to claim 6, wherein the absolute value of the difference between 9. Length change rate M at 150°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) １５０ and the length change rate T at 150 ° C. in tensile measurement in the TD direction by thermomechanical analysis (TMA). １５０ The release film according to claim 3 or claim 4, wherein the absolute value of the difference between 10. The release film according to claim 2 or 3, wherein the elastic modulus in the machine direction at 170°C is 30 MPa to 500 MPa.

11. The release film according to claim 2 or 3, wherein the elastic modulus in the machine direction at 150°C is 60 MPa to 600 MPa.

12. The release film according to claim 1 or 3, which has a thickness of 38 μm to 300 μm.

13. The release film according to claim 1 or 3, which comprises a polyester copolymer containing a butylene structure.

14. The release film according to claim 1 or 2, wherein the thickness of the substrate is 50 μm or more.

15. The release film according to claim 3, which comprises a substrate and a release layer, the thickness of the substrate being 50 μm or more.

16. A release film according to claim 1 or 3, wherein the value obtained by dividing the total thickness by the larger of the modulus of elasticity in the machine direction and the modulus of elasticity in the transverse direction at 170°C is 0.4 or more.

17. A release film according to claim 1 or 3, wherein the value obtained by dividing the total thickness by the larger of the modulus of elasticity in the machine direction and the modulus of elasticity in the transverse direction at 150°C is 0.4 or more.

18. A substrate for a release film that is uniaxially stretched in the MD or TD direction.

19. The substrate for a release film according to claim 18, which is uniaxially stretched in the machine direction.

20. The elongation in the MD direction at 170°C is 250% to 3000%, and the length change rate M at 170°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) is １７０ A substrate for a release film, wherein the content is 2.0% or less.

21. The elongation in the MD direction at 170°C is 250% to 3000%, and the length change rate M at 170°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) is １７０ The substrate for a release film according to claim 19, wherein the modulus of elasticity is 2.0% or less.

22. Length change rate M at 150°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) １５０ The substrate for a release film according to claim 20 or 21, wherein the surface roughness is 1.5% or less.

23. Length change rate T at 170°C in tensile measurement in the TD direction by thermomechanical analysis (TMA) １７０ The substrate for a release film according to claim 20 or 21, wherein the surface roughness is 4.5% or more.

24. Length change rate T at 150°C in tensile measurement in the TD direction by thermomechanical analysis (TMA) １５０ The substrate for a release film according to claim 20 or 21, wherein the surface roughness is 3.8% or more.

25. The length change rate M １７０ and the length change rate T １７０ The substrate for a release film according to claim 23, wherein the absolute value of the difference between 26. Length change rate M at 150°C in tensile measurement in the MD direction by thermomechanical analysis (TMA) １５０ and the length change rate T at 150 ° C. in tensile measurement in the TD direction by thermomechanical analysis (TMA). １５０ The substrate for a release film according to claim 20 or 21, wherein the absolute value of the difference between 27. The substrate for a release film according to claim 19 or 20, wherein the elastic modulus in the machine direction at 170°C is 30 MPa to 500 MPa.

28. The substrate for a release film according to claim 19 or 20, wherein the elastic modulus in the machine direction at 150°C is 60 MPa to 600 MPa.

29. The substrate for a release film according to claim 18 or 20, which comprises a polyester copolymer containing a butylene structure.

30. The substrate for a release film according to claim 18 or claim 20, having a thickness of 50 μm or more.

31. A substrate for a release film according to claim 18 or 20, wherein the value obtained by dividing the thickness by the larger of the modulus of elasticity in the machine direction and the modulus of elasticity in the transverse direction at 170°C is 0.4 or more.

32. A substrate for a release film according to claim 18 or 20, wherein the value obtained by dividing the thickness by the larger of the modulus of elasticity in the machine direction and the modulus of elasticity in the transverse direction at 150°C is 0.4 or more.

33. A method for producing a release film, comprising: a step of uniaxially stretching an unstretched substrate in the MD direction or the TD direction; and a step of applying a release layer-forming composition to the stretched substrate to form a release layer.

34. A method for manufacturing a semiconductor package, which comprises carrying out a transfer molding process or a compression molding process using the release film according to claim 1 or 3.

35. The method for manufacturing a semiconductor package according to claim 34, wherein the transfer molding step or the compression molding step is carried out with the release film placed in a plurality of recesses in a mold.

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