Release film and method for manufacturing a release film

Abstract

In the manufacturing process of semiconductor packages, this invention provides a release film that exhibits excellent shape conformity to the mold and superior release properties by suppressing the occurrence of bending of the release film. [Solution] A release film comprising an unstretched polyester resin layer, an adhesive layer, an stretched polyester resin layer, and a release layer, wherein the adhesive layer is provided between the unstretched polyester resin layer and the stretched polyester resin layer, and the release layer is provided on the side of the stretched polyester resin layer opposite to the adhesive layer.

Description

Technical Field

[0001] The present invention relates to a release film used when molding and sealing a semiconductor chip.

Background Art

[0002] A semiconductor chip is usually sealed with a sealing resin for blocking and protecting from the outside air, and is mounted on a substrate as a molded product called a semiconductor package. As a molding method of the semiconductor package, a transfer method or a compression method is adopted. In the compression method, a release film is adhered in the cavity of a mold. After injecting a sealing resin into the cavity, a semiconductor chip is immersed in the sealing resin, and heating and pressurization are performed. By using the release film, it is possible to prevent the sealing resin from sticking to the mold and to prevent contamination of the mold.

[0003] As the release film used in the compression method, a release film using a fluororesin typified by ethylene / tetrafluoroethylene copolymer (ETFE) (for example, Patent Document 1) is frequently used. The fluororesin is excellent in elongation at high temperatures and has excellent releasability from the sealing resin. On the other hand, the use of fluororesin tends to be avoided from the viewpoint of environmental load and the like, and substitution with an alternative product is desired.

[0004] In the compression method, since pressurization is performed at about 180°C, high heat resistance is required for the base material. Therefore, release films using polyester resins such as polybutylene terephthalate and polystyrene resins with high heat resistance have been studied. For example, Patent Document 2 discloses a release sheet (release film) for semiconductor compression molding in which a release layer containing 5 to 65% by volume of resin particles is formed on a base material layer made of a polyester film. Patent Document 3 discloses a release film having a support layer having at least one layer containing an unstretched polybutylene terephthalate resin and a release layer. Patent Document 4 discloses a release film in which a layer containing a polyamide resin and a layer containing a 4-methyl-1-pentene polymer are laminated with an adhesive layer in between. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6402786 [Patent Document 2] Japanese Patent Publication No. 2016-92272 [Patent Document 3] International Publication No. 2014 / 203872 [Patent Document 4] International Publication No. 2010 / 023907 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In the manufacturing of semiconductor packages using the compression method, release films are required to conform to the shape of the mold cavity in order to suppress molding defects. Release films using fluororesins exhibit excellent shape conformability. However, release films that do not use fluororesins, such as those described in Patent Documents 2-4, have not achieved sufficient shape conformability. Therefore, there has been a need for the development of a release film with excellent shape conformability without using organofluororesins (PFAS).

[0007] This invention has been made in view of the above problems, and aims to provide a release film that has excellent shape conformability to a mold and excellent release properties. [Means for solving the problem]

[0008] To solve the above problems, the present invention provides the following <1> ~ <10> To provide. <1> A release film comprising an unstretched polyester resin layer, an adhesive layer, an stretched polyester resin layer, and a release layer, wherein the adhesive layer is provided between the unstretched polyester resin layer and the stretched polyester resin layer, and the release layer is provided on the side of the stretched polyester resin layer opposite to the adhesive layer. <2> The tensile modulus of the aforementioned unstretched polyester resin layer, measured at 175°C in accordance with JIS K 7161-1:2014, is between 20 MPa and 100 MPa. <1> The release film described above. <3> The tensile modulus of the stretched polyester resin layer, measured at 175°C in accordance with JIS K 7161-1:2014, is between 100 MPa and 200 MPa. <1> or <2> The release film described above. <4> The tensile modulus of the stretched polyester resin layer measured at 175°C in accordance with JIS K 7161-1:2014 is greater than the tensile modulus of the unstretched polyester resin layer measured at 175°C in accordance with JIS K 7161-1:2014. <1> ~ <3> Release film as described in any of the following. <5> The melting point of the polyester resin contained in the unstretched polyester resin layer is 200°C or higher and 300°C or lower. <1> ~ <4> Release film as described in any of the following. <6> The melting point of the polyester resin contained in the stretched polyester resin layer is 200°C or higher and 300°C or lower. <1> ~ <5> Release film as described in any of the following. <7> The total thickness is between 40 μm and 100 μm. <1> ~ <6> Release film as described in any of the following. <8> The aforementioned unstretched polyester resin layer is a layer containing 60% by mass or more of polybutylene terephthalate. <1> ~ <7> Release film as described in any of the following. <9> The stretched polyester resin layer is a layer containing 60% by mass or more of polyethylene terephthalate or polybutylene terephthalate. <1> ~ <8> Release film as described in any of the following. A method for manufacturing a release film according to any one of <10><1> to <9>, comprising a step of forming a release layer on one surface of the stretched polyester resin layer, and a step of adhering an unstretched polyester resin layer to the other surface side of the stretched polyester resin layer via the adhesive layer. A method for manufacturing a release film having

Effect of the Invention

[0009] According to the present invention, it is possible to obtain a release film that is excellent in shape followability to a mold and also excellent in releasability.

Brief Description of the Drawings

[0010] [Figure 1] It is a schematic cross-sectional view of a release film according to an embodiment of the present invention. [Figure 2] It is a diagram for explaining an example of a method for manufacturing a semiconductor package using the release film of the present invention. [Figure 3] It is a schematic view of the shape of the lower mold used in the evaluation of the example. [Figure 4] It shows a cross-sectional SEM photograph of a sample in which a sealing resin was filled and cured using the release film of Example 1. [Figure 5] It shows a cross-sectional SEM photograph of a sample in which a sealing resin was filled and cured using the release film of Comparative Example 3.

Modes for Carrying Out the Invention

[0011] Hereinafter, the release film of the present invention will be described in detail. In the description of the numerical range "AA to BB" in this specification, it means "AA or more and BB or less". Also, "weight" is synonymous with "mass".

[0012] [Release Film] The release film of the present invention has an unstretched polyester resin layer, an adhesive layer, a stretched polyester resin layer, and a release layer. The adhesive layer is provided between the unstretched polyester resin layer and the stretched polyester resin layer, and the release layer is provided on the surface side of the stretched polyester resin layer opposite to the adhesive layer.

[0013] FIG. 1 is a schematic cross-sectional view of a release film according to an embodiment of the present invention. In the release film 10 of FIG. 1, an unstretched polyester resin layer 12, an adhesive layer 16, a stretched polyester resin layer 14, and a release layer 18 are provided in this order. The adhesive layer 16 adheres the unstretched polyester resin layer 12 and the stretched polyester resin layer 14. The release layer 18 is provided on the surface of the stretched polyester resin layer 14 opposite to the adhesive layer 16.

[0014] The release film of the present invention is used, for example, in the production of semiconductor packages by the compression method. An example of a method for producing a semiconductor package using the release film of the present invention will be described with reference to FIG. 2.

[0015] First, the shape of the mold used in the production of the semiconductor package will be described. FIG. 2 shows a schematic longitudinal cross-sectional view of the mold. For example, as shown in FIG. 2(a), the mold is composed of an upper mold 110 and a lower mold 120. The upper mold 110 is, for example, flat. The lower mold 120 is composed of a bottom member 122 and a side member 124. In the example shown in FIG. 2(a), the shape of the surface of the bottom member 122 on the side of the upper mold 110 is rectangular. The side member 124 has a frame shape surrounding the bottom member 122, and a cavity 126 is formed by the bottom member 122 and the side member 124. It is preferable that the inclination of the side member 124 within the cavity 126 is such that the angle formed with the surface of the bottom member 122 within the cavity 126 is within the range of 90° to 120°. The side member 124 surrounds the bottom member 122 so as to form the cavity 126, and the shape is not particularly limited as long as the inclination within the cavity 126 is within the above range.

[0016] <Step 1 (Figure 2(a))> First, the lower mold 120 is positioned so that the surface inside the cavity 126 of the bottom member 122 is horizontal, and the upper mold 110 is positioned above the lower mold 120, spaced apart. The release film 10 is inserted between the upper mold 110 and the lower mold 120. At this time, the release film 10 is positioned so that the release layer 18 is on the upper mold 110 side and the unstretched polyester resin layer 12 is on the lower mold 120 side. The lower mold 120 is heated to approximately 120-180°C. Subsequently, a vacuum is created between the lower mold 120 and the release film 10, and the lower mold 120 is further heated. The release film 10 is heated and softened through the lower mold 120, and adheres to the shape of the surface inside the cavity 126 of the lower mold 120, as shown in Figure 2(a). In particular, the release film 10 contacts the lower mold 120 in such a way that no space (air bubbles) is formed at the boundary between the side member 124 and the bottom member 122 inside the cavity 126. <Step 2 (Figure 2(b))> A semiconductor chip 130 is attached to the surface of the upper mold 110 that faces the lower mold 120. A known method can be used for attachment. <Step 3 (Figure 2(c))> The cavity 126 is filled with sealing resin 140. <Step 4 (Figure 2(d))> The upper mold 110 is lowered, bringing it into contact with the lower mold 120. <Step 5 (Figure 2(e))> The bottom member 122 of the lower mold 120 is raised, and the semiconductor chip 130 is immersed in the sealing resin 140. In this state, the sealing resin is cured while applying pressure and heating. The curing conditions are set appropriately depending on the type of sealing resin 140, but for example, pressure: 90 N / m 2 ~120 N / m 2 The temperature should be 120°C to 180°C, and the time should be 60 to 300 seconds. <Process 6 (Figure 2(f))> After the sealing resin has hardened, the bottom member 122 is lowered, separating the release film 10 from the bottom member 122. Then, the upper mold 110 is raised, peeling the release film 10 from the semiconductor package 150.

[0017] As described above, the release film of the present invention comprises an unstretched polyester resin layer, an adhesive layer, a stretched polyester resin layer, and a release layer in that order, and is used by bringing the unstretched polyester resin layer into contact with the lower mold. In step 1, the release film of the present invention can be attached to the mold without wrinkles forming and without the formation of a space (air bubbles) between the lower mold and the release film in the cavity. On the other hand, as a result of the inventors' investigations, it was found that when a release film in which the release layer is formed only on the stretched polyester resin layer is used, wrinkles and air bubbles tend to occur in step 1. Furthermore, it was found that even when a release film in which the lamination order of the stretched polyester resin layer and the unstretched polyester resin layer is reversed is used, wrinkles and air bubbles tend to occur in step 1. Wrinkles and air bubbles frequently occurred at the four corners of the bottom member and at the boundary between the bottom member and the side member. Such wrinkles and air bubbles cause shape defects in semiconductor packages. Furthermore, wrinkles can become embedded within the sealing resin, potentially preventing the release film from being peeled off the semiconductor package. In this specification, when the release film is applied to the mold, the absence of wrinkles or air bubbles is referred to as "good conformability to the mold shape."

[0018] Furthermore, in the case of a release film in which the release layer is formed only on an unstretched polyester resin layer, as shown in Figure 5, the release film is folded into the encapsulating resin and becomes embedded in a wedge shape, making it difficult to peel the release film from the semiconductor package. On the other hand, as shown in Figure 4, the release film of the present invention does not become embedded in the encapsulating resin, and the release film can be easily peeled from the semiconductor package. Therefore, excellent peelability can be obtained with the release film of the present invention. In this specification, the state in which the release film is folded and embedded within the sealing resin is referred to as "embedding".

[0019] The reason why the release film of the present invention exhibits good shape conformability to the mold, suppresses embedding, and provides excellent release properties is presumed to be as follows. As shown in Table 2 below, the unoriented polyester resin layer has a lower tensile modulus at 175°C than the oriented polyester resin layer and is more easily deformed. Therefore, in a release film composed solely of the unoriented polyester resin layer, in step 1, it deforms along the shape of the surface inside the cavity of the lower mold, allowing it to adhere without wrinkles or bubbles, and achieving good shape conformability. On the other hand, the unoriented polyester resin layer hardly shrinks in the temperature range of the semiconductor package manufacturing process described above. Therefore, when the bottom surface member of the lower mold is raised in step 5, the unoriented polyester resin layer hardly shrinks, resulting in excess film corresponding to the amount the bottom surface member is raised, which tends to fold towards the cavity. As a result, it is considered that inclusion is likely to occur in a release film composed solely of the unoriented polyester resin layer. Because the stretched polyester resin layer has a higher tensile modulus than the unstretched polyester resin layer, it is less prone to deformation. Therefore, in the case of a release film composed solely of a stretched polyester resin layer, it is difficult to deform along the shape of the surface inside the cavity in step 1, and wrinkles and bubbles are likely to occur in places with angle changes, such as the four corners of the bottom member and the boundary between the bottom member and the side member. Consequently, it is difficult to obtain sufficient shape-following ability with a stretched polyester resin layer. On the other hand, because the stretched polyester resin layer is stretched, it shrinks when the bottom member of the lower mold is raised in step 5. Therefore, in the case of a release film composed solely of a stretched polyester resin layer, bending towards the cavity is less likely to occur.

[0020] The release film of the present invention can be attached to the mold without wrinkles or bubbles occurring in step 1, because the unstretched polyester resin layer is positioned on the lower mold side. Furthermore, when the bottom surface member of the lower mold is raised in step 5, the stretched polyester resin layer positioned on the upper mold side (cavity side) contracts, thereby suppressing the occurrence of bending toward the cavity side. Therefore, the release film of the present invention can obtain good shape conformability. Moreover, it can also suppress the occurrence of embedding and obtain excellent release properties. On the other hand, in a laminate configuration opposite to that of the release film of the present invention (a laminate configuration having a stretched polyester resin layer, an adhesive layer, an unstretched polyester resin layer, and a release layer in this order), the stretched polyester resin layer is positioned on the mold side. As described above, it is difficult to deform along the shape of the surface inside the cavity, resulting in wrinkles and bubbles, and making it impossible to obtain good shape conformability. Therefore, shape defects in semiconductor packages are likely to occur. Furthermore, when the bottom surface member of the lower mold is raised in step 5, the unstretched polyester resin layer positioned on the cavity side hardly shrinks, so the release film may bend towards the cavity side, potentially causing it to become embedded.

[0021] As described above, the release film of the present invention is provided with an unoriented polyester resin layer, an adhesive layer, an oriented polyester resin layer, and a release layer in that order. That is, in the release film of the present invention, it is preferable that the unoriented polyester resin layer is provided as the outermost layer of the release film. More specifically, in the release film of the present invention, it is preferable that there is no further oriented polyester resin layer, release layer, or adhesive layer on the side of the unoriented polyester resin layer opposite to the adhesive layer. Furthermore, in the release film of the present invention, it is preferable that there are no other layers besides the oriented polyester resin layer, release layer, and adhesive layer on the side of the unoriented polyester resin layer opposite to the adhesive layer. In the release film of the present invention, since an unstretched polyester film is provided as the outermost layer of the release film, as described above, the unstretched polyester resin layer can be used in contact with the lower mold, and it can be attached to the mold in step 1 without the generation of wrinkles or air bubbles. Furthermore, when the bottom surface member of the lower mold is raised in step 5, the stretched polyester resin layer positioned on the upper mold side (cavity side) shrinks, thereby suppressing the occurrence of bending toward the cavity side. Therefore, the release film of the present invention can obtain good shape conformability, further suppress the occurrence of indentation, and obtain excellent release properties.

[0022] The release film of the present invention preferably has a tensile modulus of 50 MPa to 120 MPa at 175°C, as measured in accordance with JIS K 7161-1:2014. Having a tensile modulus within this range makes it easier to achieve both good shape conformability to the mold and suppression of mold indentation. The tensile modulus of the release film is more preferably 55 MPa or higher, even more preferably 60 MPa or higher, even more preferably 115 MPa or lower, and even more preferably 110 MPa or lower. The tensile modulus of the release film can be adjusted by the tensile modulus of the unoriented polyester resin layer, the tensile modulus of the stretched polyester resin layer, the thickness of the unoriented polyester resin layer, the tensile modulus of the stretched polyester resin layer, and the total thickness of the release film. For example, the higher the tensile modulus of the unoriented polyester resin layer and the stretched polyester resin layer, the higher the tensile modulus of the release film tends to be. Also, the greater the thickness of each film, the higher the tensile modulus of the release film tends to be. In this invention, "tensile modulus measured at 175°C in accordance with JIS K 7161-1:2014" may be simply referred to as "tensile modulus."

[0023] The release film of the present invention preferably has a shrinkage stress of 0.40 N or more at 175°C. A shrinkage stress within this range makes it easier to suppress the occurrence of indentation. A shrinkage stress of 0.50 N or more is more preferable, and 0.60 N or more is even preferable. If the shrinkage stress is too high, wrinkles will occur due to shrinkage, reducing the ability to follow the mold and potentially leading to shape defects in the resulting semiconductor package. Therefore, a shrinkage stress of 1.50 N or less is preferable, and 1.00 N or less is even preferable. The shrinkage stress of the release film can be adjusted by adjusting the shrinkage stress of the stretched polyester resin layer, the thickness of the unstretched polyester resin layer, and the thickness of the stretched polyester resin layer. For example, the greater the shrinkage stress of the stretched polyester resin layer, the greater the shrinkage stress of the release film. The smaller the thickness of the unstretched polyester resin layer, and the greater the thickness of the stretched polyester resin layer, the greater the shrinkage stress of the release film tends to be. In this invention, "shrinkage stress at 175°C" may be simply referred to as "shrinkage stress." The shrinkage stress is a value measured by the method described in the examples.

[0024] Considering the ability to conform to the shape of the mold, the total thickness of the release film of the present invention is preferably 15 μm or more and 100 μm or less. More preferably, the total thickness is 35 μm or more, and even more preferably, 40 μm or more. Furthermore, the total thickness is more preferably 80 μm or less, and even more preferably, 50 μm or less.

[0025] Each layer of the release film 10 will be described in detail below. <Unstretched polyester resin layer, stretched polyester resin layer> In the release film of the present invention, the unstretched polyester resin layer and the stretched polyester resin layer serve as support structures for the release film. Furthermore, the unstretched polyester resin layer and the stretched polyester resin layer contribute to shape conformability to the mold and suppression of mold penetration.

[0026] <<Unstretched polyester resin>> The unoriented polyester resin layer is a layer whose main component is polyester resin. "Main component is polyester resin" means that the polyester resin content in the unoriented polyester resin layer is 60% by mass or more. Preferably, the polyester resin content is 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0027] Examples of polyester resins include polyethylene terephthalate resin, polybutylene terephthalate resin, and polyethylene naphthalate resin. Considering shape conformability to the mold and suppression of mold indentation, the polyester resin is more preferably polyethylene terephthalate resin, polybutylene terephthalate resin, or a mixture of polyethylene terephthalate resin and polybutylene terephthalate resin. Among these, polybutylene terephthalate resin is particularly preferred. The unstretched polyester resin layer is preferably a layer containing 60% by mass or more of polybutylene terephthalate. More preferably, the above percentage is 70% by mass or more, more preferably 80% by mass or more, and more preferably 90% by mass or more.

[0028] The unstretched polyester resin layer may contain resins other than polyester resins. Examples of resins other than polyester resins include thermoplastic resins such as polyethylene and polypropylene, and thermosetting resins such as phenolic resins, melamine resins, silicone resins, and epoxy resins. The unstretched polyester resin layer may also contain additives such as antistatic agents, antiblocking agents, ultraviolet absorbers, colorants, and inorganic fillers.

[0029] The weight-average molecular weight (Mw) of the polyester resin in the unstretched polyester resin layer is preferably 10,000 to 100,000, more preferably 20,000 to 80,000, and even more preferably 30,000 to 60,000. The weight-average molecular weight in this invention is the average molecular weight measured by GPC analysis and converted to standard polystyrene.

[0030] The unstretched polyester resin layer preferably has a tensile modulus of 20 MPa to 100 MPa at 175°C, as measured in accordance with JIS K 7161-1:2014. Having a tensile modulus of 175°C within this range makes it easier to achieve the same tensile modulus when laminated with a stretched polyester resin film. As a result, a release film with good shape conformability to the mold can be obtained in the semiconductor package manufacturing process. The tensile modulus is more preferably 95 MPa or less, and even more preferably 90 MPa or less. The tensile modulus of an unoriented polyester resin layer can be adjusted by the weight-average molecular weight of the polyester resin, the degree of crystallinity of the polyester resin, and the thickness of the unoriented polyester resin layer. For example, the larger the weight-average molecular weight of the polyester resin, the higher the tensile modulus tends to be. The higher the degree of crystallinity of the polyester resin, the higher the tensile modulus tends to be. The thicker the unoriented polyester resin layer, the higher the tensile modulus tends to be.

[0031] Because the unoriented polyester resin layer is unoriented, the shrinkage stress at 175°C is approximately 0 in both the MD and TD directions. However, when a film is used as the unoriented polyester resin layer, it may be slightly stretched in the MD direction for manufacturing reasons. In this invention, it is permissible to refer to a material with a shrinkage stress of 0.30 N or less in the MD direction as an unoriented polyester resin layer.

[0032] The melting point of the polyester resin contained in the unstretched polyester resin layer is preferably between 180°C and 300°C. Having a melting point within this range allows the film to maintain its shape even during heating in the semiconductor package manufacturing process. A melting point of 200°C or higher is more preferable, and 210°C or higher is even more preferable. Furthermore, considering the heating temperature of the mold, a melting point of 240°C or lower is more preferable, and 230°C or lower is even more preferable. The melting point can be adjusted by the material of the polyester resin layer, its weight-average molecular weight, its degree of crystallinity, etc. For example, the larger the weight-average molecular weight, the higher the melting point tends to be.

[0033] The thickness of the unoriented polyester resin layer is preferably 5 μm to 100 μm. Having a thickness within this range makes it easier for the overall thickness of the release film to meet this range, resulting in good shape conformability and easier suppression of indentation. Furthermore, it improves the handling of the release film during manufacturing. The thickness is more preferably 10 μm or more, and even more preferably 15 μm or more. Moreover, the thickness is more preferably 50 μm or less, even more preferably 30 μm or less, and even more preferably 20 μm or less.

[0034] <<Stretched polyester resin>> The stretched polyester resin layer is a layer whose main component is polyester resin. "Main component is polyester resin" means that the polyester resin content in the stretched polyester resin layer is 60% by mass or more. Preferably, the polyester resin content is 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0035] Examples of polyester resins include polyethylene terephthalate resin, polybutylene terephthalate resin, and polyethylene naphthalate resin. Considering shape conformability to the mold and suppression of mold indentation, the polyester resin is more preferably polyethylene terephthalate resin, polybutylene terephthalate resin, or a mixture of polyethylene terephthalate resin and polybutylene terephthalate resin. Among these, polybutylene terephthalate resin is particularly preferred. The stretched polyester resin layer is preferably a layer containing 60% by mass or more of polyethylene terephthalate or polybutylene terephthalate. More preferably, the above percentage is 70% by mass or more, more preferably 80% by mass or more, and more preferably 90% by mass or more. In a release film, the unstretched polyester resin layer and the stretched polyester resin layer may be made of the same polyester resin or different polyester resins.

[0036] The stretched polyester resin layer may contain resins other than polyester resins. Examples of resins other than polyester resins include thermoplastic resins such as polyethylene and polypropylene, and thermosetting resins such as phenolic resins, melamine resins, silicone resins, and epoxy resins. The stretched polyester resin layer may also contain additives such as antistatic agents, antiblocking agents, ultraviolet absorbers, colorants, and inorganic additives.

[0037] The stretched polyester resin layer may be uniaxially stretched or biaxially stretched. From the viewpoint of dimensional stability, the stretched polyester resin layer is preferably biaxially stretched. The stretching ratio of the stretched polyester resin layer is preferably 2.0 times or more, and more preferably 2.7 times or more. Furthermore, the stretching ratio is preferably 5.0 times or less, and more preferably 4.5 times or less.

[0038] The weight-average molecular weight (Mw) of the polyester resin in the stretched polyester resin layer is preferably 10,000 to 100,000, more preferably 20,000 to 80,000, and even more preferably 30,000 to 60,000. The weight-average molecular weight in this invention is the average molecular weight measured by GPC analysis and converted to standard polystyrene.

[0039] The stretched polyester resin layer preferably has a tensile modulus of 100 MPa to 200 MPa at 175°C, as measured in accordance with JIS K 7161-1:2014. Having the tensile modulus of the stretched polyester resin layer within this range at 175°C reduces the likelihood of wrinkles and folds occurring in the release film during the semiconductor package manufacturing process, thereby suppressing the occurrence of indentation. A tensile modulus of 110 MPa or higher is more preferable, and 120 MPa or higher is even more preferable. Furthermore, a tensile modulus of 180 MPa or lower is more preferable, and 160 MPa or lower is even more preferable. The tensile modulus of a stretched polyester resin layer can be adjusted by the weight-average molecular weight of the polyester resin, the degree of crystallinity of the polyester resin, the stretching ratio, and the thickness of the stretched polyester resin layer. For example, the larger the weight-average molecular weight of the polyester resin, the higher the tensile modulus tends to be. The higher the degree of crystallinity of the polyester resin, the higher the tensile modulus tends to be. The thicker the stretched polyester resin layer, the higher the tensile modulus tends to be.

[0040] The stretched polyester resin layer preferably has a shrinkage stress of 0.40 N or more at 175°C. Having the stretched polyester resin layer within this range makes it easier to achieve a shrinkage stress of 0.40 N or more in the release film, thereby suppressing the occurrence of indentation. A shrinkage stress of 0.40 N or more is more preferable, and 0.60 N or more is even preferable. Furthermore, to suppress the occurrence of wrinkles due to shrinkage when used as a release film, a shrinkage stress of 1.50 N or less is preferable, and 1.00 N or less is even preferable. The shrinkage stress of the stretched polyester resin layer at 175°C can be adjusted by the material of the stretched polyester resin layer, the stretching ratio, the temperature during stretching, and the heat setting after stretching. For example, the larger the stretching ratio, the greater the shrinkage stress tends to be. Furthermore, because the stretched polyester resin layer is heat-set after stretching, excessive shrinkage when heated during the semiconductor package manufacturing process described above can be suppressed.

[0041] The melting point of the polyester resin contained in the stretched polyester resin layer is preferably between 180°C and 300°C. Having a melting point within this range makes it easier to maintain the film shape even during heating in the semiconductor package manufacturing process. A melting point of 200°C or higher is more preferable, and 210°C or higher is even more preferable. Furthermore, considering the heating temperature of the mold, a melting point of 240°C or lower is more preferable, and 230°C or lower is even more preferable. The melting point can be adjusted by the material of the polyester resin layer, the weight-average molecular weight, etc. For example, the larger the weight-average molecular weight, the higher the melting point tends to be.

[0042] The thickness of the stretched polyester resin layer is preferably 5 μm to 100 μm. Having a thickness within this range makes it easier for the total thickness of the release film to meet this range, resulting in better shape conformability and easier suppression of indentation. Furthermore, it improves the handling of the release film during manufacturing. The thickness is more preferably 10 μm or more, and even more preferably 15 μm or more. It is also more preferably 50 μm or less, even more preferably 20 μm or less, and even more preferably 18 μm or less.

[0043] It is preferable that the tensile modulus of the stretched polyester resin layer, measured at 175°C in accordance with JIS K 7161-1:2014, is greater than the tensile modulus of the unstretched polyester resin layer, measured at 175°C in accordance with JIS K 7161-1:2014. The ratio of the tensile modulus of the stretched polyester resin layer to the tensile modulus of the unstretched polyester resin layer is preferably greater than 1.0 and 10 or less, more preferably between 1.1 and 8, more preferably between 1.2 and 5.0, and even more preferably between 1.3 and 2.0. By satisfying the above relationship in tensile modulus, good shape conformability can be easily obtained, and the occurrence of indentation can be easily suppressed.

[0044] The ratio of the thickness of the stretched polyester resin layer to the thickness of the unstretched polyester resin layer is preferably 0.5 to 1.5, more preferably 0.6 to 1.2, even more preferably 0.75 to 1.0, even more preferably 0.75 to less than 1.0, even more preferably 0.75 to 0.9, and even more preferably 0.75 to 0.85. By having the thickness ratio within the above range, good shape conformability can be easily obtained.

[0045] <Adhesive layer> The adhesive layer is not particularly limited as long as it can bond the unstretched polyester resin layer and the stretched polyester resin layer and does not hinder shape conformability to the mold. It is more preferable that the adhesive layer does not generate gas during the semiconductor package manufacturing process described above. For forming the adhesive layer, olefin-based adhesives, polyester-based adhesives, polyimide-based adhesives, epoxy-based adhesives, etc., can be used. Among these, polyester-based adhesives are particularly preferred from the viewpoint of processability.

[0046] Considering the handling characteristics of the release film and its conformability to the mold, the thickness of the adhesive layer is preferably 1 μm to 50 μm, more preferably 3 μm to 20 μm, even more preferably 5 μm to 15 μm, and even more preferably 5 μm to 10 μm.

[0047] <Release layer> The release layer plays a role in making it easier to peel the release film from the semiconductor package. The release layer contains a binder component and a release component.

[0048] The binder component is preferably a curable resin composition. Examples of curable resin compositions include thermosetting resin compositions and ionizing radiation-curable resin compositions. Considering the shape conformability of the release film, the binder component is preferably a thermosetting resin composition.

[0049] A thermosetting resin composition is a composition containing at least a thermosetting resin, and is a resin composition that hardens upon heating. A curing agent is added to these curable resins as needed. Examples of thermosetting resins include acrylic resins, urethane resins, phenolic resins, urea-melamine resins, epoxy resins, and unsaturated polyester resins. Considering the heat resistance of the stretched polyester resin layer and the unstretched polyester resin layer, it is preferable to use a low-temperature curing type thermosetting resin. Specifically, isocyanate-curing type urethane resins and isocyanate-curing type acrylic resins are preferred. Furthermore, to suppress contamination of semiconductor chips, it is preferable to use a resin that does not contain silicon (Si) as the binder component. Also, to reduce environmental impact, it is preferable to use a resin that does not contain fluorine (F) as the binder component.

[0050] The release component plays a role in facilitating the removal of the semiconductor package from the release film. To suppress contamination of the semiconductor chip, it is preferable that the release component does not contain silicon (Si). Furthermore, to suppress the detachment of the release component during the heating process of the sealing resin in the semiconductor package manufacturing process, it is preferable that the release component reacts with the binder component to form a cross-linked structure. As the release component, fluororesins, alkyd resins, etc., can be used, but from the viewpoint of reducing environmental impact, alkyd resins are preferred. Examples of release components for alkyd resins include long-chain alkyl acrylates and long-chain alkyl-modified polymers.

[0051] The release agent content is preferably 0.1 parts by mass or more and 30 parts by mass or less, more preferably 1 part by mass or more and 20 parts by mass or less, and even more preferably 3 parts by mass or more and 15 parts by mass or less, per 100 parts by mass of the binder component.

[0052] Considering the handling characteristics of the release film and its conformability to the mold shape, the thickness of the release layer is preferably 0.1 μm to 30 μm, more preferably 0.3 μm to 20 μm, even more preferably 0.5 μm to 10 μm, even more preferably 0.8 μm to 8 μm, and even more preferably 1 μm to 5 μm.

[0053] From the viewpoint of improving readability when reading characters printed on the surface of the release layer with an electronic device, a matte finish is desirable for the surface of the release layer. One means of making the surface of the release layer matte is to add particles to the release layer. The particles may be organic particles such as acrylic urethane or polyethylene, or inorganic particles such as silica, titanium dioxide, or zirconium oxide. In particular, using silica particles with a hydrophobic surface treatment is preferable because a good appearance can be obtained. The particle size (average particle diameter) is preferably greater than or equal to the film thickness of the release layer. Furthermore, considering the acquisition of sufficient film strength and suitability for coating, the average particle diameter is preferably 1 μm or more and 50 μm or less, more preferably 3 μm or more and 20 μm or less, and even more preferably 3 μm or more and 10 μm or less. In this invention, the average particle diameter is the value measured by the Coulter counter method.

[0054] [Method for manufacturing release film] The present invention provides a method for manufacturing a release film, comprising the steps of forming a release layer on one surface of the stretched polyester resin layer and bonding an unstretched polyester resin layer to the other surface of the stretched polyester resin layer via the adhesive layer.

[0055] The method for manufacturing the release film of the present invention will be described in detail below. (1) Process of forming a release layer Prepare a release coating solution. The release coating solution contains a binder component and a release component, and may contain particles, solvents, etc., as needed. A stretched polyester resin film is prepared as the stretched polyester resin layer. A release layer resin composition is applied to the stretched polyester resin film. Known application methods such as gravure printing, bar coating, roll coating, reverse roll coating, and comma coating can be used. The coated film is then dried and heated to cure, forming a release layer. The curing temperature can be set according to the binder component.

[0056] (2) Adhesion process An unoriented polyester resin film is prepared as the unoriented polyester resin layer. The adhesive layer is formed between the side of the stretched polyester film opposite to the side where the release layer is formed, and the unoriented polyester resin film. Known methods such as coating and melt extrusion can be used to form the adhesive layer. [Examples]

[0057] The release film of the present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the embodiments described in the examples.

[0058] 1. Evaluation and Measurement 1-1. Measurement of Tensile Modulus (1) Sample collection Measurement samples were taken from the release films of the examples, comparative examples, and reference examples. For comparative examples 2 and 3 and reference example 1, the length of the sample was aligned with the width direction (TD direction) of the release film when taking the measurement samples. For the other examples and comparative examples, the length of the sample was aligned with the width direction (TD direction) and the machine direction (MD direction) of the release film, respectively, when taking the measurement samples. Measurement samples were taken from each film used in the preparation of the release films in Examples and Comparative Examples 1 to 8. In the case of unstretched polyester resin films, measurement samples were taken so that the length direction of the sample coincided with the width direction (TD direction) of the film. In the case of stretched polyester resin films, measurement samples were taken so that the length direction of the sample coincided with the width direction (TD direction) and the machine direction (MD direction) of the film, respectively. When collecting the sample for measurement, a 100 mm area from the edge in the width direction of the film was excluded. The sample shape was that of test specimen type 2 as described in JIS K 7127:1999. The sample width was 10 mm and the sample length was 200 mm. (2) Measurement The tensile modulus at 175°C was measured for each sample using tensile testing in accordance with JIS K 7161-1:2014. A Tensilon universal material tester (RTI-1310, manufactured by A&D Co., Ltd.) was used for the measurement. The measurement conditions were as follows: <Measurement conditions> After placing the sample in the measuring device, measurement will begin 2 minutes after the furnace temperature reaches 175°C. • Chuck spacing: 100mm • Tensile speed: 200 mm / min • Load cell: 500N Each film and release film was subjected to three tests, and the average value was defined as the tensile modulus.

[0059] 1-2. Melting point measurement The melting points of each film used in the preparation of the release films for the examples, comparative examples, and reference examples were measured using a high-sensitivity differential scanning calorimeter (DSC7000X, manufactured by Hitachi High-Tech Science Corporation) at a heating rate of 20°C / min.

[0060] 1-3. Evaluation of shape conformability to mold The mold conformability of the release films in the examples, comparative examples, and reference examples was evaluated. A lower mold was prepared as shown in Figure 3. Figure 3(a) is a top view of the lower mold as seen from the cavity side, and Figure 3(b) is a cross-sectional view taken along X-X' in Figure 3(a). The lower mold in Figure 3 corresponds to the shape of the lower mold described in the semiconductor package manufacturing process in Figure 2. The dimensions are as follows. • Dimensions of the base plate: L1: 50mm, L2: 200mm • Cavity depth D: 5mm (before sealing resin filling) • Angle between the side member and the bottom member θ: 100° The release films for the examples and comparative examples were cut to 150 mm x 800 mm. Each release film was placed on the lower mold so that the release layer faced away from the mold. For Reference Example 1, the side with the release layer applied was placed facing away from the mold. The lower mold was then heated to 175°C, and a vacuum was created between the lower mold and the release film. After that, the release film was visually inspected for wrinkles and any areas that were not in close contact with the lower mold (lifting). The above procedure was repeated twice, and the shape-following ability was evaluated according to the following criteria. <Rating> A: In all three operations, it can be confirmed that there are no wrinkles or lifting, and the release film adheres to the shape of the lower mold. B: Wrinkles or lifting were observed near the four corners of the bottom surface during at least one operation. C: Wrinkles and lifting were observed near the four corners of the base and at the boundary between the long side and the side of the base during at least one operation.

[0061] 1-4. Contraction stress (1) Sample collection For release films that received an A rating for shape conformability, shrinkage stress was measured. Measurement samples were taken from release films that received an A rating for shape conformability. For Comparative Examples 2 and 3 and Reference Example 1, measurement samples were taken with the length of the sample aligned with the width direction (TD direction) of the release film. For the other examples and comparative examples, measurement samples were taken with the length of the sample aligned with the width direction (TD direction) and the machine direction (MD direction) of the release film, respectively. When taking the three samples, a 100 mm area from the edge in the width direction of the film was excluded. The sample shape was that of test specimen type 2 as described in JIS K 7127:1999. The sample width was 50 mm and the sample length was 300 mm. (2) Measurement The shrinkage stress of each sample was measured using a Tensilon universal material testing machine (RTI-1310, manufactured by A&D Co., Ltd.). The measurement conditions were as follows. <Measurement conditions> • After setting the furnace temperature to 175°C and placing the sample in the measuring device, start the measurement. • Chuck spacing: 250mm • Load cell: 50N The maximum stress measured was defined as the tensile stress of each release film. Three tests were performed on each release film, and the average value was defined as the shrinkage stress. For release films measured in both the MD and TD directions, the larger value is shown in Table 3.

[0062] 1-5. Evaluation of penetration For samples that received an A rating for shape conformability, we evaluated whether or not digging occurred. Using the method described in 1-3, the release film was attached to the lower mold, and the sealing resin was poured into the cavity. The amount of sealing resin injected was 16g. Subsequently, the upper mold shown in Figure 2 (a plate-like shape measuring 54 mm x 220 mm with a thickness of 2.4 mm) was placed on the release film. Next, the bottom member was moved 1.4 mm upward. In this state, the load was 96 kN / m 2 The sealing resin was cured at 175°C for 120 seconds. After curing, the release film and cured resin were removed from the lower mold. Then, the release film was peeled off. Observation samples were taken so that the cross-section of the edge of the cured resin could be seen. For samples where the release film could not be peeled off, observation samples were taken from the area where peeling was not possible. The cross-section of the cured resin was observed at 200x magnification using an optical microscope (LEICA DM-4). The degree to which the release film adhered was evaluated according to the following criteria. <Rating> A: No adhesion of the release film was observed. C: Indentation of the release film was observed.

[0063] 2. Sample preparation The following polyester resin films were prepared. <Stretched polybutylene terephthalate film (stretched PBT film)> Stretched PBT film 1: "Boblet ST" manufactured by Kojin Film & Chemicals Co., Ltd., thickness 15 μm Stretched PBT film 2: "Boblet ST" manufactured by Kojin Film & Chemicals Co., Ltd., thickness 20 μm Stretched PBT film 3: "Boblet ST" manufactured by Kojin Film & Chemicals Co., Ltd., thickness 25 μm <Unoriented polybutylene terephthalate film (unoriented PBT film)> Unoriented PBT film A: Manufactured by Oji Film Co., Ltd., "PBT", thickness 20 μm Unoriented PBT film B: Manufactured by Oji Film Co., Ltd., "PBT", thickness 50 μm <Stretched polyethylene terephthalate film (stretched PET film)> Stretched PET film a: Manufactured by Unitika Ltd., "P860", thickness 25 μm Stretched PET film b: Manufactured by Unitika Ltd., "Emblet PHT", thickness 25 μm

[0064] [Example 1] A release layer forming solution according to the following formulation was applied to one side of a stretched PBT film 1 using gravure coating to form a coating film. Subsequently, it was heated at 120°C for 1 minute to form a release layer with a thickness of 1 μm. Using the adhesive formulation described below, an adhesive layer was formed between the unstretched PBT film A and the side of the stretched PBT film 1 opposite to the side where the release layer was formed, by gravure coating. The thickness of the adhesive layer was 6 μm. This yielded the release film of Example 1. <Coating solution for forming a release layer> • Binder component (acrylic polyol, manufactured by DIC Corporation, "Acrydec A-809-P") 100 parts by mass • Isocyanate-based curing agent (manufactured by Tosoh Corporation, "Coronate HX") 8.7 parts by mass • Release agent (Neos Co., Ltd., "Phthageent 710FL") 1.5 parts by mass • Silica filler (manufactured by Fuji Silicia Co., Ltd., "Silohobic 100") 20 parts by mass <Adhesive> • Main ingredient (manufactured by Toyo Morton Co., Ltd., TMK-76) 100 copies • Hardener (manufactured by Toyo Morton Co., Ltd., CAT10-L) 10 parts

[0065] [Example 2] The release film of Example 2 was obtained using the same process as in Example 1, except that stretched PBT film 2 was used instead of stretched PBT film 1.

[0066] [Comparative Example 1] A release layer was formed on one side of the stretched PBT film 2 using the same process as in Example 1. This yielded the release film of Comparative Example 1.

[0067] [Comparative Example 2] A release layer was formed on one side of an unoriented PBT film A using the same process as in Example 1. This yielded the release film of Comparative Example 2.

[0068] [Comparative Example 3] A release layer was formed on one side of the unstretched PBT film B using the same process as in Example 1. This yielded the release film of Comparative Example 3.

[0069] [Comparative Example 4] A release layer was formed on one side of the unstretched PBT film A using the same process as in Example 1. Subsequently, an adhesive layer was formed between the stretched PBT film 2 and the side of the unstretched PBT film A opposite to the side where the release layer was formed, using the same method as in Example 1. This yielded the release film of Comparative Example 4.

[0070] [Comparative Example 5] The release film for Comparative Example 5 was obtained using the same process as for Comparative Example 4, except that stretched PBT film 3 was used instead of stretched PBT film 2.

[0071] [Comparative Example 6] A release layer was formed on one side of the unstretched PBT film A using the same process as in Example 1. Subsequently, an adhesive layer was formed between the side of the unoriented polybutylene terephthalate film opposite to the side where the release layer was formed and another unoriented PBT film A, using the same method as in Example 1. This yielded the release film of Comparative Example 6.

[0072] [Comparative Example 7] A release layer was formed on one side of the stretched PBT film 3 using the same process as in Example 1. Subsequently, an adhesive layer was formed between the stretched PET film a and the side of the stretched PBT film 3 opposite to the side where the release layer was formed, using the same method as in Example 1. This yielded the release film of Comparative Example 7.

[0073] [Comparative Example 8] The release film of Comparative Example 5 was obtained using the same process as in Comparative Example 7, except that stretched PET film b was used instead of stretched PET film a.

[0074] [Reference example 1] A fluoropolymer film (manufactured by AGC Inc., Aflex® registered trademark, 50 μm thick) was used as the release film for Reference Example 1.

[0075] Table 1 summarizes the lamination configurations of the release films for the examples, comparative examples, and reference examples. In Table 1, the left side of the lamination configuration is the side that contacts the sealing resin, and the right side is the side that contacts the mold. In Table 1, " / " indicates a boundary between layers.

[0076] [Table 1]

[0077] Table 2 shows the tensile modulus of the films used in the examples and comparative examples. Table 3 shows the evaluation results of the release films in the examples and comparative examples.

[0078] [Table 2]

[0079] [Table 3]

[0080] As shown in Table 2, unoriented PBT film has a lower tensile modulus than oriented PBT film and oriented PET film. The release films in Examples 1 and 2 exhibited good shape conformability. On the other hand, in Comparative Examples 4 and 5, where the lamination order was reversed compared to Examples 1 and 2, sufficient shape conformability was not obtained. Although the release films in Examples 1 and 2 and Comparative Examples 4 and 5 had the same tensile modulus, it is thought that in Comparative Examples 4 and 5, the stretched PBT film with a higher tensile modulus was placed on the mold side, making it difficult for deformation to conform to the shape of the mold to occur. Comparative Examples 2 and 3, which used only unoriented PBT film, and Comparative Example 6, which had unoriented PBT film laminated on it, showed good shape conformity to the mold. This is thought to be because the tensile modulus of the release film in Comparative Examples 2, 3, and 6 was low, similar to Examples 1 and 2, and therefore easily deformed to match the shape of the mold. Comparative Example 1, which used only stretched PBT film, and Comparative Examples 7 and 8, which laminated stretched PBT film and stretched PET film, did not achieve sufficient shape conformability. This is because stretched PBT film and stretched PET film have higher tensile moduli than unstretched PBT film, resulting in higher tensile moduli of the release films in Comparative Examples 1, 7, and 8, making them less able to deform to conform to the shape of the mold. Comparative Example 8 had particularly high tensile moduli in both the TD and MD directions, resulting in poor shape conformability, and wrinkles and lifting occurred not only near the four corners of the bottom surface but also at the boundary between the long side and the side of the bottom surface.

[0081] Figure 4 shows a cross-sectional SEM image of a sample in which the release film of Example 1 was used to fill and cure the encapsulating resin. In both Examples 1 and 2, no indentation occurred as shown in Figure 4, and the release film could be peeled off from the cured resin. Figure 5 shows a cross-sectional SEM image of a sample in which the release film of Comparative Example 3 was used to fill and cure the encapsulating resin. Comparative Examples 2, 3, and 6 showed good shape conformability, but indentation of the release film occurred as shown in Figure 5. The shrinkage stress in Examples 1 and 2 was 0.76 N. This suggests that in Examples 1 and 2, the stretched polyester resin layer did not fold in the release film because it shrunk when the bottom surface member of the lower mold was raised in step 5, as described above, and therefore no indentation occurred. In contrast, the shrinkage stress in Comparative Examples 2 and 6 was less than 0 N. Furthermore, the shrinkage stress in Comparative Example 3 was 0.24 N, which was lower than in the Examples. This suggests that in Comparative Examples 2, 3, and 6, the release film hardly shrunk when the bottom surface member of the lower mold was raised in step 5, causing it to fold towards the cavity and resulting in indentation.

[0082] As shown in Table 3, in Reference Example 1, good shape conformability was obtained and no indentation occurred. In all of the examples, it can be said that the shape conformability and suppression of indentation were comparable to that of conventional release films using fluororesin films, without the use of fluororesin. [Explanation of Symbols]

[0083] 10 Release film 12. Unstretched polyester resin layer 14. Stretched polyester resin layer 16 Adhesive layer 18 Release layer 110 Upper mold 120 Lower mold 122 Bottom member 124 Side members 126 Cavity

Claims

1. It has an unstretched polyester resin layer, an adhesive layer, a stretched polyester resin layer, and a release layer. The adhesive layer is provided between the unstretched polyester resin layer and the stretched polyester resin layer. The release layer is a release film provided on the side of the stretched polyester resin layer opposite to the adhesive layer.

2. The release film according to claim 1, wherein the unstretched polyester resin layer is provided as the outermost layer of the release film.

3. The release film according to claim 1, wherein the tensile modulus of the unstretched polyester resin layer, as measured in accordance with JIS K 7161-1:2014 at 175°C, is 20 MPa or more and 100 MPa or less.

4. The release film according to claim 1, wherein the stretched polyester resin layer has a tensile modulus of 100 MPa or more and 200 MPa or less, as measured in accordance with JIS K 7161-1:2014 at 175°C.

5. The release film according to claim 1, wherein the tensile modulus of the stretched polyester resin layer measured at 175°C in accordance with JIS K 7161-1:2014 is greater than the tensile modulus of the unstretched polyester resin layer measured at 175°C in accordance with JIS K 7161-1:2014.

6. The release film according to claim 1, wherein the melting point of the polyester resin contained in the unstretched polyester resin layer is 200°C or more and 300°C or less.

7. The release film according to claim 1, wherein the melting point of the polyester resin contained in the stretched polyester resin layer is 200°C or more and 300°C or less.

8. The release film according to claim 1, wherein the total thickness is 40 μm or more and 100 μm or less.

9. The release film according to claim 1, wherein the unstretched polyester resin layer is a layer containing 60% by mass or more of polybutylene terephthalate.

10. The release film according to claim 1, wherein the stretched polyester resin layer is a layer containing 60% by mass or more of polyethylene terephthalate or polybutylene terephthalate.

11. The release film according to claim 1, wherein the ratio of the thickness of the stretched polyester resin layer to the thickness of the unstretched polyester resin layer is 0.5 or more and 1.5 or less.

12. A method for manufacturing a release film according to any one of claims 1 to 11, A step of forming a release layer on one surface of the stretched polyester resin layer, A method for manufacturing a release film, comprising the step of bonding an unstretched polyester resin layer to the other side of the stretched polyester resin layer via the adhesive layer.

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