Release film and method for producing electronic component

Abstract

To provide a release film having superior ability to follow irregularities, and a method for producing an electronic component using the release film.SOLUTION: A release film for use in a manufacturing process of an electronic component includes: a release layer forming a release surface; and a cushion layer laminated on the release layer. The release layer contains a polyethylene-based resin. The cushion layer contains an ethylene-based copolymer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a release film and a method for manufacturing an electronic component.

Background Art

[0002] Conventionally, various techniques have been developed in the field of release films. For example, release films are used when manufacturing molded products or laminates (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When manufacturing a molded product or laminate having unevenness such as steps, it is desired to realize a release film having excellent followability to the unevenness.

[0005] An object of the present invention is to provide a release film having excellent followability to unevenness and a method for manufacturing an electronic component using the release film.

Means for Solving the Problems

[0006] To solve the above problems, the present invention employs the following configuration. [1] A release film used in the manufacturing process of an electronic component, the release film having a release layer constituting a release surface and a cushion layer laminated on the release layer, the release layer containing a polyethylene-based resin, and the cushion layer containing an ethylene-based copolymer. [2] The release film according to [1], having a tensile elastic modulus at 25°C of 300 MPa or less. [3] The release film according to [1] or [2], having an elongation at break at 25°C of 400% or more. [4] The release film according to any one of [1] to [3], wherein when the dynamic viscoelasticity (DMA) of the release film is measured under the conditions of a heating rate of 5°C / min and a frequency of 1 Hz, the storage elastic modulus at 90°C is 100 MPa or less. [5] The release film according to any one of [1] to [4], having a surface free energy at 25°C of 40 mJ / m 2 or less. [6] The release film according to any one of [1] to [5], wherein the comonomer copolymerized with ethylene in the ethylene-based copolymer contains a polar vinyl-based monomer or a cycloolefin-based monomer. [7] A method for manufacturing an electronic component using the release film according to any one of [1] to [6], comprising a step of disposing the release film on the object such that the release surface of the release film faces the object side, and a step of performing a heat press on the object on which the release film is disposed, wherein in the step of disposing the release film, the surface of the object on which the release film is disposed has a concave portion or a convex portion. [Advantages of the Invention]

[0007] According to the present invention, there are provided a release film excellent in followability to unevenness and a method for manufacturing an electronic component using the release film. [Brief Description of the Drawings]

[0008]

Figure 1

[0009] Hereinafter, the present invention will be described based on preferred embodiments.

[0010] The release film according to an embodiment of the present invention is a release film used in the manufacturing process of electronic components. The release film has a release layer that constitutes a release surface, and a cushion layer laminated on the release layer. The release layer contains a polyethylene-based resin, and the cushion layer contains an ethylene-based copolymer.

[0011] In the manufacturing process of the electronic component, the release film is disposed between an object and a manufacturing member used for processing the object. The object is a material used in the manufacturing process of the electronic component.

[0012] Examples of the object include materials containing one or more selected from metals, plastics, ceramics, etc. The object may contain one or more selected from fillers, organic solvents, additives, etc. The object may be mainly composed of a conductor, or may be mainly composed of a semiconductor or an insulator. Here, when a specific material is the main component of the object, it may refer to the component with the largest mass ratio in the object, or may refer to the component essential for the object to exhibit the function of the electronic component. Even when the object is mainly composed of a semiconductor or an insulator, it may contain a conductor in an external terminal for electrically connecting the electronic component to the outside, an internal wiring for electrically connecting inside the electronic component, etc.

[0013] Examples of the manufacturing member include a mold, a heating plate, a pressure plate, etc. In the manufacturing process of the electronic component, at least one physical action selected from heat, pressure, magnetism, etc. may be applied to the object through the release film by the manufacturing member.

[0014] <Release layer> The release layer is disposed on one surface of the release film and constitutes a release surface. When the release film is used in the manufacturing process of the electronic component, the release surface is disposed on the object side.

[0015] The release layer contains a polyethylene-based resin. The polyethylene-based resin is a homopolymer of ethylene or a copolymer obtained by copolymerizing ethylene mainly with other comonomers. Examples of the comonomer of the polyethylene-based resin include α-olefins such as propylene, 1-butene, 1-hexene, 1-octene, and methylpentene.

[0016] Specific examples of the polyethylene-based resin used for the release layer include polyethylenes such as high-density polyethylene resin (HDPE), medium-density polyethylene resin (MDPE), linear low-density polyethylene resin (LLDPE), very-low-density polyethylene resin (VLDPE), and low-density polyethylene resin (LDPE). The release layer may use one of these polyethylene-based resins alone or in combination of two or more.

[0017] The release layer may be formed only from a polyethylene-based resin or may be formed containing additives or the like. Examples of the additives used for the release layer include antioxidants, slip agents, antiblocking agents, antistatic agents, colorants, stabilizers, fillers, and the like. The release layer may contain inorganic particles such as silica and alumina.

[0018] The layer thickness of the release layer is not particularly limited, but for example, it may be 1 to 50 μm. The ratio of the layer thickness of the release layer to the total thickness of the release film may be, for example, 30% or less, and may also be 20% or less, 10% or less. Further, the ratio of the layer thickness of the release layer to the total thickness of the release film may be, for example, 1% or more, and may also be 2% or more, 5% or more.

[0019] The method for forming the release layer is not particularly limited, and examples thereof include known methods such as an air-cooled inflation extrusion method, a water-cooled inflation extrusion method, and a T-die extrusion method.

[0020] <Cushion layer> The cushion layer is disposed between the release layer and the manufacturing member to improve the followability of the release film while imparting appropriate resilience.

[0021] The cushion layer contains an ethylene copolymer. The ethylene copolymer is a copolymer of ethylene and another comonomer. The ethylene copolymer is a copolymer different from the polyethylene resin. In the ethylene copolymer, it is preferable that the comonomer copolymerized with ethylene includes a polar vinyl monomer or a cycloolefin monomer.

[0022] Examples of the polar vinyl monomer include vinyl acetate, vinyl alcohol, acrylic ester, methacrylic ester, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, etc. Vinyl alcohol units can be produced by saponifying after copolymerizing a vinyl ester monomer such as vinyl acetate.

[0023] Examples of the cycloolefin include cyclopentene, cyclohexene, norbornene, norbornadiene, dicyclopentadiene, etc. The ethylene copolymer may further contain an α-olefin such as propylene, 1-butene, 1-hexene, 1-octene, methylpentene, etc. as a comonomer.

[0024] Specific examples of the ethylene copolymer include ethylene-vinyl acetate copolymer (EVA), ethylene-vinyl alcohol copolymer (EVOH), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate-maleic anhydride copolymer (E-EA-MAH), ethylene-acrylate copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA), ethylene cycloolefin copolymer (COC), and ionomer resin (ION), etc. The cushion layer may use one of these ethylene copolymers alone or in combination of two or more.

[0025] The cushion layer may be formed only from an ethylene copolymer, or may contain a resin other than the ethylene copolymer. When the cushion layer contains a resin other than the ethylene copolymer, the content of the ethylene copolymer is preferably 40% by mass or more and 80% by mass or less, more preferably 50% by mass or more and 70% by mass or less, based on the total amount of the cushion layer.

[0026] Examples of the resin other than the ethylene copolymer used in the cushion layer include α-olefin polymers such as polyethylene (PE) and polypropylene (PP); α-olefin copolymers having propylene, butene, pentene, hexene, methylpentene, etc. as polymer components; engineering plastics such as polyethersulfone (PES) and polyphenylene sulfide (PPS); polyester resins such as polybutylene terephthalate (PBT); and polymethylpentene (PMP). The cushion layer may use one of these resins alone, or may use two or more of them in combination. Among them, from the viewpoint of imparting appropriate strength and elasticity to the cushion layer and maintaining good releasability of the release film, it is preferable to contain polypropylene and polymethylpentene resin.

[0027] Examples of the resin mixture in the case where the cushion layer is composed of an ethylene copolymer and other resins include a mixture of PE and EMMA, a mixture of PP and EMMA, a mixture of PBT, PP and EMMA, a mixture of PP, EMA and PMP, a mixture of PP, EMAA and PMP, and the like.

[0028] The cushion layer may further contain a rubber component. Examples of the rubber component include styrenic thermoplastic elastomers such as styrene-butadiene copolymer and styrene-isoprene copolymer, thermoplastic elastomer materials such as olefinic thermoplastic elastomer, amide-based elastomer, and polyester-based elastomer, and rubber materials such as natural rubber, isoprene rubber, chloroprene rubber, and silicone rubber. The cushion layer may be a mixture containing an ethylene-based copolymer and a rubber component, or may be a mixture containing an ethylene-based copolymer, other resin, and a rubber component.

[0029] The cushion layer may be formed by including an additive. Examples of the additive used for the cushion layer include antioxidants, slip agents, antiblocking agents, antistatic agents, colorants, stabilizers, fillers, and the like.

[0030] The layer thickness of the cushion layer is not particularly limited, and for example, it may be 10 to 200 μm. The ratio of the layer thickness of the cushion layer to the total thickness of the release film may be, for example, 70% or less, and may also be 80% or more, 90% or more. The layer thickness of the cushion layer is preferably 1.1 times or more the layer thickness of the release layer, and may also be 3 to 10 times, 5 to 9 times, etc.

[0031] The method for forming the cushion layer is not particularly limited, and examples thereof include known methods such as air-cooled inflation extrusion method, water-cooled inflation extrusion method, and T-die extrusion method.

[0032] The cushion layer may be disposed on the other surface of the release film. Here, the other surface of the release film is the surface opposite to the one surface on the release layer side. When the cushion layer is disposed on the other surface, it may constitute a contact surface with respect to the manufacturing member in the manufacturing process of the electronic component.

[0033] <Intermediate layer> An intermediate layer may be interposed between the cushion layer and the release layer. The intermediate layer adjusts the followability and firmness of the release film. The intermediate layer may use the materials described for the cushion layer, and may include recycled materials or other materials considering the environment. Examples of the materials used for the intermediate layer include the polyethylene-based resin, the ethylene-based copolymer, the α-olefin-based copolymer, and the rubber component. The intermediate layer may use these resins alone or in combination of two or more. The intermediate layer may be a single layer or two or more layers.

[0034] <Other Layers of the Release Film> Also, another layer may be interposed between the cushion layer and the manufacturing member. The other layer may be a layer included in the release film or a member disposed separately from the release film. For example, the release film may have a second release layer on the other surface. In order to distinguish it from the second release layer, the release layer disposed on one surface may be referred to as the first release layer.

[0035] The second release layer can be formed using the same thermoplastic resin as the first release layer. The second release layer may have the same resin composition as the first release layer or a different resin composition. For example, the second release layer preferably contains a polyethylene-based resin. The second release layer may have the same layer thickness as the first release layer or a different layer thickness.

[0036] <One Embodiment of the Release Film> FIG. 1 is a cross-sectional view schematically showing an example of the release film of the present embodiment. The release film 10 has a release layer 11 having a release surface 11a and a cushion layer 12 laminated on the release layer 11. The cushion layer 12 functions as a followability-imparting layer. The cushion layer 12 may have a contact surface 12a. Although not particularly shown, a second release layer may be laminated on the cushion layer 12 on the side opposite to the release layer 11.

[0037] The total thickness of the release film is not particularly limited, but for example, it is preferably 50 to 500 μm, more preferably 80 to 400 μm or less, and even more preferably 100 to 300 μm. By doing so, it becomes possible to apply the pressing pressure uniformly to the release film without unevenness.

[0038] <Method for manufacturing release film> The release film of this embodiment can be produced using known methods such as the coextrusion method, the extrusion lamination method, the dry lamination method, the inflation method, etc. Further, for the release film, each layer including the release layer and the cushion layer may be separately manufactured and then joined by a laminator or the like.

[0039] From the viewpoint of interlayer adhesion and the like, it is preferable that the release layer and the cushion layer are laminated by coextrusion. Specific examples of coextrusion include the air-cooled coextrusion inflation method, the water-cooled coextrusion inflation method, the coextrusion T-die method, etc. From the viewpoint of controlling the thickness of each layer, the method of forming a film by the coextrusion T-die method is preferable. The release layer and the cushion layer may be directly joined, or each layer may be joined via an adhesive layer.

[0040] <Tensile properties of release film> The tensile properties of the release film of this embodiment can be measured using a tensile tester for an appropriate test piece specified in, for example, JIS K 7127.

[0041] The tensile modulus of elasticity of the release film at 25°C is preferably 300 MPa or less. When the tensile modulus of elasticity is below the upper limit value, it becomes easier for the material to be largely displaced even under a small load, and it becomes easier to improve the followability to unevenness. The lower limit value of the tensile modulus of elasticity is not particularly limited, but the tensile modulus of elasticity may be 100 MPa or more, 200 MPa or more, etc.

[0042] The elongation at break of the release film at 25°C is preferably 400% or more. When the elongation at break is at or above the lower limit value, the material is less likely to break even for large displacements, and it becomes easier to improve the followability to unevenness. The upper limit value of the elongation at break is not particularly limited, and the elongation at break may be 1000% or less, 800% or less, etc.

[0043] <Dynamic viscoelasticity of the release film> When the release film of this embodiment is measured for dynamic viscoelasticity (DMA) under the conditions of a heating rate of 5°C / min and a frequency of 1 Hz, the storage elastic modulus at 90°C is preferably 100 MPa or less. When the storage elastic modulus is at or below the upper limit value, the elasticity of the release film is suppressed, and it becomes easier to improve the followability to unevenness. The lower limit value of the storage elastic modulus is not particularly limited, and the storage elastic modulus may be 1 MPa or more, 100 MPa or less, etc.

[0044] <Wettability of the release film> The release film of this embodiment preferably has a surface free energy at 25°C of 40 mJ / m 2 or less. When the surface free energy is at or below the upper limit value, it becomes easier to obtain good releasability with respect to the object or good anti-sticking property with respect to the manufacturing member. The upper limit value of the surface free energy is not particularly limited, and it may be 25 mJ / m 2 or more, 30 mJ / m 2 or more, etc.

[0045] The surface free energy is preferably at or below the upper limit value on the release surface. Thereby, it becomes easier to obtain good releasability with respect to the object. The surface free energy is preferably at or below the upper limit value on the contact surface by the cushion layer or the contact surface by the second release layer. Thereby, it becomes easier to obtain good anti-sticking property with respect to the manufacturing member.

[0046] As a method for adjusting the surface free energy, there may be mentioned selection of the material constituting the surface, especially selection of the type of resin, presence or absence of stretching treatment, adjustment of surface roughness, and the like.

[0047] The surface free energy can be measured using a general-purpose contact angle meter. Specifically, as three kinds of liquids with known values of surface free energy and its respective components (dispersion force, polar force, hydrogen bonding force), water, diiodomethane, and n-hexadecane are used. Under an atmosphere of 23°C and 65% RH, the contact angles of these liquids are measured with a contact angle meter, and based on these measured values, the values of the respective components are calculated from the formula of Kitazaki-Hata, and the surface free energy can be calculated from the sum of the values of the respective components.

[0048] <Method for manufacturing an electronic component> The method for manufacturing an electronic component according to the present embodiment is a method using the release film of the present embodiment. Regarding the object and the manufacturing member, it is as described above. The method includes a step of disposing the release film on the object such that the release surface of the release film faces the object side, and a step of performing a predetermined process on the object on which the release film is disposed using the manufacturing member.

[0049] The manufacturing member may be a heating press member such as a heating press plate. In this case, the method includes a step of disposing the release film on the object such that the release surface of the release film faces the object side, and a step of performing a heating press on the object on which the release film is disposed.

[0050] The object may have unevenness on the surface on which the release film of the object is disposed. The unevenness is a surface shape having non-uniform height, different from the case where the entire surface of the object consists of a single plane.

[0051] The unevenness may be uniformly distributed over the entire surface of the object, or the distribution of the unevenness may be non-uniform, or the unevenness may be locally arranged. The arrangement of the unevenness may be a regular arrangement having regularity such as periodicity, or an irregular arrangement having no regularity. When the unevenness is locally arranged, the surface of the object may be flat in the region other than the unevenness.

[0052] Specific examples of the unevenness include recesses or protrusions. The surface of the object may include recesses and protrusions. Examples of the recesses include holes, grooves, openings, and the like. Examples of the protrusions include projections, ribs, bosses, and the like. When the recesses and protrusions alternate with each other like a waveform, the boundary between the recesses and protrusions does not necessarily have to be clear. In a plan view of the surface of the object, a plurality of the unevenness may be in contact with or intersect each other and arranged in a polygonal shape, a lattice shape, a zigzag shape, or the like. A plurality of the unevenness may be arranged in a parallel shape, a staggered shape, a dashed line shape, a concentric shape, a spiral shape, or the like with an interval therebetween.

[0053] The dimensions of the unevenness are not particularly limited, but the height or depth of the unevenness may be 2 times or more and 10 times or less the total thickness of the release film, and the width of the unevenness may also be 2 times or more and 10 times or less the total thickness of the release film. Here, the height or depth direction of the unevenness is the dimension in the direction in which the manufacturing member approaches or separates from the object. For example, when the object is in a substrate shape, the height or depth direction of the unevenness may be the thickness direction of the object. Further, the width of the unevenness is the direction perpendicular to the height or depth direction of the unevenness. For example, when the object is in a substrate shape, the width direction of the unevenness may be the in-plane direction of the object.

[0054] The unevenness may include a stepped portion that connects a high portion and a low portion in the height or depth direction of the unevenness. The stepped portion may include a vertical wall along the height or depth direction of the unevenness, and may also include an inclined wall inclined with respect to the height or depth direction of the unevenness. The angle of the vertical wall or the inclined wall is not particularly limited, but when the surface of the object is mainly composed of a horizontal plane, it is preferably 10° or more and 90° or less with respect to the horizontal plane, and may be 45° or more and 85° or less.

[0055] The electronic component is not particularly limited, and examples thereof include a circuit board, a semiconductor device, a resistance element, a capacitance element, an inductance element, a terminal, an electrode, and a wiring. A plurality of the same type of electronic components may be included on the same substrate. Two or more types of electronic components may be included on the same substrate.

[0056] In the method for manufacturing the electronic component, the step of performing heat pressing does not have to be a step of completing the electronic component, and any step in the process leading to the completion of the electronic component may be sufficient. In the step of performing the heat pressing, a processing step such as molding, sintering, firing, drying, or curing may be performed on the object.

[0057] As described above, the embodiments of the present invention have been described, but these are examples of the present invention, and various configurations other than the above can also be adopted.

Example

[0058] Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the examples shown below at all.

[0059] <Manufacture of Release Film> As shown below, the release films of Examples 1 to 4 and Comparative Examples 1 to 3 were manufactured.

[0060] (Example 1) A release film of Example 1 was manufactured by co-extruding a release layer with a layer thickness of 20 μm made of polyethylene (PE, Yumelite (registered trademark) 1520F manufactured by Ube Maruzen Polyethylene) and a cushion layer with a layer thickness of 130 μm made of ionomer resin (ION, Himilan (registered trademark) 1652 manufactured by Mitsui Dow Polychemical).

[0061] (Example 2) A release film of Example 2 was manufactured by co-extruding a release layer with a layer thickness of 20 μm made of polyethylene (PE, Yumelite (registered trademark) 1520F manufactured by Ube Maruzen Polyethylene), an intermediate layer with a layer thickness of 100 μm made of polyethylene (PE, Yumelite (registered trademark) 1520F manufactured by Ube Maruzen Polyethylene), and a cushion layer with a layer thickness of 30 μm made of ionomer resin (ION, Himilan (registered trademark) 1652 manufactured by Mitsui Dow Polychemical).

[0062] (Example 3) A release film of Example 3 was manufactured in the same manner as Example 2, except that the ionomer resin (ION) was changed to an ethylene-methyl methacrylate copolymer (EMMA, Acryft (registered trademark) WD106 manufactured by Sumitomo Chemical).

[0063] (Example 4) A release film of Example 4 was manufactured in the same manner as Example 2, except that the layer thickness of the intermediate layer was changed to 255 μm and the layer thickness of the cushion layer was changed to 25 μm.

[0064] (Comparative Example 1) A release film of Comparative Example 1 was manufactured by laminating a polyethylene terephthalate (PET) resin film with a layer thickness of 98 μm as a base material layer and a polyethylene (PE) resin film with a layer thickness of 48 μm as a release layer via a dry laminate adhesive layer (AD) with a layer thickness of 6 μm.

[0065] (Comparative Example 2) A release film of Comparative Example 2 was manufactured by extrusion molding polypropylene (PP, Nobrene (registered trademark) FS2011DG3 manufactured by Sumitomo Chemical) to a thickness of 150 μm.

[0066] (Comparative Example 3) A release film of Comparative Example 3 was produced in the same manner as in Comparative Example 2, except that polypropylene (PP) was changed to polymethylpentene (PMP, TPX (registered trademark) RT18 manufactured by Mitsui Chemicals).

[0067] <Evaluation of flexibility> Test pieces were prepared from each release film, and the tensile elastic modulus and elongation at break at 25 °C were measured using a tensile testing machine by a method conforming to JIS K 7127. Also, for each release film, the storage elastic modulus (E') at 90 °C was measured by dynamic viscoelasticity (DMA) measurement under the conditions of a temperature increase rate of 5 °C / min and a frequency of 1 Hz.

[0068] <Evaluation of surface free energy> As three known liquids, water, diiodomethane, and n-hexadecane were used, and the contact angles of these liquids were measured with a contact angle meter in an atmosphere of 23 °C and 65% RH. Based on these measured values, the surface free energy was calculated from the formula of Kitaoka and Hata. The number of measurements for the same sample was n = 3, and the average value was determined.

[0069] <Press evaluation of release film> After placing a release film so that the release layer faced a substrate having grooves with a width of 500 μm and a depth of 400 μm, heat pressing was performed under the conditions of a temperature of 80 °C, a pressure of about 1 MPa (about 10 kgf / cm 2 ), and a time of 3 minutes to perform heat treatment on the substrate having grooves.

[0070] The groove has a stepped surface with a depth of 400 μm between the surface of the substrate and the bottom surface with a width of 500 μm, and the stepped surface is arranged on both sides in the width direction of the bottom surface. For such a groove, the release film is expected to bend in a mountain-fold shape from the surface of the substrate toward the stepped surface of the groove, and further bend in a valley-fold shape between the stepped surface and the bottom surface of the groove.

[0071] <Evaluation of release film> Using the obtained release film, the following evaluations were performed. The results are shown in Table 1. [Release property] In the above press evaluation procedure, the release behavior when the substrate was released from the release film after molding was evaluated according to the following criteria. ○: No problems such as snagging, and no problem with release property. △: The adhesion is strong at the corners, and the release is slightly difficult but there is no problem in practical use. ×: Unable to release.

[0072] [Followability] In the above press evaluation procedure, the film shape after the release film was made to follow the grooves of the substrate by heat pressing was evaluated according to the following criteria. ○: The shape of the grooves is transferred to the film after pressing. △: The shape of the grooves is transferred to the film after pressing, but the transferred unevenness is slightly small. ×: There is a part where transfer has not occurred.

[0073]

Table 1

[0074] (Summary) As shown in Table 1, the release films of Comparative Examples 1 to 3 had low flexibility and poor followability to the unevenness due to the groove portions. On the other hand, the release film of this embodiment is excellent in flexibility and excellent in followability to the unevenness due to the groove portions.

Industrial applicability

[0075] The present invention can provide a release film excellent in followability to unevenness.

Explanation of reference numerals

[0076] 10... Release film, 11... Release layer, 11a... Release surface, 12... Cushion layer, 12a... Contact surface

Claims

1. A release film used in the manufacturing process of electronic components, wherein the release film has a release layer constituting a release surface and a cushion layer laminated on the release layer; the release layer contains a polyethylene-based resin; the cushion layer contains an ethylene copolymer, the release film.

2. The release film according to Claim 1, having a tensile modulus at 25°C of 300 MPa or less.

3. The release film according to Claim 1, having an elongation at break at 25°C of 400% or more.

4. The release film according to Claim 1, wherein when the dynamic viscoelasticity (DMA) of the release film is measured under the conditions of a heating rate of 5°C / min and a frequency of 1 Hz, the storage modulus at 90°C is 100 MPa or less.

5. The surface free energy at 25°C is 40 mJ / m ２ The release film according to claim 1, wherein the surface free energy at 25°C is 40 mJ / m or less.

6. The release film according to Claim 1, wherein the comonomer copolymerized with ethylene in the ethylene copolymer contains a polar vinyl monomer or a cycloolefin monomer.

7. A method for manufacturing an electronic component using the release film according to any one of Claims 1 to 6, comprising the steps of disposing the release film on the object such that the release surface of the release film faces the object side; and performing a heat press on the object on which the release film is disposed, wherein in the step of disposing the release film, the surface of the object on which the release film is disposed has a concave portion or a convex portion, the method for manufacturing an electronic component. ​

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