Electronic device manufacturing method

Abstract

To provide a back-grinding adhesive film that can suppress adhesive residue on an electronic component side when the adhesive film is peeled off the electronic component after a back grinding process.SOLUTION: A back-grinding adhesive film (50) is used for protecting the surface of an electronic component (30) and comprises a substrate layer (10) and an ultraviolet-ray curable adhesive resin layer (20) that is disposed on one surface of the substrate layer (10). The back-grinding adhesive film (50) is such that the elongation-to-break of the adhesive resin layer after ultraviolet-ray curing is from 20% to 200% inclusive.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an adhesive film for backgrinding and a method for manufacturing an electronic device.

Background Art

[0002] In the manufacturing process of an electronic device, in the process of grinding an electronic component, an adhesive film is attached to the circuit formation surface of the electronic component in order to fix the electronic component and prevent damage to the electronic component. As such an adhesive film, a film in which an adhesive resin layer is laminated on a base film is generally used.

[0003] With the progress of high-density mounting technology, there is a demand for thinning of electronic components such as semiconductor wafers, and for example, it is required to perform thinning processing to a thickness of 50 μm or less. As one of such thinning processes, there is a pre-dicing method in which a groove having a predetermined depth is formed on the surface of an electronic component before grinding the electronic component, and then the electronic component is diced by performing grinding. Further, there is a pre-stealth method in which a modified region is formed by irradiating a laser inside the electronic component before grinding, and then the electronic component is diced by performing grinding.

[0004] As technologies related to adhesive films for such pre-dicing methods and pre-stealth methods, for example, those described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2014-75560) and Patent Document 2 (Japanese Patent Application Laid-Open No. 2016-72546) can be mentioned.

[0005] Patent Document 1 describes a surface protection sheet having an adhesive layer on a base material, which satisfies the following requirements (a) to (d). (a) The Young's modulus of the base material is 450 MPa or more. (b) The storage elastic modulus of the adhesive layer at 25°C is 0.10 MPa or more. (c) The storage elastic modulus of the adhesive layer at 50°C is 0.20 MPa or less. (d) The thickness of the adhesive layer is 30 μm or more. Patent Document 1 describes that such a surface protection sheet can suppress the intrusion of water (sludge intrusion) from the gap formed when the work is cut and formed into the protected surface of the work during the back grinding process of the work, thereby preventing contamination of the protected surface of the work.

[0006] Patent Document 2 describes an adhesive tape for protecting the surface of a semiconductor wafer, which has a base resin film and a radiation-curable adhesive layer formed on at least one side of the base resin film. The base resin film has at least one rigid layer with a tensile elastic modulus of 1 to 10 GPa, and the peel force at a peel angle of 30° after radiation-curing the adhesive layer is 0.1 to 3.0 N / 25 mm. Patent Document 2 states that according to such an adhesive tape for protecting the surface of a semiconductor wafer, in the back grinding process of a semiconductor wafer to which the pre-dicing method or the pre-stealth method is applied, the kerf shift of the diced semiconductor chips can be suppressed, and the semiconductor wafer can be processed without being damaged or contaminated.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] According to the study by the present inventors, for example, in the manufacturing process of an electronic device using the pre-dicing method, the pre-stealth method, etc., it has been clarified that glue residue is likely to occur on the electronic component side when peeling off the adhesive film from the electronic component after the back grinding process.

[0009] The present invention has been made in view of the above circumstances, and provides a pressure-sensitive adhesive film for back grinding that can suppress adhesive residue on the electronic component side when peeling the pressure-sensitive adhesive film from the electronic component after the back grinding process. **Means for Solving the Problems**

[0010] The inventors of the present invention have conducted intensive studies to achieve the above problems. As a result, in a pressure-sensitive adhesive film including a base material layer and an ultraviolet curable pressure-sensitive adhesive resin layer, by using a pressure-sensitive adhesive resin layer having a breaking elongation after ultraviolet curing within a specific range, it has been found that adhesive residue on the electronic component side when peeling the pressure-sensitive adhesive film from the electronic component after the back grinding process can be suppressed, and the present invention has been completed.

[0011] According to the present invention, there are provided a pressure-sensitive adhesive film for back grinding and a method for manufacturing an electronic device as shown below.

[0012] [1] A pressure-sensitive adhesive film for back grinding, comprising a base material layer and an ultraviolet curable pressure-sensitive adhesive resin layer provided on one surface side of the base material layer, and used for protecting the surface of an electronic component, wherein the pressure-sensitive adhesive film for back grinding in which the breaking elongation of the pressure-sensitive adhesive resin layer after ultraviolet curing is 20% or more and 200% or less. [2] In the pressure-sensitive adhesive film for back grinding according to [1] above, the pressure-sensitive adhesive resin layer contains a (meth)acrylic resin having a polymerizable carbon-carbon double bond in the molecule and a photoinitiator, and is a pressure-sensitive adhesive film for back grinding. [3] In the pressure-sensitive adhesive film for back grinding according to [1] or [2] above, the electronic component is half-cut or a modified layer is formed, and it is a pressure-sensitive adhesive film for back grinding. [4] In the pressure-sensitive adhesive film for back grinding according to any one of [1] to [3] above, An adhesive film for back grinding, wherein the thickness of the adhesive resin layer is 10 μm or more and 100 μm or less. [5] In the adhesive film for back grinding according to any one of the above [1] to [4], An adhesive film for back grinding, wherein the resin constituting the base material layer contains one or more selected from polyolefin, polyester, polyamide, polyacrylate, polymethacrylate, polyvinyl chloride, polyvinylidene chloride, polyimide, polyetherimide, ethylene-vinyl acetate copolymer, polyacrylonitrile, polycarbonate, polystyrene, ionomer, polysulfone, polyethersulfone and polyphenylene ether. [6] A step (A) of preparing a structure including an electronic component having a circuit formation surface and an adhesive film bonded to the circuit formation surface side of the electronic component; A step (B) of back grinding the surface of the electronic component opposite to the circuit formation surface side; A step (C) of removing the adhesive film from the electronic component after irradiating the adhesive film with ultraviolet rays; A method for manufacturing an electronic device, comprising at least: A method for manufacturing an electronic device, wherein the adhesive film is the adhesive film for back grinding according to any one of the above [1] to [5]. [7] In the method for manufacturing an electronic device according to the above [6], The step (A) includes: At least one step (A1) selected from a step (A1-1) of half-cutting the electronic component and a step (A1-2) of irradiating the electronic component with a laser to form a modified layer on the electronic component; A step (A2) of attaching the adhesive film for back grinding to the circuit formation surface side of the electronic component after the step (A1); A method for manufacturing an electronic device including the above.

Advantages of the Invention

[0013] According to the present invention, it is possible to provide a pressure-sensitive adhesive film for back grinding that can suppress the remaining adhesive on the electronic component side when peeling the pressure-sensitive adhesive film from the electronic component after the back grinding process.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same components are denoted by common reference numerals, and the description will be omitted as appropriate. Also, the figures are schematic views and do not match the actual dimensional ratios. Note that the numerical range "A to B" represents A or more and B or less unless otherwise specified. In the present embodiment, "(meth)acrylic" means acrylic, methacrylic, or both acrylic and methacrylic.

[0016] 1. Pressure-Sensitive Adhesive Film FIG. 1 is a cross-sectional view schematically showing an example of the structure of the pressure-sensitive adhesive film 50 according to an embodiment of the present invention. As shown in FIG. 1, the pressure-sensitive adhesive film 50 for back grinding according to the present embodiment includes a base material layer 10 and an ultraviolet-curable pressure-sensitive adhesive resin layer 20 provided on one surface side of the base material layer 10, and is a pressure-sensitive adhesive film 50 used for protecting the surface of the electronic component 30, and the elongation at break of the pressure-sensitive adhesive resin layer 20 after ultraviolet curing is 20% or more and 200% or less. Here, the elongation at break of the pressure-sensitive adhesive resin layer 20 after ultraviolet curing is a value measured by the following method. (Method) On the corona-treated surface of a corona-treated ethylene-vinyl acetate copolymer extrusion film (MFR: 1.7 g / 10 min, vinyl acetate content: 9% by mass, thickness: 140 μm), an adhesive resin layer 20 of the adhesive film 50 for the back grind according to the present embodiment having the same thickness, composition, etc. is laminated, and further, a release film (separator) such as a polyethylene terephthalate film subjected to a silicone release treatment is laminated on the adhesive resin layer 20 side to produce a measurement sample in a laminated state. Examples of the lamination method include the following methods. An adhesive resin layer 20 is formed on the release-treated surface of a polyethylene terephthalate film subjected to a silicone release treatment, and then a corona-treated ethylene-vinyl acetate copolymer film is bonded onto the adhesive resin layer 20 to obtain a laminate. Next, the obtained laminate is heated in an oven at 40 °C for 3 days for aging. Next, from the ethylene-vinyl acetate copolymer film side of the obtained laminate, ultraviolet light with a main wavelength of 365 nm is irradiated onto the adhesive resin layer 20 using a high-pressure mercury lamp in an environment of 25 °C with an irradiation intensity of 100 mW / cm 2 to an ultraviolet dose of 1080 mJ / cm 2 to photocure the adhesive resin layer 20. Next, the laminate with the adhesive resin layer 20 photocured is cut into a length of 110 mm and a width of 10 mm, and the polyethylene terephthalate film as the separator is peeled off from the laminate. Next, the adhesive resin layer 20 together with the ethylene-vinyl acetate copolymer film is chucked by a tensile tester (for example, Autograph AGS-X, manufactured by Shimadzu Corporation) so that the initial chuck distance Lo is 50 mm. The sample is pulled at a speed of 30 mm / min, and the point where breakage is observed in the adhesive resin layer 20 visually is taken as the break point, and the chuck distance at that time is taken as L. The elongation at break (%) is obtained by (L - Lo) / Lo × 100 (%).

[0017] As described above, according to the studies by the present inventors, for example, in the manufacturing process of electronic devices using the prior dicing method, the prior stealth method, etc., it has been clarified that glue residue is likely to occur on the electronic component side when peeling the adhesive film from the electronic component after the back grind process. Although the reason for this is not clear, unlike the normal backgrinding process for electronic components, since it is necessary to peel off the backgrinding adhesive film 50 from the severed electronic components, it is considered that glue residue is likely to occur at the edge portions of the severed electronic components. The inventors of the present invention have intensively studied to achieve the above problems. As a result, in the adhesive film 50 including the base material layer 10 and the ultraviolet-curable adhesive resin layer 20, by using the adhesive resin layer 20 in which the elongation at break of the adhesive resin layer 20 after ultraviolet curing is within the above range, it has been found for the first time that it is possible to suppress glue residue on the side of the electronic component 30 when peeling off the adhesive film 50 from the electronic component 30 after the backgrinding process.

[0018] In the adhesive film 50 according to the present embodiment, the elongation at break of the adhesive resin layer 20 after ultraviolet curing is 20% or more and 200% or less. However, from the viewpoint of designing the adhesive resin layer 20 in which glue residue is unlikely to occur by giving the adhesive resin layer 20 appropriate toughness, it is preferably 30% or more, more preferably 40% or more, and preferably 150% or less, more preferably 100% or less, and still more preferably 80% or less. The elongation at break of the adhesive resin layer 20 after ultraviolet curing can be controlled within the above range, for example, by controlling the types and blending ratios of the adhesive resin, crosslinking agent, and photoinitiator constituting the adhesive resin layer 20, and the types and content ratios of the respective monomers in the adhesive resin.

[0019] The total thickness of the adhesive film 50 according to the present embodiment is preferably 50 μm or more and 600 μm or less, more preferably 50 μm or more and 400 μm or less, and still more preferably 50 μm or more and 300 μm or less, from the balance between mechanical properties and handleability.

[0020] The adhesive film 50 according to the present embodiment may be provided with other layers such as a concavo-convex absorbent resin layer, an adhesive layer, and an antistatic layer (not shown) between the layers as long as the effects of the present invention are not impaired. According to the concavo-convex absorbent resin layer, the concavo-convex absorbency of the adhesive film 50 can be improved. According to the adhesive layer, the adhesiveness between the layers can be improved. Further, according to the antistatic layer, the antistatic property of the adhesive film 50 can be improved.

[0021] The adhesive film 50 according to the present embodiment is used to protect the surface of the electronic component 30 in the manufacturing process of the electronic device. More specifically, it is used as a back grind tape to protect the circuit formation surface 30A (that is, the circuit surface including the circuit pattern) of the electronic component 30 in the process of grinding the electronic component 30, which is one of the manufacturing processes of the electronic device (also called the back grind process). Specifically, the adhesive film 50 is attached to the circuit formation surface 30A of the electronic component 30 for protection, and is used in the process of grinding the surface opposite to the circuit formation surface 30A. In particular, in the manufacturing process of an electronic device using the pre-dicing method or the pre-stealth method, etc., when the adhesive film 50 is peeled off from the electronic component 30 after the back grind process, glue residue is likely to occur on the electronic component 30 side. Therefore, the adhesive film 50 according to the present embodiment can be preferably applied to the manufacturing process of an electronic device using the pre-dicing method or the pre-stealth method, etc. Here, in the pre-dicing method, the electronic component 30 is half-cut as shown in FIG. 1. In the pre-stealth method, the electronic component 30 has a modified layer (a region internally processed by a laser inside the electronic component 30) formed by laser irradiation.

[0022] Next, each layer constituting the adhesive film 50 according to the present embodiment will be described.

[0023] <Base material layer> The base material layer 10 is a layer provided for the purpose of making the handleability, mechanical properties, heat resistance, and other properties of the adhesive film 50 better. The base material layer 10 is not particularly limited as long as it has mechanical strength capable of withstanding external forces applied during processing of the electronic component 30. Examples thereof include resin films. Examples of the resin constituting the base material layer 10 include polyolefins such as polyethylene, polypropylene, poly(4-methyl-1-pentene), and poly(1-butene); polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyamides such as nylon-6, nylon-66, and polymetaxylylene adipamide; (meth)acrylic resins; polyvinyl chloride; polyvinylidene chloride; polyimide; polyetherimide; ethylene-vinyl acetate copolymer; polyacrylonitrile; polycarbonate; polystyrene; ionomer; polysulfone; polyethersulfone; polyetheretherketone; and the like. One or more selected therefrom can be mentioned. Among these, from the viewpoint of improving mechanical properties and transparency, one or more selected from polypropylene, polyethylene terephthalate, polyethylene naphthalate, polyamide, polyimide, ethylene-vinyl acetate copolymer, and polybutylene terephthalate are preferable, and one or more selected from polyethylene terephthalate and polyethylene naphthalate are more preferable.

[0024] The base material layer 10 may be a single layer or two or more layers. Further, as the form of the resin film used to form the base material layer 10, it may be a stretched film or a film stretched in one axial direction or two axial directions. From the viewpoint of improving the mechanical strength of the base material layer 10, it is preferably a film stretched in one axial direction or two axial directions. The base material layer 10 is preferably pre-annealed from the viewpoint of suppressing warping of the electronic component after grinding. The base material layer 10 may be surface-treated to improve adhesion to other layers. Specifically, corona treatment, plasma treatment, undercoat treatment, primer coat treatment, or the like may be performed.

[0025] The thickness of the base material layer 10 is preferably 20 μm or more and 250 μm or less, more preferably 30 μm or more and 200 μm or less, and even more preferably 50 μm or more and 150 μm or less, from the viewpoint of obtaining good film properties.

[0026] <Adhesive resin layer> The pressure-sensitive adhesive film 50 according to the present embodiment includes an ultraviolet curable pressure-sensitive adhesive resin layer 20. The pressure-sensitive adhesive resin layer 20 is a layer provided on one surface side of the base material layer 10, and is a layer that comes into contact with and adheres to the circuit formation surface 30A of the electronic component 30 when the pressure-sensitive adhesive film 50 is attached to the circuit formation surface 30A of the electronic component 30.

[0027] Examples of the adhesive constituting the pressure-sensitive adhesive resin layer 20 include (meth)acrylic adhesives, silicone adhesives, urethane adhesives, olefin adhesives, styrene adhesives, and the like. Among these, (meth)acrylic adhesives based on (meth)acrylic resins are preferred because the adhesive force can be easily adjusted.

[0028] Further, as the adhesive constituting the pressure-sensitive adhesive resin layer 20, it is preferable to use an ultraviolet crosslinkable adhesive whose adhesive force is reduced by ultraviolet rays. The pressure-sensitive adhesive resin layer 20 composed of the ultraviolet crosslinkable adhesive crosslinks by irradiation with ultraviolet rays and the adhesive force is significantly reduced, so that it is easy to peel the electronic component 30 from the pressure-sensitive adhesive film 50.

[0029] Examples of the (meth)acrylic resin contained in the (meth)acrylic pressure-sensitive adhesive include a homopolymer of a (meth)acrylic acid ester compound, a copolymer of a (meth)acrylic acid ester compound and a comonomer, and the like. Examples of the (meth)acrylic acid ester compound include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, glycidyl (meth)acrylate, and the like. These (meth)acrylic acid ester compounds may be used alone or in combination of two or more. Examples of the comonomer constituting the (meth)acrylic copolymer include vinyl acetate, (meth)acrylonitrile, styrene, (meth)acrylic acid, itaconic acid, (meth)acrylamide, methylol (meth)acrylamide, maleic anhydride, and the like. These comonomers may be used alone or in combination of two or more.

[0030] Examples of the ultraviolet crosslinkable (meth)acrylic pressure-sensitive adhesive include an adhesive obtained by including a (meth)acrylic resin having a polymerizable carbon-carbon double bond in the molecule and a photoinitiator, and crosslinking the (meth)acrylic resin with a crosslinking agent as necessary. The ultraviolet crosslinkable (meth)acrylic pressure-sensitive adhesive may further contain a low molecular weight compound having two or more polymerizable carbon-carbon double bonds in the molecule.

[0031] The (meth)acrylic resin having a polymerizable carbon-carbon double bond in the molecule is specifically obtained as follows. First, a monomer having an ethylenic double bond and a copolymerizable monomer having a functional group (P) are copolymerized. Next, the functional group (P) contained in this copolymer and a monomer having a functional group (Q) capable of undergoing an addition reaction, a condensation reaction, or the like with the functional group (P) are reacted while leaving the double bond in the monomer, and a polymerizable carbon-carbon double bond is introduced into the copolymer molecule.

[0032] Examples of the monomer having an ethylenic double bond include, for example, alkyl acrylate esters and alkyl methacrylate esters such as methyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, butyl (meth)acrylate, and ethyl (meth)acrylate, vinyl esters such as vinyl acetate, and monomers having an ethylenic double bond such as (meth)acrylonitrile, (meth)acrylamide, and styrene. One or more of these are used.

[0033] Examples of the copolymerizable monomer having the functional group (P) include (meth)acrylic acid, maleic acid, 2-hydroxyethyl (meth)acrylate, glycidyl (meth)acrylate, N-methylol(meth)acrylamide, (meth)acryloyloxyethyl isocyanate, and the like. These may be used alone or in combination of two or more. The ratio of the monomer having an ethylenic double bond to the copolymerizable monomer having the functional group (P) is preferably such that the monomer having an ethylenic double bond is 70 to 99% by mass and the copolymerizable monomer having the functional group (P) is 1 to 30% by mass. More preferably, the monomer having an ethylenic double bond is 80 to 95% by mass and the copolymerizable monomer having the functional group (P) is 5 to 20% by mass. Examples of the monomer having the functional group (Q) include, for example, the same monomers as the copolymerizable monomer having the functional group (P).

[0034] As a combination of the functional group (P) and the functional group (Q) to be reacted when introducing a polymerizable carbon-carbon double bond into a copolymer of a monomer having an ethylenic double bond and a copolymerizable monomer having the functional group (P), a combination in which an addition reaction easily occurs, such as a carboxyl group and an epoxy group, a carboxyl group and an aziridyl group, a hydroxyl group and an isocyanate group, etc., is desirable. Also, any reaction may be used as long as it is a reaction in which a polymerizable carbon-carbon double bond can be easily introduced, such as a condensation reaction between a carboxylic acid group and a hydroxyl group, not limited to an addition reaction.

[0035] Examples of the low-molecular-weight compound having two or more polymerizable carbon-carbon double bonds in the molecule include tripropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tetraacrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxy penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylolpropane tetraacrylate, and the like. These may be used alone or in combination of two or more. The addition amount of the low-molecular-weight compound having two or more polymerizable carbon-carbon double bonds in the molecule is preferably 0.1 to 20 parts by mass, more preferably 5 to 18 parts by mass, based on 100 parts by mass of the above (meth)acrylic resin.

[0036] Examples of the photoinitiator include benzoin, isopropyl benzoin ether, isobutyl benzoin ether, benzophenone, Michler's ketone, chlorothioxanthone, dodecylthioxanthone, dimethylthioxanthone, diethylthioxanthone, acetophenone diethyl ketal, benzyl dimethyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 2-benzyl-2-dimethylamino-4'-morpholinobutyrophenone, 2,2-dimethoxy-2-phenylacetophenone, 2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)butan-1-one, and the like. These may be used alone or in combination of two or more. The addition amount of the photoinitiator is preferably 0.1 to 15 parts by mass, more preferably 1 to 10 parts by mass, still more preferably 4 to 10 parts by mass, based on 100 parts by mass of the above (meth)acrylic resin.

[0037] A crosslinking agent may be added to the above ultraviolet curable adhesive. Examples of the crosslinking agent include epoxy compounds such as sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, and diglycerol polyglycidyl ether; aziridine compounds such as tetramethylolmethane-tri-β -aziridinylpropionate, trimethylolpropane-tri-β -aziridinylpropionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), and N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide); and isocyanate compounds such as tetramethylene diisocyanate, hexamethylene diisocyanate, and polyisocyanate. The above ultraviolet curable adhesive may be of any type such as a solvent type, an emulsion type, or a hot melt type.

[0038] The content of the crosslinking agent is usually preferably in a range such that the number of functional groups in the crosslinking agent does not exceed the number of functional groups in the (meth)acrylic resin. However, it may be contained in excess as necessary, such as when new functional groups are generated by the crosslinking reaction or when the crosslinking reaction is slow. From the viewpoint of improving the balance between the heat resistance and the adhesive strength of the adhesive resin layer 20, the content of the crosslinking agent in the (meth)acrylic adhesive is preferably 0.1 part by mass or more and 15 parts by mass or less, more preferably 0.5 part by mass or more and 5 parts by mass or less, based on 100 parts by mass of the (meth)acrylic resin.

[0039] The adhesive resin layer 20 can be formed, for example, by applying an adhesive coating solution onto the base material layer 10. As a method for applying the adhesive coating liquid, for example, conventionally known coating methods such as the roll coater method, reverse roll coater method, gravure roll method, bar coater method, comma coater method, die coater method, etc. can be adopted. The drying conditions of the applied adhesive are not particularly limited, but generally, it is preferably dried in the temperature range of 80 to 200 °C for 10 seconds to 10 minutes. More preferably, it is dried at 80 to 170 °C for 15 seconds to 5 minutes. In order to sufficiently promote the crosslinking reaction between the crosslinking agent and the (meth)acrylic resin, after the drying of the adhesive coating liquid is completed, it may be heated at 40 to 80 °C for about 5 to 300 hours.

[0040] In the adhesive film 50 according to this embodiment, the thickness of the adhesive resin layer 20 is preferably 10 μm or more and 100 μm or less, and more preferably 10 μm or more and 50 μm or less. When the thickness of the adhesive resin layer 20 is within the above range, the balance between the adhesiveness to the surface of the electronic component 30 and the handleability is good.

[0041] 2. Method for manufacturing an electronic device FIG. 2 is a cross-sectional view schematically showing an example of the method for manufacturing an electronic device according to an embodiment of the present invention. The method for manufacturing an electronic device according to this embodiment includes at least the following three steps, for example. (A) Step of preparing a structure 100 including an electronic component 30 having a circuit formation surface 30A and an adhesive film 50 bonded to the circuit formation surface 30A side of the electronic component 30 (B) Step of backgrinding the surface on the side opposite to the circuit formation surface 30A of the electronic component 30 (C) Step of removing the adhesive film 50 from the electronic component 30 after irradiating the adhesive film 50 with ultraviolet rays And, as the adhesive film 50, the adhesive film 50 according to this embodiment is used. The method for manufacturing an electronic device according to this embodiment is characterized in that when grinding the back surface of the electronic component 30, the adhesive film 50 according to this embodiment is used as a so-called backgrinding tape. Hereinafter, each step of the method for manufacturing an electronic device according to this embodiment will be described.

[0042] (Process (A)) First, a structure 100 is prepared, which includes an electronic component 30 having a circuit formation surface 30A and an adhesive film 50 adhered to the circuit formation surface 30A side of the electronic component 30. Such a structure 100 can be manufactured, for example, by peeling a release film from the adhesive resin layer 20 of the adhesive film 50 to expose the surface of the adhesive resin layer 20, and then attaching the circuit formation surface 30A of the electronic component 30 onto the adhesive resin layer 20.

[0043] Here, the conditions for attaching the circuit formation surface 30A of the electronic component 30 to the adhesive film 50 are not particularly limited. For example, the temperature can be 20 - 80°C, the pressure can be 0.05 - 0.5 MPa, and the attachment speed can be 0.5 - 20 mm / second.

[0044] Process (A) preferably further includes at least one process (A1) selected from a process (A1 - 1) of half - cutting the electronic component 30 and a process (A1 - 2) of irradiating the electronic component 30 with a laser to form a modified layer on the electronic component 30, and a process (A2) of attaching the back - grinding adhesive film 50 to the circuit formation surface 30A side of the electronic component 30 after process (A1). As described above, the adhesive film 50 according to this embodiment can be preferably used in the manufacturing process of electronic devices using the pre - dicing method, the pre - stealth method, etc. Therefore, a manufacturing method that performs the above - mentioned process (A1 - 1) which is the pre - dicing method or the above - mentioned process (A1 - 2) which is the pre - stealth method is preferable.

[0045] In process (A2), the adhesive film 50 can be heated and attached to the circuit formation surface 30A of the electronic component 30. Thereby, the adhesion state between the adhesive resin layer 20 and the electronic component 30 can be made good over a long period of time. The heating temperature is not particularly limited, but for example, it is 60 - 80°C.

[0046] The operation of attaching the adhesive film 50 to the electronic component may be performed manually, but generally, it can be performed by a device called an automatic pasting machine equipped with a roll-shaped adhesive film.

[0047] The electronic component 30 to be attached to the adhesive film 50 is not particularly limited, but it is preferably an electronic component 30 having a circuit formation surface 30A. For example, a semiconductor wafer, an epoxy-molded wafer, a molded panel, a molded array package, a semiconductor substrate, etc. may be mentioned, and semiconductor wafers and epoxy-molded wafers are preferred. In addition, the semiconductor wafer includes, for example, a silicon wafer, a sapphire wafer, a germanium wafer, a germanium-arsenic wafer, a gallium-phosphorus wafer, a gallium-arsenic-aluminum wafer, a gallium-arsenic wafer, a lithium tantalate wafer, etc., and is preferably used for a silicon wafer. The epoxy-molded wafer includes a wafer produced by an eWLB (Embedded Wafer Level Ball Grid Array) process, which is one of the manufacturing methods of the fan-out type WLP. The semiconductor wafer and the epoxy-molded wafer having a circuit formation surface are not particularly limited, but are used, for example, for those having circuits such as wiring, capacitors, diodes, or transistors formed on the surface. Also, the circuit formation surface may be plasma-treated.

[0048] The circuit formation surface 30A of the electronic component 30 may be, for example, an uneven surface by having bump electrodes or the like. In addition, the bump electrode is, for example, joined to the electrode formed on the mounting surface when mounting the electronic device on the mounting surface, and forms an electrical connection between the electronic device and the mounting surface (the mounting surface of a printed circuit board or the like). Examples of the bump electrode include ball bumps, printed bumps, stud bumps, plated bumps, pillar bumps, etc. That is, the bump electrode is usually a convex electrode. These bump electrodes may be used alone or in combination of two or more. The height and diameter of the bump electrodes are not particularly limited, but are preferably 10 to 400 μm, more preferably 50 to 300 μm, respectively. The bump pitch at that time is also not particularly limited, but is preferably 20 to 600 μm, more preferably 100 to 500 μm. Also, the metal species constituting the bump electrodes is not particularly limited, and examples thereof include solder, silver, gold, copper, tin, lead, bismuth, and alloys thereof. However, the adhesive film 50 is preferably used when the bump electrodes are solder bumps. These metal species may be used alone or in combination of two or more.

[0049] (Step (B)) Next, the surface on the side opposite to the circuit formation surface 30A side of the electronic component 30 (also referred to as the back surface) is backgrinded. Here, backgrinding means thinning the electronic component to a predetermined thickness without damaging it. For example, the structure 100 is fixed to a chuck table of a grinding machine or the like, and the back surface (non-circuit formation surface) of the electronic component is ground.

[0050] In such a back surface grinding operation, the electronic component 30 is ground until its thickness becomes equal to or less than the desired thickness. The thickness of the electronic component before grinding is appropriately determined according to the diameter, type, etc. of the electronic component 30, and the thickness of the electronic component 30 after grinding is appropriately determined according to the size of the obtained chip, the type of circuit, etc. Also, when the electronic component 30 is half-cut or a modified layer is formed by laser irradiation, as shown in FIG. 1, the electronic component 30 is separated into individual pieces by step (B).

[0051] Although the back grinding method is not particularly limited, known grinding methods can be adopted. Each grinding can be performed while cooling by applying water to the electronic component and the grindstone. If necessary, a dry polishing process, which is a grinding method that does not use grinding water, can be performed at the end of the grinding process. After the back grinding is completed, chemical etching is performed if necessary. The chemical etching is performed by a method such as immersing the electronic component in an etching solution selected from the group consisting of an acidic aqueous solution composed of a single or mixed solution of hydrofluoric acid, nitric acid, sulfuric acid, acetic acid, etc., an alkaline aqueous solution such as a potassium hydroxide aqueous solution or a sodium hydroxide aqueous solution, with the adhesive film 50 attached. The etching is performed for the purpose of removing the distortion generated on the back surface of the electronic component, further thinning the electronic component, removing an oxide film, etc., and pre-treatment when forming an electrode on the back surface. The etching solution is appropriately selected according to the above purposes.

[0052] (Step (C)) Next, after irradiating the adhesive film 50 with ultraviolet rays, the adhesive film 50 is removed from the electronic component 30. Before removing the adhesive film from the electronic component 30, the electronic component 30 may be mounted on a dicing tape or a dicing tape with a die attach film. The operation of removing the adhesive film 50 from the electronic component 30 may be performed manually, but generally can be performed by a device called an automatic peeling machine. The surface of the electronic component 30 after the adhesive film 50 is peeled off may be cleaned if necessary. Examples of the cleaning method include wet cleaning such as water cleaning and solvent cleaning, and dry cleaning such as plasma cleaning. In the case of wet cleaning, ultrasonic cleaning may be used in combination. These cleaning methods can be appropriately selected according to the contamination status of the surface of the electronic component.

[0053] In step (C), for the adhesive film 50, for example, ultraviolet rays with a dose of 200 mJ / cm 2 or more and 2000 mJ / cm 2 or less are irradiated to photocure the adhesive resin layer 20 and reduce the adhesive force of the adhesive resin layer 20, and then the adhesive film 50 is removed from the electronic component 30. In addition, ultraviolet irradiation can be carried out using ultraviolet light with a main wavelength of 365 nm, for example, by using a high-pressure mercury lamp. The irradiation intensity of the ultraviolet light is, for example, 50 mW / cm 2 or more and 500 mW / cm 2 or less.

[0054] (Other steps) After performing steps (A) to (C), steps such as mounting the obtained semiconductor chip on a circuit board may be further performed. These steps can be carried out based on known information.

[0055] The preferred embodiments of the present invention have been described above, but these are examples of the present invention, and various configurations other than the above can also be adopted.

Example

[0056] Hereinafter, the present invention will be specifically described by way of examples and comparative examples, but the present invention is not limited thereto. Details regarding the production of the adhesive film are as follows.

[0057] <Base material layer> Base material layer 1: Polyethylene terephthalate film (manufactured by Toyobo Co., Ltd., product name: E7180, thickness: 50 μm, one-sided corona-treated product)

[0058] Base material layer 2: A laminated film composed of a low-density polyethylene film / a polyethylene terephthalate film / a low-density polyethylene film (total thickness: 110 μm) A low-density polyethylene film (density: 0.925 kg / m 3 and thickness: 30 μm) was laminated on both sides of a polyethylene terephthalate film (manufactured by Toray Industries, Inc., product name: Lumirror S10, thickness: 50 μm). Corona treatment was performed on one side of the obtained laminated film.

[0059] Base material layer 3: A laminated film composed of a polyethylene terephthalate film / an ethylene-vinyl acetate copolymer film / an acrylic film (total thickness: 145 μm) A polyethylene terephthalate film (manufactured by Toyobo Co., Ltd., product name: E7180, thickness: 50 μm) and an ethylene-vinyl acetate copolymer (manufactured by Mitsui Dow Chemical Co., Ltd., MFR: 2.5 g / 10 min) film (thickness: 70 μm) were laminated by subjecting the bonding surface side of the ethylene-vinyl acetate copolymer film to the polyethylene terephthalate film to corona treatment. Further, corona discharge treatment was also applied to the opposite surface side of the polyethylene terephthalate film of the ethylene-vinyl acetate copolymer film. Next, the following acrylic resin coating solution for the base material was coated and dried to a dry thickness of 20 μm on the release surface of the released polyethylene terephthalate film (separator), and laminated via the ethylene-vinyl acetate copolymer film to the laminated film composed of the above polyethylene terephthalate film / ethylene-vinyl acetate copolymer film, and aged (40 °C, 3 days). Next, the separator was peeled off to obtain a base material layer 3.

[0060] <Acrylic resin coating solution for the base material> 0.5 part by mass of 4,4'-azobis-4-cyanovaleric acid (manufactured by Otsuka Chemical Co., Ltd., product name: ACVA) was used as a polymerization initiator, 74 parts by mass of butyl acrylate, 14 parts by mass of methyl methacrylate, 9 parts by mass of 2-hydroxyethyl methacrylate, 2 parts by mass of methacrylic acid, 1 part by mass of acrylamide, and 3 parts by mass of an aqueous solution of ammonium polyoxyethylene nonylpropenyl phenyl ether sulfate (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Aqualon HS-1025) were emulsion-polymerized in deionized water at 70 °C for 9 hours. After completion of the polymerization, the pH was adjusted to 7 with aqueous ammonia to obtain an acrylic polymer aqueous emulsion having a solid content concentration of 42.5%. Next, with respect to 100 parts by mass of this acrylic polymer aqueous emulsion, the pH was adjusted to 9 or more using aqueous ammonia, and 0.75 part by mass of an aziridine-based crosslinking agent (manufactured by Nippon Shokubai Kagaku Kogyo Co., Ltd., Chemitec PZ-33) and 5 parts by mass of diethylene glycol monobutyl ether were blended to obtain a coating solution for the base material.

[0061] <(Meth)acrylic resin solution> (Meth)acrylic resin solution 1: 49 parts by mass of ethyl acrylate, 20 parts by mass of 2-ethylhexyl acrylate, 21 parts by mass of methyl acrylate, 10 parts by mass of glycidyl methacrylate, and 0.5 part by mass of a benzoyl peroxide-based polymerization initiator as a polymerization initiator were reacted at 80°C for 10 hours in 65 parts by mass of toluene and 50 parts by mass of ethyl acetate. After completion of the reaction, the obtained solution was cooled, and 25 parts by mass of xylene, 5 parts by mass of acrylic acid, and 0.5 part by mass of tetradecyldimethylbenzylammonium chloride were added to the cooled solution, and the mixture was reacted at 85°C for 32 hours while blowing air thereinto to obtain (meth)acrylic resin solution 1.

[0062] (Meth)acrylic resin solution 2: 77 parts by mass of n-butyl acrylate, 16 parts by mass of methyl methacrylate, 16 parts by mass of 2-hydroxyethyl acrylate, and 0.3 part by mass of t-butyl peroxy-2-ethylhexanoate as a polymerization initiator were reacted at 85°C for 10 hours in 20 parts by mass of toluene and 80 parts by mass of ethyl acetate. After completion of the reaction, the solution was cooled, and 30 parts by mass of toluene, 7 parts by mass of methacryloyloxyethyl isocyanate (manufactured by Showa Denko, product name: Karenz MOI), and 0.05 part by mass of dibutyltin dilaurate were added thereto, and the mixture was reacted at 85°C for 12 hours while blowing air thereinto to obtain (meth)acrylic resin solution 2.

[0063] (Meth)acrylic resin solution 3: 30 parts by mass of ethyl acrylate, 11 parts by mass of methyl acrylate, 26 parts by mass of 2-ethylhexyl acrylate, 7 parts by mass of 2-hydroxyethyl methacrylate, and 0.8 part by mass of a benzoyl peroxide-based polymerization initiator as a polymerization initiator were reacted at 80°C for 9 hours in 7 parts by mass of toluene and 50 parts by mass of ethyl acetate. After completion of the reaction, the obtained solution was cooled, and 25 parts by mass of toluene was added to the cooled solution to obtain (meth)acrylic resin solution 3.

[0064] <Adhesive film for elongation at break evaluation> An adhesive coating solution for the pressure-sensitive resin layer was prepared by adding the additives shown in Table 1 to an acrylic resin solution. This coating solution was applied to the release-treated surface of a silicone release-treated polyethylene terephthalate film (separator), and dried at 120 °C for 3 minutes to form a pressure-sensitive resin layer with a thickness of 20 μm. Next, the corona-treated surface of a corona-treated ethylene-vinyl acetate copolymer extrusion film (MFR: 1.7 g / 10 min, vinyl acetate content: 9% by mass, thickness: 140 μm) was laminated onto the pressure-sensitive resin layer to obtain a laminate. Subsequently, the obtained laminate was heated in an oven at 40 °C for 3 days for aging.

[0065] <Pressure-sensitive adhesive film for adhesion force and pre-dicing evaluation> An adhesive coating solution for the pressure-sensitive resin layer was prepared by adding the additives shown in Table 1 to an acrylic resin solution. This coating solution was applied to a silicone release-treated polyethylene terephthalate film (separator). Next, it was dried at 120 °C for 3 minutes to form a pressure-sensitive resin layer with a thickness of 20 μm, and laminated onto the base material layer. For base material layers 1 and 2, they were laminated onto the corona-treated surface. For base material layer 3, the separator was peeled off and laminated onto the acrylic layer side. The obtained laminate was heated in an oven at 40 °C for 3 days for aging.

[0066] <Evaluation method> (1) Elongation at break of the pressure-sensitive resin layer after UV curing From the ethylene-vinyl acetate copolymer extrusion film side of the pressure-sensitive adhesive film for elongation at break evaluation, ultraviolet rays with a main wavelength of 365 nm were irradiated onto the pressure-sensitive resin layer using a high-pressure mercury lamp in an environment at 25 °C with an irradiation intensity of 100 mW / cm 2 with an ultraviolet ray dose of 1080 mJ / cm 2 Then, it was cut into a length of 110 mm and a width of 10 mm, and the polyethylene terephthalate film, which is the separator, was peeled off from the laminate. Next, the adhesive resin layer was chucked with an ethylene-vinyl acetate copolymer extruded film using a tensile tester (Shimadzu Corporation, product name: Autograph AGS-X) so that the initial chuck distance Lo was 50 mm. The sample was pulled at a speed of 30 mm / min, and the point where breakage was observed in the adhesive resin layer visually was defined as the breaking point, and the chuck distance at that time was designated as L. The elongation at break (%) was determined by (L - Lo) / Lo × 100 (%). The evaluation was carried out with N = 2, and the values were averaged to obtain the measured value.

[0067] (2) Adhesion evaluation Adherend wafer: The mirror surface of a silicon mirror wafer (manufactured by SUMCO Corporation, 4-inch single-sided mirror wafer) was ozone-cleaned using a UV ozone cleaning apparatus (manufactured by Technovision, UV-208) (ozone treatment time: 60 seconds). Thereafter, the wafer mirror surface wiped with ethanol was used as the adherend wafer.

[0068] Adhesion before UV irradiation: In an environment of 23°C and 50% RH, the adhesive film for adhesion evaluation was cut to a width of 50 mm, the separator was peeled off, and using a hand roller, the adhesive film was attached to the mirror surface of the adherend wafer through its adhesive resin layer and left for 1 hour. After leaving, using a tensile tester (Shimadzu Corporation, product name: Autograph AGS-X), one end of the adhesive film was clamped, and the adhesive film was peeled off from the surface of the adherend wafer at a peeling angle of 180 degrees and a peeling speed of 300 mm / min. The stress at that time was measured and converted to N / 25 mm to obtain the adhesion. The evaluation was carried out with N = 2, and the values were averaged to obtain the measured value. Adhesion after UV irradiation: In an environment of 23°C and 50% RH, the adhesive film for adhesion evaluation was cut to a width of 50 mm, the separator was peeled off, and using a hand roller, the adhesive film was attached to the mirror surface of the adherend wafer through its adhesive resin layer and left for 1 hour. After leaving, in an environment of 25°C, ultraviolet rays with a main wavelength of 365 nm were irradiated onto the adhesive film with an irradiation intensity of 100 mW / cm 2 and an ultraviolet ray dose of 1080 mJ / cm was applied to the adhesive film. 2It was irradiated. Then, using a tensile testing machine (Shimadzu Corporation, product name: Autograph AGS-X), one end of the adhesive film was clamped, and the adhesive film was peeled off from the surface of the adherend wafer at a peeling angle of 180 degrees and a peeling speed of 300 mm / min. The stress at that time was measured and converted to N / 25 mm to obtain the adhesive strength. The evaluation was carried out with N = 2, and the values were averaged as the measured values.

[0069] Residue evaluation of adhesive: The adherend wafer after the above peeling was visually observed and evaluated according to the following criteria. 〇: No residue of adhesive was confirmed. ×: Residue of adhesive was confirmed.

[0070] (3) Evaluation of the pre-dicing method Evaluation wafer 1: Using a dicing saw, the mirror surface of a mirror wafer (manufactured by C.S.T. World, 8-inch mirror wafer, diameter: 200 ± 0.5 mm, thickness: 725 ± 50 μm, single-sided mirror) was half-cut to obtain Evaluation wafer 1. (Blade: ZH05-SD3500-N1-70-DD, chip size: 5 mm × 8 mm, cutting depth: 58 μm, blade rotation speed: 30,000 rpm). When Evaluation wafer 1 was observed with an optical microscope, the kerf width was 35 μm.

[0071] Evaluation wafer 2: Using a dicing saw, a first-stage half-cut was performed on the mirror surface of a mirror wafer (manufactured by C.S.T. World, 8-inch mirror wafer, diameter: 200 ± 0.5 mm, thickness: 725 ± 50 μm, single-sided mirror) (Blade: Z09-SD2000-Y1 58×0.25A×40×45E-L, chip size: 5 mm × 8 mm, cutting depth: 15 μm, blade rotation speed: 30,000 rpm). When observed with an optical microscope, the kerf width was 60 μm. Subsequently, a second-stage half-cut was performed (Blade: ZH05-SD3500-N1-70-DD, chip size: 5 mm × 8 mm, cutting depth: 58 μm, blade rotation speed: 30,000 rpm) to obtain Evaluation wafer 2.

[0072] Pre-dicing method: Using a tape laminator (manufactured by Nitto Denko Corporation, DR3000II), an adhesive film for pre-dicing evaluation was attached to the half-cut surface of the above evaluation wafer (23°C, attachment speed: 5 mm / min, attachment pressure: 0.36 MPa). Subsequently, using a grinder (manufactured by DISCO Corporation, DGP8760), the above wafer was ground on the back side (rough grinding and precision grinding, precision grinding amount: 40 μm, no polishing, thickness after grinding: 38 μm) and diced into individual pieces. Chip ejection during pre-dicing was evaluated visually according to the following criteria after the back side grinding was performed. 〇: No chip ejection was confirmed including the triangular corner part. ×: Chip ejection was confirmed including the triangular corner part.

[0073] Furthermore, UV irradiation and peeling of the adhesive film for pre-dicing evaluation were performed, and the residue of the adhesive after the pre-dicing method was evaluated. UV irradiation was performed using a high-pressure mercury lamp in an environment of 25°C with ultraviolet rays of a main wavelength of 365 nm at an irradiation intensity of 100 mW / cm 2 and the adhesive film for pre-dicing evaluation was irradiated with an ultraviolet dose of 1080 mJ / cm 2 . Peeling of the adhesive film for pre-dicing evaluation was performed according to the following procedure. First, using a wafer mounter (manufactured by Nitto Denko Corporation, MSA300), a separately prepared dicing tape (used as a mounting tape) was attached to the wafer side of the 8-inch wafer ring frame and the above diced wafer through the adhesive surface of the dicing tape. Subsequently, using a tape peeling machine (manufactured by Nitto Denko Corporation, HR3000III), the adhesive film for pre-dicing evaluation was peeled from the wafer notch part using a peeling tape (manufactured by Rusting Systems Corporation, PET38REL). The device peelability was evaluated according to the following criteria. 〇: The adhesive film for pre-dicing evaluation could be peeled from the wafer on the first attempt. ×: The adhesive film for pre-dicing evaluation could not be peeled from the wafer on the first attempt.

[0074] The adhesive residue on the singulated wafer after the pre-dicing method was evaluated using an optical microscope (manufactured by Olympus Corporation) according to the following criteria. 〇: No adhesive residue was confirmed. ×: Adhesive residue was confirmed.

[0075] [Example 1] To 100 parts by mass of (meth)acrylic resin solution 1 (solid content), 6.9 parts by mass of benzyl dimethyl ketal (manufactured by IGM, trade name: Omnirad 651) as a photoinitiator and 0.93 parts by mass of an isocyanate-based crosslinking agent (manufactured by Mitsui Chemicals, trade name: Orestar P49-75S) were added to obtain an adhesive coating solution 1 for the adhesive resin layer. According to the above method, an adhesive film for elongation at break evaluation, an adhesive film for adhesive force evaluation, and an adhesive film for pre-dicing evaluation were produced. Also, based on the evaluation method described above, the elongation at break, adhesive force evaluation, and pre-dicing method evaluation of the adhesive material after ultraviolet curing were carried out. The results are shown in Table 1.

[0076] [Examples 2 to 10 and Comparative Examples 1 and 2] Adhesive films were produced in the same manner as in Example 1 except that the types of the adhesive resin layer and the base material layer were changed to those shown in Table 1. Also, each evaluation was carried out in the same manner as in Example 1. The obtained results are shown in Table 1 respectively. The compounds described in Table 1 are as follows. Omnirad 651 (manufactured by IGM): 2,2-dimethoxy-2-phenylacetophenone Omnirad 369 (manufactured by IGM): 2-benzyl-2-dimethylamino-4'-morpholinobutyrophenone Aronix M400 (manufactured by Toagosei Co., Ltd.): A mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate NK Ester AD-TMP (manufactured by Shin-Nakamura Chemical Co., Ltd.): Ditrimethylolpropane tetraacrylate

[0077]

Table 1

[0078] This application claims priority based on Japanese Patent Application No. 2020-076702 filed on April 23, 2020, and incorporates all of its disclosures herein.

Description of Reference Numerals

[0079] 10 Substrate layer 20 Adhesive resin layer 30 Electronic component 30A Circuit formation surface 50 Adhesive film 100 Structure

Claims

【Claim 1】 An adhesive film for backgrinding, comprising a base material layer and an ultraviolet-curable adhesive resin layer provided on one surface side of the base material layer, and being used for protecting the surface of an electronic component, wherein the elongation at break of the adhesive resin layer after ultraviolet curing is 20% or more and 200% or less.

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