Encapsulant sheet for a system board on which a processor is mounted, and system board

Abstract

Provided is an encapsulant sheet that can enhance adhesion to a functional layer even when the functional layer is laminated on the surface of the encapsulant sheet. [Solution] The sealing material sheet 1 is for a system board on which a processor is mounted, and has a multilayer structure comprising a core layer 11 and a skin layer 12a, in which the core layer 11 contains a polyethylene-based resin as a base resin, and the skin layer 12a contains a polypropylene-based resin as a base resin.

Description

[Technical Field]

[0001] The present invention relates to an encapsulant sheet for a system board on which a processor is mounted, and to the system board. [Background technology]

[0002] 2. Description of the Related Art Conventionally, system boards equipped with processors that transmit electrical signals for controlling various devices have been widely used in various fields.

[0003] In addition, in miniaturized electronic devices commonly referred to as "smartphones" and "tablets," there is an increasing demand to mount numerous electronic circuit devices in a small space and to arrange these electronic circuit devices in an even more compact configuration.

[0004] However, miniaturized electronic devices have disadvantages because many circuits are integrated into a small space. For example, electromagnetic interference can occur due to electromagnetic waves that are generated by the electronic device itself, that enter the electronic device from the outside, or that flow through the connected circuit wiring. Also, heat is inevitably generated due to electrical resistance at the connections between each component during operation.

[0005] For example, Patent Document 1 describes a technique relating to an electronic circuit board assembly including an electronic circuit board, an electronic circuit device, an electromagnetic interference shield structure (electromagnetic reflection shield), and a heat dissipation pad.

[0006] Patent Document 1 describes that the electromagnetic interference shield structure and heat dissipation pad of this electronic circuit board assembly can be attached to the electronic circuit board at low cost and with ease, and that by using the electromagnetic interference shield and one heat dissipation pad, the electronic circuit board assembly can be made extremely thin.

[0007] In this way, sealing material sheets for system boards on which processors are mounted may be provided with functional layers such as an electromagnetic interference shielding structure to suppress electromagnetic interference and heat dissipation pads to dissipate heat from the processor. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 2017-536693 Summary of the Invention [Problem to be solved by the invention]

[0009] The encapsulant sheet for a system board on which a processor is mounted is laminated on the board to cover the processor, and as a result, the encapsulant sheet conforms to the shape of the processor, which can cause unevenness on the surface of the encapsulant sheet on the side opposite the board.

[0010] Research by the inventors revealed that even if a functional layer is laminated on the surface of the sealing material sheet opposite the substrate, a partial gap will be created between the sealing material sheet and the functional layer, making it impossible to improve adhesion to the functional layer.

[0011] An object of the present invention is to provide an encapsulant sheet that can enhance adhesion to a functional layer even when the functional layer is laminated on the surface of the encapsulant sheet. [Means for solving the problem]

[0012] The present inventors have found that the above problems can be solved by the following configuration: The present invention has been completed. Specifically, the present invention provides the following.

[0013] (1) An encapsulant sheet for a system board on which a processor is mounted, a multilayer structure including a core layer and a skin layer, the core layer contains a polyethylene-based resin as a base resin, Vicat softening point is in the range of 30°C to 100°C Encapsulating sheet.

[0014] (2) The surface roughness Ra of the skin layer is 15 μm or less. The encapsulant sheet according to (1).

[0015] (3) A system board including a processor, A substrate; a processor disposed on a surface of the substrate; The encapsulant sheet according to (1) or (2), Equipped with The encapsulant sheet is laminated on the substrate, covering the processor, with the core layer positioned closer to the substrate than the skin layer. System board.

[0016] (4) A functional layer is provided on the surface of the skin layer of the sealing material sheet. (3) The system board according to (3). [Effects of the Invention]

[0017] The sealing material sheet for a system substrate on which a processor of the present invention is mounted can enhance adhesion to a functional layer even if the functional layer is laminated on the surface of the sealing material sheet opposite the substrate. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view schematically illustrating a layer structure of an encapsulant sheet according to one embodiment of the present invention. [Figure 2] 1 is a cross-sectional view schematically illustrating an example of a layer configuration of an encapsulant sheet according to an embodiment of the present invention and a system substrate on which a processor is mounted. DETAILED DESCRIPTION OF THE INVENTION

[0019] Specific embodiments of the present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the object of the present invention.

[0020] ≪1. Encapsulating material sheet≫ The encapsulant sheet according to the present embodiment is a encapsulant sheet for a system board on which a processor is mounted. Specifically, the encapsulant sheet is a resin sheet that can be used as a encapsulant sheet for covering and laminating various components, such as a processor, on a system board to protect the various components, such as a processor, mounted on the board from physical impact.

[0021] The encapsulant sheet according to this embodiment has a multilayer structure including a core layer and a skin layer, and is characterized in that the core layer contains a polyethylene-based resin as a base resin, and the skin layer contains a polypropylene-based resin as a base resin.

[0022] In this specification, the term "polyethylene resin" and the like are used to refer not only to "polyethylene resin" but also to a copolymer containing, for example, 50% or more (preferably 70% or more, more preferably 80% or more) of a polyethylene main chain and in which a part of the main chain is replaced with another main chain different from polyethylene.

[0023] By providing a skin layer containing such a polypropylene-based resin and providing a functional layer on the surface of this skin layer, an encapsulant sheet can be obtained that can enhance adhesion to the functional layer.

[0024] Furthermore, laminating the skin layer and the functional layer via an adhesive layer can further impart releasability to the functional layer, which allows the functional layer to be relatively easily peeled off without damaging the functional layer or the encapsulant sheet, etc., in order to reattach the functional layer to the encapsulant sheet during system substrate manufacturing or to promote reuse (recycling) of the functional layer.

[0025] Furthermore, by providing a core layer containing a polyethylene-based resin, it is possible to impart a desirable level of molding properties to the sealing material sheet for system substrates.

[0026] The encapsulant sheet according to the present embodiment may be a two-layer film including a core layer containing a polyethylene-based resin and a skin layer (first skin layer) containing a polypropylene-based resin, or may have a three-layer structure as shown in Fig. 1. Specifically, a first skin layer 12a containing a polypropylene-based resin may be provided on one surface of the core layer 11, and a second skin layer 12b may be provided on the other surface of the core layer 11. For convenience, in this specification, the skin layer disposed on the side where the functional layer is laminated (the side opposite the substrate, hereinafter also referred to as the functional layer lamination side) may be referred to as the first skin layer, and the skin layer disposed on the substrate side (hereinafter also referred to as the substrate lamination side) may be referred to as the second skin layer.

[0027] When a second skin layer 12b disposed on the substrate side is laminated on the encapsulant sheet 1 according to the present embodiment, the second skin layer 12b preferably contains a polyethylene resin as a base resin, similar to the core layer 11. Specifically, it is preferable that a layer with a lower MFR is disposed in the center as the core layer 11, and a layer with a higher MFR is disposed on the substrate side as the second skin layer 12b. The encapsulant sheet 1 according to the present embodiment has sufficiently favorable molding properties even when it does not include the second skin layer 12b. However, by disposing a layer with a relatively high MFR as the second skin layer 12b, the encapsulant sheet can have improved molding properties while also having improved adhesion to other laminate members such as substrates and processors.

[0028] Furthermore, when the second skin layer 12b is laminated on the substrate side of the sealing material sheet 1 according to the present embodiment, it is preferable that the base resin contains a silane copolymer (silane-modified resin), which can further enhance adhesion to other laminate members such as the substrate and the processor.

[0029] The Vicat softening point of the encapsulant sheet 1 (the Vicat softening point measured from the side where the substrate is placed) is not particularly limited, but is preferably 30°C or higher and 100°C or lower, more preferably 35°C or higher and 95°C or lower, and even more preferably 40°C or higher and 90°C or lower. The lower limit of the Vicat softening point of the encapsulant sheet 1 is preferably 30°C or higher, more preferably 35°C or higher, and even more preferably 40°C or higher. The upper limit of the Vicat softening point of the encapsulant sheet 1 is preferably 100°C or lower, more preferably 95°C or lower, and even more preferably 90°C or lower.

[0030] The thickness (total thickness) of the encapsulant sheet 1 according to the present embodiment is not particularly limited and varies depending on the type of device in which it is used, but is preferably 250 μm or more and 600 μm or less, and more preferably 300 μm or more and 550 μm or less. The lower limit of the thickness (total thickness) of the encapsulant sheet 1 according to the present embodiment is preferably 250 μm or more, and more preferably 300 μm or more. The upper limit of the thickness (total thickness) of the encapsulant sheet 1 according to the present embodiment is preferably 600 μm or less, and more preferably 550 μm or less.

[0031] The thickness of the skin layer (first skin layer 12a) arranged on the functional layer stacking side of the sealing material sheet 1 according to this embodiment is not particularly limited, but is preferably from 1 / 20 to 1 / 3, and more preferably from 1 / 15 to 1 / 4, of the total thickness of the sealing material sheet 1. This more effectively prevents irregularities from occurring on the surface of the skin layer (first skin layer 12a), thereby further improving adhesion to the functional layer even when the functional layer is stacked on the surface of the skin layer (first skin layer 12a).

[0032] The thickness of core layer 11 in sealing material sheet 1 according to the present embodiment is not particularly limited, but is preferably 200 μm or more and 400 μm or less, and more preferably 250 μm or more and 350 μm or less. The lower limit of the thickness of core layer 11 in sealing material sheet 1 according to the present embodiment is preferably 200 μm or more, and more preferably 250 μm or more. The upper limit of the thickness of core layer 11 in sealing material sheet 1 according to the present embodiment is preferably 400 μm or less, and more preferably 350 μm or less.

[0033] When second skin layer 12b is laminated on the substrate side of sealing material sheet 1 according to the present embodiment, the thickness of second skin layer 12b is not particularly limited, but is preferably from 1 / 20 to 1 / 3, and more preferably from 1 / 15 to 1 / 4, of the total thickness of sealing material sheet 1. This can further enhance adhesion to other laminate members such as a substrate or a processor.

[0034] By providing a skin layer (first skin layer 12a) containing a polypropylene resin and providing a functional layer on the surface of this skin layer, an encapsulant sheet can be obtained that can enhance adhesion to the functional layer. The surface roughness Ra of the skin layer containing a polypropylene resin is preferably 15.0 μm or less, and more preferably 12.0 μm or less. By providing a surface roughness Ra of the skin layer of 10.0 μm or less, it is possible to further enhance adhesion to the functional layer.

[0035] The encapsulant sheet for a system board on which a processor is mounted may be applied to computers including boards for system PCs used in data centers that handle large volumes of data on the cloud, desktop computers, notebook computers, etc., and may also be applied to compact electronic devices such as tablet computers, smartphones, telephones (including mobile phones and stationary telephones), game consoles (including portable game consoles and stationary game consoles), music players, car navigation systems, PDAs, etc. It may also be applied to system boards on which processors for controlling various home appliances and transportation vehicles are mounted.

[0036] The following describes an encapsulant composition used in producing the core layer 11 and skin layers (first skin layer 12a, second skin layer 12b) that constitute the encapsulant sheet 1 according to the present embodiment. The encapsulant sheet 1 according to the present embodiment will be described in detail later, but can be produced, for example, by melt-molding the encapsulant composition described in detail below.

[0037] [Encapsulant composition for forming core layer] The encapsulant composition for forming the core layer used in producing the "encapsulant sheet" according to this embodiment is a resin composition having a polyethylene resin (preferably a low-density polyethylene resin) as a base resin. In this specification, the term "base resin" refers to the resin with the largest content ratio among the resin components of a resin composition containing the base resin. When a mixed resin is made of the same type of resin but with different densities (for example, multiple polyethylenes each with a different density), the entire mixed resin is referred to as the base resin.

[0038] The base resin of the encapsulant composition for forming the core layer can be selected from a wide variety of polyethylene resins, among which low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene linear low-density polyethylene (M-LLDPE), and various other polyethylene resins are preferably used.

[0039] The density of the polyethylene resin used as the base resin of the "encapsulant composition for forming the core layer" is 0.880 g / cm 3 More than 0.930g / cm 3 Preferably, it is 0.880 g / cm or less. 3 More than 0.925g / cm 3 Preferably, it is 0.880 g / cm or less. 3 More than 0.920g / cm 3 The upper limit of the density of the polyolefin resin used as the base resin of the "encapsulant composition for forming a core layer" is 0.930 g / cm or less. 3 Preferably, it is 0.925 g / cm or less. 3 Preferably, it is 0.920 g / cm or less. 3 The density of the base resin of the encapsulant composition is more preferably 0.880 g / cm or less. 3 By setting the density to 0.930 g / cm or more, the heat resistance of the sealing material sheet can be stably improved to a sufficient level. 3 By setting the thickness as follows, it is possible to improve the adhesiveness to other laminated members such as a substrate and a processor.

[0040] The MFR of the polyethylene resin used as the base resin of the "encapsulant composition for forming a core layer" is not particularly limited, but is preferably 2.0 g / 10 min or more and 5.0 g / 10 min or less, more preferably 2.2 g / 10 min or more and 4.5 g / 10 min or less, and even more preferably 2.3 g / 10 min or more and 4.0 g / 10 min or less. When the polyethylene resin used as the base resin of the "encapsulant composition for forming a core layer" has an MFR of 5.0 g / 10 min or less, the encapsulant sheet can be provided with the necessary heat resistance, and when the polyethylene resin used as the base resin of the "encapsulant composition for forming a core layer" has an MFR of 2.0 g / 10 min or more, the encapsulant sheet can be provided with the necessary molding properties.

[0041] Furthermore, the term "polyethylene resin" as used herein includes not only ordinary polyethylene obtained by polymerizing ethylene, but also resins obtained by polymerizing compounds having ethylenically unsaturated bonds such as α-olefins, resins obtained by copolymerizing a plurality of different compounds having ethylenically unsaturated bonds, and modified resins obtained by grafting other chemical species onto these resins.

[0042] Among these, a "silane copolymer (silane-modified resin) obtained by copolymerizing an α-olefin and an ethylenically unsaturated silane compound as a comonomer" can be preferably used as part of the base resin of the "encapsulant composition for forming a core layer." By using such a resin, it is possible to obtain a sufficiently strong adhesive strength between the "encapsulant sheet" and other laminate members such as the substrate or processor, particularly when the core layer is brought into contact with the substrate.

[0043] The content of the ethylenically unsaturated silane compound in the copolymer (silane-modified resin) of an α-olefin and an ethylenically unsaturated silane compound is, for example, preferably 0.001% by mass to 15% by mass, more preferably 0.01% by mass to 5% by mass, and even more preferably 0.05% by mass to 2% by mass, based on the total copolymer mass. The lower limit of the content of the ethylenically unsaturated silane compound in the copolymer (silane-modified resin) of an α-olefin and an ethylenically unsaturated silane compound is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.05% by mass or more, based on the total copolymer mass. The upper limit of the content of the ethylenically unsaturated silane compound in the copolymer (silane-modified resin) of an α-olefin and an ethylenically unsaturated silane compound is preferably 15% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less, based on the total copolymer mass.

[0044] [Other added ingredients] An adhesion improver can be added to the encapsulant composition as appropriate. As the adhesion improver, a known silane coupling agent can be used, but a silane coupling agent having an epoxy group (hereinafter also referred to as an "epoxy-based silane coupling agent") or a silane coupling agent having a mercapto group (hereinafter also referred to as a "mercapto-based silane coupling agent") can be particularly preferably used.

[0045] The encapsulant composition may further contain other components, such as a weather-resistant masterbatch for imparting weather resistance to the encapsulant sheet, a thermally conductive filler, a crosslinking agent, a crosslinking aid, a light stabilizer, an ultraviolet absorber, a heat stabilizer, a flame retardant, a colorant, an antioxidant, and a nucleating agent.

[0046] Among these, the inclusion of a thermally conductive filler makes it possible to dissipate heat generated from various parts of the processor, etc. Examples of thermally conductive fillers include metal oxides such as zinc oxide, magnesium oxide, aluminum oxide, and titanium oxide, metal nitrides such as aluminum nitride and boron nitride, silicon compounds such as silicon oxide, and diamond.

[0047] When other components are contained in the encapsulant composition, the content of each of these components varies depending on the particle shape, density, etc., but is preferably within a range of approximately 0.001% by mass or more and 5% by mass or less in the encapsulant composition.

[0048] [Sealant composition for first skin layer] The encapsulant composition for the skin layer (first skin layer) to be placed on the functional layer stack side used in manufacturing the "encapsulant sheet" of this embodiment is a resin composition having a base resin containing a polypropylene-based resin (preferably unstretched polypropylene).

[0049] The polypropylene-based resin is contained, for example, in an amount of 50% by mass or more of the total amount of the base resin. As the polypropylene-based resin, it is preferable to use a homopolypropylene (homoPP) resin. HomoPP is a polymer consisting only of simple polypropylene and has high crystallinity, resulting in excellent rigidity. By using this for the first skin layer arranged on the functional layer lamination side, it is possible to effectively prevent the occurrence of irregularities on the surface of the first skin layer, thereby improving adhesion to the functional layer even when the functional layer is laminated on the surface of the first skin layer.

[0050] The density of the polypropylene resin used as the base resin of the "encapsulant composition for the first skin layer" is 0.890 g / cm 3 More than 0.930g / cm 3 Preferably, it is 0.890 g / cm or less. 3 More than 0.925g / cm 3 Preferably, it is 0.890 g / cm or less. 3 More than 0.920g / cm 3 The upper limit of the density of the polypropylene resin used as the base resin of the "encapsulant composition for the first skin layer" is 0.930 g / cm or less. 3 Preferably, it is 0.925 g / cm or less. 3 Preferably, it is 0.920 g / cm or less. 3 More preferably, it is:

[0051] The MFR at 230°C of the polypropylene-based resin used as the base resin of the "sealant composition for the first skin layer" is not particularly limited, but is preferably 2.0 g / 10 min to 20.0 g / 10 min, more preferably 4.0 g / 10 min to 17.0 g / 10 min, and even more preferably 5.0 g / 10 min to 15.0 g / 10 min. When the polypropylene-based resin used as the base resin of the "sealant composition for the first skin layer" has an MFR of 20.0 g / 10 min or less, the occurrence of unevenness on the surface of the skin layer can be more effectively suppressed, thereby further improving adhesion to the functional layer even when the functional layer is laminated on the surface of the skin layer. When the polypropylene-based resin used as the base resin of the "sealant composition for the first skin layer" has an MFR of 2.0 g / 10 min or more, film formation of the skin layer can be facilitated.

[0052] The content of the polypropylene resin is preferably 60% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 70% by mass or more, of the total amount of the base resin.

[0053] The "encapsulant composition for the first skin layer" may contain a resin other than the polypropylene-based resin. Examples of the resin other than the polypropylene-based resin include a wide range of polyethylene-based resins that can be used as the base resin of the encapsulant composition for forming the core layer.

[0054] The content of the resin different from the polypropylene resin is preferably less than 40% by mass, more preferably less than 35% by mass, and even more preferably less than 30% by mass, of the total amount of the base resin.

[0055] [Sealant composition for second skin layer] The encapsulant composition for the skin layer (second skin layer 12b) placed on the substrate stack side used in manufacturing the "encapsulant sheet" of this embodiment can be the same as the encapsulant composition for forming the core layer described above.

[0056] As with the encapsulant composition for forming the core layer described above, a "silane copolymer (silane-modified resin) obtained by copolymerizing an α-olefin with an ethylenically unsaturated silane compound as a comonomer" can be preferably used as part of the base resin of the encapsulant composition. By using such a resin, sufficient adhesive strength can be obtained between the "encapsulant sheet" and other laminate members such as a substrate or a processor.

[0057] Furthermore, by including a silane copolymer (silane-modified resin) as part of the base resin of the encapsulant composition, it is possible to provide sufficient adhesive strength (adhesion) between other laminated members and the "encapsulant sheet" while also imparting peelability to the substrate. This allows the encapsulant sheet to be relatively easily peeled off without damaging the various components mounted on the system board, which facilitates re-attachment of the encapsulant sheet to the system board during system board manufacture and promotes reuse (recycling) of some components, such as the encapsulant sheet and various components mounted on the system board.

[0058] The preferred content of the ethylenically unsaturated silane compound when constituting the copolymer of an α-olefin and an ethylenically unsaturated silane compound (silane-modified resin) is the same as that of the encapsulant composition for forming the core layer described above.

[0059] The encapsulant composition for the skin layer (second skin layer) disposed on the substrate lamination side may contain other additive components. The types and preferred contents of the other additive components are the same as those of the encapsulant composition for forming the core layer described above.

[0060] <Method of manufacturing encapsulant sheet> The "encapsulant sheet" according to the present embodiment can be produced by a method of melt-molding the "encapsulant composition" described in detail above. The encapsulant composition can be melt-molded by known molding methods, specifically, various molding methods such as injection molding, extrusion molding, blow molding, compression molding, and rotational molding. When the encapsulant sheet is a multilayer sheet, an example of the sheet formation method is a method of molding by co-extrusion using three types of melt-kneading extruders. The lower limit of the molding temperature during molding may be any temperature as long as it exceeds the melting point of the encapsulant composition.

[0061] The melt molding temperature in the production of the encapsulant sheet is preferably at least 30°C higher than the melting point of the resin with the highest melting point among the base resins of the encapsulant composition contained in the encapsulant composition. Specifically, a high temperature of 175°C to 230°C is preferred, and a high temperature in the range of 190°C to 210°C is more preferred.

[0062] Even when the encapsulant composition contains a small amount (for example, less than 0.5% by mass) of a crosslinking agent, the gel fraction of the resulting encapsulant sheet is 25% or less, preferably 10% or less, and more preferably 1% or less, including zero. By setting the gel fraction to 10% or less, it is possible to effectively prevent gel generation during film formation and improve film formability. Furthermore, by setting the gel fraction to 1% or less, it is possible to improve the embedding ability of the encapsulant sheet in the modularization process, i.e., its ability to conform to irregularities.

[0063] 2. System board The system board 10 of this embodiment is implemented by placing a processor 21 on a substrate 20 as shown in FIG. 2, and the system board 10 of this embodiment includes an encapsulant sheet 1 that covers the processor and is laminated on the substrate.

[0064] More specifically, when the encapsulant sheet is composed of two layers, a core layer and a skin layer (first skin layer), the encapsulant sheet 1 is stacked on the substrate 20 and the processor 21 so that the core layer is positioned on the substrate stacking side and the skin layer (first skin layer) is positioned on the functional layer stacking side of the system substrate 10.

[0065] Furthermore, when the encapsulant sheet is composed of three layers having a first skin layer, a core layer, and a second skin layer, the encapsulant sheet 1 is laminated on the substrate 20 and the processor 21 so that the second skin layer is positioned on the substrate lamination side and the first skin layer is positioned on the functional layer lamination side of the system substrate 10.

[0066] The system substrate 10 can be manufactured by sequentially stacking components including an encapsulant sheet, integrating them by vacuum suction or the like, and then heat-pressing the above components into an integrated molded body using a molding method such as lamination.

[0067] Furthermore, a functional layer 30 can be disposed and laminated on the surface of the first skin layer 12a of the system substrate according to this embodiment. The functional layer 30 is not particularly limited, but examples thereof include an electromagnetic reflection shield that can reflect electromagnetic waves to suppress electromagnetic interference, and a heat dissipation pad or heat sink for dissipating heat generated from various components such as a processor.

[0068] Another method for providing a functional layer on the surface of a skin layer containing a polypropylene-based resin as a base resin is to laminate it via an adhesive. Laminating the skin layer and functional layer via an adhesive layer can provide releasability to the functional layer. This allows the functional layer to be relatively easily peeled off without damaging the functional layer or the encapsulant sheet, allowing for reattachment to the encapsulant sheet during system substrate manufacturing or for promoting reuse (recycling) of the functional layer. [Example]

[0069] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0070] <Manufacturing of sealing material sheets for system boards> Polyethylene resins 1 to 5 (represented as "PE1 to 5" in the table) and polypropylene resin (represented as "PP" in the table) were prepared as base resins. The densities, molar numbers of α-olefins, carbon numbers, and MFR at 190°C of PE1 to 5 and PP are as shown in Table 1.

[0071] [Table 1]

[0072] Among the polyethylene resins 1 to 5, PE1 was a silane-modified polyethylene resin obtained as follows: Specifically, the silane-modified polyethylene resin PE1 had a density of 0.898 g / cm 3 The resin was obtained by mixing 95 parts by mass of a metallocene-based linear low-density polyethylene resin having an MFR of 3.5 g / 10 min with 5 parts by mass of vinyltrimethoxysilane and 0.15 parts by mass of dicumyl peroxide as a radical generator (reaction catalyst), and then melting and kneading the mixture at 200°C.

[0073] In the above table, PE5 is a low-density polyethylene resin (LDPE), and PP is a homopolymer resin.

[0074] The encapsulant composition raw materials described below were mixed in the proportions shown in Table 2 below to form the encapsulant compositions for the encapsulant sheets of the Examples and Comparative Examples. Each encapsulant composition was extruded using a film molding machine equipped with a 30 mm diameter extruder and a 200 mm wide T-die at an extrusion temperature of 210°C and a take-up speed of 1.1 m / min to produce a resin sheet. The encapsulant sheets of the Examples and Comparative Examples were manufactured using these resin sheets. The total thickness of each encapsulant sheet in the Examples and Comparative Examples was 450 μm. In Table 2, the contents of PE1 to PE5 and PP are expressed in parts by mass relative to 100 parts by mass of the base resin, and the contents of other additives (silane coupling agent, crosslinking agent, UV absorber, light stabilizer) are expressed in % by mass relative to the total amount of the encapsulant composition.

[0075] In Examples 1 and 2, the encapsulant sheet had a two-layer structure (first skin layer / core layer), in Example 3, the encapsulant sheet had a three-layer structure (first skin layer / core layer / second skin layer), and in Comparative Examples 1 and 2, the encapsulant sheet had a single-layer structure.

[0076] [Table 2]

[0077] The ultraviolet absorber in Table 2 is KEMISORB79. The light stabilizer in Table 2 is KEMISTAB 62 (HALS).

[0078] The Vicat softening point, Shore A hardness (JIS K6253), melt viscosity, thickness, volume resistivity, water absorption, water vapor permeability, and gel fraction were measured for the encapsulant sheets of the examples and comparative examples listed in Table 2. The measurement results are shown in Table 3.

[0079] The Vicat softening point was measured using a 533HDT testing device 6M-2 manufactured by Toyo Seiki Seisakusho. The Shore A hardness was measured using an EA617DK-1 manufactured by ESCO. The melt viscosity was measured using a Capillograph 1D PMD-C manufactured by Toyo Seiki Seisakusho. The volume resistivity was measured using an ADC Digital Ultra-High Resistance / Micro Current Meter 5450 in accordance with JIS K6911-1995 at a temperature of 23° C. and after 30 seconds of application of a voltage of 500 V. Regarding the water absorption rate, the encapsulant sheet test piece was immersed in water (ion-exchanged water) at 60°C, and the water absorption rate ((Aba - Abb) / Abb × 100) (%) was calculated from the ratio of the increase in weight Aba when saturated to the weight Abb before immersion in water (ion-exchanged water) (in a dry state). Water vapor permeability (g / (m 2·day) was measured using a water vapor transmission rate measuring device (manufactured by Mocon, product name "PERMATORAN-W 3 / 31") under measurement conditions of 40°C and 90% RH in accordance with JIS K 7129 Method B. Water vapor permeability2 (g / (m 2 ·day) was measured using a water vapor transmission rate measuring device (manufactured by Mocon, product name "PERMATORAN-W 3 / 31") under measurement conditions of 50°C and 90% RH in accordance with JIS K 7129 Method B. The gel fraction was determined by placing 0.1 g of the encapsulant sheet in a resin mesh, extracting it with toluene at 60°C for 4 hours, removing it from the resin mesh, drying it, weighing it, and comparing the masses before and after extraction to determine the mass % of the remaining insoluble matter.

[0080] <Evaluation example 1: Molding characteristics 1> A lead wire (250 μm diameter) was placed on the surface of a flat-surfaced white tempered glass plate, and each of the sealing material sheets of the Examples and Comparative Examples, cut to 150 mm × 150 mm, was laminated over the lead wire. The resulting laminate was subjected to a vacuum heating lamination process (vacuum lamination process) at a set temperature of 150°C, evacuation for 3 minutes, release of the upper chamber to atmospheric pressure, and vacuum pressure for 7 minutes to obtain an evaluation sample for each Example and Comparative Example. The resin temperature (achieved temperature) of the sealing material sheet during lamination during this heat treatment was 147°C. These evaluation samples were visually observed, and the molding properties were evaluated according to the following evaluation criteria. (Evaluation criteria) A: The encapsulant sheet completely conforms to the irregularities of the facing substrate surface, and no voids are observed. B: 2mm 2 Up to five bubbles were observed. C: A part of the encapsulant sheet did not completely conform to the unevenness of the facing substrate surface, and a defective lamination part (void) was formed in the vicinity of the lead wire. The evaluation results are shown in the table below as "Molding Properties 1."

[0081] <Evaluation example 2: Molding characteristics 2> The molding characteristics were evaluated in the same manner and with the same evaluation criteria as in Molding Characteristics 1 above, except that epoxy-like chip-shaped molded bodies, 2 cm long, 1.5 cm wide, and 1.5 mm thick, were arranged in a 3 x 3 array with a 3 mm gap between them on a 1.2 mm thick glass epoxy substrate, assuming a CPU. The evaluation results are shown in the table below as "molding properties 2."

[0082] <Evaluation Example 3: Adhesion retention rate against humidity and heat> A 450 μm thick encapsulant sheet of each of the Examples and Comparative Examples was vacuum laminated and adhered to a 1.2 mm thick glass epoxy substrate using a diaphragm-type vacuum laminator with upper and lower chambers at a temperature of 150°C, under the following conditions: vacuuming for 5 minutes (both upper and lower chambers were vacuumed from 100 kPa to 0.1 Pa or less), pressing for 10 seconds (upper chamber pressure: 0.1 Pa to 100 kPa over 10 seconds, lower chamber maintained at 0.1 Pa or less), and maintaining the pressure for 7 minutes (upper chamber pressure: 100 kPa, lower chamber maintained at 0.1 Pa or less). After cooling to room temperature and storing in a humidity and heat test environment at 85°C and 85% humidity, the encapsulant sheets of each of the Examples and Comparative Examples were cut to 15 mm widths, and the adhesion strength was measured at 180° peeling using a Tensilon universal material testing machine (manufactured by A&D Co., Ltd.). The retention rate (Adb / Adb×100) (%) was calculated from the ratio of the adhesion strength Ada after the wet heat test to the adhesion strength Adb before the wet heat test, and is shown in the table below as "wet heat resistant adhesion retention rate."

[0083] <Evaluation Example 4: Heat Creep Resistance> To evaluate heat resistance, a "heat creep test" was conducted using the method described below. In the "heat creep test," one encapsulant sheet cut to 75mm x 50mm was laminated on a 250mm square piece of semi-tempered glass, followed by another 75mm x 50mm piece of semi-tempered glass. The laminate was then pressed together at 150°C for 15 minutes using a vacuum laminator used for manufacturing solar cell modules. The laminate sample was then left standing vertically in an oven at 140°C for 12 hours, and the distance (mm) that the semi-tempered glass shifted was measured. The measurement results are shown in the table below as "heat creep."

[0084] <Evaluation Example 5: Adhesion evaluation to functional layer> The encapsulant sheets of Examples 1 to 3 and Comparative Examples 1 and 2 were evaluated for adhesion to a functional layer (electromagnetic wave shielding layer: a copper foil (12 μm thick) and a PET (100 μm thick) laminated together with a two-component curing adhesive, followed by photolithography to form a grid-shaped electromagnetic wave shielding material with a copper foil line width of 100 μm and a copper foil-free width of 2 mm). Specifically, the surface of the encapsulant sheet of Examples 1 to 3 (the substrate lamination side) not having the first skin layer was placed opposite the surface of the system board on which the processor was mounted, and the encapsulant sheet was laminated on the board so as to cover the processor, thereby forming an integral structure. An electromagnetic wave reflective sheet was then adhered as a functional layer to the surface of the first skin layer located on the uppermost surface of the system board via a 25 μm thick adhesive layer formed from an acrylic pressure-sensitive adhesive, and the adhesion between the encapsulant sheet and the functional layer was evaluated according to the following evaluation criteria. The evaluation results are shown in the table below as "adhesion."

[0085] For the encapsulant sheets of Comparative Examples 1 and 2, which did not have a first skin layer, one surface of the encapsulant sheet was placed opposite the surface of the system board on which the processor was mounted, and the encapsulant sheet was laminated on the board so as to cover the processor, thereby forming an integral unit. An electromagnetic wave reflecting sheet was adhered to the top surface of the encapsulant sheet on the system board as a functional layer, and the adhesion between the encapsulant sheet and the functional layer was evaluated according to the evaluation criteria below.

[0086] [Evaluation criteria] ◯: The encapsulant sheet and the functional layer were in close contact with each other with no gaps. ×: Gaps were partially generated between the encapsulant sheet and the functional layer.

[0087] <Evaluation Example 6: Evaluation of releasability> The encapsulant sheets of the Examples and Comparative Examples adhered in Evaluation Example 5 were left in an environment of 23°C and 60% Rh for 168 hours, after which the functional layers were peeled off and the releasability of the functional layers was evaluated visually. The evaluation results are shown in the table below as "releasability".

[0088] [Evaluation criteria] ◯: The functional layer was released cleanly at the interface between the encapsulant sheet and the functional layer. ×: The functional layer was not released cleanly at the interface between the encapsulant sheet and the functional layer, and the peeled surface was torn.

[0089] [Table 3]

[0090] As can be seen from the above table, the sealing material sheet has a multilayer structure including a core layer containing a polyethylene-based resin as a base resin and a skin layer containing a polypropylene-based resin as a base resin, so that even when a functional layer is laminated on the surface of the sealing material sheet, the formation of partial gaps between the sealing material sheet and the functional layer is suppressed, thereby improving adhesion to the functional layer. [Explanation of symbols]

[0091] 1. Encapsulating material sheet 11 Core layer 12 Skin Layer 12a First Skin Layer 12b Second Skin Layer 10 system board 20 Substrate 21 processors

Claims

1. An encapsulant sheet for a system board on which a processor is mounted, a multilayer structure including a core layer and a skin layer, the core layer contains a polyethylene-based resin as a base resin, the skin layer contains a polypropylene-based resin as a base resin and further contains a silane-modified polyethylene resin; The Vicat softening point of the encapsulant sheet measured from the side where the substrate is placed is in the range of 30°C or higher and 100°C or lower. Encapsulating sheet.

2. The surface roughness Ra of the skin layer is 15 μm or less. The encapsulant sheet according to claim 1 .

3. A system board including a processor, A substrate; a processor disposed on a surface of the substrate; The sealing material sheet according to claim 1 or 2; Equipped with The encapsulant sheet is laminated on the substrate, covering the processor, with the core layer positioned closer to the substrate than the skin layer. System board.

4. A functional layer is provided on the surface of the skin layer of the sealing material sheet. The system board according to claim 3 .

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