Coating agent and method for manufacturing module using the same

Abstract

[Technical Problem] Provide an electronic component that has thermal insulation and insulation resistance and can be preferably used in modularization processes such as injection molding. [Solution] Provide an electronic component comprising: a circuit substrate on which electronic components are mounted; and a coating layer covering the surface of the circuit substrate, wherein the coating layer contains at least a thermoplastic resin and hollow particles, and the coating layer has a concentration gradient of the hollow particles in the thickness direction, wherein the concentration gradient causes the content of the hollow particles in the coating layer to decrease on the side of the coating layer that contacts the circuit substrate.

Description

Technical Field

[0001] The present invention relates to a coating agent, and more particularly to a coating agent for protecting electronic components having various electronic elements mounted on a circuit board from heat, and a method for manufacturing a module using the coating agent. Background Art

[0002] Conventionally, automotive ECUs typically consist of a circuit board with electronic components such as semiconductors mounted on it, and a housing that houses the circuit board. The electronic components, such as their terminals, are soldered to the wiring pattern of the circuit board to secure them. The housing typically includes a base that secures the circuit board, as described in Patent Document 1, and a cover mounted on the base to enclose the circuit board.

[0003] In recent years, due to space limitations, there has been a need to miniaturize such in-vehicle control devices. Consequently, the need for device miniaturization has increased. For example, Patent Document 2 discloses a method in which a circuit substrate with various electronic components mounted on the substrate is placed in an injection molding mold, and the circuit substrate is sealed with a thermoplastic resin to form a single unit, thereby forming a module.

[0004] However, to address environmental concerns, lead-free solder has been increasingly used in recent years. Such lead-free solder is known to generate whiskers over time. In the automotive field, for example, as circuit boards become smaller, electronic circuits also become smaller. In circuit boards using lead-free solder, the growth of whiskers can cause short circuits between adjacent electronic components or between solders. To address this issue, Patent Document 3 and other publications have proposed coating the solder with hollow particles.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2017-38343

[0008] Patent Document 2: Japanese Patent Application Publication No. 2012-151296

[0009] Patent Document 3: Japanese Patent Application Publication No. 2013-131559 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] While attempting to reduce the space inevitably created between the electronic components and the exterior by sealing the circuit substrate with a thermoplastic resin through in-mold molding, rather than using an exterior body to protect the circuit substrate, the inventors discovered that the solder on the circuit substrate remelted due to heat from the molten resin or mold during in-mold molding, creating a risk of poor contact between the solder and the substrate, a manufacturing problem. Therefore, the inventors attempted to coat the solder by applying a coating containing hollow particles and a thermoplastic resin, as disclosed in Patent Document 3, to the surface of the circuit substrate. While the coating was able to suppress the transfer of heat from in-mold molding to the electronic components, it presented a new technical problem: the volume resistivity of the coating decreased, reducing the insulation resistance of the electronic substrate.

[0012] Therefore, an object of the present invention is to provide an electronic component that has heat insulation and insulation resistance and can be preferably used for modularization by injection molding or the like.

[0013] At the same time, another object of the present invention is to provide a method for manufacturing the electronic component, a module using the electronic component, and a method for manufacturing the module.

[0014] Technical solutions to solve problems

[0015] As a result of intensive research to solve the above-mentioned technical problems, the present inventors have discovered that the reason for the reduction in volume resistivity is the hollow particles contained in the coating. Furthermore, the present inventors have discovered that by providing a concentration gradient of the hollow particles in the coating layer in the thickness direction so that the content of the hollow particles decreases on the side in contact with the circuit board, it is possible to simultaneously ensure excellent thermal insulation and high volume resistivity, and have completed the following invention. The main points of the present invention are shown in the following [1] to

[13] .

[0016] [1] An electronic component comprising: a circuit board on which an electronic element is mounted, and a coating covering a surface of the circuit board, wherein:

[0017] The coating contains at least a thermoplastic resin and hollow particles,

[0018] The coating layer has a concentration gradient of hollow particles in a thickness direction, and the concentration gradient causes the content of the hollow particles in the coating layer to decrease on a side of a surface of the coating layer in contact with the circuit substrate.

[0019] [2] The electronic component according to [1], wherein the coating comprises at least:

[0020] The first layer has a hollow particle content of less than 1% by mass, and the second layer has a hollow particle content of 1% by mass or more.

[0021] [3] The electronic component according to [1] or [2], further comprising a third layer on the coating layer, the third layer having a hollow particle content of 0% by mass or more.

[0022] [4] The electronic component according to [2] or [3], wherein the first layer is provided on a surface in contact with the circuit substrate.

[0023] [5] The electronic component according to any one of [1] to [4], wherein the hollow particles contain an acrylic resin.

[0024] [6] The electronic component according to any one of [2] to [5], wherein the second layer has a thermal conductivity of less than 0.2 W / m·K.

[0025] [7] The electronic component according to any one of [2] to [6], wherein the first layer has 3×10 9 Volume resistivity above MΩ·cm.

[0026] [8] The electronic component according to any one of [1] to [7], wherein the coating layer has a thickness of 50 to 500 μm.

[0027] [9] A method for manufacturing an electronic component, which is a method for manufacturing the electronic component according to any one of [2] to [8], the method comprising:

[0028] A step of applying a first layer forming composition to a surface of a circuit board on which an electronic component is mounted to form a first layer, and

[0029] A step of applying a second layer-forming composition on the surface of the first layer to form the second layer.

[0030]

[10] The method as described in [9], wherein the coating is an immersion treatment.

[0031]

[11] The method according to [9] or

[10] , wherein the coating film is dried after the first layer-forming composition is applied, and the first layer-forming composition is repeatedly applied on the coating film.

[0032]

[12] A module comprising the electronic component according to any one of [1] to [8], and an exterior body covering a surface of the electronic component.

[0033]

[13] A method for manufacturing a module, which is a method for manufacturing the module described in

[12] ,

[0034] The method includes: arranging the electronic component in a mold and performing injection molding to form an outer body to cover the surface of the electronic component.

[0035] Effects of the Invention

[0036] According to the electronic component of the present invention, since the coating provided on the surface of the circuit substrate on which the electronic elements are mounted has a concentration gradient of hollow particles in the thickness direction which is set in such a manner that the content of hollow particles in the coating decreases on the side of the surface in contact with the circuit substrate, the portion of the coating with a higher content of hollow particles exhibits a heat-insulating effect, which can suppress the remelting of conductive adhesive components such as solder caused by the heat during injection molding and thermal degradation of the substrate (stress damage caused by thermal expansion of the resin, etc.). At the same time, the portion of the coating with a lower content of hollow particles exhibits an electrical insulating effect, and an electronic component having a circuit substrate with excellent insulation resistance can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic cross-sectional view of an electronic component according to one embodiment of the present invention.

[0038] Figure 2 This is a schematic cross-sectional view of an electronic component according to another embodiment of the present invention.

[0039] Figure 3 This is a schematic cross-sectional view showing an enlarged coating portion of an electronic component according to one embodiment of the present invention.

[0040] Figure 4 This is a schematic cross-sectional view showing an enlarged coating portion of an electronic component according to another embodiment of the present invention.

[0041] Figure 5 This is a schematic cross-sectional view showing an enlarged coating portion of an electronic component according to another embodiment of the present invention. DETAILED DESCRIPTION

[0042] Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. However, it should be noted that the embodiments described below are examples for illustrating the present invention, and the present invention is not limited to the embodiments described below.

[0043] [Electronic components]

[0044] Figure 1 FIG is a schematic cross-sectional view of an electronic component according to an embodiment of the present invention. Figure 1 As shown, the electronic component 1 comprises: a circuit substrate 20 on which electronic components 40A and 40B are mounted via solder 30A and 30B, and a coating 10. The surface of the circuit substrate 20 including the electronic components 40A and 40B is covered by the coating 10. The coating may be provided so as to cover the entire circuit substrate, but as shown in FIG. Figure 2As shown, the coating layer 10 may cover only the vicinity of the electronic components 40A and 40B to which solder is attached, which is easily affected by heat or the like.

[0045] Figure 3 This is a simplified cross-sectional view of an enlarged coating portion of an electronic component of the present invention. Figure 3 As shown, coating layer 10 contains at least thermoplastic resin 10A and hollow particles 10B. Coating layer 10 has a concentration gradient of the hollow particles in the thickness direction, such that the content of hollow particles 10B in coating layer 10 decreases toward surface 20A in contact with the circuit board. The concentration gradient in the present invention refers to a distribution of hollow particles at different locations within or between layers.

[0046] In the present invention, the part that hollow particle content is many plays heat insulation effect, can suppress the remelting of the conductive adhesive parts such as solder and the thermal degradation (stress damage etc. that resin generation thermal expansion causes) of the substrate of heat when injection molding.On the other hand, the part that hollow particle content is less plays electrical insulation effect in coating, can maintain excellent dielectric breakdown strength when making module as described later.That is, for the problem that electrical insulation is reduced by containing hollow particle, by arranging the few part of hollow particle content in coating, thus taking into account heat insulation and electrical insulation.

[0047] In an embodiment of the present invention, the coating 10 may be Figure 3 As shown in FIG. , the concentration gradient of the hollow particles is set in a form in which the content of the hollow particles gradually changes in the thickness direction, but it can also be set as Figure 4 As shown, the coating layer 10 is formed into a double-layer structure of a first layer 11 not containing hollow particles 10B and a second layer 12 containing hollow particles 10B. Figure 4 In the embodiment shown, the first layer 11 is preferably provided on the side of the surface 20A in contact with the circuit board. It should be noted that the first layer 11 does not substantially contain hollow particles, and the content of the hollow particles can be less than 1% by mass. At the same time, the second layer 12 preferably contains more than 1% by mass of hollow particles.

[0048] Furthermore, in an embodiment of the present invention, Figure 5 As shown, the coating layer may also be composed of three or more layers, for example, a first layer 11 containing no hollow particles, a second layer 13 containing hollow particles, and a third layer 14 containing hollow particles. From the perspective of balancing thermal insulation and electrical insulation, in this case, it is also preferred that the first layer 11 is provided on the side in contact with the circuit board 20A. In addition, the content of hollow particles in the second layer 13 and the third layer 14 may be the same, but from the perspective of balancing thermal insulation and electrical insulation, it is preferred that the third layer 14 contain more hollow particles than the second layer 13.

[0049] Although not shown, in the present invention, if the coating layer has three or more layers, the first layer may contain no hollow particles, the second layer may contain hollow particles, and the third layer may contain no hollow particles.

[0050] Hereinafter, the composition for forming the coating layer constituting the electronic component of the present invention will be described.

[0051] The coating layer constituting the above-mentioned electronic component can be formed by using a composition containing at least a thermoplastic resin and hollow particles, applying the composition on the surface of a circuit board on which the electronic element is mounted, and drying the composition.

[0052] <Thermoplastic resin>

[0053] As the thermoplastic resin contained in the coating composition, known materials can be used in the past, for example, synthetic resins and water-based emulsion resins can be enumerated. As synthetic resins, polyolefin resins, phenolic resins, alkyd resins, aminoalkyd resins, urea resins, silicone resins, melamine urea, resins, epoxy resins, polyurethane resins, vinyl acetate resins, acrylic resins, chlorinated rubber resins, vinyl chloride resins, fluororesins etc. can be enumerated, and one or more of the above-mentioned materials can be used or combined to use two or more thereof. From the perspective of the adhesiveness of circuit substrate and hollow particles, polyolefin resins are preferably used, more preferably polyolefin elastomers are used. As polyolefin elastomers, specifically, ethylene-propylene rubbers, chlorosulfonated polyethylene (CSM) etc. of the copolymer of propylene and alpha olefin, alpha olefin polymers, ethylene-propylene rubber (EPM), ethylene-propylene-di-rubber (EPDM) etc. can be enumerated. In addition, as water-based emulsions, silicone acrylic emulsions, polyurethane emulsions, acrylic emulsions etc. can be enumerated.

[0054] The coating-forming composition of the present invention preferably contains 5 to 40% by mass of a thermoplastic resin. From the perspective of impact protection for electronic components such as semiconductors, the amount of the thermoplastic resin is more preferably 8 to 30% by mass, and even more preferably 10 to 20% by mass. It should be noted that the amount of the thermoplastic resin herein refers to the amount of the thermoplastic resin calculated on a solids basis.

[0055] <Organic Solvents>

[0056] The coating layer forming composition may also contain an organic solvent. The organic solvent acts as a dispersion medium for dissolving or decomposing the above-mentioned thermoplastic resin, the hollow particles described below, and other components. As long as the organic solvent has such a function, it can be used without special restrictions. Considering the solubility of the thermoplastic resin, the volatilization rate, the dispersibility of the hollow particles, the compatibility with other fillers, dispersants, etc., it can be appropriately selected and used from organic solvents such as ketones, alcohols, and aromatics. Specifically, acetone, methyl ethyl ketone, alkylcyclohexanes, cyclohexene, ethylene glycol, propylene glycol, methanol, ethanol, isopropyl alcohol, butanol, benzene, toluene, xylene, ethyl acetate, butyl acetate, etc. can be listed. Among the above substances, cyclohexane having an alkyl group with 1 to 5 carbon atoms is preferably used. One of the above substances can be used or two or more thereof can be used in combination.

[0057] When a polyolefin resin is used as the thermoplastic resin, an aliphatic hydrocarbon having 1 to 12 carbon atoms is preferably used as the organic solvent from the viewpoint of solubility, and methylcyclohexane can be used particularly preferably.

[0058] The coating-forming composition of the present invention preferably contains 5 to 95% by mass of an organic solvent. From the viewpoint of ensuring fluidity during the coating process and simplification of the drying process after coating, the proportion of the organic solvent is more preferably 30 to 92% by mass, and further preferably 60 to 90% by mass.

[0059] <Hollow Particles>

[0060] The hollow particles contained in the coating-forming composition impart thermal insulation to the coating. As such hollow particles, they can be any of single-hole hollow particles or porous hollow particles. It should be noted that single-hole hollow particles refer to particles having one empty hole inside the particle. Porous hollow particles refer to particles having multiple empty holes inside the particle. The multiple empty holes in the porous hollow particles can exist independently of each other or can be interconnected.

[0061] The hollow particles preferably have a hollowness of 40 to 95% by volume, more preferably 40 to 70% by volume, and even more preferably 45 to 60% by volume, from the perspective of maintaining the heat-insulating shape after the organic solvent evaporates. It should be noted that the hollowness in the present invention is a value measured by the following method.

[0062] When the theoretical density of the material constituting the hollow particles is defined as (A), the hollowness ratio (C) can be calculated by the following formula relative to the measured value (B) of the density of the hollow particles.

[0063] C(%)=(AB) / A×100

[0064] In addition, from the viewpoint that the hollow particles are preferably coated in a state where they are uniformly dispersed in the thermoplastic resin, the hollow particles preferably have a specific gravity of 5.0 or less, and more preferably a specific gravity of 0.1 to 1.5. It should be noted that the specific gravity of the hollow particles in the present invention refers to the density of the hollow particles relative to water (1.0 / cm 3 ) density (i.e., measured value (B)). In addition, it should be further explained that, in a composition in which a thermoplastic resin and hollow particles are dissolved or dispersed in an organic solvent, if the hollow particles have a smaller specific gravity than the thermoplastic resin, then when the coating composition is applied to the surface of the circuit substrate to form a coating film, during the period until the organic solvent evaporates and the coating film dries, due to the difference in specific gravity between the thermoplastic resin and the hollow particles, the closer to the surface of the coating film, the higher the concentration of the hollow particles. Therefore, the result is as follows: Figure 3 As shown, a concentration gradient of hollow particles can be provided in the coating layer in the thickness direction, where the content of hollow particles in the coating layer decreases on the side of the surface in contact with the circuit substrate.

[0065] From the perspective of suppressing slippage, the average particle size of the hollow particles is preferably 1 to 500 μm, more preferably 5 to 100 μm, and even more preferably 10 to 70 μm. It should be noted that the average particle size in the present invention refers to the average value (D50) of the particle size of the hollow particles in a powder state measured by a laser diffraction scattering particle size distribution measurement method.

[0066] The hollow particles may be any of thermoplastic resin particles, thermosetting resin particles, organic hollow particles with a glass shell (resin hollow particles), or inorganic hollow particles such as glass particles and ceramic particles. However, from the viewpoint of mechanical properties, thermoplastic resin particles can be preferably used. Examples of thermoplastic resins that can be used as hollow particles include monomers having a styrene skeleton (styrene, p-chlorostyrene, α-methylstyrene, etc.), monomers having a (meth)vinyl group (acrylic acid, methacrylic acid, (meth)acrylates (methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, acrylic acid nitrile, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), vinyl acetate, vinyl ethers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropyl ketone, etc.), organic hollow particles having a shell thereof, such as homopolymers of monomers, or copolymers combining two or more of the above monomers.

[0067] In addition, as hollow particles, organic hollow particles with shells made of non-ethylene resins (epoxy resins, polyester resins, polyurethane resins, polyamide resins, polyimide resins, cellulose resins, polyether resins, modified rosin, etc.), mixtures of these with the above-mentioned ethylene resins, or graft copolymers obtained by polymerizing ethylene monomers in the presence of these resins can also be listed.

[0068] From the viewpoint of heat resistance, polyacrylonitrile and acrylic resins are preferably used among the above-mentioned resins.

[0069] Hollow particles may be either expandable or non-expandable. It should be noted that expandable hollow particles refer to particles whose volume (or internal pores) increases due to external stimulation such as heat.

[0070] The above-mentioned hollow particles can use commercially available products. As an example, there can be cited resin hollow particles such as Advancell EM, HB (all manufactured by Sekisui Chemical Co., Ltd.), Expancel U, E (all manufactured by Nippon Fillite Co., Ltd.), Matsumoto Microsphere F, FE (all manufactured by Matsumoto Oil and Fat Pharmaceutical Co., Ltd.), or inorganic hollow particles such as Sirinax (manufactured by Nippon Steel Industries, Ltd.), E-SPHERES (manufactured by Taiyo Cement Co., Ltd.), Hardlite (manufactured by Showa Chemical Co., Ltd.), Cenolite, Marlite, Glass Ballon (all manufactured by Bassin Industry Co., Ltd.).

[0071] The content of the hollow particles in the coating layer-forming composition is preferably 1 to 10% by mass, more preferably 3 to 8% by mass, based on solid content. Figure 4 and Figure 5 As shown, if coating is made of multilayer, then the content of the hollow particles in the composition when adjusting each coating is formed is final product. Particularly, preferably, hollow particles are not contained in the composition for forming the first layer arranged on the face side in contact with the circuit substrate.

[0072] In the coating forming composition, other ingredients other than the above-mentioned ingredients may also be contained. For example, an aliphatic amide compound may be contained. By containing an aliphatic amide compound, the dispersion stability of the thermoplastic resin and the hollow particles in the coating forming composition is improved. When the coating forming composition is applied to the circuit substrate surface and a coating is formed, the thermoplastic resin and the hollow particles are uniformly dispersed in the coating (film). As a result, it can be considered that the coating has uniform heat insulation. The aliphatic amide compound is a compound having an -NH-CO- bond in the molecule, and for example, a reactant or oligomer of a fatty acid and an aliphatic amine and / or an alicyclic amine can be cited. Since the compound with an amide bond forms a lattice-like network structure in which hydrogen bonds participate, it can be considered that the formation of this network structure is relevant to the uniform dispersion of the hollow particles.

[0073] The aliphatic amide compound is preferably a thixotropic compound. By using a thixotropic aliphatic amide compound, the hollow particles can be easily maintained in a uniformly dispersed state for a long period of time.

[0074] The aliphatic amide compound preferably used in the coating-forming composition is preferably a compound having a fatty acid polyamide structure in which the fatty acid has a long-chain alkyl group with 8 to 30 carbon atoms. The long-chain alkyl group may be either a linear group or a branched group. Furthermore, the long-chain alkyl group may be a group repeatedly linked to the long chain via carbon-carbon bonds. As specific examples, for example, the saturated fatty acid monoamides such as lauric acid amide, stearic acid amide, the unsaturated fatty acid monoamides such as oleic acid amide, N-lauryl lauric acid amide, N-stearyl stearic acid amide, the hydroxymethylamides such as hydroxymethyl stearic acid amide, methylene bisstearic acid amide, ethylene bislauric acid amide, ethylene bishydroxy stearic acid amide, the unsaturated fatty acid bisamides such as methylene bisoleic acid amide, the aromatic bisamides such as metaxylylene bisstearic acid amide, the ethylene oxide adducts of fatty acid amide, fatty acid ester amide, fatty acid ethanolamide, N-butyl-N '-stearyl urea, etc. can be enumerated, and the above-mentioned substances can be used alone, or two or more of the above-mentioned substances can be used in combination. From the viewpoint of improving the dispersibility of the hollow particles in the composition by thixotropic action, saturated fatty acid monoamide is more preferably used among these substances.

[0075] The above-mentioned aliphatic amide compounds can be commercially available ones. Examples thereof include DISPARLON 6900-20X, DISPARLON 6900-10X, DISPARLON A603-20X, DISPARLON A603-10X, DISPARLON A670-20M, DISPARLON 6810-20X, DISPARLON 6850-20X, DISPARLON 6820-20M, DISPARLON 6810-10M, DISPARLON FS-6010, DISPARLON PFA-131, and DISPARLON PFA-231 (all manufactured by Kusumoto Chemicals Co., Ltd.), Fronon RCM-210 (manufactured by Kyoei Chemical Co., Ltd.), and BYK-450 (manufactured by BYK Corporation).

[0076] The coating layer-forming composition preferably contains 0.001 to 10% by mass of the aliphatic amide compound. From the perspective of uniform dispersibility of the hollow particles, the amount of the aliphatic amide compound is more preferably 0.05 to 7% by mass, and even more preferably 0.1 to 1% by mass. It should be noted that the content of the aliphatic amide compound herein refers to the ratio of the aliphatic amide compound to the total amount of the (A) thermoplastic resin and the (B) organic solvent.

[0077] <Circuit Board>

[0078] The circuit substrate is not particularly limited, but is preferably a circuit substrate on which electronic components such as semiconductor elements, resistors, capacitors, and external connection terminals are mounted, and particularly preferably a circuit substrate constituting various electronic control units (ECUs). An electronic control unit can be prepared by mounting various electronic components such as semiconductor elements, resistors, capacitors, and external connection terminals on a circuit substrate such as a printed wiring board, and modularizing the electronic components electrically connecting the circuit substrate to each component using a conductive adhesive such as solder. Various electronic control units are preferably electronic control units for aircraft or automobiles, and more preferably sensor-related electronic control units.

[0079] Various electronic components such as semiconductor element, resistor, capacitor, and externally connected connection terminals are installed on the circuit substrate. In addition, the circuit substrate and the electronic component have been electrically connected by conductive adhesive components. As the conductive adhesive components, synthetic resins and solders containing conductive fillers can be enumerated, and solders are preferably used. The solder contains tin (Sn), and Sn-Pb alloys, Sn-Ag-Cu alloys, Sn-Zn-Bi alloys, Sn-Zn-Al alloys, etc. can be enumerated. For the consideration of the laws and regulations relevant to the environment, so-called lead-free solders such as Sn-Ag-Cu alloys, Sn-Zn-Bi alloys, and Sn-Zn-Al alloys are preferably used.

[0080] As the resin containing the conductive filler, it is preferable to use a resin containing a conductive filler such as gold, silver, copper, nickel, or aluminum in thermosetting resins such as epoxy resins and phenolic resins, or thermoplastic resins such as polyester resins, polyolefin resins, polyurethane resins, and polycarbonate resins.

[0081] From the perspective of workability when electrically connecting a circuit board to various components, the melting point of the conductive adhesive is generally 250°C or lower, preferably 220°C or lower, more preferably 200°C or lower, and even more preferably 190°C or lower. It should be noted that when a thermosetting resin or the like is used as the resin containing the conductive filler, if the melting point of the thermosetting resin cannot be measured, its heat resistance temperature may be used as a substitute.

[0082] [Method for manufacturing electronic components]

[0083] The electronic component of the present invention can be formed by applying the above-mentioned coating layer forming composition on the surface of a circuit substrate on which electronic components are mounted and drying it. Figure 4 or Figure 5 In the case of a coating composed of multiple layers as shown, first, a first layer-forming composition not containing hollow particles is applied to the surface of a circuit substrate on which electronic components are mounted to form a first layer, and then a second layer-forming composition containing hollow particles is applied to the surface of the first layer to form a second layer, thereby forming a coating composed of multiple layers.

[0084] In the case of applying the coating composition, the coating agent is applied to the electronic component in a manner that covers at least the conductive adhesive component portion of the electronic component. From the perspective of protecting various electronic components from the effects of heat, it is preferred to apply the coating composition not only to the conductive adhesive component portion but also to cover the entire circuit substrate on which the various electronic components are mounted. The coating composition can be applied to the surface of the circuit substrate by conventional methods such as screen printing, a bar coater, a knife coater, and dipping, but in the present invention, it is preferably applied by dipping.

[0085] After applying the coating layer-forming composition, the coating layer can be formed by drying the composition to remove the organic solvent. Drying can be performed at room temperature or using a hot air dryer or the like.

[0086] Furthermore, the coating and drying steps may be repeated to adjust the thickness of the coating layer. In particular, by applying the first layer-forming composition and then drying the coating film, and then repeatedly applying the first layer-forming composition and drying the coating film, the thickness of the first layer can be made greater than that of the second layer.

[0087] The thickness of the coating formed as described above is preferably 50 to 500 μm, more preferably 100 to 300 μm. Figure 4 As shown, if the coating layer consists of two layers, the first layer and the second layer, the ratio of the thickness of the first layer to the thickness of the second layer is preferably 1:1 to 3:1, more preferably 1.5:1 to 2.5:1.

[0088] In an embodiment of the present invention, Figure 4 As shown, if the coating consists of two layers, the first layer and the second layer, the first layer does not contain hollow particles and has a 3×10 9 The volume resistivity is greater than MΩ·cm. Therefore, it can be used as an electronic component with excellent insulation resistance. In addition, it should be noted that the volume resistivity refers to the value measured in accordance with JIS K6911.

[0089] Furthermore, because the second layer contains hollow particles, it has a thermal conductivity of less than 0.2 W / m·k. This prevents remelting of conductive adhesive components such as solder and thermal degradation of the substrate (such as stress fracture caused by thermal expansion of the resin) caused by the heat of injection molding. Furthermore, it should be noted that the melting point of solder is 217°C. Assuming a mold temperature of 240°C and the module is manufactured by injection molding polybutylene terephthalate, simulations were performed to calculate the thermal conductivity required to prevent the solder from being heated to temperatures above its melting point during injection molding, and the result was a thermal conductivity of less than 0.2 W / m·k.

[0090] Furthermore, as described above, by forming the coating layer into a laminated structure of a first layer not containing hollow particles and a second layer containing hollow particles, the dielectric breakdown strength thereof can be improved beyond expectation.

[0091] <module>

[0092] In order to protect the electronic components, the electronic components of the present invention can be housed in an outer casing to achieve integration to form a module. In recent years, due to the need to miniaturize the module, as an alternative to housing the electronic components in the outer casing, a solution has been used in which the electronic components themselves are sealed with thermoplastic resins and integrated to form modules. Such modules are manufactured by arranging the electronic components in a mold and performing injection molding (in-mold molding). At this time, the heat of the molten thermoplastic resin is conducted to the electronic components, sometimes causing the conductive adhesive components such as solder to remelt, and sometimes causing the electronic components to be damaged due to partial remelting of the solder or thermal expansion of the resin. If the electronic components of the present invention are used, the above-mentioned heat from the outside can be shielded, thereby suppressing the damage of the electronic components. In addition, due to its high volume resistivity, it can be made into a module with a circuit substrate having excellent insulation properties.

[0093] The module can be manufactured by coating electronic components, sensors, and connection terminals for external connection with a sealing material. In the present invention, the electronic components, sensors, and connection terminals for external connection with a sealing material can be arranged in a mold and injection molded to form an outer body of a thermoplastic resin in a manner that covers the surface of the electronic components, thereby manufacturing the module. In addition, it should be noted that the module may contain parts such as a portion of a circuit board, sensors, cables, etc. that are not coated with a sealing material. In addition, by performing so-called in-mold molding, it is possible to manufacture a module in which the electronic components are sealed by a sealing material containing a thermoplastic resin to achieve integration and a desired shape.

[0094] The sealing material is not particularly limited as long as it is a resin that can be injection molded. Examples thereof include polyacetal, polyamide, polycarbonate, polybutylene terephthalate, polyethylene terephthalate, polyphenylene sulfide, polyacrylic resin, and ABS resin. From the viewpoint of moldability and mechanical properties, polybutylene terephthalate is preferably used.

[0095] When polybutylene terephthalate is used as a sealing material, the injection molding temperature is approximately 230-270°C, which poses a risk of remelting the conductive adhesive. In the present invention, by pre-forming a coating film on the surface of the electronic component, the amount of heat transferred to the electronic component is reduced, thereby preventing damage to the electronic component caused by remelting of the conductive adhesive or thermal expansion of the resin.

[0096] Example

[0097] Hereinafter, the present invention will be described in further detail with reference to examples, but the present invention is not limited to these examples.

[0098] [Example 1]

[0099] The following coating compositions 1 and 2 were prepared as coating layer-forming compositions.

[0100] <Coating composition 1>

[0101] As coating composition 1, a mixture of a thermoplastic resin and an organic solvent (Humiseal 1B51NSLU-40 manufactured by ARBROWN CO., LTD. (14% by mass of polyolefin elastomer, 86% by mass of methylcyclohexane)) was prepared.

[0102] <Coating composition 2>

[0103] To 100 parts by mass of a mixture of a thermoplastic resin and an organic solvent (Humiseal 1B51NSLU-40 manufactured by ARBROWN CO., LTD.), 3 parts by mass of hollow particles (ADVANCEL HB2051 manufactured by SEKISUI CHEMICAL CO., LTD., material: acrylonitrile, specific gravity: 0.4 g / cm 3 , hollow ratio: 50%, average particle size: 20 μm), and 0.6 parts by mass of an aliphatic amide compound were thoroughly stirred to prepare a coating composition 2.

[0104] The polyimide film was dipped in the coating composition 1, then pulled up and dried in air at 60°C for 30 minutes. This dipping process was repeated twice, thereby forming a first layer on the surface of the polyimide film. Subsequently, the polyimide film with the first layer formed thereon was dipped in the coating composition 2, then pulled up and dried in air at 60°C for 30 minutes. This dipping process was repeated once more, thereby forming a second layer.

[0105] In the polyimide film formed with the coating obtained by the above process, the total thickness of the first layer and the second layer was 307 μm, and the thickness ratio of the first layer to the second layer was approximately 2:1.

[0106] The volume resistivity of the polyimide film on which the coating layer was formed was measured in accordance with JIS-K 6911 using ULTRA HIGH RESISTANCE METER R8340 manufactured by ADCMT.

[0107] Furthermore, the dielectric breakdown strength of the polyimide film having the coating formed thereon was measured using a voltage withstand tester manufactured by Kojima Electric Co., Ltd. in accordance with JIS C 2110-1: 2016. The evaluation results are shown in Table 1 below.

[0108] [Comparative Example 1]

[0109] Coating composition 1 was applied to a polyimide film using a bar coater and dried to evaporate the organic solvent, thereby forming only the first layer. The coating film thickness was 300 μm. The resulting sample sheet was evaluated in the same manner as in Example 1, and the thermal conductivity of the resulting coating was measured using the unsteady fine-wire heating method. The results are shown in Table 1 below.

[0110] [Comparative Example 2]

[0111] Coating composition 2 was applied to a polyimide film using a bar coater and dried to evaporate the organic solvent, thereby forming only the second layer. The coating film thickness was 300 μm. The resulting sample sheet was evaluated in the same manner as in Example 1, and the thermal conductivity of the resulting coating was measured using the unsteady fine-wire heating method. The results are shown in Table 1 below.

[0112] [Table 1]

[0113] Example 1 Comparative Example 1 Comparative Example 2 Thickness of the first layer (μm) 205 300 — Thickness of the second layer (μm) 102 — 300 Volume resistivity (MΩ·cm) <![CDATA[1.1×10 10 ]]> <![CDATA[3.8×10 10 ]]> <![CDATA[2.1×10 9 ]]> Dielectric strength (kV / mm) 48.2 45.6 34.1 Thermal conductivity (W / m·k) <![CDATA[(0.2) *1 ]]> 0.3 0.1

[0114] In addition, it should be noted that the melting point of solder is 217°C. Assuming that polybutylene terephthalate is injection molded on a substrate at a mold temperature of 240°C, simulation calculations show the thermal conductivity required to prevent the solder from being heated to a temperature above its melting point during injection molding. If the thermal conductivity is 0.2 W / m·K or less, remelting of the solder can be suppressed. Based on this result, it can be considered that a thermal conductivity of 0.2 W / m·K or less can solve the technical problem of the present invention.

[0115] From the evaluation results in Table 1, it can be seen that although the polyimide film having only a coating layer containing hollow particles (Comparative Example 2) has excellent thermal insulation properties, its volume resistivity is one order of magnitude lower than that of the polyimide film having only a coating layer without hollow particles (Comparative Example 1), and its dielectric breakdown strength is also poor.

[0116] On the other hand, the polyimide film having a first layer and a second layer (Example 1) has a concentration gradient of hollow particles in the coating in the thickness direction, which causes the content of hollow particles in the coating to decrease on the side of the surface in contact with the polyimide film. Therefore, it is found that not only the thermal insulation and volume resistivity are excellent, but also the dielectric breakdown strength is improved by lamination.

[0117] Generally speaking, the dielectric breakdown strength of air is lower than that of semiconductor coating resins. However, it is believed that by forming a layer containing hollow particles on the surface, the current is dispersed and uniformed on the surface layer, resulting in an improvement in the dielectric breakdown strength compared to a single layer.

Claims

1. An electronic component for manufacturing a module by placing the electronic component in a mold and performing in-mold molding, the electronic component comprising: a circuit substrate on which electronic elements are mounted, and a coating covering the surface of the circuit substrate, wherein: The coating contains at least a thermoplastic resin and hollow particles, The hollow particles are thermoplastic resin particles, The coating layer has a concentration gradient of hollow particles in the thickness direction, and the concentration gradient causes the content of hollow particles in the coating layer to decrease on the side of the coating layer in contact with the circuit substrate. The coating layer includes at least a first layer having a hollow particle content of less than 1% by mass and a second layer having a hollow particle content of 1% by mass or more. 2 . The electronic component according to claim 1 , further comprising a third layer on the coating layer, wherein the third layer has a hollow particle content of 0% by mass or more.

3. The electronic component according to claim 1 or 2, wherein The first layer is provided on a surface in contact with the circuit substrate.

4. The electronic component according to claim 1 or 2, wherein The hollow particles contain acrylic resin.

5. The electronic component according to claim 1 or 2, wherein The second layer has a thermal conductivity of less than 0.2 W / m·K.

6. The electronic component according to claim 1 or 2, wherein The first layer has 3×10 9 Volume resistivity above MΩ·cm.

7. The electronic component according to claim 1 or 2, wherein The thickness of the coating is 50 to 500 μm.

8. A method for manufacturing an electronic component, which is a method for manufacturing the electronic component according to any one of claims 1 to 7, the method comprising: A step of applying a first layer forming composition to a surface of a circuit board on which an electronic component is mounted to form a first layer, and A step of applying a second layer-forming composition on the surface of the first layer to form the second layer.

9. The method of claim 8, wherein: The coating is a dipping process.

10. The method according to claim 8 or 9, wherein After the first layer forming composition is applied, the coating film is dried, and the first layer forming composition is repeatedly applied on the coating film. 11 . A module comprising the electronic component according to claim 1 , and an exterior body covering a surface of the electronic component.

12. A method for manufacturing a module, which is a method for manufacturing the module according to claim 11, The method includes: placing the electronic component in a mold and performing injection molding to form an outer casing to cover the surface of the electronic component.

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