Circuit boards and their manufacturing methods, automotive electrical components, servers

Abstract

The present invention provides a circuit board insulated and protected with a thermoplastic resin that has excellent heat resistance and chemical resistance, and a method for insulating and protecting a circuit board. [Solution] A circuit board that is insulated and protected with a thermoplastic resin (A), and is used by being immersed in a coolant. Or, a circuit board that is insulated and protected with a thermoplastic resin (A), wherein the thermoplastic resin (A) is at least one selected from the group consisting of crystalline resins with a glass transition temperature of 70°C or higher and amorphous resins with a glass transition temperature of 160°C or higher.

Description

【Technical Field】 【0001】 The present invention relates to a circuit board that is subjected to an insulation protection treatment with a thermoplastic resin having excellent heat resistance and chemical resistance, and a method for insulating and protecting a circuit board. 【Background Art】 【0002】 In recent years, in xEVs such as electric vehicles, in order to improve convenience such as extending the cruising range and expanding the interior space of the vehicle, miniaturization and weight reduction of in-vehicle electrical components have been promoted. Among them, an inverter including components such as a power module, a bus bar, and a current sensor is a core component that converts power from a battery into motor output, and active research and development are being conducted on a technology called eAxle that integrates an inverter, a motor, a speed reducer, etc. into one housing. 【0003】 In the above-mentioned inverter, there is a means to make a small and lightweight inverter by mounting or incorporating components such as a power module, a bus bar, and a current sensor on a circuit board. However, heat accumulation by integrating the control circuit on one circuit board, and cooling technology to cope with heat generation by applying a SiC (silicon carbide) semiconductor with higher heat resistance and high frequency compatibility are important. 【0004】 Also in data centers, as the amount of data processed increases, the power consumption per server rack is acceleratingly increasing, and active research and development are being conducted to improve the efficiency of cooling heat generated from circuit boards and semiconductors in the server. 【0005】 Regarding the cooling of the circuit board mentioned above, one method is to immerse the circuit board in a cooling liquid, but this requires an insulating treatment that provides excellent heat resistance and chemical resistance to the circuit board. As a means of insulating treatment, for example, Patent Document 1 describes overlay molding and covering the circuit board with a stretchable film. Patent Document 2 describes a method of laminating the circuit board with a film and then simply cutting off the excess film portion. Patent Document 3 describes a stretchable thermosetting adhesive sheet for covering a circuit board. [Prior art documents] [Patent Documents] 【0006】 [Patent Document 1] Japanese Patent Publication No. 2015-228421 [Patent Document 2] International Publication No. 2019 / 216089 [Patent Document 3] Japanese Patent Publication No. 2014-80489 [Overview of the Initiative] [Problems that the invention aims to solve] 【0007】 However, Patent Document 1 does not contain any description of a means for immersing a circuit board in a cooling liquid, nor does it contain any specific description of a film material with excellent heat resistance and chemical resistance. Patent Document 2 describes a method using an acrylic resin film, and does not envision immersion in a cooling liquid. Patent Document 3 describes a thermosetting sheet, but thermosetting sheets require heat treatment for curing, which presents the problem of a long insulation treatment process. 【0008】 Therefore, the object of the present invention is to provide a circuit board that has been insulated and protected with a thermoplastic resin that has excellent heat resistance and chemical resistance, and a method for insulating and protecting a circuit board. [Means for solving the problem] 【0009】 To solve the above problems, the present invention has the following configuration. That is, (1) A circuit board that has been insulated and protected with a thermoplastic resin (A), and is used by being immersed in a cooling liquid. (2) A circuit board that has been insulated and protected with a thermoplastic resin (A), wherein the thermoplastic resin (A) is at least one selected from the group consisting of crystalline resins with a glass transition temperature of 70°C or higher and amorphous resins with a glass transition temperature of 160°C or higher. (3) The circuit board of (1), wherein the thermoplastic resin (A) is at least one selected from the group consisting of crystalline resins with a glass transition temperature of 70°C or higher and amorphous resins with a glass transition temperature of 160°C or higher. (4) A circuit board according to any one of (1) to (3), wherein the thermoplastic resin (A) has a liquid absorption rate of 0% or more and 10% or less when immersed in a coolant (a mixture of ethylene glycol and pure water in a weight ratio of 1:1) at 150°C for 250 hours. (5) The circuit board according to any one of (1) to (4), wherein the thermoplastic resin (A) mainly consists of polyphenylene sulfide, polyether ether ketone, polyphenyl sulfone, polyether sulfone, or polysulfone. (6) A method for manufacturing a circuit board according to any one of (1) to (5), wherein a sheet made of thermoplastic resin (A) is spread out and set to cover the entire circuit board, and then the sheet is molded to cover the circuit board by utilizing the pressure difference to obtain a circuit board that is insulated and protected with thermoplastic resin (A). (7) The method for manufacturing a circuit board according to (6), wherein the sheet has a tensile elongation of 50% or more at 250°C. (8) The method for manufacturing a circuit board according to (6), wherein the sheet has a tensile elongation of 50% or more at 200°C. (9) The method for manufacturing a circuit board according to (6), wherein the sheet has a tensile elongation of 50% or more at 150°C. (10) An automotive electrical component comprising a circuit board as described in (1) or (2). (11) An eAxle including the automotive electrical components described in (10). (12) An xEV including the in-vehicle electrical components described in (10). (13) A server comprising the circuit board described in (1) or (2). (14) A data center including the servers described in (13). [Effects of the Invention] 【0010】 According to the present invention, it is possible to provide a circuit board and a method for insulating and protecting a circuit board, which are insulated and protected with a thermoplastic resin that has excellent heat resistance and chemical resistance and are used by immersion in a coolant. This circuit board enables efficient cooling of automotive electronic components and servers, thereby achieving miniaturization and weight reduction. Furthermore, it enables process efficiency through a simple insulating and protecting treatment method using a sheet, and improves reliability and safety through a crack-resistant sheet. [Modes for carrying out the invention] 【0011】 The embodiments of the present invention will be described in detail below. 【0012】 The circuit board of the present invention must be insulated and protected with a thermoplastic resin (A). Specifically, the insulated and protected state refers to a state in which the surface of the circuit board on which components such as elements and coils are mounted is electrically isolated. By insulating and protecting the circuit board with thermoplastic resin (A), it is possible to safely use the circuit board even when it is immersed in a cooling liquid, as it accumulates and generates heat. It is also possible to protect the board from sand and dust from the outside. This is useful for various components, including automotive electronic components and servers. Furthermore, unlike thermosetting resins, post-curing treatment is not required, so the circuit board can be easily insulated and protected. 【0013】 The circuit board of the present invention is used by immersing it in a coolant. By immersing it in a coolant, the heat-accumulating and heat-generating circuit board can be efficiently cooled. Suitable coolants include water, ethylene / propylene glycol-based coolants such as long-life coolant (LLC), oils such as automatic transmission fluid (ATF), fluorine-based refrigerants, and insulating oils. When the circuit board of the present invention is used in a server, water is preferred from the viewpoint of heat transfer efficiency, specific heat, and environmental impact. When the circuit board of the present invention is used in an automotive electrical component, long-life coolant is preferred from the viewpoint of heat transfer efficiency, specific heat, and prevention of freezing in winter. 【0014】 The thermoplastic resin (A) used in the embodiments of the present invention is preferably at least one resin selected from the group consisting of crystalline resins with a glass transition temperature of 70°C or higher and amorphous resins with a glass transition temperature of 160°C or higher, i.e., a super engineering plastic. By insulating and protecting the circuit board with at least one resin selected from the group consisting of crystalline resins with a glass transition temperature of 70°C or higher and amorphous resins with a glass transition temperature of 160°C or higher, it is possible to perform insulating and protecting treatment with excellent heat resistance and chemical resistance, and to obtain a circuit board that can withstand immersion in a coolant. Examples of crystalline resins with a glass transition temperature of 70°C or higher and amorphous resins with a glass transition temperature of 160°C or higher include crystalline resins such as polyphenylene sulfide (hereinafter sometimes abbreviated as PPS), aromatic polyamide, liquid crystal polymer, polyether ether ketone (hereinafter sometimes abbreviated as PEEK), and polytetrafluoroethylene, as well as amorphous resins such as polyphenyl sulfone (hereinafter sometimes abbreviated as PPSU), polyether sulfone (hereinafter sometimes abbreviated as PES), polysulfone (hereinafter sometimes abbreviated as PSU), polyetherimide, and polyamideimide. Among these, from the viewpoint of durability to coolant, liquid absorption rate, and environmental impact, it is preferable to use one of the following as the main component: polyphenylene sulfide, polyether ether ketone, polyphenyl sulfone, polyether sulfone, or polysulfone. 【0015】 The thermoplastic resin (A) used in the embodiments of the present invention preferably has a liquid absorption rate of 0% or more and 10% or less when immersed in a coolant (a mixture of ethylene glycol and pure water in a weight ratio of 1:1) at 150°C for 250 hours. The upper limit of this liquid absorption rate is more preferably 8% or less, even more preferably 6% or less, particularly preferably 4% or less, and especially preferably 3% or less. A liquid absorption rate of less than 0% indicates that the thermoplastic resin (A) is partially dissolved in the coolant. By performing insulating protection treatment with a thermoplastic resin (A) having a liquid absorption rate of 0% or more and 10% or less when immersed in a coolant (a mixture of ethylene glycol and pure water in a weight ratio of 1:1) at 150°C for 250 hours, dielectric breakdown can be made less likely to occur even when the circuit board is immersed in the coolant. Here, the mixture of ethylene glycol and pure water in a weight ratio of 1:1 is used as a test coolant that mimics the composition of a long-life coolant. 【0016】 The thermoplastic resin (A) used in the embodiments of the present invention may contain other resin components, as long as the effects of the present invention are not impaired. Specific examples of other resin components include polyester resins such as polyamide, polyethylene terephthalate, polybutylene terephthalate, polycyclohexyldimethylene terephthalate, and polynaphthalene terephthalate, polyethylene, polypropylene, polytetrafluoroethylene, polyamide-imide, polyacetal, polyimide, polyetherimide, polyketone resin, liquid crystal polymer, polyetherketone resin, polythioetherketone resin, polyetheretherketone resin, olefin-based elastomer, and silicone-based elastomer. 【0017】 The circuit board of the present invention preferably undergoes an insulation protection treatment with a thermoplastic resin (A) by spreading a sheet made of the thermoplastic resin (A) so as to cover the entire circuit board and then forming the sheet to cover the circuit board by utilizing a pressure difference. By forming a sheet made of the thermoplastic resin (A) to cover the circuit board using a pressure difference, insulation treatment can be carried out simply and solvent-free, suppressing the environmental load as compared with methods such as resin coating and potting. In addition, since the sheet is flexible, the insulated resin is less likely to crack compared to the case of resin coating and potting, and a highly reliable circuit board can be obtained. As a method of forming a sheet of thermoplastic resin (A) to cover the circuit board using a pressure difference, for example, the sheet is spread and set above the circuit board so as to cover the entire circuit board, a pressure difference is generated in the upper and lower spaces surrounding the upper and lower parts of the set sheet, and the heated and softened sheet is shaped onto the circuit board; or the sheet is spread and set above the circuit board so as to cover the circuit board, vacuum suction is performed through the holes in the circuit board from the holes in the base at the lower part of the circuit board, and the heated and softened sheet is shaped onto the circuit board; or the circuit board is set in a tube and a bag made of the sheet, and the inside of the tube and the bag is depressurized to generate a pressure difference, etc. 【0018】 The sheet of the thermoplastic resin (A) used in the embodiment of the present invention preferably has a tensile elongation at 250 °C of 50% or more, more preferably 100% or more, still more preferably 150% or more, and even more preferably 200% or more. Specific examples of such sheets include unstretched sheets obtained by press-molding any of PPS, PEEK, PPSU, PES, and PSU, unstretched sheets obtained by extruding any of PPS, PEEK, PPSU, PES, and PSU heated and melted by an extruder from a T-die, taking up the formed sheet with a cooling roll, and then winding it up, and tubes obtained by inflating and molding any of PPS, PEEK, PPSU, PES, and PSU heated and melted by an extruder by blowing air simultaneously while extruding from a circular die. By using a sheet of the thermoplastic resin (A) having a tensile elongation at 250 °C of 50% or more, when forming the sheet to cover the circuit board using a pressure difference, the sheet does not break and is coated following the mounting components on the upper part of the circuit board, so that it is easy to obtain a circuit board with high reliability and high cooling efficiency when immersed in the coolant. 【0019】 The sheet of the thermoplastic resin (A) used in the embodiment of the present invention preferably has a tensile elongation at 200 °C of 50% or more, more preferably 100% or more, still more preferably 150% or more, and even more preferably 200% or more. Specific examples of such sheets include unstretched sheets obtained by press-molding any of PPS, PEEK, and PSU, unstretched sheets obtained by extruding any of PPS, PEEK, and PSU heated and melted by an extruder from a T-die, taking up the formed sheet with a cooling roll, and then winding it up, and tubes obtained by inflating and molding any of PPS, PEEK, and PSU heated and melted by an extruder by blowing air simultaneously while extruding from a circular die. By using a sheet of the thermoplastic resin (A) having a tensile elongation at 200 °C of 50% or more, when forming the sheet to cover the circuit board using a pressure difference, the sheet does not break and is coated following the mounting components on the upper part of the circuit board, so that it is easy to obtain a circuit board with high reliability and high cooling efficiency when immersed in the coolant. 【0020】 The thermoplastic resin (A) sheet used in the embodiments of the present invention preferably has a tensile elongation of 50% or more at 150°C, more preferably 90% or more, more preferably 130% or more, and even more preferably 170% or more. Specific examples of such sheets include unstretched PPS sheets obtained by press-molding PPS, unstretched sheets obtained by extruding PPS heated and melted in an extruder from a T-die, taking it up with a cooling roll for molding, and then winding it up, and tubes obtained by blowing air into a circular die while extruding PPS heated and melted in an extruder for inflation molding. By using a thermoplastic resin (A) sheet with a tensile elongation of 50% or more at 150°C, when the sheet is molded to cover the circuit board using the pressure difference, the sheet does not tear and follows and covers the mounted components on the top of the circuit board, making it easier to obtain a circuit board that is highly reliable and has high cooling efficiency when immersed in a coolant. 【0021】 The thermoplastic resin (A) sheet used in the embodiments of the present invention preferably has a tensile stress of 0.1 MPa to 30 MPa when 100% elongated at 250°C, more preferably 0.2 MPa to 25 MPa, and even more preferably 0.3 MPa to 20 MPa. Specific examples of such sheets include unstretched sheets press-molded from any of PPS, PEEK, PPSU, PES, or PSU; unstretched sheets obtained by extruding PPS, PEEK, PPSU, PES, or PSU heated and melted in an extruder from a T-die, taking them up with a cooling roll, molding, and then winding them up; and tubes obtained by extruding PPS, PEEK, PPSU, PES, or PSU heated and melted in an extruder from a circular die while simultaneously blowing air into them for inflation molding. By using a thermoplastic resin (A) sheet with a tensile stress of 0.1 MPa or more when 100% elongated at 250°C, the sagging of the thermoplastic resin (A) sheet during heating can be reduced, making it easier to shape the sheet onto a substrate. By using a thermoplastic resin (A) sheet with a tensile stress of 30 MPa or less at 100% elongation at 250°C, it becomes easier to uniformly stretch the sheet overall when shaping the heated sheet onto the substrate, and the ability to follow the shape at corners is improved. 【0022】 The thermoplastic resin (A) sheet used in the embodiments of the present invention preferably has a tensile stress of 0.1 MPa to 30 MPa when 100% elongated at 200°C, more preferably 0.2 MPa to 25 MPa, and even more preferably 0.3 MPa to 20 MPa. Specific examples of such sheets include unstretched sheets press-molded from PPS, PEEK, or PSU; unstretched sheets obtained by extruding PPS, PEEK, or PSU, heated and melted in an extruder, through a T-die, taking the material back into a cooling roll, and then winding it up; and tubes obtained by extruding PPS, PEEK, or PSU, heated and melted in an extruder, through a circular die, and simultaneously blowing air into it for inflation molding. By using a thermoplastic resin (A) sheet with a tensile stress of 0.1 MPa or higher when 100% elongated at 200°C, the sagging of the thermoplastic resin (A) sheet during heating can be reduced, making it easier to shape the sheet onto a substrate. By using a thermoplastic resin (A) sheet with a tensile stress of 30 MPa or less at 100% elongation at 200°C, it becomes easier to uniformly stretch the sheet overall when shaping the heated sheet onto the substrate, and the ability to follow the shape at corners is improved. 【0023】 The thermoplastic resin (A) sheet used in the embodiments of the present invention preferably has a tensile stress of 0.1 MPa to 30 MPa when 100% elongated at 150°C, more preferably 0.2 MPa to 25 MPa, and even more preferably 0.3 MPa to 20 MPa. Specific examples of such sheets include unstretched PPS sheets press-molded from PPS, unstretched sheets obtained by extruding heated and melted PPS from a T-die, taking it up with a cooling roll, and then winding it, and tubes obtained by blowing heated and melted PPS from a circular die while simultaneously blowing air into it for inflation molding. By using a thermoplastic resin (A) sheet with a tensile stress of 0.1 MPa or more when 100% elongated at 150°C, the sagging of the thermoplastic resin (A) sheet during heating can be reduced, making it easier to shape the sheet onto a substrate. By using a thermoplastic resin (A) sheet with a tensile stress of 30 MPa or less at 150°C when fully elongated, it becomes easier to uniformly stretch the sheet overall when shaping the heated sheet onto the substrate, and the ability to follow the shape at corners is improved. 【0024】 In the embodiments of the present invention, if the thermoplastic resin (A) is a crystalline resin, the degree of crystallinity of the thermoplastic resin (A) is preferably 5% to 30%, more preferably 10% to 25%, and even more preferably 15% to 20%. By using a thermoplastic resin (A) sheet with a degree of crystallinity of 5% or more, the liquid absorption rate when immersed in a coolant (a mixture of ethylene glycol and pure water in a weight ratio of 1:1) at 150°C for 250 hours can be set to 0% to 10%. By using a thermoplastic resin (A) sheet with a degree of crystallinity of 30% or less, the tensile elongation at 250°C can be set to 50% or more, and the tensile stress at 100% elongation at 250°C can be set to 30 MPa or less. 【0025】 In the embodiments of the present invention, the thermoplastic resin (A) sheet is preferably compounded with a black pigment. By using a thermoplastic resin (A) sheet compounded with a black pigment, when the sheet is heated using an infrared (IR) heater, the absorption wavelength band of the sheet is broadened, allowing for efficient absorption of infrared rays, thereby increasing the heating rate and shortening the molding time. 【0026】 In embodiments of the present invention, the thermoplastic resin (A) sheet used is preferably used together with an adhesive layer (B) to form a multilayer sheet. Examples of materials that constitute the adhesive layer (B) include acrylic, epoxy, olefin, urethane, silicone, rubber, polyimide, polyamide-imide, polyetherimide, and polyethersulfone. In particular, when the temperature at which the circuit board, which has been insulated and protected with thermoplastic resin (A), is used as a final product is high, it is desirable that the heat resistance temperature of the adhesive layer (B) is high. For example, when the final product is an automotive electrical component, eAxle, xEV, server, data center, etc., the circuit board may reach temperatures of 100°C or higher. In such cases, the heat resistance temperature of the adhesive layer (B) is preferably 100°C or higher, more preferably 150°C or higher, even more preferably 190°C or higher, and in some cases 230°C or higher may be required. When such high-temperature use is anticipated, among the materials that constitute the adhesive layer (B) described above, polyimide, polyamide-imide, polyetherimide, and polyethersulfone are particularly preferred as suitable materials. Among these, polyamide-imide materials are preferred because their heat resistance temperature can be controlled by their molecular structure. It is preferable to select materials with a glass transition temperature of 150°C or higher, more preferably 190°C or higher, and it is also possible to select materials with a glass transition temperature of 230°C or higher. Examples of such polyamide-imide materials include thermoplastic polyamide-imide adhesives manufactured by Resonaq Corporation (SF-10D-30, SF-21C-01, SF-32A-1010). When a sheet of thermoplastic resin (A) is coated onto a substrate and then heated, the sheet may shrink and peel off the substrate. However, by using a multilayer sheet having a sheet of thermoplastic resin (A) and an adhesive layer (B), the substrate and the multilayer sheet are fixed together, preventing shrinkage of the thermoplastic resin (A) sheet and peeling off the substrate even when heated. Therefore, it is preferable that the adhesive layer (B) has a high adhesive strength such that the multilayer sheet does not peel off when heated after the multilayer sheet containing the thermoplastic resin (A) is formed onto the substrate.On the other hand, when the circuit board of the present invention is used in a server, the multilayer sheet containing the thermoplastic resin (A) may need to be peeled off the circuit board for periodic maintenance. Therefore, it is preferable that the adhesive strength between the circuit board and the adhesive layer (B) is low enough that mounted components on the circuit board do not fall off when the multilayer sheet containing the thermoplastic resin (A) is peeled off the circuit board. Furthermore, it is preferable that the adhesive layer (B) has a large tensile elongation when heated and low tensile stress, such that after the multilayer sheet containing the thermoplastic resin (A) is spread and set to cover the entire circuit board, the multilayer sheet can be molded to cover the circuit board by utilizing the pressure difference. Methods for laminating the adhesive layer (B) onto the thermoplastic resin (A) sheet include applying a liquid obtained by dissolving or dispersing the adhesive layer (B) material in water or an organic solvent onto the thermoplastic resin (A) sheet and drying the water or organic solvent in a hot air oven, or pressing or heat-pressing the sheet-like adhesive layer (B) onto the thermoplastic resin (A) sheet. 【0027】 Applicable applications for circuit boards treated with the insulating protection treatment of the present invention include, for example, power semiconductors such as power modules, electrical and electronic components such as sensors, servers, and printed circuit boards, automotive electrical components such as inverters, electric control units, and eAxles, and various other applications such as xEVs, internal combustion vehicles, and data centers. [Examples] 【0028】 The present invention will be further described with reference to the following examples, but the present invention is not limited to the descriptions in these examples. 【0029】 The evaluation and measurement methods used in the examples are shown below. 【0030】 [Liquid absorption rate] A sheet of thermoplastic resin (A) was punched out to 50 mm x 8 mm, immersed in a cooling solution prepared by mixing ethylene glycol and pure water in a 1:1 weight ratio in an autoclave container, and then heat-treated in an oven at 150°C for 250 hours. The liquid absorption rate was calculated from the weight of the punched sheet before and after heat treatment using the following formula. A liquid absorption rate of less than 0% indicates that some of the thermoplastic resin (A) has dissolved in the cooling solution. Liquid absorption rate (%) = (Sheet weight after heat treatment - Sheet weight before immersion in coolant) / (Sheet weight before immersion in coolant) × 100 【0031】 [Tensile elongation at 250°C, 200°C, and 150°C] A sheet of thermoplastic resin (A) was punched out to 50 mm x 8 mm, and pulled at a test speed of 500 mm / min in constant temperature chambers of 250°C, 200°C, and 150°C using an Instron tensile testing machine ("INSTRON" (registered trademark) 5985). The tensile elongation at which the sheet broke was calculated as follows. Chuck distance before testing: A (20mm), Chuck distance at sheet breakage: B Tensile elongation (%) = (BA) / A × 100 【0032】 [Tensile stress at 100% elongation at 250°C, 200°C, and 150°C] A sheet of thermoplastic resin (A) was punched out to 50 mm x 8 mm, and then pulled at a test speed of 500 mm / min in constant temperature chambers of 250°C, 200°C, and 150°C using an Instron tensile testing machine ("INSTRON" (registered trademark) 5985). The tensile stress when the sheet was 100% elongated was measured. 【0033】 [Degree of crystallinity] Approximately 10 mg of a sheet of thermoplastic resin (A) was used as a sample. Using a TA Instruments DSC (Q200) with nitrogen as the carrier gas, the temperature was raised from 50°C to 340°C at a heating rate of 20°C / min. The degree of crystallinity was calculated from the observed heat of fusion (ΔHm) and heat of cold crystallization (ΔHcc) using the following formula. Crystallinity (%) = (ΔHm - ΔHcc) / Melting heat of perfectly crystalline thermoplastic resin (A) × 100 ÷ Thermoplastic resin (A) content (Melting heat of perfectly crystalline thermoplastic resin (A): 146.2 [J / g] when thermoplastic resin (A) is PPS, quoted from International Polymer Processing, 1988, Vol.3, No.2, pp.79-85. Similarly, for thermoplastic resins (A) other than PPS, the value of the melting heat of the thermoplastic resin (A) in its perfectly crystalline state, as described in publicly available academic papers and technical reports, is used for calculation.) 【0034】 The materials used in the examples are shown below. 【0035】 (Reference Example 1) PPS1 In an autoclave equipped with a stirrer and a bottom valve, 8.27 kg (70.00 mol) of 47.5% sodium hydrosulfide, 2.94 kg (70.63 mol) of 96% sodium hydroxide, 11.45 kg (115.50 mol) of N-methyl-2-pyrrolidone (NMP), 2.24 kg (27.30 mol) of sodium acetate, and 5.50 kg of deionized water were charged. The mixture was gradually heated to 245°C over approximately 3 hours under atmospheric pressure while passing nitrogen through it. After distilling off 9.77 kg of water and 0.28 kg of NMP, the reaction vessel was cooled to 200°C. The amount of hydrogen sulfide released was 0.02 mol per mole of alkali metal sulfide charged. 【0036】 Subsequently, 10.36 kg (70.46 mol) of p-dichlorobenzene, 0.04 kg (0.20 mol) of 1,2,4-trichlorobenzene, and 9.37 kg (94.50 mol) of NMP were added. The reaction vessel was sealed under nitrogen gas, and the temperature was raised from 200°C to 270°C at a rate of 0.6°C / min while stirring at 240 rpm. The reaction was then carried out at 270°C for 140 minutes. After that, the mixture was cooled from 270°C to 250°C over 15 minutes. Then, it was gradually cooled from 250°C to 220°C over 75 minutes, and then rapidly cooled to near room temperature before the contents were removed. 【0037】 The contents were diluted with approximately 35 liters of NMP to form a slurry, which was stirred at 85°C for 30 minutes. The slurry was then filtered through an 80-mesh wire mesh (mesh opening 0.175 mm) to obtain solid material. The obtained solid material was similarly washed and filtered with approximately 35 liters of NMP. The obtained solid material was diluted with 70 liters of deionized water, stirred at 70°C for 30 minutes, and filtered through an 80-mesh wire mesh to recover the solid material. This process was repeated a total of three times. The obtained solid material and 36 g of calcium acetate were diluted with 70 liters of deionized water, stirred at 70°C for 30 minutes, and filtered through an 80-mesh wire mesh. The obtained solid material was then diluted with 70 liters of deionized water, stirred at 70°C for 30 minutes, and filtered through an 80-mesh wire mesh to recover the solid material. The solid material thus obtained was dried under a nitrogen atmosphere at 120°C to obtain PPS1 with a glass transition temperature of 90°C. 【0038】 (Reference Example 2) PPS2 In an autoclave equipped with a stirrer, 8.27 kg (70.00 mol) of 47.5% sodium hydroxide, 2.96 kg (70.97 mol) of 96% sodium hydroxide, 11.43 kg (115.50 mol) of N-methyl-2-pyrrolidone (NMP), 2.58 kg (31.50 mol) of sodium acetate, and 10.50 kg of deionized water were charged. The mixture was gradually heated to 245°C over approximately 3 hours under atmospheric pressure while passing nitrogen through it. After distilling off 14.80 kg of water and 0.28 kg of NMP, the reaction vessel was cooled to 160°C. The amount of residual water in the system per mole of alkali metal sulfide charged was 1.06 mol, including the water consumed in the hydrolysis of NMP. The amount of hydrogen sulfide released was 0.02 mol per mole of alkali metal sulfide charged. 【0039】 Next, 10.24 kg (69.63 mol) of p-dichlorobenzene, 0.55 g (0.003 mol) of 1,2,4-trichlorobenzene, and 9.00 kg (91.00 mol) of NMP were added. The reaction vessel was sealed under nitrogen gas, and the temperature was raised to 238°C at a rate of 0.6°C / min while stirring at 240 rpm. After the reaction was carried out at 238°C for 95 minutes, the temperature was raised to 270°C at a rate of 0.8°C / min. After the reaction was carried out at 270°C for 100 minutes, the temperature was cooled to 250°C at a rate of 1.3°C / min while injecting 1.26 kg (70 mol) of water over 15 minutes. After that, the temperature was cooled to 200°C at a rate of 1.0°C / min, and then rapidly cooled to near room temperature. 【0040】 The contents were removed, diluted with 26.3 kg of NMP, and the solvent and solids were filtered off using an 80-mesh sieve. The resulting particles were washed and filtered with 31.90 kg of NMP. These were then washed and filtered several times with 56.00 kg of deionized water, and finally washed and filtered with 70.00 kg of 0.05 wt% calcium acetate aqueous solution. Subsequently, the obtained hydrated PPS particles were hot-air dried at 80°C and then vacuum-dried at 120°C to obtain PPS2 with a glass transition temperature of 90°C. 【0041】 Sheet 1 of thermoplastic resin (A) The PPS1 obtained in Reference Example 1 was sandwiched between "Kapton" (registered trademark) films and melted under a pressure of 4 MPa using a press heated to 320°C. Next, the "Kapton" (registered trademark) films containing the molten PPS were transferred to a press heated to 150°C and held without pressure to crystallize. The "Kapton" (registered trademark) films were peeled off to obtain an unstretched PPS sheet with a thickness of 200 μm. The obtained thermoplastic resin (A) sheet 1 had a liquid absorption rate of 0.2%, a tensile elongation of 224% at 200°C, a tensile elongation of 181% at 150°C, a tensile stress of 20 MPa at 100% elongation at 200°C, a tensile stress of 26 MPa at 150°C, and a crystallinity of 21.7%. 【0042】 Sheet 2 of thermoplastic resin (A) The PPS1 obtained in Reference Example 1 was sandwiched between "Kapton" (registered trademark) films and melted under a pressure of 4 MPa using a press heated to 320°C. Next, the "Kapton" (registered trademark) film containing the molten PPS was transferred to a press heated to 120°C and held without pressure to crystallize. The "Kapton" (registered trademark) film was peeled off to obtain an unstretched PPS sheet with a thickness of 150 μm. The obtained thermoplastic resin (A) sheet 2 had a liquid absorption rate of 0.1%, a tensile elongation of 450% at 200°C, a tensile elongation of 414% at 150°C, a tensile stress of 5 MPa at 100% elongation at 200°C, a tensile stress of 8 MPa at 100% elongation at 150°C, and a crystallinity of 19.9%. 【0043】 Sheet 3 of thermoplastic resin (A) Using a TEX30α twin-screw extruder manufactured by Japan Steel Works Ltd., with the cylinder temperature set to 300°C and the screw rotation speed to 200 rpm, 0.3 parts by weight of carbon black was added to 100 parts by weight of PPS1 obtained in Reference Example 1 through the raw material supply port and melted. The resin extruded from the extruder was pelletized using a strand cutter, and then hot-air dried overnight at 120°C to obtain black PPS1 pellets. The obtained black PPS1 pellets were sandwiched between "Kapton" (registered trademark) films and melted under a pressure of 4 MPa using a press heated to 320°C. Next, the "Kapton" (registered trademark) film containing the molten PPS was transferred to a press heated to 120°C and held without pressure to crystallize. The "Kapton" (registered trademark) film was peeled off to obtain an unstretched PPS sheet with a thickness of 150 μm. The obtained thermoplastic resin (A) sheet 3 had a liquid absorption rate of 0.1%, a tensile elongation of 439% at 200°C, a tensile elongation of 401% at 150°C, a tensile stress of 5 MPa at 100% elongation at 200°C, a tensile stress of 8 MPa at 150°C, and a crystallinity of 19.9%. 【0044】 Sheet 4 of thermoplastic resin (A) PPSU pellets with a glass transition temperature of 220°C (BASF Japan Ltd.'s "Ultrason"® P3010) were sandwiched between "Kapton"® films and melted under a pressure of 4 MPa using a press heated to 370°C. Next, the "Kapton"® films containing the molten PPSU were transferred to a press at room temperature and held without pressure to solidify. The "Kapton"® films were peeled off to obtain a PPSU sheet with a thickness of 150 μm. The resulting thermoplastic resin (A) sheet 4 had a liquid absorption rate of 1.4%, a tensile elongation of 380% at 250°C, and a tensile stress of 2 MPa at 100% elongation at 250°C. 【0045】 Sheet 5 of thermoplastic resin (A) Using a TEX30α twin-screw extruder manufactured by Japan Steel Works Ltd., with the cylinder temperature set to 300°C and the screw rotation speed to 200 rpm, the PPS2 obtained in Reference Example 2 was fed in through the raw material supply port and melted. The resin extruded from the extruder was pelletized using a strand cutter, and then dried with hot air overnight at 120°C to obtain PPS2 pellets. The obtained PPS2 pellets were supplied to a single-screw extruder and melted at 310°C. The molten resin was filtered through a stainless steel fiber sintered filter with an average mesh size of 10 μm, and then extruded from a 900 mm wide T-die to form a sheet. Next, this sheet was wrapped around a cooling roll with a surface temperature of 100°C while being pressed with a rubber nip roll, and cooled and solidified to obtain a PPS sheet with a thickness of 150 μm. The obtained thermoplastic resin (A) sheet 5 had a liquid absorption rate of 0.1%, a tensile elongation of 441% at 200°C, a tensile elongation of 400% at 150°C, a tensile stress of 5 MPa at 100% elongation at 200°C, a tensile stress of 8 MPa at 150°C, and a crystallinity of 19.5%. 【0046】 Sheet 6 of thermoplastic resin (A) Using a TEX30α twin-screw extruder manufactured by Japan Steel Works Ltd., with the cylinder temperature set to 300°C and the screw rotation speed to 200 rpm, 0.3 parts by weight of carbon black was added to 100 parts by weight of PPS2 obtained in Reference Example 2 through the raw material supply port and melted. The resin extruded from the extruder was pelletized using a strand cutter, and then dried with hot air overnight at 120°C to obtain PPS2 pellets. The obtained PPS2 pellets were supplied to a single-screw extruder and melted at 310°C. The molten resin was filtered through a stainless steel fiber sintered filter with an average mesh size of 10 μm, and then extruded into a sheet from a 900 mm wide T-die. Next, this sheet was wrapped around a cooling roll with a surface temperature of 100°C while being pressed with a rubber nip roll, and cooled and solidified to obtain a PPS sheet with a thickness of 150 μm. The obtained thermoplastic resin (A) sheet 5 had a liquid absorption rate of 0.1%, a tensile elongation of 439% at 200°C, a tensile elongation of 398% at 150°C, a tensile stress of 5 MPa at 100% elongation at 200°C, a tensile stress of 8 MPa at 150°C, and a crystallinity of 19.6%. 【0047】 Sheet 7 of thermoplastic resin (A) The PPS1 obtained in Reference Example 1 was sandwiched between "Kapton" (registered trademark) films and melted using a press heated to 320°C under a pressure of 4 MPa. Next, the "Kapton" (registered trademark) film containing the molten PPS was rapidly cooled by immersion in ice water to obtain an amorphous PPS sheet. The obtained amorphous PPS sheet was stretched 3.5 times x 3.5 times at 103°C using an automatic biaxial stretching machine (IMC-11A9) manufactured by Imoto Seisakusho, and then heat-treated at 265°C while holding the sheet to crystallize it, obtaining a biaxially oriented PPS sheet. The obtained thermoplastic resin sheet 7 had a liquid absorption rate of 0.5%, a tensile elongation of 26% at 200°C, a tensile elongation of 23% at 150°C, a tensile stress at break of 38 MPa at 200°C, a tensile stress at break of 49 MPa at 150°C, and a crystallinity of 31.4%. 【0048】 Sheet 8 of thermoplastic resin (A) Polyetherimide (PEI) pellets (Ultem® Resin1000, manufactured by SABIC Japan LLC) with a glass transition temperature of 215°C were sandwiched between Kapton® films and melted under a pressure of 4 MPa using a press heated to 370°C. Next, the Kapton® films containing the molten PEI were transferred to a press at room temperature and held without pressure to solidify. The Kapton® films were peeled off to obtain a PEI sheet with a thickness of 150 μm. The resulting thermoplastic resin (A) sheet 8 had a liquid absorption rate of -1.0%, a tensile elongation of 390% at 250°C, and a tensile stress of 2 MPa at 100% elongation at 250°C. 【0049】 Thermoplastic resin (A) sheet 9 Thermoplastic polyimide (PI) pellets ("Surprim"® TO65, manufactured by Mitsubishi Gas Chemical Company, Inc.) with a glass transition temperature of 185°C were sandwiched between "Kapton"® films and melted under a pressure of 4 MPa using a press heated to 355°C. Next, the "Kapton"® films containing the molten PI were transferred to a press at room temperature and held without pressure to solidify. The "Kapton"® films were peeled off to obtain a PI sheet with a thickness of 150 μm. The resulting thermoplastic resin (A) sheet 9 had a liquid absorption rate of -2.0%, a tensile elongation of 370% at 250°C, and a tensile stress of 2 MPa at 100% elongation at 250°C. 【0050】 Thermoplastic resin (A) sheet 10 Acrylic (PMMA) pellets (Mitsubishi Chemical Corporation's "Acrypet"® VH) with a glass transition temperature of 100°C were sandwiched between "Kapton"® films and melted under a pressure of 4 MPa using a press heated to 200°C. Next, the "Kapton"® films containing the molten PMMA were transferred to a press at room temperature and held without pressure to solidify. The "Kapton"® films were peeled off to obtain a PMMA sheet with a thickness of 150 μm. The resulting thermoplastic resin (A) sheet 10 had a liquid absorption rate of 14.0%, a tensile elongation of 480% at 150°C, and a tensile stress of 3 MPa at 100% elongation at 150°C. 【0051】 Circuit board A circuit board with capacitors and IC chips mounted on a printed circuit board measuring 150mm in width and 110mm in length. 【0052】 [Example 1] Using a TOM molding machine (NGF-0406-T) manufactured by Fuse Vacuum Co., Ltd., a sheet 1 of thermoplastic resin (A), cut to A4 size, was placed on the frame, and the circuit board was set on the lifting table. Then, the upper and lower boxes were closed and the boxes were vacuumed. Next, the sheet was heated to 200°C for 145 seconds using an IR heater, and then the lifting table was raised while the upper box was pressurized to 0.2 MPa to make the sheet adhere tightly to the circuit board, resulting in a circuit board with insulating protection treatment. Subsequently, a circuit board with insulating protection treatment applied to both sides was obtained by following the same procedure. Next, the sheet that protruded around the circuit board was heat-sealed at 275°C, and then the excess sheet was removed by trimming. Because the circuit board of this embodiment is covered with insulating thermoplastic resin, it can be used safely even when immersed in a coolant. 【0053】 [Example 2] Using a TOM molding machine (NGF-0406-T) manufactured by Fuse Vacuum Co., Ltd., a sheet 1 of thermoplastic resin (A), cut to A4 size, was placed on the frame, and the circuit board was set on the lifting table. Then, the upper and lower boxes were closed and the boxes were vacuumed. Next, the sheet was heated to 150°C for 47 seconds using an IR heater, and then the lifting table was raised while the upper box was pressurized to 0.2 MPa to make the sheet adhere tightly to the circuit board, resulting in a circuit board with insulating protection treatment. Subsequently, a circuit board with insulating protection treatment applied to both sides was obtained by following the same procedure. Next, the sheet that protruded around the circuit board was heat-sealed at 275°C, and then the excess sheet was removed by trimming. Because the circuit board of this embodiment is covered with insulating thermoplastic resin, it can be used safely even when immersed in a coolant. 【0054】 [Example 3] Using a TOM molding machine (NGF-0406-T) manufactured by Fuse Vacuum Co., Ltd., a sheet 3 of thermoplastic resin (A) cut to A4 size was placed on the frame, and the circuit board was set on the lifting table. Then, the upper and lower boxes were closed and the boxes were vacuumed. Next, the sheet was heated to 200°C for 80 seconds using an IR heater, and then the lifting table was raised while the upper box was pressurized to 0.2 MPa to make the sheet adhere tightly to the circuit board, resulting in a circuit board with insulating protection treatment. Subsequently, a circuit board with insulating protection treatment applied to both sides was obtained by following the same procedure. Next, the sheet that protruded around the circuit board was heat-sealed at 275°C, and then the excess sheet was removed by trimming. Because the circuit board of this embodiment is covered with insulating thermoplastic resin, it can be used safely even when immersed in a coolant. 【0055】 [Example 4] Using a vacuum pressure forming machine (KFS-062-20) manufactured by Asano Research Institute Co., Ltd., a sheet 1 of thermoplastic resin (A), cut to A4 size, was placed on the frame, and a circuit board was set on the lifting table. Next, the sheet was heated to 264°C from both sides using an IR heater for 21 seconds. Then, the lifting table was moved to the position of the sheet and raised, and the area below the circuit board was vacuumed to make the sheet adhere tightly to the circuit board, resulting in a circuit board with insulating protection treatment. Subsequently, a circuit board with insulating protection treatment applied to both sides was obtained by following the same procedure. Next, the sheet that protruded around the circuit board was heat-sealed at 275°C, and the excess sheet was removed by trimming. Because the circuit board of this embodiment is covered with insulating thermoplastic resin, it can be used safely even when immersed in a coolant. 【0056】 [Example 5] Using a vacuum pressure forming machine (KFS-062-20) manufactured by Asano Research Institute Co., Ltd., a sheet 2 of thermoplastic resin (A), cut to A4 size, was placed on the frame, and a circuit board was set on the lifting table. Next, the sheet was heated to 206°C from both sides using an IR heater for 15 seconds. Then, the lifting table was moved to the position of the sheet and raised, and the area below the circuit board was vacuumed to make the sheet adhere tightly to the circuit board, resulting in a circuit board with insulating protection treatment. Subsequently, a circuit board with insulating protection treatment applied to both sides was obtained by following the same procedure. Next, the sheet that protruded around the circuit board was heat-sealed at 275°C, and the excess sheet was removed by trimming. Because the circuit board of this embodiment is covered with insulating thermoplastic resin, it can be used safely even when immersed in a coolant. 【0057】 [Example 6] Using a vacuum pressure forming machine (KFS-062-20) manufactured by Asano Research Institute Co., Ltd., a sheet 3 of thermoplastic resin (A), cut to A4 size, was placed on the frame, and a circuit board was set on the lifting table. Next, the sheet was heated to 206°C from both sides using an IR heater for 10 seconds. Then, the lifting table was moved to the position of the sheet and raised, and the area below the circuit board was vacuumed to make the sheet adhere tightly to the circuit board, resulting in a circuit board with insulating protection treatment. Subsequently, a circuit board with insulating protection treatment applied to both sides was obtained by following the same procedure. Next, the sheet that protruded around the circuit board was heat-sealed at 275°C, and the excess sheet was removed by trimming. Because the circuit board of this embodiment is covered with insulating thermoplastic resin, it can be used safely even when immersed in a coolant. 【0058】 [Example 7] Using a vacuum pressure forming machine (KFS-062-20) manufactured by Asano Research Institute Co., Ltd., a sheet 4 of thermoplastic resin (A), cut to A4 size, was placed on the frame, and a circuit board was set on the lifting table. Next, the sheet was heated to 300°C from both sides using an IR heater for 18 seconds. Then, the lifting table was moved to the position of the sheet and raised, and the area below the circuit board was vacuumed to make the sheet adhere tightly to the circuit board, resulting in a circuit board with insulating protection treatment. Subsequently, a circuit board with insulating protection treatment applied to both sides was obtained by following the same procedure. Next, the sheet that protruded around the circuit board was heat-sealed at 340°C, and the excess sheet was removed by trimming. Because the circuit board of this embodiment is covered with insulating thermoplastic resin, it can be used safely even when immersed in a coolant. 【0059】 [Example 8] A sheet 3 of thermoplastic resin (A), cut to A4 size, was bonded with an acrylic adhesive (X3(50)) manufactured by Nichiei Shinka Co., Ltd., and then heat-treated at 80°C for 5 minutes using a hot air oven. Using a vacuum pressure forming machine (KFS-062-20) manufactured by Asano Research Institute Co., Ltd., the sheet 3 with the adhesive bonded to it was placed on the frame, and the circuit board was set on the lifting table. Next, the sheet was heated to 232°C from both sides using an IR heater for 12 seconds, then the lifting table was moved to the position of the sheet and raised, while the area below the circuit board was vacuumed to make the sheet adhere tightly to the circuit board, resulting in a circuit board with insulation protection treatment. Subsequently, a circuit board with insulation protection treatment on both sides was obtained by following the same procedure. Next, the sheet that protruded around the circuit board was heat-sealed at 275°C, and then the excess sheet was removed by trimming. In this embodiment, the circuit board is covered with an insulating thermoplastic resin, so it can be used safely even when immersed in a coolant. Furthermore, because the thermoplastic resin (A) sheet and the circuit board are bonded together, the thermoplastic resin (A) sheet does not peel off the circuit board even when heat-treated in a hot air oven at 150°C for 10 minutes, resulting in a circuit board with higher heat resistance and cooling efficiency with a coolant. 【0060】 [Example 9] Using a vacuum pressure forming machine (KFS-062-20) manufactured by Asano Research Institute Co., Ltd., a sheet 5 of thermoplastic resin (A) cut to A4 size was placed on the frame, and a circuit board was set on the lifting table. Next, the sheet was heated to 231°C from both sides using an IR heater for 12 seconds. Then, the lifting table was moved to the position of the sheet and raised, and the area below the circuit board was vacuumed to make the sheet adhere tightly to the circuit board, resulting in a circuit board with insulating protection treatment. Subsequently, a circuit board with insulating protection treatment applied to both sides was obtained by following the same procedure. Next, the sheet that protruded around the circuit board was heat-sealed at 275°C, and the excess sheet was removed by trimming. Because the circuit board of this embodiment is covered with insulating thermoplastic resin, it can be used safely even when immersed in a coolant. 【0061】 [Example 10] Using a vacuum pressure forming machine (KFS-062-20) manufactured by Asano Research Institute Co., Ltd., a sheet 6 of thermoplastic resin (A) cut to A4 size was placed on the frame, and a circuit board was set on the lifting table. Next, the sheet was heated to 231°C from both sides using an IR heater for 9 seconds. Then, the lifting table was moved to the position of the sheet and raised, and the area below the circuit board was vacuumed to make the sheet adhere tightly to the circuit board, resulting in a circuit board with insulating protection treatment. Subsequently, a circuit board with insulating protection treatment applied to both sides was obtained by following the same procedure. Next, the sheet that protruded around the circuit board was heat-sealed at 275°C, and the excess sheet was removed by trimming. Because the circuit board of this embodiment is covered with insulating thermoplastic resin, it can be used safely even when immersed in a coolant. 【0062】 [Example 11] A sheet 6 of thermoplastic resin (A), cut to A4 size, was bonded with an acrylic adhesive (X3(50)) manufactured by Nichiei Shinka Co., Ltd., and then heat-treated at 80°C for 5 minutes using a hot air oven. Using a vacuum pressure forming machine (KFS-062-20) manufactured by Asano Research Institute Co., Ltd., the sheet 6 with the adhesive bonded to it was placed on the frame, and the circuit board was set on the lifting table. Next, the sheet was heated to 231°C from both sides using an IR heater for 9 seconds, then the lifting table was moved to the position of the sheet and raised, while the area below the circuit board was vacuumed to make the sheet adhere tightly to the circuit board, resulting in a circuit board with insulation protection treatment. Subsequently, a circuit board with insulation protection treatment on both sides was obtained by following the same procedure. Next, the sheet that protruded around the circuit board was heat-sealed at 275°C, and then the excess sheet was removed by trimming. In this embodiment, the circuit board is covered with an insulating thermoplastic resin, so it can be used safely even when immersed in a coolant. Furthermore, because the thermoplastic resin (A) sheet and the circuit board are bonded together, the thermoplastic resin (A) sheet does not peel off the circuit board even when heat-treated in a hot air oven at 150°C for 10 minutes, resulting in a circuit board with higher heat resistance and cooling efficiency with a coolant. 【0063】 [Comparative Example 1] Using a TOM molding machine (NGF-0406-T) manufactured by Fuse Vacuum Co., Ltd., a thermoplastic resin sheet 7 cut to A4 size was placed on the frame, and the circuit board was set on the lifting table. Next, the sheet was heated to 200°C from both sides using an IR heater for 146 seconds. After that, the lifting table was moved to the position of the sheet and raised, and an attempt was made to create a vacuum under the circuit board to make the sheet adhere tightly to the circuit board. However, the sheet could not be stretched and broke, making it impossible to perform the insulating protection treatment. 【0064】 [Comparative Example 2] Using a vacuum pressure forming machine (KFS-062-20) manufactured by Asano Research Institute Co., Ltd., a sheet 8 of thermoplastic resin (A) cut to A4 size was placed on the frame, and the circuit board was set on the lifting table. Next, the sheet was heated to 300°C from both sides using an IR heater for 20 seconds. Then, the lifting table was moved to the position of the sheet and raised, and the area below the circuit board was vacuumed to make the sheet adhere tightly to the circuit board, resulting in a circuit board with insulating protection treatment. Subsequently, a circuit board with insulating protection treatment applied to both sides was obtained by following the same procedure. Next, the sheet that protruded around the circuit board was heat-sealed at 340°C, and the excess sheet was removed by trimming. The circuit board in this embodiment was covered with thermoplastic resin (A), which dissolves in LLC, so insulating protection treatment could not be performed. 【0065】 [Comparative Example 3] Using a vacuum pressure forming machine (KFS-062-20) manufactured by Asano Research Institute Co., Ltd., a sheet 9 of thermoplastic resin (A) cut to A4 size was placed on the frame, and the circuit board was set on the lifting table. Next, the sheet was heated to 300°C from both sides using an IR heater for 21 seconds. Then, the lifting table was moved to the position of the sheet and raised, and the area below the circuit board was vacuumed to make the sheet adhere tightly to the circuit board, resulting in a circuit board with insulating protection treatment. Subsequently, a circuit board with insulating protection treatment on both sides was obtained by following the same procedure. Next, the sheet that protruded around the circuit board was heat-sealed at 340°C, and the excess sheet was removed by trimming. The circuit board in this embodiment was covered with thermoplastic resin (A), which dissolves in LLC, so insulating protection treatment could not be performed. 【0066】 [Comparative Example 4] Using a vacuum pressure forming machine (KFS-062-20) manufactured by Asano Research Institute Co., Ltd., a sheet 10 of thermoplastic resin (A) cut to A4 size was placed on the frame, and the circuit board was set on the lifting table. Next, the sheet was heated to 150°C from both sides using an IR heater for 7 seconds. Then, the lifting table was moved to the position of the sheet and raised, and the area below the circuit board was vacuumed to make the sheet adhere tightly to the circuit board, resulting in a circuit board with insulating protection treatment. Subsequently, a circuit board with insulating protection treatment on both sides was obtained by following the same procedure. Next, the sheet that protruded around the circuit board was heat-sealed at 190°C, and the excess sheet was removed by trimming. In this embodiment, the circuit board was covered with thermoplastic resin (A), which absorbs a large amount of liquid from LLC, so insulating protection treatment could not be performed. 【0067】 [Table 1] 【0068】 [Table 2]

Claims

[Claim 1] A circuit board that is insulated and protected with a thermoplastic resin (A), and is used by being immersed in a cooling liquid. [Claim 2] A circuit board that has been insulated and protected with a thermoplastic resin (A), wherein the thermoplastic resin (A) is at least one selected from the group consisting of crystalline resins with a glass transition temperature of 70°C or higher and amorphous resins with a glass transition temperature of 160°C or higher. [Claim 3] The circuit board according to claim 1, wherein the thermoplastic resin (A) is at least one selected from the group consisting of crystalline resins with a glass transition temperature of 70°C or higher and amorphous resins with a glass transition temperature of 160°C or higher. [Claim 4] The circuit board according to claim 1 or 2, wherein the thermoplastic resin (A) has a liquid absorption rate of 0% or more and 10% or less when immersed in a cooling liquid (a mixture of ethylene glycol and pure water in a weight ratio of 1:1) at 150°C for 250 hours. [Claim 5] The circuit board according to claim 1 or 2, wherein the thermoplastic resin (A) mainly consists of polyphenylene sulfide, polyether ether ketone, polyphenyl sulfone, polyether sulfone, or polysulfone. [Claim 6] A method for manufacturing a circuit board according to claim 1 or 2, comprising spreading and setting a sheet made of thermoplastic resin (A) so as to cover the entire circuit board, and then using a pressure difference to mold the sheet so that it covers the circuit board, thereby obtaining a circuit board that is insulated and protected with thermoplastic resin (A). [Claim 7] The method for manufacturing a circuit board according to claim 6, wherein the tensile elongation of the sheet at 250°C is 50% or more. [Claim 8] The method for manufacturing a circuit board according to claim 6, wherein the sheet has a tensile elongation of 50% or more at 200°C. [Claim 9] The method for manufacturing a circuit board according to claim 6, wherein the tensile elongation of the sheet at 150°C is 50% or more. [Claim 10] An automotive electrical component comprising a circuit board according to claim 1 or 2. [Claim 11] An eAxle comprising the automotive electrical component described in claim 10. [Claim 12] xEV including the in-vehicle electrical component described in claim 10. [Claim 13] A server comprising the circuit board according to claim 1 or 2. [Claim 14] A data center including the server described in claim 13.

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