Polyimide resin composition and metal-based substrate

Abstract

To provide a resin composition containing a filler and a resin which prevents voids and is excellent in thermal conductivity and voltage resistance, and a metal base substrate using the resin composition as an insulating film.SOLUTION: A polyimide resin composition contains a polyimide resin, and a filler dispersed in the polyimide resin, wherein the polyimide resin has dicarboxylic acid groups or acid anhydride groups of dicarboxylic acid groups in both terminals, and the filler has at least one inorganic compound selected from the group consisting of an aluminum oxide, an aluminum hydroxide, a magnesium oxide, and a magnesium hydroxide thereon.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a polyimide resin composition and a metal-based substrate.

Background Art

[0002] As one of the substrates for mounting electronic components such as semiconductor elements and LEDs, a metal-based substrate is known. The metal-based substrate is a laminate in which a metal substrate, an insulating film, and a metal circuit layer are laminated in this order. The electronic component is mounted on the metal circuit layer via solder. In such a metal-based substrate configured as described above, the heat generated in the electronic component is transmitted to the metal substrate through the insulating film and dissipated to the outside from the metal substrate.

[0003] The insulating film of the metal-based substrate is generally formed from an insulating composition containing a resin excellent in insulation and withstand voltage properties and a filler excellent in thermal conductivity. As the resin for the insulating film, polyimide resin, polyamide resin, polyamideimide resin, epoxy resin, silicone resin, etc. are used. Further, as the filler for the insulating film, aluminum oxide particles, aluminum hydroxide particles, magnesium oxide particles, magnesium hydroxide particles, aluminum nitride particles, silica particles, silicon carbide particles, titanium oxide particles, boron nitride particles, etc. are used (Patent Documents 1 to 5).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, a metal base substrate is manufactured, for example, by forming an insulating film on a metal substrate and then thermocompression bonding the insulating film and a metal circuit layer. As a method of forming an insulating film on a metal substrate, for example, a method of applying a resin solution in which fillers are dispersed on the substrate and drying the obtained coating film is used. In the case of this method, voids (pores) may be generated between the resin and the fillers when the coating film is dried. When voids are generated between the resin and the fillers in the insulating film, since heat hardly conducts through the void portions, the thermal conductivity of the insulating film may decrease. Further, partial discharge occurs in the void portions, which may cause breakdown of the insulating film, and thus the withstand voltage of the insulating film may decrease.

[0006] The present invention has been made in view of the above circumstances, and provides a resin composition containing a filler and a resin, which is less likely to generate voids and is excellent in thermal conductivity and withstand voltage, and a metal base substrate using this resin composition as an insulating film.

Means for Solving the Problems

[0007] In order to solve the above problems, the resin composition of the present invention contains a resin and a filler dispersed in the resin. The resin contains a polyimide resin having a dicarboxylic acid group or an acid anhydride group of a dicarboxylic acid group at both ends. The filler has at least one inorganic compound selected from the group consisting of aluminum oxide, aluminum hydroxide, magnesium oxide, and magnesium hydroxide on its surface. The content of the filler is in the range of 60% by mass or more and 90% by mass or less, and the average particle diameter of the filler is 0.1 μm or more 3 μm or less, which is a polyimide resin composition.

[0008] According to the polyimide resin composition of this configuration, the polyimide resin contained in the resin as the base material has dicarboxylic acid groups or acid anhydride groups of dicarboxylic acid groups at both ends, and the filler has inorganic compounds such as aluminum oxide, aluminum hydroxide, magnesium oxide, and magnesium hydroxide on the surface. Therefore, the resin and the filler have high affinity for each other and are likely to chemically bond. For this reason, the bonding force between the resin and the filler becomes strong, and voids are less likely to be generated between the two. Therefore, the polyimide resin composition of the above configuration has improved thermal conductivity and breakdown voltage. In addition, since the filler content is in the range of 60% by mass or more and 90% by mass or less, the thermal conductivity is surely improved.

[0009] Here, in the polyimide resin composition of the present invention, the polyimide resin may be configured to be a compound represented by the following general formula (1) or general formula (2). In this case, since the polyimide resin is a compound represented by the following general formula (1) or general formula (2), the bonding force between the polyimide resin and the filler becomes stronger, and voids are less likely to be generated between the two.

[0010]

Chemical formula

[0011]

Chemical formula

[0012] However, in general formula (1) and general formula (2), R1 represents a tetravalent organic group, R2 represents a divalent organic group, and S represents a number in the range of 10 or more and 200 or less calculated from the number average molecular weight.

[0013] Further, in the polyimide resin composition of the present invention, the number average molecular weight of the polyimide resin may be configured to be in the range of 5000 or more and 50000 or less. In this case, since the number average molecular weight of the polyimide resin is in the range of 5,000 or more and 50,000 or less, the fluidity of the polyimide resin is controlled, and defects during resin-metal bonding are less likely to occur.

[0015] Further, in the polyimide resin composition of the present invention, in the resin, the proportion of the polyimide resin may be configured to be in the range of 66% by mass or more and 100% by mass or less. In this case, since the resin contains a polyimide resin having dicarboxylic acid groups or acid anhydride groups of dicarboxylic acid groups at both ends within the above range, the bonding strength between the resin and the filler is further enhanced.

[0016] The metal-based substrate of the present invention is a metal-based substrate in which a metal substrate, an insulating film, and a metal circuit layer are laminated in this order, and the insulating film is characterized by being made of the above-described polyimide resin composition. According to the metal-based substrate having this configuration, since an insulating film made of the above-described polyimide resin composition is disposed between the metal substrate and the metal circuit layer, it is excellent in thermal conductivity and withstand voltage.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a resin composition containing a filler and a resin, which hardly generates voids and is excellent in thermal conductivity and withstand voltage, and a metal-based substrate using this resin composition as an insulating film.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0019] A polyimide resin composition and a metal-based substrate which are one embodiment of the present invention will be described with reference to the accompanying drawings.

[0020] <Polyimide resin composition> FIG. 1 is a schematic cross-sectional view of a polyimide resin composition according to an embodiment of the present invention. As shown in FIG. 1, the polyimide resin composition 10 according to this embodiment includes a polyimide resin 11 and a filler 12 dispersed in the polyimide resin 11. The content of the filler 12 in the polyimide resin composition 10 is preferably in the range of 60% by mass or more and 90% by mass or less, and particularly preferably in the range of 70% by mass or more and 88% by mass or less, based on mass. Further, the content of the filler 12 in the polyimide resin composition 10 is preferably in the range of 40% by volume or more and 80% by volume or less, and particularly preferably in the range of 45% by volume or more and 75% by volume or less, based on volume.

[0021] (Polyimide resin 11) The polyimide resin 11 is the base material (matrix resin) of the polyimide resin composition 10. The polyimide resin 11 has dicarboxylic acid groups or acid anhydride groups of dicarboxylic acid groups at both ends. Therefore, the polyimide resin 11 has a high affinity for inorganic compounds such as aluminum oxide, aluminum hydroxide, magnesium oxide, and magnesium hydroxide, and is likely to chemically bond. The polyimide resin 11 may be a compound represented by the following general formula (1) or general formula (2).

[0022]

Chemical formula

[0023]

Chemical formula

[0024] However, in the general formula (1) and the general formula (2), R 1 represents a tetravalent organic group, R 2 represents a divalent organic group, and S represents a number from 10 to 200 calculated from the number average molecular weight.

[0025] R 1 The tetravalent organic group represented by 1 may be a tetravalent aromatic hydrocarbon group obtained by removing four hydrogen atoms from an aromatic hydrocarbon, or a tetravalent alicyclic hydrocarbon group obtained by removing four hydrogen atoms from an alicyclic hydrocarbon. The aromatic hydrocarbon may include monocyclic aromatic, condensed polycyclic aromatic, and non-condensed polycyclic aromatic in which two monocyclic aromatics are directly or linked to each other by a bridging group. The alicyclic hydrocarbon may have 4 to 8 carbon atoms.

[0026] R 1 The tetravalent organic group represented by 1 may be, for example, a group represented by the following general formulas (3) to (6).

[0027]

Chemical formula

[0028] In general formulas (3) to (6), * represents a bond. In general formula (6), X represents a bridging group. The bridging group may be a divalent hydrocarbon group, an oxygen atom, a sulfur atom, a carbonyl group, a sulfonyl group, an imino group, or a group combining these groups. The divalent hydrocarbon group may be, for example, an aliphatic group having 1 to 10 carbon atoms (alkylene group, alkenylene group, alkynylene group), a cycloalkylene group having 4 to 10 carbon atoms, an arylene group, or a group combining these. The divalent aliphatic group and imino group may have substituents. Examples of the substituents include a monovalent hydrocarbon group, a fluorocarbon group in which a monovalent hydrocarbon group is substituted with fluorine, an alkoxy group having 1 to 10 carbon atoms, and -OCOCH3 group. The monovalent hydrocarbon group may be, for example, an aliphatic group having 1 to 10 carbon atoms (alkyl group, alkenyl group, alkynyl group), a cycloalkyl group having 4 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, or an aralkyl group having 7 to 10 carbon atoms. The bridging group represented by X may be, for example, a group represented by the following formulas (7) to (13).

[0029]

Chemical formula

[0030] R 2 The divalent organic group represented by the formula (I) preferably has a methylene chain. The methylene chain preferably has 3 or more carbon atoms. The divalent organic group may be a group formed by combining a methylene chain with a divalent linking group. The divalent linking group may be a divalent hydrocarbon group, an oxygen atom, a sulfur atom, a carbonyl group, a sulfonyl group, an imino group, -(Si(R 3 R 4 )-O) n - group (wherein, R 3 and R 4 each independently represents an alkyl group having 1 to 10 carbon atoms, and n represents a number in the range of 1 to 30.) or a group formed by combining these groups. The divalent hydrocarbon group may be, for example, an aliphatic group having 1 to 10 carbon atoms (alkylene group, alkenylene group, alkynylene group), a cycloalkylene group having 4 to 10 carbon atoms, an arylene group having 6 to 10 carbon atoms, or a group formed by combining these groups. The divalent hydrocarbon group and the imino group may have a substituent. An example of the substituent is a monovalent hydrocarbon group. The monovalent hydrocarbon group may be, for example, an aliphatic group having 1 to 10 carbon atoms (alkyl group, alkenyl group, alkynyl group), a cycloalkyl group having 4 to 20 carbon atoms, an aryl group having 6 to 10 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms.

[0031] R 2 The divalent organic group represented by the formula (14) or (15) may be, for example, a group represented by the formula (14) or (15) below. 2 The divalent organic group represented by the formula (1) may be, for example, a hydrocarbon group derived from a dimer diamine having a methylene chain. The hydrocarbon group derived from a dimer diamine may have a carbon atom number in the range of 20 to 50, and the number of hydrogen atoms may be in the range of (m×2−6) or more and (m×2) or less, where m is the number of carbon atoms.

[0032] [ka]

[0033] In general formula (14), p represents a number in the range of 3 or more and 10 or less. In general formula (15), q and r each independently represent a number in the range of 3 or more and 8 or less, and n represents a number in the range of 1 or more and 30 or less.

[0034] The polyimide resin 11 can be produced, for example, by a method having a step of reacting a tetracarboxylic dianhydride and a diamine in an organic solvent to form a polyamic acid, and a step of imidizing the polyamic acid. As the tetracarboxylic dianhydride, a compound represented by the following general formula (16) may be used. As the diamine, a compound represented by the following general formula (17) may be used.

[0035]

Chemical formula

[0036] In general formula (16), R 1 is the same as in the cases of the above general formulas (1) and (2).

[0037]

Chemical formula

[0038] In general formula (17), R 2 is the same as in the cases of the above general formulas (1) and (2).

[0039] As the organic solvent, a polar organic solvent may be used. Examples of the polar organic solvent include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), N-methyl-2-pyrrolidone (NMP), and cyclohexanone.

[0040] In the step of producing the polyamic acid, an organic solvent, a tetracarboxylic dianhydride, and a diamine may be stirred and mixed to react the tetracarboxylic dianhydride with the diamine to produce the polyamic acid. The reaction temperature may be, for example, in the range of 10°C or higher and 100°C or lower. The reaction atmosphere may be an air atmosphere or an inert gas atmosphere (e.g., argon, nitrogen).

[0041] In the polyimide resin 11, the dicarboxylic acid groups or their acid anhydride groups present at both ends thereof are derived from the tetracarboxylic dianhydride as a raw material. In order to make the dicarboxylic acid groups or their acid anhydride groups present at both ends of the polyimide resin 11, the amount of the tetracarboxylic dianhydride in the organic solvent may be made more than that of the diamine. The mixing ratio of the tetracarboxylic dianhydride to the diamine in the organic solvent (tetracarboxylic dianhydride / diamine ratio) may be in the range of 1.005 or more and 1.2 or less.

[0042] In the step of imidizing the polyamic acid, as a method of imidizing the polyamic acid in the polyamic acid solution, a method of heating the polyamic acid solution or a method of adding an imidization catalyst to the polyamic acid solution can be used. When heating the polyamic acid solution, the heating temperature may be in the range of 100°C or higher and 300°C or lower. When adding an imidization catalyst, as the imidization catalyst, amine compounds that have been conventionally used as imidization catalysts, such as aliphatic amines, alicyclic amines, and aromatic amines, can be used.

[0043] The number average molecular weight of the polyimide resin 11 is preferably in the range of 5000 or more and 50000 or less, and particularly preferably in the range of 8000 or more and 30000 or less.

[0044] (Filler 12) Filler 12 has, on its surface, at least one inorganic compound selected from the group consisting of aluminum oxide, aluminum hydroxide, magnesium oxide, and magnesium hydroxide. The presence of the inorganic compound on the surface of filler 12 strengthens the bonding force between polyimide resin 11 and filler 12, making it difficult for voids to form between the two. The filler may be single particles containing only one of the above inorganic compounds, or composite particles combining two or more of the above inorganic compounds. Further, filler 12 may be coated particles in which part or all of the surface of the core particles is coated with one or more of the above inorganic compounds. As the core particles, for example, aluminum nitride particles, silica particles, silicon carbide particles, titanium oxide particles, and boron nitride particles can be used. These particles may be used alone or in combination of two or more kinds.

[0045] Filler 12 preferably has an average particle diameter in the range of 0.1 μm or more and 20 μm or less. When the average particle diameter of filler 12 is 0.1 μm or more, the thermal conductivity of the resin composition is improved. When the average particle diameter of filler 12 is 20 μm or less, the breakdown voltage resistance of the resin composition is improved. Further, when the average particle diameter of filler 12 is within the above range, filler 12 is less likely to form aggregated particles and less likely to sediment, so that filler 12 can be easily dispersed uniformly in polyimide resin 11. When filler 12 is dispersed in the insulating resin as primary particles or fine particles close to them without forming aggregated particles, the breakdown voltage resistance of polyimide resin 11 is improved. The average particle diameter of filler 12 preferably is in the range of 0.3 μm or more and 20 μm or less.

[0046] (Method for manufacturing polyimide resin composition 10) Next, the method for manufacturing polyimide resin composition 10 of the present embodiment will be described. Polyimide resin composition 10 can be manufactured, for example, by a method including a preparation step of preparing a filler-dispersed polyimide resin solution, and a molding step of applying the filler-dispersed polyimide resin solution and drying the obtained coating film.

[0047] In the preparation process, the filler-dispersed polyimide resin solution may be prepared, for example, as follows. First, polyimide resin 11 is dissolved in an organic solvent to obtain a polyimide resin solution. As the organic solvent, for example, a polar organic solvent used in the production of the polyimide resin may be used. Next, the polyimide solution and filler 12 are mixed to obtain a mixture. Then, a dispersion treatment is performed on the mixture to disperse filler 12 in the solution of polyimide resin 11. As the dispersion treatment, an ultrasonic dispersion treatment, a dispersion treatment using a ball mill, or a treatment of colliding high-pressure-injected raw materials with each other to disperse particles can be used.

[0048] In the molding process, as the method for applying the filler-dispersed polyimide resin solution, a spin coating method, a bar coating method, a knife coating method, a roll coating method, a blade coating method, a die coating method, a gravure coating method, a dip coating method, etc. can be used. As the method for drying the coating film, methods such as heat drying, hot air drying, and vacuum drying can be used. The drying temperature is preferably 100°C or higher and lower than the thermal decomposition temperature of the polyimide resin. By heating to 100°C or higher, the bonding strength between the polyimide resin and the filler becomes stronger.

[0049] According to the polyimide resin composition 10 of the present embodiment configured as described above, the polyimide resin 11 as the base material has dicarboxylic acid groups or acid anhydride groups of dicarboxylic acid groups at both ends, and the filler 12 has inorganic compounds such as aluminum oxide, aluminum hydroxide, magnesium oxide, and magnesium hydroxide on its surface. Therefore, the polyimide resin 11 and the filler 12 have high affinity for each other and are easily chemically bonded. For this reason, the bonding strength between the polyimide resin 11 and the filler 12 becomes strong, and it becomes difficult for voids to be generated between the two. Therefore, the polyimide resin composition 10 of the present embodiment has improved thermal conductivity and withstand voltage.

[0050] In the polyimide resin composition 10 of the present embodiment, when the polyimide resin 11 is a compound represented by the above general formula (1) or general formula (2), the bonding strength between the polyimide resin 11 and the filler 12 becomes stronger, and voids are less likely to be generated between the two. Further, in the polyimide resin composition 10 of the present embodiment, when the number average molecular weight of the polyimide resin 11 is in the range of 5000 or more and 50000 or less, the balance between the hardness and flexibility of the polyimide resin 11 is good and it is difficult to deform, so the thermal conductivity and breakdown voltage of the polyimide resin composition 10 are stable over a long period. Furthermore, in the polyimide resin composition 10 of the present embodiment, when the content of the filler 12 is in the range of 60% by mass or more and 90% by mass or less, the thermal conductivity is surely improved.

[0051] <Metal base substrate 20> FIG. 2 is a schematic cross-sectional view of a metal base substrate according to an embodiment of the present invention. The metal base substrate 20 is a laminate in which a metal substrate 21, an insulating film 22, and a metal circuit layer 23 are laminated in this order.

[0052] The metal substrate 21 is a member that serves as the base of the metal base substrate 20. As the metal substrate 21, a copper plate, an aluminum plate, and a laminate of these can be used.

[0053] The insulating film 22 is a member for insulating the metal substrate 21 and the metal circuit layer 23. The insulating film 22 is composed of the polyimide resin composition 10 shown in FIG. 1 and includes a polyimide resin 11 and a filler 12 dispersed in the polyimide resin 11. For this reason, the same reference numerals are given and detailed description is omitted.

[0054] The metal circuit layer 23 is formed in a circuit pattern shape. Electronic components are joined onto the metal circuit layer 23 formed in the circuit pattern shape via solder or the like. As the material of the metal circuit layer 23, copper, aluminum, gold, or the like can be used.

[0055] Examples of electronic components mounted on the metal circuit layer 23 are not particularly limited and include semiconductor elements, resistors, capacitors, crystal oscillators, and the like. Examples of semiconductor elements include MOSFET (Metal-oxide-semiconductor field effect transistor), IGBT (Insulated Gate Bipolar Transistor), LSI (Large Scale Integration), LED (light-emitting diode), LED chip, and LED-CSP (LED-Chip Size Package).

[0056] Next, a method for manufacturing the metal base substrate 20 of the present embodiment will be described. The metal base substrate 20 of the present embodiment can be manufactured, for example, by a method including an insulating film forming step of forming an insulating film 22 on one surface of a metal substrate 21 and a metal circuit layer pressing step of pressing a metal circuit layer 23 onto the insulating film 22.

[0057] In the insulating film forming step, the insulating film 22 can be formed, for example, by applying a filler-dispersed polyimide resin solution to one surface of the metal substrate 21 and then drying the obtained coating film. The method for preparing the filler-dispersed polyimide resin solution, the method for applying the filler-dispersed polyimide resin solution, and the method for drying the coating film are the same as those in the case of the manufacturing method of the above-described polyimide resin composition 10.

[0058] In the metal circuit layer pressing step, the metal circuit layer 23 can be pressed, for example, by laminating the metal circuit layer 23 on the insulating film 22 and then applying pressure in the lamination direction while heating the obtained laminate. The heating temperature is preferably 200°C or higher, particularly preferably 250°C or higher. The upper limit of the heating temperature is lower than the thermal decomposition temperature of the polyimide resin 11, preferably 30°C lower than the thermal decomposition temperature or lower. The pressure during pressing is preferably in the range of 1 MPa or more and 30 MPa or less, particularly preferably in the range of 3 MPa or more and 25 MPa or less. The pressing time varies depending on the heating temperature and pressure, but is generally 10 minutes or more and 180 minutes or less.

[0059] According to the metal base substrate 20 of the present embodiment configured as described above, since the insulating film 22 composed of the above-described polyimide resin composition 10 is disposed between the metal substrate 21 and the metal circuit layer 23, it is excellent in thermal conductivity and withstand voltage.

[0060] As described above, the embodiments of the present invention have been described. However, the present invention is not limited thereto, and can be appropriately changed without departing from the technical idea of the invention. For example, in the present embodiment, as an example of the resin contained in the polyimide resin composition 10, an example in which the polyimide resin 11 having a dicarboxylic acid group or an acid anhydride group of a dicarboxylic acid group at both ends is used alone has been described. However, the polyimide resin composition 10 may contain other resins. As other resins, for example, a polyimide resin having an amine group at at least one end and an epoxy resin can be used. However, it is preferable that the content of the polyimide resin 11 having a dicarboxylic acid group or an acid anhydride group of a dicarboxylic acid group at both ends in the polyimide resin composition 10 is in the range of 66% by mass or more and 100% by mass or less.

[0061] Also, in the present embodiment, an example in which the polyimide resin composition 10 is used as an insulating layer of the metal base substrate 20 has been described. However, the use of the polyimide resin composition 10 is not limited thereto. The polyimide resin composition 10 may be used, for example, as an insulating film of an insulating conductor coated with an insulating film such as an enameled wire.

Example

[0062] [Synthesis Example 1: Synthesis of Polyimide Resin A] In 100 g of DMF (N,N-dimethylformamide, manufactured by Fujifilm Wako Pure Chemical Corporation), 6.20 g of PMDD (3,3'-(pentamethylenedioxy)dianiline, manufactured by Merck KGaA) was added and dissolved, and then 10.10 g of 6FDA (4,4'-(hexafluoroisopropylidene)diphthalic anhydride, manufactured by Tokyo Chemical Industry Co., Ltd.) was added. Thereafter, under an argon atmosphere, the mixture was stirred and mixed at room temperature for 72 hours to produce a polyamic acid. The obtained polyamic acid solution was transferred to an evaporating dish and dried and fired in order at a temperature of 50°C for 24 hours, a temperature of 200°C for 5 hours, and a temperature of 250°C for 30 minutes under a reduced pressure atmosphere to obtain a polyimide resin A having dicarboxylic anhydride at both ends. The molar ratio of 6FDA / PMDD in the mixed solution was 1.05. The number average molecular weight of the obtained polyimide resin A was 11,000.

[0063] [Synthesis Example 2: Synthesis of Polyimide Resin B] In 100 g of DMF, 6.20 g of PMDD was added and dissolved, and then 9.14 g of 6FDA was added. Thereafter, under an argon atmosphere, the mixture was stirred and mixed at room temperature for 72 hours to produce a polyamic acid. The obtained polyamic acid solution was transferred to an evaporating dish and dried and fired in order at a temperature of 50°C for 24 hours, a temperature of 200°C for 5 hours, and a temperature of 250°C for 30 minutes under a reduced pressure atmosphere to obtain a polyimide resin B having amine groups at both ends. The molar ratio of 6FDA / PMDD in the mixed solution was 0.95. The number average molecular weight of the obtained polyimide resin B was 11,000.

[0064] [Synthesis Example 3: Synthesis of Polyimide Resin C] 6.20 g of V551 (Versamine 551, manufactured by BASF Japan Ltd.) was added to 100 g of cyclohexanone and dissolved, and then 4.93 g of ODPA (4,4'-oxydiphthalic anhydride, manufactured by Tokyo Chemical Industry Co., Ltd.) was added. Thereafter, the mixture was stirred and mixed at room temperature for 72 hours under an argon atmosphere to produce a polyamic acid. The obtained polyamic acid solution was transferred to an evaporating dish and dried and baked at a temperature of 50 °C for 24 hours and then at a temperature of 150 °C for 5 hours under a reduced pressure atmosphere to obtain a polyimide resin C having dicarboxylic anhydride groups at both ends. The molar ratio of ODPA / V551 in the mixed solution was 1.05. The number average molecular weight of the obtained polyimide resin C was 11,000.

[0065] [Synthesis Example 4: Synthesis of Polyimide Resin D] 6.20 g of V551 was added to 100 g of cyclohexanone and dissolved, and then 4.46 g of ODPA was added. Thereafter, the mixture was stirred and mixed at room temperature for 72 hours under an argon atmosphere to produce a polyamic acid. The obtained polyamic acid solution was transferred to an evaporating dish and dried and baked at a temperature of 50 °C for 24 hours and then at a temperature of 150 °C for 5 hours under a reduced pressure atmosphere to obtain a polyimide resin D having amine groups at both ends. The molar ratio of ODPA / V551 in the mixed solution was 0.95. The number average molecular weight of the obtained polyimide resin D was 11,000.

[0066] [Example 1 of the Present Invention] 5 g of polyimide resin A was added to 10 g of DMF and stirred until it was uniformly dissolved. Aluminum oxide powder (average particle diameter: 3 μm) was added to the obtained polyimide resin solution so that the mass conversion was 60% by mass (volume conversion: 35% by volume) with respect to the total amount of polyimide resin A and aluminum oxide powder, and the mixture was stirred with a magnetic stirrer. The obtained mixture was subjected to a dispersion treatment by repeating a high-pressure injection treatment at a pressure of 50 MPa 10 times using a Starburst manufactured by Sugino Machine Co., Ltd. to prepare a filler-dispersed polyimide resin solution. The resin contained in the filler-dispersed polyimide resin solution was 100% by mass of a polyimide resin (polyimide resin A) having dicarboxylic anhydrides at both ends.

[0067] [Examples 2 to 4 of the present invention] A filler-dispersed polyimide resin solution was prepared in the same manner as in Example 1 of the present invention, except that the amount of aluminum oxide powder added was adjusted to the content shown in Table 1 below.

[0068] [Example 5 of the present invention] A filler-dispersed polyimide resin solution was prepared in the same manner as in Example 1 of the present invention, except that 4 g of polyimide resin A and 2 g of polyimide resin B were added to 10 g of DMF, and the amount of aluminum oxide powder added was adjusted to the content shown in Table 1 below. The resin contained in the filler-dispersed polyimide resin solution was composed of 66.7% of a polyimide resin (polyimide resin A) with dicarboxylic acid anhydride at both ends and 33.3% by mass of a polyimide resin (polyimide resin B) with amine groups at both ends.

[0069] [Example 6 of the present invention] A filler-dispersed polyimide resin solution was prepared in the same manner as in Example 1 of the present invention, except that cyclohexanone was used instead of DMF, 1 g of polyimide resin C was added to 10 g of cyclohexanone instead of polyimide resin A, and the amount of aluminum oxide powder added was adjusted to the content shown in Table 1 below. The resin contained in the filler-dispersed polyimide resin solution was composed of 100% by mass of a polyimide resin (polyimide resin C) with dicarboxylic acid anhydride at both ends.

[0070] [Example 7 of the present invention] A filler-dispersed polyimide resin solution was prepared in the same manner as in Example 1 of the present invention, except that magnesium oxide powder (average particle size: 10 μm) was added in an amount corresponding to the content shown in Table 1 below instead of aluminum oxide powder.

[0071] [Example 8 of the present invention] An aluminum hydroxide powder (average particle diameter: 3 μm) was introduced in an amount corresponding to the content described in Table 1 below, instead of the aluminum oxide powder. A filler-dispersed polyimide resin solution was prepared in the same manner as in Invention Example 1, except for this.

[0072] [Invention Example 9] 4.85 g of polyimide resin A was added to 10 g of DMF and stirred until uniformly dissolved. 0.15 g of an epoxy resin raw material (JER-630, manufactured by Mitsubishi Chemical Corporation) was added to the obtained polyimide resin solution. Further, aluminum oxide powder (average particle diameter: 3 μm) was introduced in an amount such that it was 79% by mass (57% by volume in terms of volume conversion) with respect to the total amount of polyimide resin A, epoxy resin, and aluminum oxide powder, and stirred with a magnetic stirrer. The obtained mixture was subjected to a dispersion treatment by repeating a high-pressure injection treatment at a pressure of 50 MPa 10 times using a starburst manufactured by Sugino Machine Limited, thereby preparing a filler-dispersed polyimide resin solution. The resin contained in the filler-dispersed polyimide resin solution has a content of 97% by mass of a polyimide resin (polyimide resin A) having dicarboxylic anhydride at both ends, and a content of 3% by mass of an epoxy resin.

[0073] [Invention Example 10] A filler-dispersed polyimide resin solution was prepared in the same manner as in Invention Example 1, except that aluminum oxide powder having an average particle diameter of 0.7 μm was introduced in an amount corresponding to the content described in Table 1 below, instead of the aluminum oxide powder having an average particle diameter of 3 μm.

[0074] [Comparative Example 1] A filler-dispersed polyimide resin solution was prepared in the same manner as in Invention Example 1, except that 5 g of polyimide resin B was added instead of polyimide resin A to 10 g of DMF, and the amount of aluminum oxide powder introduced was set to the amount corresponding to the content described in Table 1 below.

[0075] [Comparative Example 2] A filler-dispersed polyimide resin solution was prepared in the same manner as in Invention Example 1, except that silica powder (average particle diameter: 0.7 μm) was introduced in an amount corresponding to the content described in Table 1 below instead of aluminum oxide powder.

[0076] [Comparative Example 3] A filler-dispersed polyimide resin solution was prepared in the same manner as in Invention Example 1, except that 1 g of polyimide resin D was introduced instead of polyimide resin A into 10 g of DMF, and the amount of aluminum oxide powder introduced was set to the amount corresponding to the content described in Table 1 below.

[0077] [Evaluation] Using the filler-dispersed polyimide resin solutions obtained in Invention Examples 1 to 10 and Comparative Examples 1 to 3, a polyimide resin composition film containing a filler was produced, and the filler dispersibility, void occupancy, thermal conductivity, and withstand voltage per film thickness of the obtained polyimide resin film were evaluated by the following methods. The results are shown in Table 1 below.

[0078] (Filler dispersibility) On a copper substrate measuring 50 mm in length × 50 mm in width × 1 mm in thickness, the filler-dispersed polyimide resin solution was spin-coated at a rotation speed of 500 rpm to obtain a coating film with a thickness of 20 μm. The obtained coating film was heated and dried at a temperature of 100°C for 3 hours to form a polyimide resin composition film containing a filler, thereby obtaining a copper substrate with a polyimide resin composition film. The obtained polyimide resin composition film was observed using an optical microscope, and the number of aggregates of fillers with a particle size of 0.1 mm or more was counted. When the number of aggregates per 1 cm 2 of the polyimide resin composition film was 3 or less, it was judged as ○; when it was 4 or more and 10 or less, it was judged as △; and when it was 11 or more, it was judged as ×.

[0079] (Void occupancy) On a PTFE (polytetrafluoroethylene) plate with a length of 50 mm, a width of 50 mm, and a thickness of 1 mm, a filler-dispersed polyimide resin solution is applied using a bar coater to obtain a coating film with a thickness of 100 μm. The obtained coating film is heated at a temperature of 100 °C for 30 minutes and then at a temperature of 150 °C for 30 minutes, and dried to form a polyimide resin composition film containing a filler. The obtained polyimide resin composition film is peeled from the PTFE plate and resin-embedded. The resin-embedded polyimide resin composition film is cross-sectionally exposed by CP processing. Next, the cross-section of the exposed polyimide resin composition film is observed using an SEM (scanning electron microscope). For the cross-sectional area of 100 μm of the polyimide resin composition film 2 the area occupied by voids is measured, and the occupancy rate is calculated.

[0080] (Thermal conductivity) On a copper substrate with a length of 50 mm, a width of 50 mm, and a thickness of 1 mm, a filler-dispersed polyimide resin solution is applied using a bar coater to obtain a coating film with a thickness of 100 μm. The obtained coating film is heated at a temperature of 100 °C for 3 hours and dried to form a polyimide resin composition film containing a filler, thereby obtaining a copper substrate with a polyimide resin composition film. The thermal conductivity of the polyimide resin composition film (the thermal conductivity in the thickness direction of the polyimide resin composition film) is measured by the laser flash method using an LFA477 Nanoflash manufactured by NETZSCH-Geratebau GmbH.

[0081] (Breakdown voltage per unit film thickness) The breakdown voltage of the polyimide resin composition film is measured using a multifunctional safety tester 7440 manufactured by Measurement Technology Research Institute Co., Ltd. In the same manner as the measurement of the above thermal conductivity, a copper substrate with a polyimide resin composition film is obtained. An electrode (φ6 mm) is disposed on the surface of the polyimide resin composition film of the copper substrate with the polyimide resin composition film. The copper substrate of the copper substrate with the polyimide resin composition film and the electrode disposed on the surface of the polyimide resin composition film are each connected to a power supply, and the voltage is increased to 6000 V in 30 seconds. The voltage at the time when the current value flowing between the copper substrate and the electrode reaches 5000 μA was defined as the breakdown voltage of the polyimide resin composition film. The film thickness was measured with a micrometer, and the breakdown voltage per film thickness was calculated by dividing the breakdown voltage by the film thickness.

[0082]

Table 1

[0083] Using a polyimide resin having dicarboxylic acid groups or acid anhydride groups thereof at both ends, and using the filler-dispersed polyimide resin solutions of Examples 1 to 10 of the present invention containing any one of aluminum oxide powder, aluminum hydroxide powder, magnesium oxide powder, and magnesium hydroxide powder as a filler, the polyimide resin composition film formed has excellent filler dispersibility, a low void occupancy rate, and high thermal conductivity and breakdown voltage. This is because the affinity between the dicarboxylic acid groups or acid anhydride groups at both ends of the polyimide resin and the filler is high, and defects are less likely to occur between the polyimide resin and the filler. For example, when the filler is aluminum oxide powder, the terminal dicarboxylic acid anhydride group of the polyimide resin is easily hydrolyzed by adsorbed water on the aluminum oxide particles or moisture in the air to form a dicarboxylic acid group. The dicarboxylic acid group reacts with the hydroxyl groups on the aluminum oxide particles to form two carboxylate groups. The two generated carboxylate groups are stabilized by bidentate cross-linking to two aluminum atoms, respectively, and the polyimide resin is immobilized on the surface of the aluminum oxide particles. Heating at 100 ° C or higher is preferred for the progress of the bidentate cross-linking reaction.

[0084] On the other hand, in Comparative Examples 1 and 3 using a polyimide resin having no dicarboxylic acid group and its acid anhydride group at both ends, and in Comparative Example 2 using silica powder as a filler, the filler dispersibility of the polyimide resin composition film decreased. Note that since a large number of aggregates were generated in the polyimide resin composition films obtained in Comparative Examples 1 and 3 and Comparative Example 2, the void occupancy rate, thermal conductivity, and breakdown voltage could not be measured.

Explanation of Signs

[0085] 10 Polyimide resin composition 11 Polyimide resin 12 Filler 20 Metal-based substrate 21 Metal substrate 22 Insulating film 23 Metal circuit layer

Claims

1. A polyimide resin composition comprising a resin and a filler dispersed in the resin, wherein the resin includes a polyimide resin having a dicarboxylic acid group or an acid anhydride group of the dicarboxylic acid group at both ends, the filler has at least one inorganic compound selected from the group consisting of aluminum oxide, aluminum hydroxide, magnesium oxide, and magnesium hydroxide on its surface, the content of the filler is in the range of 60% by mass or more and 90% by mass or less, and the average particle diameter of the filler is 0.1 μm or more and 3 μm or less.

2. The polyimide resin composition according to claim 1, wherein the polyimide resin is a compound represented by the following general formula (1) or general formula (2). 【Chemical 1】 [Chemical Formula 2] However, in General Formula (1) and General Formula (2), R １ represents a tetravalent organic group, R ２ represents a divalent organic group, and S represents a number of 10 or more and 200 or less calculated from the number average molecular weight.

3. The polyimide resin composition according to claim 1 or claim 2, wherein the number average molecular weight of the polyimide resin is in the range of 5,000 or more and 50,000 or less.

4. The polyimide resin composition according to any one of claims 1 to 3, wherein the content of the polyimide resin in the resin is in the range of 66% by mass or more and 100% by mass or less.

5. A metal base substrate in which a metal substrate, an insulating film, and a metal circuit layer are laminated in this order, wherein the insulating film is made of the polyimide resin composition according to any one of claims 1 to 4.

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