Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G59/00—Polycondensates containing more than one epoxy group per molecule; Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/01—Use of inorganic substances as compounding ingredients characterized by their specific function
  • C08K3/013—Fillers, pigments or reinforcing additives
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/38—Boron-containing compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L101/00—Compositions of unspecified macromolecular compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L63/00—Compositions of epoxy resins; Compositions of derivatives of epoxy resins
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K1/00—Printed circuits
  • H05K1/02—Details
  • H05K1/03—Use of materials for the substrate
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W40/00—Arrangements for thermal protection or thermal control
  • H10W40/10—Arrangements for heating
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W40/00—Arrangements for thermal protection or thermal control
  • H10W40/20—Arrangements for cooling
  • H10W40/25—Arrangements for cooling characterised by their materials
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W70/00—Package substrates; Interposers; Redistribution layers [RDL]
  • H10W70/60—Insulating or insulated package substrates; Interposers; Redistribution layers

Definitions

• thermosetting composition having thermosetting properties, for example, a thermosetting composition whose cured product can be suitably used as a heat sink for a power semiconductor device, a method for producing a thermosetting sheet using the thermosetting composition, a thermally conductive sheet using the thermosetting composition, and a heat-dissipating laminate, a heat-dissipating circuit board, and a power semiconductor device using the thermally conductive sheet.
• a power semiconductor device generally has a configuration in which a power semiconductor that converts and controls electric power and electronic components are mounted on a substrate that functions as a heat sink.
• power semiconductor devices used in various fields such as railways, automobiles, industry, and general home appliances are being replaced by power semiconductors using SiC, AlN, GaN, etc. in order to achieve further miniaturization, cost reduction, and efficiency improvement.
• heat generation due to the increasing density of integrated circuits has become a major problem in the electrical and electronic fields, making methods for dissipating heat an urgent issue.
• heat dissipation components such as heat sinks and heat dissipation fins are essential for heat dissipation, and there is a demand for materials that combine thermal conductivity and insulation to join components such as circuits containing power semiconductors to heat dissipation components such as heat sinks.
• ceramic substrates with high thermal conductivity such as alumina substrates and aluminum nitride substrates, have been used as materials that combine thermal conductivity and insulation.
• ceramic substrates have had issues such as being prone to cracking when subjected to impact, and being difficult to make thin and compact.
• Hexagonal boron nitride is generally in the form of thin plate crystals, which have high thermal conductivity in the planar direction of the thin plate, but low thermal conductivity in the thickness direction of the plate. Furthermore, when thin plate-shaped boron nitride is incorporated into heat-dissipating resin sheets, it is oriented parallel to the sheet surface when formed into a sheet, so the thermal conductivity in the thickness direction of the sheet is never good.
• Boron nitride agglomerated particles are an example of a material that increases the thermal conductivity of a sheet in the thickness direction. It is widely known that the use of boron nitride agglomerated particles can improve the thermal conductivity of a sheet in the thickness direction.
• the present applicant has previously developed a house-of-cards structure of boron nitride agglomerated particles (see, for example, Patent Document 2).
• Patent Document 3 agglomerated boron nitride particles that have a relatively large average particle size and a house-of-card structure that is less likely to collapse even when pressure is applied.
• boron nitride agglomerated particles ensure a heat conduction path due to their card-house structure, and by incorporating them into a heat-dissipating resin sheet, excellent heat conductivity in the thickness direction of the sheet is achieved. Furthermore, the boron nitride agglomerated particles are formed by agglomerating boron nitride particles without the use of a separate binder. Therefore, even when external force is applied during sheeting, the card-house structure does not easily collapse, maintaining the heat conduction path, allowing heat to be dissipated in the thickness direction of the sheet, and achieving excellent thermal conductivity (see, for example, Patent Documents 4 and 5). Furthermore, a known molding method for increasing the thermal conductivity in the thickness direction of a sheet involves bringing agglomerated boron nitride particles into surface contact with each other within the sheet to increase the thermal conductivity (see, for example, Patent Document 6).
• the applicant has proposed a resin composition containing an inorganic filler and a thermosetting compound, wherein the inorganic filler accounts for 50% by volume or more of the solid content of the resin composition, the inorganic filler accounts for 82% by volume or more of boron nitride filler (A), the boron nitride filler includes an aggregated filler, the thermosetting compound contains an epoxy resin with a mass average molecular weight of 5,000 or more, the epoxy equivalent (WPE) of the resin component in the resin composition is 100 ⁇ WPE ⁇ 300, and the storage modulus E' of the cured resin composition is 1 ⁇ (E' at 270°C)/(E' at 30°C) ⁇ 0.2 (Patent Document 7).
• thermosetting resin composition containing a thermosetting compound, an inorganic filler, and a polymer with a mass-average molecular weight of 10,000 or more, characterized in that the inorganic filler contains agglomerated boron nitride particles and the thermosetting compound contains an epoxy compound and a benzoxazine compound, as well as a thermally conductive sheet formed from the thermosetting resin composition (Patent Document 8).
• solder reflow process In which components are rapidly heated to melt the solder and join the metal components together.
• internal stress is applied due to the expansion of the components and moisture, causing deterioration of the components used in power semiconductor devices.
• the insulating performance of the cured product decreases, which has been an issue in reducing the reliability of the power semiconductor device. Therefore, a cured product of a thermosetting composition containing an inorganic filler and a thermosetting compound is required to have sufficient insulating properties even after reflow.
• sinter bonding a semiconductor chip with a thermally conductive sheet to a support substrate
• the semiconductor chip is first placed on the support substrate at the intended chip bonding location via a sinter bonding material under predetermined temperature and load conditions.
• a heat treatment is performed under high temperature and pressure conditions between the support substrate and the semiconductor chip on it, so that the solvent in the sinter bonding material evaporates and sintering proceeds between the sinterable particles.
• thermosetting composition containing an inorganic filler and a thermosetting compound
• the object of the present invention is to provide a thermosetting composition containing an inorganic filler and a thermosetting compound, in which the cured product (also referred to as the "cured product of the thermosetting composition") obtained by curing the thermosetting composition not only has sufficient insulating performance after the reflow process, but also has excellent high-temperature resistance, preventing cracks from occurring in the cured product or peeling when the cured product is bonded to a substrate under conditions in which an external force is applied at high temperatures, such as sinter bonding.
• the object of the present invention is to provide a thermosetting composition as well as a method for producing a thermosetting sheet using the thermosetting composition, a thermally conductive sheet made of a sheet-like cured product of the thermosetting composition, and a heat dissipation laminate, a heat dissipation circuit board, and a power semiconductor device that include the thermally conductive sheet.
• thermosetting compositions thermally conductive sheets, heat dissipation laminates, heat dissipation circuit boards, power semiconductor devices, and methods for producing thermosetting sheets.
• the first aspect of the present invention is a thermosetting composition containing an inorganic filler and a thermosetting compound, characterized in that the cured product of the thermosetting composition (also referred to as the "cured product of the thermosetting composition") has a breaking energy of 55 kPa or more as measured by three-point bending at 190°C, and a breaking energy of 80 kPa or more as measured by three-point bending at 150°C.
• a second aspect of the present invention is a thermosetting composition containing an inorganic filler and a thermosetting compound, wherein, when the breaking energy of a cured product (also referred to as a "cured product of the thermosetting composition") obtained by curing the thermosetting composition is determined by three-point bending measurement at 190°C as x and the breaking energy of a cured product (also referred to as a "cured product of the thermosetting composition") obtained by three-point bending measurement at 150°C as y, the value of x/y is 0.7 or more and 1.15 or less, and the value of x is 55 kPa or more.
• the second aspect of the present invention may also be the first aspect but also the second aspect.
• a third aspect of the present invention is the thermosetting composition according to the first or second aspect, characterized in that a cured product of the thermosetting composition has a Young's modulus of 5.5 GPa or more as determined by three-point bending measurement at 190°C.
• a fourth aspect of the present invention is the thermosetting composition according to any one of the first to third aspects, characterized in that a sheet-like cured product obtained by curing the thermosetting composition (also referred to as a "sheet-like cured product of the thermosetting composition”) has a thermal conductivity in the thickness direction at 25°C of 14 W/m K or more.
• a fifth aspect of the present invention is the thermosetting composition according to any one of the first to fourth aspects, characterized in that a sheet-like cured product of the thermosetting composition has a breakdown voltage of 6.5 kV or more when the thickness of the sheet-like cured product is 150 ⁇ m.
• a sixth aspect of the present invention is the thermosetting composition according to any one of the first to fifth aspects, characterized in that a sheet-shaped cured product of the thermosetting composition has a volume resistivity (1000 V, 200°C) of 3.0E+10 ⁇ cm or more.
• a seventh aspect of the present invention is the thermosetting composition according to any one of the first to sixth aspects, characterized in that the moisture absorption rate of the sheet-shaped cured product of the thermosetting composition is 0.7% by mass or more and 1.2% by mass or less.
• An eighth aspect of the present invention is the thermosetting composition according to any one of the first to seventh aspects, characterized in that the storage modulus at 200°C of a sheet-like cured product of the thermosetting composition is 6.0 GPa or more and 100 GPa or less.
• a ninth aspect of the present invention is the thermosetting composition according to any one of the first to eighth aspects, characterized in that the glass transition temperature (Tg) of a sheet-shaped cured product of the thermosetting composition is 170°C or higher.
• a tenth aspect of the present invention is a thermosetting composition according to any one of the first to ninth aspects, which comprises an epoxy compound and at least one of a phenolic resin, a benzoxazine compound, a polyarylate, a cyanate, and a maleimide.
• An eleventh aspect of the present invention is a thermosetting composition according to any one of the first to tenth aspects, which contains an epoxy compound and a phenolic resin.
• a twelfth aspect of the present invention is a thermosetting composition according to any one of the first to eleventh aspects, comprising a polyfunctional epoxy compound having three or more epoxy groups in one molecule and a mass average molecular weight (Mw) of less than 5,000.
• a thirteenth aspect of the present invention is a thermosetting composition according to any one of the first to twelfth aspects, comprising a high-molecular-weight epoxy compound having a mass-average molecular weight (Mw) of 5,000 or more.
• a fourteenth aspect of the present invention is the thermosetting composition according to any one of the first to thirteenth aspects, further comprising a polymer having a mass average molecular weight (Mw) of 5,000 or more in a proportion of 5% by mass or more and less than 30% by mass, relative to 100% by mass of the solid content excluding the inorganic filler.
• Mw mass average molecular weight
• a fifteenth aspect of the present invention is the thermosetting composition according to any one of the first to thirteenth aspects, wherein the thermosetting composition contains a polymer having a mass average molecular weight (Mw) of 5,000 or more in a proportion of 5% by mass to 23% by mass, relative to 100% by mass of the solid content excluding the inorganic filler.
• a sixteenth aspect of the present invention is the thermosetting composition according to any one of the first to fifteenth aspects, which comprises an epoxy compound, and wherein the epoxy equivalent (WPE) of the solid content of the thermosetting composition excluding the inorganic filler is 200 g/equivalent or more and less than 250 g/equivalent.
• WPE epoxy equivalent
• a seventeenth aspect of the present invention is the thermosetting composition according to any one of the first to sixteenth aspects, wherein the inorganic filler comprises agglomerated particles of boron nitride.
• An eighteenth aspect of the present invention is the thermosetting composition according to any one of the first to seventeenth aspects, wherein the inorganic filler is contained in a proportion of 30% by mass or more and less than 90% by mass relative to 100% by mass of the solid content of the total composition.
• a nineteenth aspect of the present invention is a thermally conductive sheet comprising a sheet-shaped cured product of the thermosetting composition of any one of the first to eighteenth aspects.
• a twentieth aspect of the present invention is a heat dissipation laminate comprising the thermally conductive sheet of the nineteenth aspect.
• a twenty-first aspect of the present invention is a heat dissipation circuit board comprising the thermally conductive sheet of the nineteenth aspect.
• a twenty-second aspect of the present invention is a power semiconductor device comprising the thermally conductive sheet of the nineteenth aspect.
• the 23rd aspect of the present invention is a method for producing a thermosetting sheet, comprising forming a thermosetting composition according to any one of aspects 1 to 18 into a sheet and subjecting it to low-temperature aging at an ambient temperature of 0°C or below.
• thermosetting composition proposed by the present invention not only provides sufficient insulating performance after a reflow process for the cured product, but also prevents cracks from occurring in the cured product and peeling from the bond when the cured product is bonded to a substrate under conditions where an external force is applied at a high temperature of 150°C or higher, such as in sinter bonding.
• the cured product of the thermosetting composition proposed by the present invention has such excellent high-temperature resistance that it can be suitably applied to various processes at high temperatures of 150°C or higher, and for example, when bonded to a substrate by sinter bonding, it can ensure excellent electrical conductivity and continuous bonding stability. Therefore, it is possible to provide a thermally conductive sheet that can be suitably used in heat dissipation laminates, heat dissipation circuit boards, power semiconductor devices, etc.
• FIG. 1 is a conceptual diagram of a particle cross section according to an example of a boron nitride agglomerated particle having a house-of-card structure.
• composition according to an embodiment of the present invention is a thermosetting composition containing a thermosetting compound and an inorganic filler.
• thermosetting composition refers to a composition containing a compound or resin that has the property of being cured by heat. That is, the term “thermosetting composition” is used as long as the composition has the property of being cured by heat, and may be one that has already been cured to a state where there is still room for curing (also referred to as “temporarily cured"), or one that has not yet been cured at all (also referred to as “uncured”).
• the term “resin” encompasses organic compounds, monomers, oligomers, and polymers, regardless of molecular weight.
• composition of the present invention may be in any form, such as a powder, a slurry, a liquid, a solid, or a molded product formed into a sheet, etc.
• the composition of the present invention also includes a thermosetting composition in a slurry form to be subjected to the coating step described below, a sheet that has undergone the coating step, and a sheet that has undergone steps such as coating and drying.
• thermosetting composition of the present invention i.e., a cured product obtained by curing the composition of the present invention (also referred to as the "cured product of the thermosetting composition")
• cured product of the thermosetting composition a sheet-like cured product obtained by curing the sheet-like composition of the present invention (also referred to as the "cured product of the thermosetting composition”)
• cured product of the present sheet a sheet-like cured product obtained by curing the sheet-like composition of the present invention
• the composition of the present invention can be converted into a fully cured product by heating.
• composition of the present invention can be formed into a sheet-like thermosetting composition (also referred to as the "present thermosetting sheet"), and the present thermosetting sheet can be cured to form a sheet with thermal conductivity (also referred to as the "present thermally conductive sheet”).
• the present thermally conductive sheet is the present sheet-like cured product, and is also a cured product of the present thermosetting sheet.
• the breaking energy of the fully cured product measured by three-point bending at 190°C is preferably 55 kPa or more, and the breaking energy of the fully cured product measured by three-point bending at 150°C is preferably 80 kPa or more.
• thermosetting compositions tend to accumulate strain during curing, and stress due to strain tends to accumulate at temperatures around the curing temperature. For example, in the case of a thermosetting composition containing an epoxy compound, stress due to strain tends to accumulate at 120 to 200°C.
• the breaking energy value of the present cured product obtained by three-point bending measurement at 190°C is 55 kPa or more and the breaking energy value of the present cured product obtained by three-point bending measurement at 150°C is 80 kPa or more, not only is the present sheet-like cured product less likely to crack when stress due to warping or distortion is applied, but the present cured product also deteriorates little even after being exposed to conditions in which internal stress is applied at high temperatures, such as in a reflow process, and can maintain its dielectric strength voltage, and further when the present cured product is bonded to a substrate by sinter bonding under conditions in which further external force is applied at high temperatures, the present cured product can be prevented from cracking or the bond from peeling off.
• the composition of the present invention is preferably one in which the breaking energy of the cured product, as measured by three-point bending at 190° C., is 55 kPa or more, more preferably 60 kPa or more, even more preferably 70 kPa or more, and even more preferably 80 kPa or more.
• the upper limit is not particularly limited, but is likely to be around 500 kPa, and may be 300 kPa or less, or even 150 kPa or less.
• the composition of the present invention is preferably one in which the breaking energy of the cured product, as measured by three-point bending at 150° C., is 80 kPa or more, more preferably 85 kPa or more, even more preferably 90 kPa or more, and even more preferably 100 kPa or more.
• the upper limit is not particularly limited, but is presumed to be around 500 kPa, and may be 300 kPa or less, or even 200 kPa or less.
• the breaking energy of the fully cured product obtained by three-point bending measurement at 190°C is defined as x
• the breaking energy of the fully cured product obtained by three-point bending measurement at 150°C is defined as y
• the value of x/y is preferably 0.7 or more and 1.15 or less
• the value of x is 55 kPa or more.
• the ratio (x/y) of the breaking energy x obtained by three-point bending measurement at 190°C to the breaking energy y obtained by three-point bending measurement of the cured product at 150°C is 0.7 or more, and the value of x is 55 kPa or more, bending stress can be maintained even in high temperature ranges of 150°C and above, so that the cured product will deteriorate little even after being exposed to conditions in which internal stress is applied at high temperatures, such as in a reflow process, and will be able to maintain its dielectric strength voltage.Furthermore, when the cured product is bonded to a substrate by sinter bonding under conditions in which external force is applied at high temperatures, cracks will occur in the cured product and the bond will not peel off.On the other hand, if the ratio (x/y) is 1.15 or less, the breaking energy will be similar at 150°C and 190°C, so that deterioration will be reduced when the heating cycle is repeated.
• the difference in breaking strength between 150°C and 190°C becomes smaller and the ratio (x/y) approaches 1, so that even when internal stress or external force is applied at temperatures above 200°C or when the temperature is subsequently lowered, the stress is dispersed, and it is thought that not only is the insulation resistance improved in reflow tests and sinter resistance tests, but the sheet is also less likely to crack or peel at the interface with the substrate.
• the composition of the present invention preferably has a ratio (x/y) of the breaking energy x obtained by three-point bending measurement at 190°C to the breaking energy y obtained by three-point bending measurement at 150°C of the cured product, of 0.7 or more, more preferably 0.72 or more, even more preferably 0.74 or more, and even more preferably 0.76 or more.
• it is preferably 1.15 or less, even more preferably 1.1 or less, even more preferably 1.05 or less, and even more preferably 1.03 or less.
• the breaking energy value of the cured product obtained by three-point bending measurement at 190°C, the breaking energy value obtained by three-point bending measurement at 150°C, or the ratio (x/y) of the breaking energy x obtained by three-point bending measurement at 190°C to the breaking energy y obtained by three-point bending measurement at 150°C falls within the above-mentioned ranges
• Tg glass transition temperature
• One preferred example is to prepare the composition of the present invention by increasing the content of a polyfunctional epoxy compound as a thermosetting compound and reducing the content of a polymer, such as an epoxy polymer, to increase the number of crosslinking points, and further using a phenolic resin-based curing agent as a curing agent to promote crosslinking, thereby increasing the crosslink density of the cured product, and by performing low-temperature aging.
• Increasing the crosslink density of the cured product increases the strength of contact between inorganic fillers, thereby increasing the fracture energy at high temperatures.
• increasing the strength of contact between inorganic fillers reduces the thermal resistance between the inorganic fillers, thereby increasing, for example, the thermal conductivity.
• the method is not limited to the above. For the methods for measuring the breaking energy of the cured product by three-point bending at 190°C and the breaking energy by three-point bending at 150°C, see the methods described in the Examples below.
• the breaking energy of the fully cured product at 190°C is within the above range
• the breaking energy of the fully cured product at 150°C is within the above range
• the ratio (x/y) of the breaking energy x at 190°C to the breaking energy y at 150°C of the fully cured product is within the above range.
• the composition of the present invention is preferably one that, when cured, i.e., when formed into a fully cured product, has a Young's modulus of 5.5 GPa or more as determined by three-point bending measurement at 190°C.
• the Young's modulus value obtained by three-point bending measurement of the present cured product at 190°C is 5.5 GPa or more, not only will the present sheet-shaped cured product be less likely to crack when stress due to warping or distortion is applied, but the present cured product will also be less likely to deteriorate and be able to maintain its dielectric strength voltage even after being exposed to conditions in which internal stress is applied at high temperatures, such as in a reflow process, and will be able to prevent cracking of the present cured product and separation of the bond when bonded to a substrate by sinter bonding under conditions in which an external force is applied at high temperatures of 150°C or more.
• the composition of the present invention is preferably one in which the Young's modulus of the cured product, as determined by three-point bending measurement at 190° C., is 5.5 GPa or more, more preferably 5.6 GPa or more, even more preferably 5.7 GPa or more, even more preferably 5.8 GPa or more, even more preferably 5.9 GPa or more, and even more preferably 6.0 GPa or more.
• the upper limit is not particularly limited, but is presumed to be around 100 GPa, and may be 50 GPa or less, or even 10 GPa or less.
• the composition of the present invention is preferably one that, when cured, i.e., when formed into a fully cured product, has a Young's modulus of 5.5 GPa or more as determined by three-point bending measurement at 150°C.
• the Young's modulus value obtained by three-point bending measurement of the present cured product at 150°C is 5.5 GPa or more, not only will the present sheet-like cured product be less likely to crack when stress due to warping or distortion is applied, but the present cured product will also be less likely to deteriorate and be able to maintain its dielectric strength voltage even after being exposed to conditions in which internal stress is applied at high temperatures, such as in a reflow process, and will be able to prevent cracking of the present cured product and separation of the bond when bonded to a substrate by sinter bonding under conditions in which an external force is applied at a high temperature of 150°C or more.
• the composition of the present invention is preferably one in which the Young's modulus of the cured product, as determined by three-point bending measurement at 150° C., is 5.5 GPa or more, more preferably 5.8 GPa or more, even more preferably 6.0 GPa or more, and even more preferably 6.3 GPa or more.
• the upper limit is not particularly limited, but is presumed to be around 100 GPa, and may be 50 GPa or less, or even 10 GPa or less.
• the composition of the present invention so that the Young's modulus values obtained by three-point bending measurement at 190°C and 150°C of the cured product fall within the above-mentioned ranges, it is preferable to adjust the type and content of the thermosetting compound or curing agent to increase the crosslink density of the cured product, and to adjust the polymer concentration or low-temperature aging conditions, thereby preparing the composition of the present invention so that the cured product can maintain its bending stress at temperatures above the glass transition temperature (Tg).
• Tg glass transition temperature
• One preferred example is to increase the content of a polyfunctional epoxy compound as a thermosetting compound and reduce the content of a polymer, such as an epoxy polymer, to increase the number of crosslinking points, and further use a phenolic resin-based curing agent as a curing agent to promote crosslinking, thereby increasing the crosslink density of the cured product, and to perform low-temperature aging.
• Increasing the crosslink density of the cured product can increase the Young's modulus at high temperatures.
• the method is not limited to the above. For the method of measuring the Young's modulus of the cured product by three-point bending at 150°C and 190°C, see the method described in the Examples below.
• the composition of the present invention is preferably one that, when formed into a sheet and cured, i.e., into the present sheet-like cured product, has a thermal conductivity in the thickness direction at 25°C of 14 W/m K or more. If the thermal conductivity of the sheet-like cured product in the thickness direction at 25° C. is 14 W/m ⁇ K or more, it can be suitably used in power semiconductor devices that operate at high temperatures. From this viewpoint, the composition of the present invention is preferably one that results in a sheet-like cured product with a thermal conductivity in the thickness direction at 25°C of 14 W/m K or more, more preferably 15 W/m K or more, and even more preferably 17 W/m K or more.
• the composition of the present invention can be prepared so that the thermal conductivity of the sheet-like cured product falls within the above range by adjusting, for example, the type of thermosetting compound, the type and content of the inorganic filler, the conditions in the low-temperature aging step, the conditions in the pressurizing step, the conditions in the curing step, etc.
• the present invention is not limited to these methods.
• the method of measuring the thermal conductivity in the thickness direction of the sheet-like cured product please refer to the method in the Examples described below.
• the composition of the present invention is preferably one that, when formed into a sheet and cured, i.e., when formed into the present sheet-like cured product, has a dielectric breakdown voltage of 6.5 kV or more when the thickness of the present sheet-like cured product is 150 ⁇ m. If the dielectric breakdown voltage of the sheet-like cured product is 6.5 kV or more, it can be suitably used in power semiconductor devices that operate power semiconductors at high voltages.
• the composition of the present invention is preferably one that results in a dielectric breakdown voltage of the sheet-like cured product of 6.5 kV or more, more preferably 7 kV or more, even more preferably 7.5 kV or more, even more preferably 8 kV or more, and even more preferably 9 kV or more.
• the composition of the present invention can be prepared so that the breakdown voltage of the sheet-like cured product falls within the above range by adjusting, for example, the type of thermosetting compound, the type and content of the inorganic filler, the conditions in the low-temperature aging step, the conditions in the pressure step, the conditions in the curing step, etc.
• the present invention is not limited to these methods.
• the method for measuring the breakdown voltage of the sheet-like cured product please refer to the method in the Examples described below.
• the composition of the present invention is preferably one in which, when formed into a sheet and cured, i.e., into the present sheet-like cured product, the volume resistivity (1000 V, 200°C) of the present sheet-like cured product is 3.0E+10 ⁇ cm or more. It is preferable that the volume resistivity of the sheet-like cured product is 3.0E+10 ⁇ cm or more, since this is favorable from the viewpoint of electrical insulation.
• the composition of the present invention is preferably one that results in a sheet-like cured product with a volume resistivity of 3.0E+10 ⁇ cm or more, more preferably 3.1E+10 ⁇ cm or more, and even more preferably 3.2E+10 ⁇ cm or more.
• thermosetting compound or curing agent is adjusted to increase the crosslink density of the cured product, and the polymer concentration is adjusted to allow the cured product to maintain electrical insulation even at temperatures above the glass transition temperature (Tg).
• a preferred example is to increase the content of a polyfunctional epoxy compound as a thermosetting compound, reduce the content of a polymer, such as an epoxy polymer, to increase the number of crosslinking points, and further use a phenolic resin-based curing agent as a curing agent to promote crosslinking, thereby increasing the crosslink density of the cured product, and then perform low-temperature aging to prepare the composition of the present invention.
• a polyfunctional epoxy compound as a thermosetting compound
• reduce the content of a polymer such as an epoxy polymer
• a phenolic resin-based curing agent as a curing agent to promote crosslinking, thereby increasing the crosslink density of the cured product, and then perform low-temperature aging to prepare the composition of the present invention.
• the volume resistivity (1000 V, 200° C.) of the sheet-like cured product can be measured by the method described in the Examples below.
• the composition of the present invention is preferably one in which, when the composition of the present invention is formed into a sheet and cured, i.e., when the composition is formed into the present sheet-like cured product, the moisture absorption rate of the present sheet-like cured product is 0.7 mass % or more and 1.2 mass % or less.
• a moisture absorption rate of 0.7% by mass or more of the cured sheet material is preferable because the absorbed moisture and the hydroxyl groups in the cured sheet material form hydrogen bonds to toughen the cured sheet material and improve its bending resistance, whereas a moisture absorption rate of 1.2% by mass or less is preferable because it is good from the viewpoint of moisture absorption reflow resistance.
• the composition of the present invention is such that the moisture absorption rate of the sheet-like cured product is preferably 0.7% by mass or more, more preferably 0.72% by mass or more, and even more preferably 0.75% by mass or more, and is preferably 1.2% by mass or less, more preferably 1.1% by mass or less, and even more preferably 1.0% by mass or less.
• composition of the present invention so that the moisture absorption rate of the sheet-like cured product falls within the above range, methods such as adjusting the amount of epoxy monomer (i.e., epoxy compound other than epoxy polymer) and the amount of curing agent to strengthen crosslinking or adjust the hydroxyl group concentration in the resin component, or adjusting low-temperature aging conditions, can be used.
• epoxy monomer i.e., epoxy compound other than epoxy polymer
• curing agent to strengthen crosslinking or adjust the hydroxyl group concentration in the resin component, or adjusting low-temperature aging conditions
• a preferred example is to increase the content of a polyfunctional epoxy compound as a thermosetting compound and reduce the content of a polymer, such as an epoxy polymer, to increase the number of crosslinking points, and further use a phenolic resin-based curing agent as a curing agent to promote crosslinking, thereby increasing the crosslink density of the cured product, and then perform low-temperature aging to prepare the composition of the present invention.
• a polyfunctional epoxy compound as a thermosetting compound and reduce the content of a polymer, such as an epoxy polymer, to increase the number of crosslinking points, and further use a phenolic resin-based curing agent as a curing agent to promote crosslinking, thereby increasing the crosslink density of the cured product, and then perform low-temperature aging to prepare the composition of the present invention.
• a phenolic resin-based curing agent as a curing agent to promote crosslinking, thereby increasing the crosslink density of the cured product, and then perform low-temperature aging to prepare the composition
• the composition of the present invention is preferably such that when the composition of the present invention is formed into a sheet and cured, i.e., when the composition is formed into a sheet-like cured product, the storage modulus of the sheet-like cured product at 200°C is 6.0 GPa or more and 100 GPa or less. When the storage modulus at 200°C of the present sheet-shaped cured product is within the above range, the present sheet-shaped cured product is less likely to crack at high temperatures.
• the storage modulus of the composition of the present invention in the form of a cured sheet at 200°C is preferably 6.0 GPa or more, more preferably 7.0 GPa or more, even more preferably 7.5 GPa or more, and even more preferably 7.7 GPa or more.
• it is preferably 100 GPa or less, even more preferably 90 GPa or less, even more preferably 80 GPa or less, and may be 50 GPa or less, 20 GPa or less, or 15 GPa or less.
• the epoxy equivalent weight of the resin component for example, the amount of polyfunctional epoxy, the ratio of epoxy polymer to epoxy compound other than epoxy polymer, or the low-temperature aging conditions may be adjusted.
• a preferred example is to increase the content of polyfunctional epoxy compound as a thermosetting compound and reduce the content of polymer, e.g., epoxy polymer, to increase the number of crosslinking points, and further use a phenolic resin-based curing agent as a curing agent to promote crosslinking, thereby increasing the crosslink density of the cured product, and then perform low-temperature aging.
• the present invention is not limited to these methods.
• the storage modulus of the sheet-like cured product at 200°C can be measured by laminating a sheet-like thermosetting composition, adjusting the sample thickness to 0.1 to 1.0 mm, heat-curing to form a sheet-like cured product, cutting the sheet-like cured product into strips 4 mm wide, and subjecting the strips to a dynamic viscoelasticity test in a tensile mode.
• a sheet-like thermosetting composition adjusting the sample thickness to 0.1 to 1.0 mm
• heat-curing to form a sheet-like cured product
• cutting the sheet-like cured product into strips 4 mm wide and subjecting the strips to a dynamic viscoelasticity test in a tensile mode.
• the composition of the present invention is preferably one that, when formed into a sheet and cured, i.e., when formed into the present sheet-like cured product, has a glass transition temperature (Tg) of 170°C or higher. It is preferable that the glass transition temperature (Tg) of the cured sheet material is 170° C. or higher, since the cured sheet material is strong even at high temperatures of 175° C. or higher.
• the upper limit is preferably 300° C. or lower, from the viewpoint of the cracking tendency of the cured sheet material. From this viewpoint, the composition of the present invention is one that results in a sheet-like cured product having a glass transition temperature (Tg) of preferably 170° C.
• composition of the present invention is one that preferably has a glass transition temperature of 300° C. or lower, more preferably 275° C. or lower, and even more preferably 250° C. or lower.
• thermosetting compound or curing agent are adjusted to increase the crosslink density of the cured product and the polymer concentration is adjusted.
• a preferred example is to increase the content of a polyfunctional epoxy compound as a thermosetting compound and reduce the content of a polymer, such as an epoxy polymer, to increase the number of crosslinking points, and further use a phenolic resin-based curing agent as a curing agent to promote crosslinking, thereby increasing the crosslink density of the cured product, and to perform low-temperature aging to prepare the composition of the present invention.
• the present invention is not limited to these methods.
• the method for measuring the glass transition temperature (Tg) of the sheet-like cured product please refer to the method in the Examples section described below.
• the epoxy equivalent weight (WPE) of the component (also referred to as the "resin component") excluding the solvent and the inorganic filler from the composition of the present invention is preferably WPE ⁇ 250 g/equivalent.
• the solid content of the composition of the present invention means the components remaining after excluding the solvent from the composition of the present invention.
• the epoxy equivalent weight (WPE) here refers to the mass (g/equivalent) of the resin component per equivalent of epoxy group.
• the epoxy equivalent (WPE) of the resin component of the composition of the present invention is preferably less than 250 g/equivalent, more preferably 245 g/equivalent or less, even more preferably 240 g/equivalent or less, even more preferably 235 g/equivalent or less, and even more preferably 230 g/equivalent or less.
• the epoxy equivalent (WPE) of the resin component of the composition of the present invention is preferably 100 g/eq or more, more preferably 110 g/eq or more, even more preferably 120 g/eq or more, even more preferably 150 g/eq or more, even more preferably 170 g/eq or more, even more preferably 200 g/eq or more, and even more preferably 210 g/eq or more.
• methods include adjusting the content ratio of epoxy compounds having a specified epoxy equivalent weight, such as epoxy polymers and polyfunctional epoxy compounds, or adjusting the type and content of curing agents.
• One preferred example is to increase the content ratio of polyfunctional epoxy compounds as thermosetting compounds and reduce the content ratio of polymers, such as epoxy polymers, and further adjust the content of a phenolic resin-based curing agent to adjust the epoxy equivalent weight (WPE) of the resin component of the composition of the present invention within the above range.
• methods are not limited to these.
• thermosetting compound contained in the composition of the present invention examples include epoxy compounds, phenolic resins, unsaturated polyester resins, melamine resins, urea resins, benzoxazine compounds, cyanates, and maleimides.
• the content of the thermosetting compound is preferably 10% by mass or more and 70% by mass or less relative to 100% by mass of the components excluding volatile components, such as solvents, in the composition of the present invention (also referred to as "solids content"). If the content of the thermosetting compound is 10% by mass or more, it is preferable because the moldability is good, and on the other hand, if it is 70% by mass or less, it is preferable because the content of other components can be secured and, for example, thermal conductivity can be increased.
• the content of the thermosetting compound is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, relative to 100% by mass of the solid content in the composition of the present invention, while it is even more preferable for the content to be 60% by mass or less.
• an epoxy compound is used as the thermosetting compound
• the curing agent or the thermosetting catalyst corresponds to the thermosetting compound, and therefore is included in the thermosetting compound in the above-mentioned "content of thermosetting compound.”
• composition of the present invention preferably contains an epoxy compound as the thermosetting compound.
• the epoxy compounds preferably account for 30 to 100 mass%, more preferably 40 mass% or more, even more preferably 50 mass% or more, even more preferably 60 mass% or more, and even more preferably 70 mass% or more.
• the epoxy compound in this case also includes the epoxy polymer described below.
• the epoxy compound used as the thermosetting compound in the composition of the present invention may be any compound having one or more oxirane rings, i.e., epoxy groups, in one molecule.
• the epoxy group contained in the epoxy compound may be either an alicyclic epoxy group or a glycidyl group. From the standpoint of reaction speed and heat resistance, a glycidyl group is more preferable.
• epoxy compounds include epoxy group-containing silicon compounds, aliphatic epoxy compounds, bisphenol A or F epoxy compounds, novolac epoxy compounds, aromatic epoxy compounds, alicyclic epoxy compounds, glycidyl ester epoxy compounds, polyfunctional epoxy compounds, and polymeric epoxy compounds.
• the epoxy compound may be an aromatic epoxy group-containing compound.
• Specific examples include bisphenol-type epoxy compounds obtained by glycidylating bisphenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol AD, tetramethylbisphenol S, and tetrafluorobisphenol A; biphenyl-type epoxy compounds; epoxy compounds obtained by glycidylating dihydric phenols such as dihydroxynaphthalene and 9,9-bis(4-hydroxyphenyl)fluorene; epoxy compounds obtained by glycidylating trisphenols such as 1,1,1-tris(4-hydroxyphenyl)methane; epoxy compounds obtained by glycidylating tetrakisphenols such as 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane; novolac-type epoxy compounds obtained by glycidylating novolacs such as
• an epoxy compound having at least one skeleton selected from epoxy compounds having a biphenyl skeleton, epoxy compounds having a dicyclopentadiene skeleton, and epoxy compounds having a naphthalene skeleton.
• the composition of the present invention preferably contains a polyfunctional epoxy compound as described below.
• polyfunctional epoxy compound refers to an epoxy compound having two or more epoxy groups in one molecule and a mass average molecular weight (Mw) of less than 5,000, and the composition of the present invention preferably contains a polyfunctional epoxy compound having three or more epoxy groups in one molecule and a mass average molecular weight (Mw) of less than 5,000. It is more preferable that the polyfunctional epoxy compound contains a compound having four or more epoxy groups in one molecule.
• polyfunctional epoxy compound allows for the introduction of highly polar epoxy groups at a high density, thereby enhancing the effects of physical interactions such as van der Waals forces and hydrogen bonding, thereby improving the adhesion between the thermally conductive sheet formed from the composition of the present invention and electrical conductors such as metal plates and circuit boards. Furthermore, the inclusion of a polyfunctional epoxy compound increases the storage modulus of the thermally conductive sheet, thereby providing a strong anchoring effect after the cured product penetrates into the irregularities on the surface of the electrical conductor to be adhered, thereby improving the adhesion between the thermally conductive sheet and electrical conductors such as metal plates and circuit boards.
• the inclusion of a polyfunctional epoxy compound in the composition of the present invention further increases the crosslink density of the cured product, thereby increasing the breaking energy of the cured product measured by three-point bending at 150°C and 190°C.
• the inclusion of a polyfunctional epoxy compound tends to increase the hygroscopicity of the composition of the present invention, but by improving the reactivity of the epoxy groups, the amount of hydroxyl groups during the reaction can be reduced, and the increase in hygroscopicity can be suppressed.
• by preparing the composition of the present invention by combining an epoxy polymer and a polyfunctional epoxy compound, which will be described later, it becomes possible to achieve both high elasticity and low moisture absorption in the thermally conductive sheet.
• the polyfunctional epoxy compound is an epoxy compound having two or more epoxy groups per molecule, from the perspective of increasing the storage modulus of the cured product, particularly at high temperatures, which is important in devices such as power semiconductor devices that generate a lot of heat.
• epoxy compounds having three or more epoxy groups per molecule are preferred, and epoxy compounds having four or more epoxy groups per molecule are even more preferred.
• Having multiple epoxy groups, particularly glycidyl groups, per molecule improves the crosslink density of the cured product, and the cured product, the thermally conductive sheet, becomes stronger.
• the thermally conductive sheet retains its shape without deforming or breaking, thereby preventing the formation of voids and other gaps within the thermally conductive sheet.
• the molecular weight of the polyfunctional epoxy compound is preferably 800 or less, more preferably 700 or less, even more preferably 650 or less, particularly preferably 100 or more or 630 or less, even more preferably 200 or more or 600 or less.
• the composition contains one that is liquid at 25°C.
• the polyfunctional epoxy compound does not contain an amine-based or amide-based structure containing a nitrogen atom.
• the epoxy equivalent of a polyfunctional epoxy compound is preferably 75 g/equivalent or more, and more preferably 80 g/equivalent or more, from the viewpoint of improving the heat resistance of the thermally conductive sheet.
• it is preferably 200 g/equivalent or less, and even more preferably 180 g/equivalent or less, even more preferably 160 g/equivalent or less, and even more preferably 150 g/equivalent or less.
• the polyfunctional epoxy compound may be any compound having two or more epoxy groups in one molecule, and is preferably a polyfunctional epoxy compound having three or more epoxy groups in one molecule and a molecular weight of 800 or less, and more preferably 650 or less.
• EX321L, DLC301, DLC402, etc., manufactured by Nagase ChemteX Corporation can be used. These polyfunctional epoxy compounds may be used alone or in combination of two or more.
• the composition of the present invention preferably contains a high-molecular-weight epoxy compound (also referred to as an "epoxy polymer”) having a mass-average molecular weight (Mw) of 5,000 or more.
• a high-molecular-weight epoxy compound also referred to as an "epoxy polymer” having a mass-average molecular weight (Mw) of 5,000 or more.
• epoxy polymers include phenoxy resins having at least one skeleton selected from the group consisting of a bisphenol A skeleton, a bisphenol F skeleton, a bisphenol A/F mixed skeleton, a naphthalene skeleton, a fluorene skeleton, a biphenyl skeleton, anthracene skeleton, a pyrene skeleton, a xanthene skeleton, an adamantane skeleton, and a dicyclopentadiene skeleton.
• the epoxy polymer is preferably an epoxy polymer having at least one structure selected from the structure represented by the following formula (1) (also referred to as “structure (1)”) and the structure represented by the following formula (2) (also referred to as “structure (2)”):
• R1 and R2 each represent an organic group, at least one of which is an organic group having a molecular weight of 16 or more, and in formula (2), R3 represents a divalent cyclic organic group.
• organic group refers to any group containing carbon atoms. Specific examples include alkyl groups, alkenyl groups, and aryl groups, which may be substituted with halogen atoms, groups containing heteroatoms, or other hydrocarbon groups. The same applies hereinafter.
• At least one of R1 and R2 represents an organic group having a molecular weight of 16 or more, preferably a molecular weight of 16 to 1,000.
• Examples include alkyl groups such as ethyl, propyl, butyl, pentyl, hexyl, and heptyl, and aryl groups such as phenyl, tolyl, xylyl, naphthyl, and fluorenyl.
• Both R1 and R2 may be organic groups having a molecular weight of 16 or more, or one may be an organic group having a molecular weight of 16 or more and the other may be an organic group having a molecular weight of 15 or less or a hydrogen atom.
• one is an organic group having a molecular weight of 16 or more and the other is an organic group having a molecular weight of 15 or less, and in particular, one being a methyl group and the other being a phenyl group, which is preferred from the standpoint of easier control of handleability such as resin viscosity and the strength of the cured product.
• R3 is a divalent cyclic organic group, which may be an aromatic ring structure such as a benzene ring structure, a naphthalene ring structure, or a fluorene ring structure, or an aliphatic ring structure such as cyclobutane, cyclopentane, or cyclohexane. These may also independently have a substituent such as a hydrocarbon group or a halogen atom.
• the divalent bond may be a divalent group on a single carbon atom or on different carbon atoms.
• Preferred examples include divalent aromatic groups having 6 to 100 carbon atoms and groups derived from cycloalkanes having 2 to 100 carbon atoms, such as cyclopropane and cyclohexane.
• the 3,3,5-trimethyl-1,1-cyclohexylene group (also referred to as "structure (4)") represented by the following formula (4) is preferred from the viewpoints of controlling handleability such as resin viscosity and the strength of the cured product.
• the epoxy polymer has a fluorene skeleton represented by the following formula (5).
• the rigidity of the fluorene skeleton represented by the following formula (5) results in excellent heat resistance and low linear expansion, and the molecular weight per unit is larger than that of ordinary epoxy compounds, so the proportion of secondary hydroxyl groups, which cause moisture absorption, in the overall molecular structure is relatively low, resulting in low moisture absorption.
• the epoxy polymer may include an epoxy polymer having a structure represented by the following formula (3) (also referred to as "structure (3)").
• R 4 , R 5 , R 6 , and R 7 are each an organic group having a molecular weight of at least 15. Preferably, they are alkyl groups having a molecular weight of 15 to 1,000, and it is particularly preferred that R 4 , R 5 , R 6 , and R 7 are all methyl groups from the viewpoints of controlling handleability such as resin viscosity and the strength of the cured product.
• the epoxy polymer is preferably an epoxy polymer containing either one of Structure (1) or Structure (2) and Structure (3), from the viewpoint of achieving both reduced moisture absorption and strength retention in the present cured product and the present thermal conductive sheet.
• Such epoxy polymers contain more hydrophobic hydrocarbon and aromatic structures than general epoxy polymers having a bisphenol A or bisphenol F skeleton, and therefore, by blending such epoxy polymers, it is possible to reduce the moisture absorption amount of the thermally conductive sheet, which is the cured product obtained.
• the epoxy polymer contains a large amount of hydrophobic structures (1), (2), and (3).
• the mass average molecular weight (Mw) of the epoxy polymer is preferably 5,000 or more, and more preferably 10,000 or more, more preferably 15,000 or more, more preferably 20,000 or more, more preferably 25,000 or more, and even more preferably 30,000 or more.
• An upper limit of 100,000 or less is preferred. Keeping the Mw in this range tends to improve the film-forming properties of the composition of the present invention and improve the handleability of the uncured thermosetting sheet. Improved film-forming properties also have the effect of binding fillers together in the uncured thermosetting sheet, making voids less likely to occur.
• the epoxy equivalent of the epoxy polymer is preferably 5,000 g/equivalent or more, 7,000 g/equivalent or more, and more preferably 8,000 g/equivalent or more.
• it is preferably 25,000 g/equivalent or less, and more preferably 20,000 g/equivalent or less.
• the mass average molecular weight (Mw) of the epoxy polymer is a value calculated as polystyrene measured by gel permeation chromatography.
• the epoxy equivalent is defined as "the mass of an epoxy polymer containing one equivalent of epoxy groups" and can be measured in accordance with JIS K7236.
• the above epoxy polymers may be used alone or in combination of two or more.
• the content of the epoxy polymer is preferably 5% by mass or more and less than 30% by mass relative to 100% by mass of the components (resin components) excluding the solvent and inorganic filler from the composition of the present invention, in other words, the solid content of the composition of the present invention excluding the inorganic filler.
• the epoxy polymer content of the composition of the present invention is preferably 5% by mass or more relative to 100% by mass of the solids content excluding the inorganic filler, since film-forming properties can be maintained, while the epoxy polymer content of less than 30% by mass is preferably less than 30% by mass, since flexibility of the thermosetting sheet in an uncured state can be maintained.
• the content of the epoxy polymer is preferably 5% by mass or more, more preferably 7.5% by mass or more, and even more preferably 10% by mass or more, based on 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler.
• the content is preferably less than 30% by mass, more preferably 27.5% by mass or less, even more preferably 25% by mass or less, even more preferably 24% by mass or less, even more preferably 23% by mass or less, and even more preferably 22% by mass or less.
• the content of the polyfunctional epoxy compound is preferably 5% by mass or more and 95% by mass or less based on the components (resin components) excluding the solvent and inorganic filler from the composition of the present invention, in other words, 100% by mass of the solid content excluding the inorganic filler from the composition of the present invention.
• the content of the polyfunctional epoxy compound is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, based on 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler, and is preferably 95% by mass or less, and even more preferably 90% by mass or less.
• the content of the polyfunctional epoxy compound having three or more epoxy groups in one molecule is preferably 5% by mass or more and 50% by mass or less, based on 100% by mass of the solid content excluding the inorganic filler from the composition of the present invention. If the content of the polyfunctional epoxy compound having three or more epoxy groups in one molecule is 5% by mass or more, the crosslink density of the cured product can be increased and the storage modulus of the cured product can be maintained, thereby improving resistance, for example, when exposed to conditions in which internal stress or external force is applied at high temperatures, such as reflow resistance and sintering resistance, which is preferable.
• the content of the polyfunctional epoxy compound having three or more epoxy groups in one molecule is preferably 5% by mass or more, more preferably 7.5% by mass or more, and even more preferably 10% by mass or more, based on 100% by mass of the solids content excluding the inorganic filler from the composition of the present invention.
• the content of the polyfunctional epoxy compound having three or more epoxy groups in one molecule is 50% by mass or less, the toughness of the present thermosetting sheet in an uncured state can be maintained and the moisture absorption rate of the present sheet-like cured product can be reduced, which is preferable.
• the content of the polyfunctional epoxy compound having three or more epoxy groups in one molecule is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less, based on 100% by mass of the solids content excluding the inorganic filler from the composition of the present invention.
• the content of polyfunctional epoxy compounds having three or more epoxy groups per molecule and an epoxy equivalent of 25 to 200 g/equivalent is preferably 5% by mass or more and 50% by mass or less, based on 100% by mass of the solids content excluding the inorganic filler from the composition of the present invention, from the viewpoint of adjusting the epoxy equivalent (WPE) of the resin component of the composition of the present invention within a suitable range, and is more preferably 7.5% by mass or more or 45% by mass or less, and even more preferably 10% by mass or more or 40% by mass or less.
• the content of the polyfunctional epoxy compound having three or more epoxy groups in one molecule is preferably 20 parts by mass or more and 500 parts by mass or less per 100 parts by mass of the epoxy polymer.
• the content of the polyfunctional epoxy compound having three or more epoxy groups in one molecule is 20 parts by mass or more per 100 parts by mass of the epoxy polymer, this is preferred because it can increase the crosslink density of the cured product and improve resistance, for example, when exposed to conditions where internal stress or external force is applied at high temperatures, such as reflow resistance and sintering resistance.
• the content of the polyfunctional epoxy compound having three or more epoxy groups in one molecule is preferably 20 parts by mass or more and 500 parts by mass or less, more preferably 30 parts by mass or more or 400 parts by mass or less, even more preferably 40 parts by mass or more or 350 parts by mass or less, even more preferably 60 parts by mass or more or 300 parts by mass or less, and even more preferably 90 parts by mass or more or 200 parts by mass or less, relative to 100 parts by mass of the epoxy polymer.
• the content ratio of inorganic filler to epoxy polymer is preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.03 or more, from the viewpoint of maintaining the film-forming properties of the thermosetting sheet.
• it is preferably less than 0.2, more preferably 0.15 or less, and even more preferably 0.14 or less.
• the mass ratio of the inorganic filler to the polyfunctional epoxy compound having three or more epoxy groups in one molecule is preferably 0.02 or more, more preferably 0.03 or more, and even more preferably 0.04 or more, from the viewpoint of improving the retention of the inorganic filler.
• it is preferably 0.2 or less, more preferably 0.18 or less, and even more preferably 0.16 or less.
• the mass ratio of the inorganic filler to the epoxy compound (epoxy compound/inorganic filler) is preferably 0.2 or more, more preferably 0.22 or more, and even more preferably 0.25 or more.
• the thermal conductivity of the thermally conductive sheet it is preferably 0.6 or less, more preferably 0.57 or less, and even more preferably 0.55 or less.
• the composition of the present invention may contain, in place of or together with the epoxy polymer, a polymer other than the epoxy polymer having a mass average molecular weight (Mw) of 5,000 or more (also referred to as "other polymer”).
• Mw mass average molecular weight
• the term "polymer” encompasses epoxy polymers and other polymers.
• the other polymer may be either a thermoplastic resin or a thermosetting resin.
• the thermoplastic resins and thermosetting resins include thermoplastic resins such as polyphenylene ether, polyphenylene sulfide, polyarylate, polysulfone, polyether sulfone, polyether ether ketone, and polyether ketone.
• the thermoplastic resins and thermosetting resins may also include heat-resistant resins known as super engineering plastics, such as thermoplastic polyimide, thermosetting polyimide, benzoxazine, and reaction products of polybenzoxazole and benzoxazine.
• thermosetting resins examples include styrene-based polymers such as styrene and alkylstyrene, (meth)acrylic polymers such as alkyl (meth)acrylate and glycidyl (meth)acrylate, styrene-based-(meth)acrylic copolymers such as styrene-glycidyl methacrylate, polyvinyl alcohol derivatives such as polyvinyl butyral, polyvinyl benzal, and polyvinyl acetal, norbornene-based polymers containing norbornene compounds, and phenoxy resins.
• phenoxy resins are preferred in terms of their heat resistance and compatibility with thermosetting resins.
• the thermoplastic resin and the thermosetting resin may each be used alone or in combination of two or more thereof. Either a thermoplastic resin or a thermosetting resin may be used alone, or a thermoplastic resin and a thermosetting resin may be used in combination.
• the content of the polymer having a mass average molecular weight (Mw) of 5,000 or more is preferably 5% by mass or more and less than 30% by mass, based on 100% by mass of the solid content excluding the inorganic filler from the composition of the present invention.
• Mw mass average molecular weight
• the content of the polymer having a mass average molecular weight (Mw) of 5,000 or more is preferably 5% by mass or more, more preferably 7.5% by mass or more, and even more preferably 10% by mass or more, based on 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler.
• it is preferably less than 30% by mass, and even more preferably 27.5% by mass or less, even more preferably 25% by mass or less, even more preferably 24% by mass or less, even more preferably 23% by mass or less, and even more preferably 20% by mass or less.
• it is even more preferably 18% by mass or less.
• the other polymers are preferably those having a functional group that reacts with the epoxy compound.
• the functional group that reacts with the epoxy compound include a phenolic hydroxyl group, an epoxy group, a carboxylic acid group, a carboxylic anhydride group, and an active ester.
• the composition of the present invention preferably contains a curing agent as needed.
• the curing agent include phenolic resins, compounds having a heterocyclic structure containing a nitrogen atom (also referred to as "nitrogen-containing heterocyclic compounds"), acid anhydrides having an aromatic skeleton or an alicyclic skeleton, water additives of such acid anhydrides, and modified products of such acid anhydrides.
• the curing agent may be used alone or in combination of two or more kinds. By using these preferred curing agents, it is possible to obtain a cured product that has an excellent balance of heat resistance, moisture resistance, and electrical properties.
• the composition of the present invention contains the above-mentioned epoxy compound as a thermosetting compound, it is preferable to use in combination with a curing agent having an active group capable of reacting with an epoxy group.
• a curing agent having an active group capable of reacting with an epoxy group For example, it is preferable to use in combination with an epoxy compound at least one of a phenolic resin, a benzoxazine compound, a polyarylate, a cyanate, and a maleimide. That is, it is preferable that the composition of the present invention contains an epoxy compound and at least one of a phenolic resin, a benzoxazine compound, a polyarylate, a cyanate, and a maleimide.
• phenolic resin examples include phenol novolac, o-cresol novolac, p-cresol novolac, t-butylphenol novolac, dicyclopentadiene cresol, polyparavinylphenol, bisphenol A novolac, xylylene-modified novolac, decalin-modified novolac, poly(di-o-hydroxyphenyl)methane, poly(di-m-hydroxyphenyl)methane, and poly(di-p-hydroxyphenyl)methane.
• novolac-type phenolic resins with rigid main chain skeletons and phenolic resins with triazine skeletons are preferred for further improving the flexibility of the present composition, the present cured product, and the present thermally conductive sheet, and for improving the mechanical properties and heat resistance of the present cured product.
• phenolic resins containing allyl groups are preferred for improving the flexibility of the present thermosetting sheet in an uncured state and the toughness of the present cured product. The inclusion of a phenolic resin increases the curing rate of the epoxy compound and effectively improves heat resistance by minimizing residual groups.
• the benzoxazine compound is a compound that crosslinks and hardens when heated, and also functions as a curing agent for the epoxy compound. Therefore, by using an epoxy compound and a benzoxazine compound in combination, the hydroxyl groups generated when the benzoxazine compound crosslinks react with the epoxy groups of the epoxy compound to bond, so that the crosslinked structure of the epoxy compound and the crosslinked structure of the benzoxazine compound are combined to form a stronger crosslinked structure, which can increase the glass transition temperature (Tg) of the cured product and further improve heat resistance.
• Tg glass transition temperature
• the benzoxazine compound preferably has a structure represented by formula (I) or (II) below.
• a represents an integer of 0 to 3, preferably 0 or 1, and more preferably 0.
• R 1 and R 2 each independently represent a hydrogen atom or a monovalent organic group.
• R1 include a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an aralkyl group, an alkynyl group, etc.
• R1 may be substituted with any substituent.
• R2 include an aliphatic hydrocarbon group and an aromatic hydrocarbon group. * indicates a bond to another chemical structure.
• b represents an integer of 0 to 4, preferably 0 or 1, and more preferably 0.
• R3 represents a hydrogen atom or a monovalent organic group, and when b is 2 or greater, multiple R3s may be the same or different. Specific examples of R3 include an aliphatic hydrocarbon group and an aromatic hydrocarbon group. * indicates a bond to another chemical structure.
• the benzoxazine compound preferably has multiple structures represented by formula (I) and/or formula (II) per molecule. More specifically, the benzoxazine compound preferably has two to four, and more preferably two, structures represented by formula (I) and/or formula (II) per molecule. It is believed that the use of such a benzoxazine compound can further enhance curing performance and improve heat resistance.
• the benzoxazine compound preferably includes a benzoxazine compound represented by formula (III).
• the benzoxazine compound represented by formula (III) is often also called a Pd-type benzoxazine.
• X2 is a single bond or a divalent linking group. More specifically, X 2 can be a single bond, a linear or branched alkylene group having 1 to 10 carbon atoms, —O—, —SO 2 —, —CO—, or a structure in which two or more of these are linked together.
• the benzoxazine compound may include a benzoxazine compound represented by the following formula (IV):
• the benzoxazine compound represented by the following formula (IV) is often also called Fa-type benzoxazine.
• the definition and specific examples of X2 are the same as those of X2 in formula (III) above.
• Benzoxazine compounds are available in solid and liquid forms at 25°C. From the perspective of increasing the glass transition temperature (Tg) of the composition of the present invention and its cured product, thereby enhancing heat resistance, those that are solid at 25°C are more preferred.
• the content of the benzoxazine compound is preferably 3% by mass or more and 50% by mass or less, more preferably 5% by mass or more or 30% by mass or less, and even more preferably 7% by mass or more or 25% by mass or less, based on 100% by mass of the solids content of the composition of the present invention excluding the inorganic filler.
• the content of benzoxazine compound in the composition of the present invention is preferably lower than the content of epoxy compound.
• the mass ratio of the content of the benzoxazine compound to the content of the epoxy compound in the solid content excluding the inorganic filler from the composition of the present invention is preferably less than 0.8, and more preferably 0.7 or less, even more preferably 0.6 or less, and even more preferably 0.5 or less.
• this mass ratio is preferably 0.05 or more, even more preferably 0.07 or more, and even more preferably 0.08 or more.
• polyarylate is a compound represented by the following formula (A):
• each X may independently represent a hydrogen atom group, an aliphatic group, or an aromatic group, such as a hydrogen atom, a substituted or unsubstituted alkyl group, or an aryl group.
• Each Y may independently be a single bond, —CR 1 R 2 —, O, CO, or S.
• Each of R 1 and R 2 independently represents a hydrogen atom, a methyl group, or an ethyl group, or a cyclohexylidene group formed by bonding R 1 and R 2.
• alkylene groups include linear, branched, or cyclic alkylene groups having 1 to 12 carbon atoms.
• Each Z may independently be a hydrogen atom, a hydroxy group, or an alkoxy group.
• n is the number of repetitions and may be an integer of 1 or more, for example, an integer of 1 to 100 is preferred, and among these, an integer of 1 or more or 90 or less, and among these, an integer of 2 or more or 80 or less is more preferred.
• the molecular weight of the polyarylate is preferably 500 or more, more preferably 700 or more, and even more preferably 1,000 or more.
• the molecular weight is preferably 10,000 or less, more preferably 8,000 or less, and even more preferably 5,000 or less.
• the glass transition temperature of the polyarylate is preferably 80° C. or higher, more preferably 100° C. or higher, and even more preferably 120° C. or higher.
• the glass transition temperature is preferably 300° C. or lower, more preferably 270° C. or lower, and even more preferably 250° C. or lower.
• the functional group equivalent weight (amount of hydroxyl groups and ester groups) of the polyarylate is preferably 100 g/equivalent or more, more preferably 120 g/equivalent or more, and even more preferably 140 g/equivalent or more, from the viewpoint of reducing moisture absorption. On the other hand, from the viewpoint of improving heat resistance, it is preferably 1000 g/equivalent or less, more preferably 800 g/equivalent or less, and even more preferably 600 g/equivalent or less.
• the cyanate may be, for example, a compound having an -OCN group in the molecule, which reacts with the -OCN group upon heating.
• Specific examples include 1,3-dicyanatobenzene, 1,4-dicyanatobenzene, 1,3,5-tricyanatobenzene, 1,3-dicyanatonaphthalene, 1,4-dicyanatonaphthalene, 1,6-dicyanatonaphthalene, 1,8-dicyanatonaphthalene, 2,6-dicyanatonaphthalene, 2,7-dicyanatonaphthalene, 1,3,6-tricyanatonaphthalene, 4,4'-dicyanatobiphenyl, bis(4-cyanatophenyl)methane, bis(3,5-dimethyl-4-cyanatophenyl)methane, and 2,2-bis(4-cyanatophenyl)propane.
• Suitable cyanates include bis(4-cyanatophenyl)propane, 2,2-bis(3,5-dibromo-4-cyanatophenyl)propane, bis(4-cyanatophenyl)ether, bis(4-cyanatophenyl)thioether, bis(4-cyanatophenyl)sulfone, tris(4-cyanatophenyl)phosphite, tris(4-cyanatophenyl)phosphate, and cyanates obtained by reacting a novolak resin with a cyanogen halide.
• Prepolymers having a triazine ring formed by trimerizing the cyanate groups of these polyfunctional cyanates can also be used.
• the maleimide may be a compound having one or more, preferably two or more, maleimide groups (2,5-dihydro-2,5-dioxo-1H-pyrrol-1-yl groups) in one molecule.
• Maleimides can react with epoxy compounds in the presence of an appropriate catalyst to form bonds.
• maleimides can also bond with each other because radical polymerization can occur due to the ethylenic carbon-carbon unsaturated bond contained in the maleimide group.
• the maleimide may be, for example, an aliphatic maleimide containing an aliphatic amine skeleton, or an aromatic maleimide containing an aromatic amine skeleton.
• the curing agent is preferably contained in an amount of 1% by mass or more and 50% by mass or less, more preferably 3% by mass or more or 40% by mass or less, even more preferably 5% by mass or more or 30% by mass or less, and even more preferably 10% by mass or more or 25% by mass or less, based on 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler.
• content of the curing agent is equal to or greater than the lower limit, the reaction proceeds effectively and sufficient curing performance can be obtained, whereas when the content is equal to or less than the upper limit, the crosslinking density can be increased, thereby increasing the strength, which is preferable.
• composition of the present invention may contain a thermosetting catalyst as a curing accelerator, if necessary, in order to adjust the curing rate and the physical properties of the cured product.
• thermosetting catalyst is preferably selected appropriately depending on the type of thermosetting compound and curing agent.
• specific examples of the thermosetting catalyst include linear or cyclic tertiary amines, organophosphorus compounds, diazabicycloalkenes such as quaternary phosphonium salts or organic acid salts, and imidazoles.
• Organometallic compounds, quaternary ammonium salts, metal halides, etc. may also be used.
• organometallic compounds include zinc octoate, tin octoate, and aluminum acetylacetone complex.
• the nitrogen-containing heterocyclic compound described above as a curing agent also functions as a thermosetting catalyst, and therefore may be blended as a thermosetting catalyst.
• imidazole-based compounds compounds containing imidazole are preferred as the thermosetting catalyst, particularly from the viewpoints of storage stability, heat resistance, and curing speed.
• imidazole compounds include, for example, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2, Examples include 4-diamino-6-[2'-undecylimidazolyl-(1')]
• an imidazole compound having a melting point of 100° C. or higher, more preferably 200° C. or higher a cured product having excellent storage stability and adhesion can be obtained.
• those containing a nitrogen-containing heterocyclic compound other than the above-mentioned imidazole ring are more preferred from the viewpoint of adhesiveness.
• the thermosetting catalyst may be used alone or in combination of two or more.
• two or more imidazole compounds having a melting point of 100° C. or higher it is possible to obtain a composition of the present invention having excellent storage stability and a cured product having excellent heat resistance.
• thermosetting catalyst is preferably contained in an amount of 0.1% by mass or more and 10% by mass or less, and more preferably 0.1% by mass or more and 5% by mass or less, based on 100% by mass of the solid content of the composition of the present invention excluding the inorganic filler.
• content of the thermosetting catalyst is equal to or greater than the lower limit, the progress of the curing reaction can be sufficiently promoted to achieve good curing, whereas when the content is equal to or less than the upper limit, the curing rate is not too fast, and therefore the storage stability of the composition of the present invention can be improved.
• the inorganic filler contained in the composition of the present invention preferably has a thermal conductivity of 2.0 W/m K or more, more preferably 3.0 W/m K or more, even more preferably 5.0 W/m K or more, and even more preferably 10.0 W/m K or more.
• inorganic fillers include electrically insulating fillers made solely of carbon, fillers made of metal carbides or semi-metal carbides, metal oxides or semi-metal oxides, and metal nitrides or semi-metal nitrides.
• An example of the electrically insulating filler made only of carbon is diamond (thermal conductivity: approximately 2000 W/m ⁇ K).
• Examples of the metal carbide or semi-metal carbide include silicon carbide (thermal conductivity: approximately 60 to 270 W/m ⁇ K), titanium carbide (thermal conductivity: approximately 21 W/m ⁇ K), and tungsten carbide (thermal conductivity: approximately 120 W/m ⁇ K).
• metal oxide or semi-metal oxide examples include magnesium oxide (thermal conductivity: about 40 W/m ⁇ K), aluminum oxide (thermal conductivity: about 20 to 35 W/m ⁇ K), zinc oxide (thermal conductivity: about 54 W/m ⁇ K), yttrium oxide (thermal conductivity: about 27 W/m ⁇ K), zirconium oxide (thermal conductivity: about 3 W/m ⁇ K), ytterbium oxide (thermal conductivity: about 38.5 W/m ⁇ K), beryllium oxide (thermal conductivity: about 250 W/m ⁇ K), and sialon (ceramics composed of silicon, aluminum, oxygen, and nitrogen, thermal conductivity: about 21 W/m ⁇ K).
• metal nitride or semi-metal nitride examples include boron nitride (thermal conductivity in the plane direction of plate-like particles of hexagonal boron nitride (h-BN): about 200 to 500 W/m ⁇ K), aluminum nitride (thermal conductivity: about 160 to 285 W/m ⁇ K), and silicon nitride (thermal conductivity: about 30 to 80 W/m ⁇ K).
• These inorganic fillers may be used alone or in combination of two or more.
• the volume resistivity of the inorganic filler at 20°C is preferably 10 13 ⁇ cm or more, and more preferably 10 14 ⁇ cm or more.
• metal oxides, semi-metal oxides, metal nitrides, or semi-metal nitrides are preferred because they make it easier to ensure sufficient electrical insulation of the thermally conductive sheet.
• inorganic fillers include aluminum oxide (Al 2 O 3 , volume resistivity: >10 14 ⁇ cm), aluminum nitride (AlN, volume resistivity: >10 14 ⁇ cm), boron nitride (BN, volume resistivity: >10 14 ⁇ cm), silicon nitride (Si 3 N 4 , volume resistivity: >10 14 ⁇ cm), and silica (SiO 2 , volume resistivity: >10 14 ⁇ cm).
• aluminum oxide, aluminum nitride, and boron nitride are preferred, with aluminum oxide and boron nitride being particularly preferred because they can impart high insulating properties to the thermally conductive sheet.
• the inorganic filler may be in the form of irregular particles, spheres, whiskers, fibers, plates, or aggregates or mixtures thereof.
• “spherical” generally means that the aspect ratio (ratio of major axis to minor axis) is 1 or more and 2 or less, preferably 1 or more and 1.75 or less, more preferably 1 or more and 1.5 or less, and even more preferably 1 or more and 1.4 or less.
• the aspect ratio can be determined by randomly selecting 10 or more particles from an image of a cross section of the composition of the present invention or the thermally conductive sheet taken with a scanning electron microscope (SEM), determining the ratio of the major axis to the minor axis of each particle, and calculating the average value.
• the inorganic filler contained in the composition of the present invention preferably contains "boron nitride agglomerated particles" formed by agglomeration of primary particles of boron nitride, because these have fewer problems with moisture absorption when the composition of the present invention is formed into a sheet and cured, i.e., when the composition is formed into a sheet-like cured product, are low in toxicity, can efficiently increase thermal conductivity, and can impart high insulating properties to the thermally conductive sheet.
• the composition of the present invention preferably contains boron nitride agglomerated particles as the inorganic filler.
• boron nitride agglomerated particles may be used in combination with other inorganic fillers.
• the heat transfer behavior within the thermally conductive sheet does not depend solely on the thermal conductivity within the inorganic filler. Therefore, even if diamond particles, among the inorganic fillers exemplified above, which have extremely high thermal conductivity but are also extremely expensive, are used, the thermal conductivity of the thermally conductive sheet in the thickness direction will not increase significantly. Therefore, when using boron nitride agglomerated particles in combination with other inorganic fillers, the main focus is on reducing the cost of the composition of the present invention.
• the inorganic filler to be used in combination with boron nitride agglomerated particles is preferably selected from magnesium oxide, aluminum oxide, tungsten carbide, silicon carbide, aluminum nitride, etc., with aluminum oxide being more preferred.
• boron nitride agglomerated particles account for 75% or more by mass of the inorganic filler contained in the composition of the present invention, and even more preferably 80% or more by mass, and even more preferably 85% or more by mass (including 100% by mass) of that.
• the shape of the boron nitride agglomerated particles is preferably spherical.
• the agglomerated structure of the boron nitride agglomerated particles is preferably a house-of-card structure from the viewpoint of improving thermal conductivity.
• the agglomerated structure of the boron nitride agglomerated particles can be confirmed by a scanning electron microscope (SEM).
• the house-of-card structure is a structure in which plate-like particles are stacked in a complex manner without being oriented, and is described in "Ceramics 43 No. 2" (published by the Ceramic Society of Japan, 2008). More specifically, it refers to a structure in which the flat surfaces of the primary particles forming the aggregated particles are in contact with the edge surfaces of other primary particles present within the aggregated particles.
• a schematic diagram of the house-of-card structure is shown in Figure 1.
• the card-house structured agglomerated particles have extremely high fracture strength due to their structure, and do not collapse even during the pressurization process performed during sheet formation of the thermally conductive sheet. Therefore, primary particles that are normally oriented in the longitudinal direction of the thermally conductive sheet can be made to exist in a random direction.
• card-house structured agglomerated particles can further increase the proportion of primary particles with ab planes oriented in the thickness direction of the thermally conductive sheet, thereby enabling effective heat conduction in the thickness direction of the sheet and further increasing the thermal conductivity in the thickness direction.
• Boron nitride agglomerated particles having a house-of-cards structure can be produced, for example, by the method described in WO 2015/119198.
• the particles When using agglomerated boron nitride particles having a house-of-card structure, the particles may be surface-treated with a surface treatment agent.
• a surface treatment agent for example, a known surface treatment agent such as a silane coupling treatment can be used. It is believed that by increasing the adhesion at the interface between the inorganic filler and the thermosetting compound, i.e., the matrix resin, by chemical treatment, it is possible to further reduce the attenuation of thermal conductivity at the interface.
• the thermosetting compound is also referred to as a "matrix resin" in the sense that it plays a role in enveloping the inorganic filler and maintaining the overall shape of the composition of the present invention.
• the particle size can be made larger than that of an inorganic filler that uses primary particles as they are.
• the heat transfer paths between the inorganic fillers via the thermosetting compound with low thermal conductivity can be reduced, and therefore the increase in thermal resistance in the heat transfer paths in the thickness direction can be reduced.
• the lower limit of the maximum particle size of the boron nitride agglomerated particles is preferably 20 ⁇ m or more, more preferably 30 ⁇ m or more, and even more preferably 40 ⁇ m or more.
• the upper limit of the maximum particle size is preferably 300 ⁇ m or less, more preferably 200 ⁇ m or less, even more preferably 100 ⁇ m or less, and even more preferably 90 ⁇ m or less.
• the average particle size of the boron nitride agglomerated particles is not particularly limited. Among these, 5 ⁇ m or more is preferable, 10 ⁇ m or more is more preferable, and 15 ⁇ m or more is even more preferable. 100 ⁇ m or less is preferable, and 90 ⁇ m or less is more preferable.
• the average particle size of the boron nitride agglomerated particles is 5 ⁇ m or more, the number of particles in the composition of the present invention and the present cured product is relatively small, and the number of interparticle interfaces is reduced, which reduces thermal resistance and may result in the present thermal conductive sheet having high thermal conductivity. Furthermore, when the average particle size is equal to or less than the above upper limit, the present cured product tends to have good surface smoothness.
• the average particle size or maximum particle size of the boron nitride agglomerated particles be equal to or less than the above upper limit, a high-quality film without surface roughness can be formed when the boron nitride agglomerated particles are incorporated into a thermosetting compound, i.e., a matrix resin.
• a thermosetting compound i.e., a matrix resin.
• the average particle size or maximum particle size be equal to or greater than the above lower limit, the interface between the matrix resin and the boron nitride agglomerated particles is reduced, resulting in lower thermal resistance and achieving high thermal conductivity, while also providing the sufficient thermal conductivity-enhancing effect required of an inorganic filler in thermally conductive sheets for power semiconductor devices.
• thermal resistance at the interface between the matrix resin and the boron nitride agglomerated particles becomes significant when the size of the boron nitride agglomerated particles relative to the thickness of the thermally conductive sheet is 1/10 or less.
• thermally conductive sheets with thicknesses of 100 ⁇ m to 300 ⁇ m are often used, so from the viewpoint of thermal conductivity as well, it is preferable that the maximum particle size of the boron nitride agglomerated particles be larger than the above lower limit.
• the maximum particle size of the boron nitride agglomerated particles is equal to or greater than the above lower limit, not only is the increase in thermal resistance caused by the interface between the boron nitride agglomerated particles and the matrix resin suppressed, but the number of required thermal conduction paths between particles is reduced, increasing the probability that thermal conduction will be connected from one surface to the other in the thickness direction of the thermally conductive sheet.
• the maximum particle size of the boron nitride agglomerated particles be equal to or less than the above upper limit, protrusion of the boron nitride agglomerated particles onto the surface of the thermal conductive sheet is suppressed, and a good surface shape without surface roughness is obtained. Therefore, for example, when producing a sheet bonded to a copper substrate, sufficient adhesion is achieved and excellent voltage resistance characteristics can be obtained.
• the ratio of the size (maximum particle diameter) of the boron nitride agglomerated particles to the thickness of the thermally conductive sheet (maximum particle diameter/thickness) is preferably 0.3 or more and 1.0 or less, more preferably 0.35 or more or 0.95 or less, and even more preferably 0.4 or more or 0.9 or less.
• the maximum particle size and average particle size of the boron nitride agglomerated particles can be measured, for example, by the following method.
• the maximum particle size and average particle size of the boron nitride agglomerated particles used as a raw material can be determined as the maximum particle size Dmax and average particle size D50 of the boron nitride agglomerated particles from the particle size distribution obtained by measuring the particle size distribution of a sample prepared by dispersing the boron nitride agglomerated particles in a solvent, specifically, a sample prepared by dispersing the boron nitride agglomerated particles in a pure water medium containing a dispersion stabilizer, using a laser diffraction/scattering particle size distribution analyzer.
• Dmax and D50 are the maximum particle size and the particle size at 50% cumulative volume in a volume-based particle size distribution obtained by measurement using a laser diffraction/scattering particle size distribution measurement method.
• the maximum particle size and the average particle size can also be determined using a dry particle size distribution measuring device such as Morphologi G3 (manufactured by Malvern Instruments).
• the maximum particle size Dmax and average particle size D50 of the boron nitride agglomerated particles in the composition of the present invention or the present thermally conductive sheet can also be measured in the same manner as above by dissolving and removing organic components such as thermosetting compounds in a solvent (including a heated solvent), or by swelling the components to reduce the adhesive strength to the boron nitride agglomerated particles and then physically removing them, and then heating the organic components in air to incinerate them and remove them.
• organic components such as thermosetting compounds in a solvent (including a heated solvent)
• the maximum particle size of the boron nitride agglomerated particles in the composition of the present invention or the thermally conductive sheet can be determined by directly observing a cross section of the composition of the present invention or the thermally conductive sheet using a scanning electron microscope, a transmission electron microscope, a micro-Raman spectrometer, an atomic force microscope or the like to arbitrarily select 10 or more boron nitride agglomerated particles, and determining the maximum particle size among them.
• the average particle size of the boron nitride agglomerated particles in the composition of the present invention or the thermally conductive sheet can also be determined by directly observing a cross section of the composition of the present invention or the thermally conductive sheet using a scanning electron microscope, a transmission electron microscope, a micro-Raman spectrometer, an atomic force microscope or the like to arbitrarily select 10 or more boron nitride agglomerated particles, and calculating the arithmetic mean value of the particle sizes.
• the longest and shortest diameters are measured, and the average value thereof is taken as the particle diameter of the particles.
• the content of the inorganic filler is preferably 30% by mass or more and less than 90% by mass relative to 100% by mass of the solid content in the composition of the present invention, that is, 100% by mass of the solid content of the entire composition. If the content of the inorganic filler is 30% by mass or more relative to 100% by mass of the solid content in the composition of the present invention, the insulating property and thermal conductivity can be improved. From this viewpoint, the content of the inorganic filler is preferably 30% by mass or more relative to 100% by mass of the solid content in the composition of the present invention, more preferably 40% by mass or more, even more preferably 50% by mass or more, and even more preferably 60% by mass or more.
• the thermal conductivity it is more preferably 65% by mass or more.
• the content is less than 90% by mass, handling properties and film-forming properties can be maintained.
• the content of the inorganic filler is preferably less than 90% by mass, more preferably 85% by mass or less, even more preferably 80% by mass or less, and even more preferably 75% by mass or less.
• the content of the agglomerated boron nitride particles is preferably 50% by mass or more relative to 100% by mass of the total inorganic filler.
• the content of the boron nitride particles is 50% by mass or more relative to 100% by mass of the total inorganic filler, the insulating property and thermal conductivity can be improved.
• the content of the boron nitride agglomerated particles is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, relative to 100% by mass of the total inorganic filler.
• the composition of the present invention may contain an organic solvent as needed, for example, to improve the coatability when forming a sheet-like cured product through a coating step.
• organic solvents that may be contained in the composition of the present invention include methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, butyl acetate, isobutyl acetate, propylene glycol monomethyl ether, etc. These organic solvents may be used alone or in combination of two or more.
• the content thereof is appropriately determined depending on the handleability during production of the thermally conductive sheet, etc.
• the organic solvent is preferably used so that the solids concentration (total of components other than the solvent) in the composition of the present invention is 10% by mass or more and 90% by mass or less, and particularly preferably 40% by mass or more or 80% by mass or less.
• the organic solvent is preferably used so that the solids concentration (total of components other than the solvent) in the composition of the present invention is 95% by mass or more, more preferably 97% by mass or more, even more preferably 98% by mass or more, and still more preferably 99% by mass or more.
• the composition of the present invention may contain other components in addition to the above components.
• other components include dispersants, additives such as silane coupling agents that improve the interfacial adhesion strength between thermoplastic resins, organic fillers, and inorganic fillers and resin components, additives that are expected to have the effect of increasing the adhesion strength between the thermally conductive sheet and conductors such as metal plates and circuit boards, insulating carbon components such as reducing agents, viscosity adjusters, thixotropic agents, flame retardants, colorants, various phosphorus-based, phenol-based and other antioxidants, phenol acrylate-based and other process stabilizers, heat stabilizers, hindered amine radical scavengers (HAAS), impact modifiers, processing aids, metal deactivators, copper inhibitors, antistatic agents, extenders, and the like.
• additives such as silane coupling agents that improve the interfacial adhesion strength between thermoplastic resins, organic fillers, and inorganic fillers and resin components,
• the composition of the present invention preferably contains a silane coupling agent as needed.
• a silane coupling agent By incorporating a silane coupling agent, the interfacial adhesive strength between the inorganic filler and the thermosetting compound can be increased, and when the composition of the present invention is cured, voids and the like can be suppressed, thereby maintaining insulation resistance and insulation stability.
• silane coupling agents include N-phenyl- ⁇ -aminopropyltrimethoxysilane, ⁇ -aminopropyltriethoxysilane, ⁇ -aminopropyltrimethoxysilane, ⁇ -glycidoxypropyltrimethoxysilane, ⁇ -glycidoxypropyltriethoxysilane, ⁇ -(3,4-epoxycyclohexyl)ethyltrimethoxysilane, p-styryltrimethoxysilane, vinyltrimethoxysilane, and vinyltriethoxysilane. These agents can be used alone or in combination of two or more.
• the content of the silane coupling agent is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.15 parts by mass or more, and even more preferably 0.18 parts by mass or more, per 100 parts by mass of the total inorganic filler.
• the content is preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, and even more preferably 1 part by mass or less, per 100 parts by mass of the total inorganic filler.
• composition of the present invention can be converted into a fully cured product by heating. Furthermore, the composition of the present invention can be formed into a sheet to form the present thermosetting sheet, and the present thermosetting sheet can be cured to form the present sheet-like cured product, which can be used as the present thermally conductive sheet.
• the cured product and the thermally conductive sheet can be used in a variety of applications, including as components of the composite molded product, heat dissipating laminate, heat dissipating circuit board, and power semiconductor device described below, although the applications are not limited to these.
• thermosetting sheet ⁇ Method for producing the thermosetting sheet> Next, an example of a method for producing the thermosetting sheet will be described.
• thermosetting sheet can be obtained by forming the composition of the present invention into a sheet (this process is also referred to as the "film-forming process"), optionally drying the film (this process is also referred to as the “drying process”), optionally carrying out low-temperature aging by placing the film in a temperature environment of 0°C or below (this process is also referred to as the "low-temperature aging process”), and optionally further applying pressure (this process is also referred to as the "pressuring process”).
• An example of a method for producing the thermosetting sheet of the present invention is a method in which the composition of the present invention is formed into a sheet and then subjected to low-temperature aging at an environmental temperature of 0°C or below.
• the order of the steps can be changed as appropriate.
• the low-temperature aging step may be performed after the pressurizing step.
• thermosetting compound for example, a thermosetting compound, an inorganic filler, and optionally other components (raw materials) are mixed, and the solvent is added as needed to the mixture, followed by kneading to prepare a slurry of the composition of the present invention.
• This slurry of the composition of the present invention can be formed into a sheet by a coating method such as a blade method, a solvent casting method, or an extrusion film-forming method.
• a coating film is formed by first coating the surface of a substrate with the composition of the present invention in a slurry form, i.e., by dipping, spin coating, spray coating, blade coating, or any other method using the composition of the present invention in a slurry form.
• the slurry-like composition of the present invention can be applied using a coating device such as a spin coater, a slit coater, a die coater, a blade coater, etc.
• a coating device makes it possible to form a uniform coating film of a predetermined thickness on a substrate.
• the substrate is generally a copper plate or copper foil or a PET film, as described below, but is not limited thereto.
• the composition of the present invention formed into a sheet as described above is dried at a temperature (heated atmosphere temperature) of usually 10 to 150°C, preferably 25°C or higher or 120°C or lower, more preferably 30°C or higher or 110°C or lower, and most preferably 100°C or lower, in order to remove the solvent and low-molecular-weight components.
• a temperature heatated atmosphere temperature
• the drying temperature is equal to or lower than the upper limit, curing of the resin in the composition of the present invention is suppressed, and the resin in the sheet-shaped composition of the present invention tends to flow in the subsequent pressurizing step, making it easier to remove voids.
• the drying temperature is equal to or higher than the lower limit, the solvent can be effectively removed, and productivity tends to improve.
• the drying time is not particularly limited and can be adjusted appropriately depending on the state of the composition of the present invention, the drying environment, etc.
• the drying time is preferably 1 minute or more, more preferably 2 minutes or more, and even more preferably 5 minutes or more.
• the drying time is preferably 24 hours or less, more preferably 10 hours or less, even more preferably 4 hours or less, and particularly preferably 2 hours or less.
• a drying time of at least the lower limit tends to sufficiently remove the solvent and inhibit the residual solvent from forming voids in the sheet-like cured product, whereas a drying time of not more than the upper limit tends to improve productivity and reduce production costs.
• the temperature (ambient temperature) during low-temperature aging is preferably lower, as a faster cooling rate results in finer ice. From this perspective, a temperature of 0°C or lower is preferred, with -5°C or lower being particularly preferred, -10°C or lower being particularly preferred, and -15°C or lower being even more preferred. On the other hand, if the temperature is too low, the uncured thermosetting sheet will fall below the glass transition temperature (Tg) and become more susceptible to cracking, so a temperature of -50°C or higher is preferred, and if an epoxy compound is included, a temperature of -30°C or higher is particularly preferred, with -25°C or higher being even more preferred.
• Tg glass transition temperature
• the time for low-temperature aging is not particularly limited, as long as the composition of the present invention is frozen. It is sufficient to rapidly freeze and hold for 10 minutes or more, preferably 30 minutes or more, and of these, holding for 1 hour or more is preferred, more preferably 2 hours or more, more preferably 4 hours or more, more preferably 8 hours or more, more preferably 16 hours or more, and even more preferably 24 hours or more.
• the time to be aged it is preferable for the time to be aged to be 365 days or less, more preferably 180 days or less, more preferably 90 days or less, more preferably 30 days or less, and of these, 7 days or less is preferred.
• the pressing step it is desirable to apply a load of 2 MPa or more to the sheet-like composition of the present invention on the substrate.
• the pressing method include a plate press, a hydrostatic press, a vacuum press, a calendar press, a belt press, a servo press, etc.
• the load is preferably 5 MPa or more, more preferably 7 MPa or more, and even more preferably 9 MPa or more.
• the load is preferably 1500 MPa or less, more preferably 1000 MPa or less, and even more preferably 800 MPa or less.
• the load during compression By setting the load during compression to the above upper limit or less, voids in the sheet-like composition of the present invention can be eliminated without destroying the secondary particles of the inorganic filler, such as the boron nitride agglomerated particles, and the thermal conductivity of the cured product of the thermosetting sheet, i.e., the thermal conductive sheet, can be increased.
• the load By setting the load to the above lower limit or more, contact between the inorganic fillers is improved, making it easier to form thermal conductive paths, and the thermal conductivity of the cured product of the thermosetting sheet, i.e., the thermal conductive sheet, can be increased.
• the heating temperature of the sheet-like composition of the present invention on the substrate in the pressurizing step is not particularly limited.
• the heating temperature (product temperature) is preferably 0°C or higher, more preferably 5°C or higher, and even more preferably 10°C or higher.
• the heating temperature is preferably 300°C or lower, more preferably 250°C or lower, even more preferably 200°C or lower, still more preferably 100°C or lower, and particularly preferably 90°C or lower.
• the time for the pressurizing step is not particularly limited.
• the time for the pressurizing step is preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 3 minutes or more, and particularly preferably 5 minutes or more.
• the time for the pressurizing step is preferably 1 hour or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less.
• the present cured product and the present sheet-like cured product can have the above-mentioned physical properties, i.e., the breaking energy obtained by three-point bending measurement at 190°C, the breaking energy obtained by three-point bending measurement at 150°C, the ratio (x/y) of the breaking energy x obtained by three-point bending measurement at 190°C to the breaking energy y obtained by three-point bending measurement at 150°C, the Young's modulus obtained by three-point bending measurement at 190°C, the Young's modulus obtained by three-point bending measurement at 150°C, the thermal conductivity in the thickness direction at 25°C, the breakdown voltage at a thickness of 150 ⁇ m, the volume resistivity (1000 V, 200°C), the moisture absorption rate, the storage modulus at 200°C, and the glass transition temperature (Tg), within the above-mentioned ranges.
• the breaking energy obtained by three-point bending measurement at 190°C the breaking energy obtained by three-point bending measurement at 150°
• the present thermally conductive sheet may be any thermally conductive sheet formed from the present cured product, in other words, any thermally conductive sheet made of the present sheet-like cured product.
• the physical properties as described above i.e., the breaking energy obtained by three-point bending measurement at 190°C, the breaking energy obtained by three-point bending measurement at 150°C, the ratio (x/y) of the breaking energy x obtained by three-point bending measurement at 190°C to the breaking energy y obtained by three-point bending measurement at 150°C, the Young's modulus obtained by three-point bending measurement at 190°C, the Young's modulus obtained by three-point bending measurement at 150°C, the thermal conductivity in the thickness direction at 25°C, the breakdown voltage, the volume resistivity (1000V, 200°C), the moisture absorption rate, the storage modulus at 200°C, and the glass transition temperature (Tg) can be set
• the lower limit of the thickness of the thermally conductive sheet is preferably 50 ⁇ m or more, more preferably 60 ⁇ m or more, and even more preferably 70 ⁇ m or more, while the upper limit is preferably 400 ⁇ m or less, more preferably 300 ⁇ m or less, and even more preferably 250 ⁇ m or less.
• the present thermally conductive sheet can be produced as a sheet-like cured product by curing the present thermosetting sheet produced as described above (this process is also referred to as the "curing process").
• thermosetting sheet prepared as described above can be cured by heating.
• the heating temperature is preferably 30 to 400°C, and is more preferably 50°C or higher, more preferably 90°C or higher, more preferably 120°C or higher, more preferably 150°C or higher, and even more preferably 175°C or higher.
• it is more preferably 300°C or lower, and even more preferably 250°C or lower.
• the curing step for completely curing the thermosetting sheet may be carried out under pressure or without pressure.
• the pressurizing step and the curing step may be carried out simultaneously.
• the load when pressing and curing are performed simultaneously is not particularly limited. In this case, for example, it is preferable to apply a load of 5 MPa or more to the thermosetting sheet on the substrate, more preferably 7 MPa or more, and even more preferably 9 MPa or more.
• the load is preferably 2000 MPa or less, more preferably 1500 MPa or less, more preferably 1000 MPa or less, even more preferably 500 MPa or less, and even more preferably 100 MPa or less.
• the secondary particles of the inorganic filler such as boron nitride agglomerated particles, are not destroyed, voids in the thermosetting sheet are eliminated, and the thermal conductivity of the thermal conductive sheet is improved. Furthermore, by setting the load at or above the lower limit, contact between the inorganic filler particles is improved, making it easier to form thermal conduction paths, thereby improving the thermal conductivity of the thermal conductive sheet.
• the pressure application time is not particularly limited.
• the pressure application time is preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 3 minutes or more, and particularly preferably 5 minutes or more.
• the pressure application time is preferably 4 hours or less, more preferably 3 hours or less, and even more preferably 2 hours or less.
• a composite molded body (also referred to as "the present composite molded body") as an example of an embodiment of the present invention has a sheet-like cured product of the composition of the present invention, i.e., a cured product part made of the present thermally conductive sheet, and a metal part, and the cured product part and the metal part are laminated together.
• the metal part may be provided on only one surface of the cured product part made of the thermally conductive sheet, or on two or more surfaces.
• the thermally conductive sheet may have a metal part on only one surface, or on both surfaces.
• the metal part may also be patterned.
• Such a composite molded product can be produced by using a metal part as the substrate and forming the thermally conductive sheet on this substrate according to the method described above.
• the composite molded product can be produced by forming the thermally conductive sheet on a substrate other than the metal part, peeling it from the substrate, and then hot-pressing the sheet onto a metal member that will become the metal part.
• the thermally conductive sheet is formed in the same manner as described above, except that it is applied to a substrate such as PET, which may be treated with a release agent, and then peeled off from the substrate. The thermally conductive sheet is then placed on another metal plate or sandwiched between two metal plates and pressed together to form a single sheet.
• the metal plate can be a metal plate made of copper, aluminum, nickel-plated metal, or the like, with a thickness of approximately 10 ⁇ m to 10 cm.
• the surface of the metal plate may be physically roughened or chemically treated with a surface treatment agent, and it is more preferable that the metal plate be subjected to such treatment in terms of adhesion between the thermally conductive sheet and conductors such as metal plates and circuit boards.
• this composite molded product includes heat dissipation laminates, heat dissipation circuit boards, and power semiconductor devices. These will be explained in turn below. However, the present invention is not limited to these.
• a heat dissipation laminate according to an embodiment of the present invention may be any laminate including the thermally conductive sheet.
• this heat dissipation laminate is one in which a heat dissipation metal layer containing a heat dissipation material is laminated on one surface of this thermally conductive sheet.
• the heat dissipating material is not particularly limited as long as it is made of a material with good thermal conductivity.
• a heat dissipating metal material in order to increase the thermal conductivity in the laminated structure, it is preferable to use a heat dissipating metal material, and it is more preferable to use a flat metal material.
• the metal material is not particularly limited, but among them, copper plate, aluminum plate, aluminum alloy plate, etc. are preferred because they have good thermal conductivity and are relatively inexpensive.
• press molding which is a batch process
• the press equipment and press conditions may be within the same range as the press molding conditions used to obtain the thermally conductive sheet described above. However, they do not necessarily have to be within the same range.
• a heat dissipation circuit board according to an embodiment of the present invention may be any circuit board provided with the thermally conductive sheet.
• An example of the present heat dissipating circuit board is one in which the heat dissipating metal layer is laminated on one surface of the present thermally conductive sheet, and a conductive circuit, for example, a circuit board is formed on the surface of the present thermally conductive sheet opposite the heat dissipating metal layer by etching or the like. Specific examples include those in which the "heat dissipating metal layer/the present thermally conductive sheet/conductive circuit" are integrated.
• Examples of the state before circuit etching include an integrated configuration of the "heat dissipating metal layer/the present thermally conductive sheet/metal layer for forming a conductive circuit," in which the metal layer for forming a conductive circuit is flat and formed over the entire surface of one side of the present thermally conductive sheet, or formed over a partial area.
• the material of the metal layer for forming the conductive circuit there are no particular restrictions on the material of the metal layer for forming the conductive circuit.
• a power semiconductor device (also referred to as "the present power semiconductor device") is a product in which a circuit combining multiple power semiconductors is integrated into a single package module, and it is sufficient if it is equipped with the present thermally conductive sheet.
• An example of the power semiconductor device of the present invention is one in which a power semiconductor is mounted using the thermally conductive sheet as a heat dissipating circuit board.
• conventionally known materials can be appropriately used for the aluminum wiring, sealing material, packaging material, heat sink, thermal paste, solder, and other materials other than the present thermally conductive sheet or the present heat dissipation laminate.
• Inorganic filler 1 Spherical agglomerated boron nitride particles having a house-of-card structure, produced in accordance with the method for producing agglomerated boron nitride particles disclosed in the examples of WO 2015/561028.
• Inorganic filler 2 Spherical alumina particles manufactured by Admatechs Co., Ltd. Average particle size (D50): 7 to 13 ⁇ m
• the maximum particle size (Dmax) and average particle size (D50) of the inorganic filler were determined by dispersing the inorganic filler in a pure water medium containing sodium hexametaphosphate as a dispersion stabilizer, measuring the volumetric particle size distribution using a laser diffraction/scattering particle size distribution analyzer LA-300 (manufactured by Horiba, Ltd.), and determining the maximum particle size (Dmax) and the particle size at 50% of the cumulative volume (average particle size (D50)) from the resulting particle size distribution.
• Epoxy compound 1 manufactured by Mitsubishi Chemical Corporation, biphenyl-type solid epoxy compound, having two glycidyl groups per molecule. Mass average molecular weight (Mw): approximately 400. Epoxy equivalent (WPE): 200 g/equivalent
• Epoxy compound 2 manufactured by Nagase ChemteX Corporation, a polyfunctional epoxy compound containing a structure having four or more glycidyl groups in one molecule, which does not contain an amine or amide structure containing a nitrogen atom.
• Epoxy compound 3 alkyl diglycidyl ether manufactured by Mitsubishi Chemical Corporation, a multifunctional epoxy compound having two glycidyl groups in one molecule. Mass average molecular weight (Mw): approximately 240 Epoxy equivalent (WPE): 120 g/equivalent
• Epoxy compound 4 bisphenol A novolac solid epoxy compound manufactured by Mitsubishi Chemical Corporation, a polyfunctional epoxy compound containing a structure having four or more glycidyl groups in one molecule, and does not contain an amine or amide structure containing a nitrogen atom.
• Epoxy compound 5 manufactured by Mitsubishi Chemical Corporation, bisphenol A diglycidyl ether, a multifunctional epoxy compound having two glycidyl groups in one molecule. Mass average molecular weight (Mw): approximately 400. Epoxy equivalent (WPE): 200 g/equivalent
• Curing agent 1 "H-4" manufactured by UBE Corporation, phenolic resin curing agent (phenol novolac)
• Curing agent 2 Pd-type benzoxazine, solid (25°C), manufactured by Shikoku Chemical Industry Co., Ltd., in which X2 is CH2 in formula (III).
• Curing agent 3 "MEH-8000H", phenolic resin-based curing agent (allylphenol novolac), manufactured by Meiwa Chemical Industry Co., Ltd.
• (polymer) Epoxy polymer 1 a bifunctional epoxy polymer manufactured by Mitsubishi Chemical Corporation and disclosed as resin component 1 in JP 2020-63438 A, having the above structures (2) and (3), in which R 3 in formula (2) was structure (4), and R 4 , R 5 , R 6 , and R 7 in formula (3) were all methyl groups.
• Thermosetting catalyst 1 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, which has both an imidazole-derived structure and a triazine-derived structure in one molecule (manufactured by Shikoku Chemical Industry Co., Ltd., "Curesol 2E4MZ-A"), melting point: 215-225°C
• Thermosetting catalyst 2 2-phenyl-4,5-dihydroxymethylimidazole (manufactured by Shikoku Chemicals Corporation, "Curezol 2PHZ-PW”), melting point: dec. 230, so the melting point is 230°C or higher
• Silane coupling agent 1 Silane coupling agent 1: glycidyloxypropyltrimethoxysilane (KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.)
• Examples 1 to 4 Each raw material was weighed out so as to obtain the composition (parts by mass) shown in Table 1, and mixed using a planetary stirring device to prepare a mixture.
• a slurry-like thermosetting composition was prepared using 20% by mass each of methyl ethyl ketone and cyclohexanone so that the mixture would account for 60% by mass (solid content concentration) of the coating slurry.
• thermosetting composition was applied to a PET substrate by a doctor blade method and then dried by heating at 60°C (heating atmosphere temperature) for 120 minutes to obtain a sheet-like thermosetting composition.
• the total content of methyl ethyl ketone and cyclohexanone in the sheet-like thermosetting composition was 1 mass% or less.
• the sheet-shaped thermosetting composition was placed in a vacuum packing bag, the air inside the bag was removed, and the opening of the bag was heat-sealed to seal it. The bag was then stored in a freezer at -20°C for 72 hours to perform low-temperature aging.
• the sheet-shaped thermosetting composition was placed in a sealed vacuum packing bag, and aging was performed for 72 hours in an environment of 60°C without performing the low-temperature aging.
• the sheet-shaped thermosetting compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 5 were set in a pressure press and pressed at 40°C under a load of 150 MPa for 10 minutes to prepare sheet-shaped thermosetting compositions (samples).
• thermosetting composition for the cured product (sheet-shaped cured product) of the sheet-shaped thermosetting composition (sample), the numerical values indicating the amount of each component in the thermosetting composition indicate the mass proportion (parts by mass) of each component, and "WPE” is the epoxy equivalent (g/equivalent) of the resin component excluding the solvent and inorganic filler from the thermosetting composition.
• thermosetting composition excluding the solvent and inorganic filler
• the resin components i.e., epoxy compounds 1, 2, 3, 4, and 5, curing agents 1, 2, and 3, epoxy polymer 1, thermosetting catalysts 1 and 2, and silane coupling agent 1 were mixed in the mass ratios shown in Table 1 below to obtain thermosetting compositions.
• the potential was measured by potentiometric titration in accordance with JIS K7236, and the epoxy equivalent (g/equivalent) was calculated by converting the potential into the value of the entire resin components.
• thermosetting composition Three sheets of the sheet-like thermosetting composition (sample) prepared in each Example and Comparative Example were stacked and pressed under a load of 10 MPa while being heated at 120°C (product temperature) for 30 minutes, 175°C (product temperature) for 30 minutes, and then 200°C (product temperature) for 30 minutes to cure, yielding a sheet-like cured product with a thickness of 0.6 mm, which was then cut into a 50 mm x 8 mm test piece.
• test piece shape approx. 50 mm x 8 mm x 0.6 mm
• Test temperature 150°C
• 190°C Number of tests: n 2 Distance between supports: 40 mm
• a load was applied from the top surface of the test piece to the center between the supports, and the load was terminated at the point where the test piece broke (break point).
• ⁇ is the displacement (mm) at the breaking point
• h is the thickness (mm) of the test piece before the load is applied
• L is the distance between the supports (mm).
• the breaking bending stress ⁇ (kPa) was calculated from the following formula.
• ⁇ (3 ⁇ P ⁇ L)/(2 ⁇ b ⁇ h ⁇ h) ⁇ 1000
• P represents the load (N) at the breaking point
• b represents the width (mm) of the measurement sample before the load is applied
• h represents the thickness (mm) of the test piece before the load is applied
• L represents the distance between the supports (mm).
• Young's modulus (GPa) ⁇ ( ⁇ ;0.1)- ⁇ ( ⁇ ;0.01) ⁇ /(0.1-0.01)/1000000
• ⁇ ( ⁇ ; 0.1) is the stress when the strain is 0.1
• ⁇ ( ⁇ ; 0.01) is the stress when the strain is 0.01.
• thermosetting compositions (samples) prepared in each of the Examples and Comparative Examples were cured by heating at 175°C (product temperature) for 30 minutes and then at 200°C (product temperature) for 30 minutes while applying a load of 10 MPa to obtain sheet-shaped cured products (samples) having a thickness of 150 ⁇ m. Furthermore, four types of sheet-shaped cured products (samples) with different thicknesses were obtained by stacking two, three, or four sheets of the sheet-shaped thermosetting composition (sample) prepared in each Example and Comparative Example and applying pressure and heat in the same manner as described above.
• Thickness Thickness ( ⁇ m) when pressed at a pressure of 3400 kPa using a T3Star-DynTIM manufactured by Mentor Graphics
• Measurement area Area (cm 2 ) of the heat transfer portion when measuring using a T3Star-DynTIM manufactured by Mentor Graphics
• Thermal resistance value Thermal resistance value (K/W) when pressed at a pressure of 3400 kPa using a T3Star-DynTIM manufactured by Mentor Graphics.
• Thermal conductivity The thermal resistance values of four types of sheet-shaped cured products (samples) with different thicknesses were measured, and the thermal conductivity (W/m ⁇ K) was calculated using the following formula.
• Formula: Thermal conductivity (W/m ⁇ K) 1/((slope (thermal resistance value/thickness): K/(W ⁇ m)) ⁇ (area: cm 2 )) ⁇ 10 ⁇ 2
• thermosetting composition (sample) prepared in each Example and Comparative Example was placed on a 2 mm thick copper plate, and while applying a pressure of 10 MPa, the composition was heated at 175°C (product temperature) for 30 minutes, and then at 200°C (product temperature) for 30 minutes to bond the composition by heat-pressure curing. A 150 ⁇ m-thick sheet-like cured product was laminated on the copper plate to prepare a composite molded product (evaluation sample).
• the composite molded product (evaluation sample) was immersed in insulating oil (Fluorinert FC-40 manufactured by 3M Corporation), and an ultra-high voltage withstand voltage tester 7470 (manufactured by Keisoku Gijutsu Kenkyusho Co., Ltd.) was used to place electrodes on a patterned copper plate with a diameter of 25 mm. A voltage of 0.5 kV was applied, and the voltage was increased by 500 V every minute to measure the voltage (BDV: dielectric breakdown voltage) until the sheet-like cured product was broken down.
• insulating oil Feluorinert FC-40 manufactured by 3M Corporation
• an ultra-high voltage withstand voltage tester 7470 manufactured by Keisoku Gijutsu Kenkyusho Co., Ltd.
• thermosetting composition (sample) prepared in each Example and Comparative Example was cut into a test piece measuring 8.5 cm x 8.5 cm, and the sample was heated and cured at 120°C (product temperature) for 30 minutes, 175°C (product temperature) for 30 minutes, and then 200°C (product temperature) for 30 minutes while applying a load of 10 MPa from above and below.
• the resulting sheet-like cured product had a thickness of 150 ⁇ m and was used as an evaluation sample.
• the volume resistivity of this evaluation sample was measured under the following conditions using measuring devices: Digital Superresistance/Microcurrent Meter 5451 (manufactured by ACDMT Corporation) and Resistivity Chamber 12708 (manufactured by Espec Corporation).
• Main electrode outer diameter 50mm Guard electrode inner diameter: 70 mm Measurement temperature conditions: 200°C Measurement voltage: 1000V Power frequency: 50 Hz Current limiter: 10mA Discharge time: 10 seconds Charge time: 1 minute Measurement interval: 2 seconds Number of measurements: 90 seconds
• thermosetting composition (sample) prepared in each Example and Comparative Example was cut into a size of 6 cm x 7 cm, and while applying a load of 10 MPa from above and below, the sample was heated and cured at 120°C (product temperature) for 30 minutes, at 175°C (product temperature) for 30 minutes, and then at 200°C (product temperature) for 30 minutes, to obtain a sheet-like cured product with a thickness of 150 ⁇ m, which was used as an evaluation sample.
• the evaluation samples were dried at 150°C (product temperature) for 1 hour, and their masses a were measured.
• the storage modulus (E') of this evaluation sample was measured under the following conditions using a measuring device: Hitachi High-Tech Science "DMS6100", and the storage modulus (E') at 200°C is shown in the table.
• Measurement temperature conditions -110 to 270°C, temperature rise rate 10°C/min
• Measurement mode Tensile mode Measurement frequency: 1 Hz
• Chuck distance 35 mm
• Tg Glass Transition Temperature
• the composite molded body obtained above was subjected to an etching treatment to pattern a 500 ⁇ m copper plate, so that two circular patterns of ⁇ 25 mm remained.
• the composite molded body for the reflow test prepared as described above was stored for 3 days in an environment of 85°C and 85% RH using a thermo-hygrostat SH-221 (manufactured by Espec Corporation), and then heated from room temperature to 290°C (product temperature) in 12 minutes in a nitrogen atmosphere within 30 minutes, held at 290°C (product temperature) for 10 minutes, and then cooled to room temperature (moisture absorption reflow test). If the BDV (dielectric breakdown voltage) after the reflow test was less than 5 kV, the reflow resistance was evaluated as " ⁇ : Fail", and if it was 5 kV or more, it was evaluated as " ⁇ : Pass”.
• an evaluation sample was prepared simulating the silver sintering process.
• a copper plate simulating a chip and having a thickness of 0.2 mmt x 5 mm x 4 mm was placed on the circuit pattern of the composite molded body, which was approximately 100 mm2 , and then a 0.1 mmt Teflon TM was placed on top of that as a cushioning material to form a laminate consisting of the composite molded body, the copper plate, and the Teflon TM .
• This laminate was then sandwiched between SUS plates and heated and pressurized at 250°C (product temperature) for 10 minutes while adjusting the pressure applied to the 0.2 mmt copper plate to 19 MPa, to prepare an evaluation sample.
• the evaluation sample obtained by the process simulating the silver sintering process as described above was subjected to heating and pressing, and the interface between the 500 ⁇ m thick copper plate and the sheet-like cured product was observed using an ultrasonic imaging device FinSAT (FS300III) (manufactured by Hitachi Power Solutions).
• FinSAT ultrasonic imaging device
• the observation using the ultrasonic imaging device was carried out by using a probe with a frequency of 50 MHz, with a gain of 30 dB and a pitch of 0.1 mm, and placing the evaluation sample in water. If peeling occurred at the interface between the copper plate and the sheet-like cured product, the sinter resistance was evaluated as " ⁇ : Fail", and if no peeling occurred, it was evaluated as " ⁇ : Pass”.
• thermosetting composition (sample) prepared in Examples 1 and 2 were stacked, and while applying a load of 10 MPa from above and below, the sheets were heated and cured at 120°C (product temperature) for 30 minutes, 175°C (product temperature) for 30 minutes, and then at 200°C (product temperature) for 30 minutes, to obtain a sheet-like cured product with a thickness of approximately 450 ⁇ m.
• This cured product was cut to a predetermined size to obtain a test piece, which was used as an evaluation sample.
• the thermal diffusivity, density and specific heat were measured as described below, and the thermal conductivity was calculated using these values.
• Density measurement The density was measured under the following conditions.
• the volume expansion coefficient was set to three times the linear expansion coefficient measured by TMA, and the densities at 150°C and 175°C were determined.
• Thermal conductivity (W/mK) thermal diffusivity (m 2 /sec) ⁇ density (kg/m 3 ) ⁇ specific heat (J/KgK)
• the ratio of the thermal conductivity at 175°C ⁇ (175°C) to the thermal conductivity at 150°C ⁇ (150°C): ⁇ (175°C)/ ⁇ (150°C) was evaluated as " ⁇ (very unsatisfactory)” if it was less than 0.92, “ ⁇ (unsatisfactory)” if it was 0.92 or more but less than 0.95, “ ⁇ (satisfactory)” if it was 0.85 or more but less than 0.97, and " ⁇ (very satisfactory)” if it was 0.97 or more.
• thermosetting composition (mandrel test)
• each raw material was weighed out to obtain the composition (parts by mass) shown in Table 1, and mixed using a planetary centrifugal stirrer to prepare a mixture.
• a slurry-like thermosetting composition was prepared using 20% by mass each of methyl ethyl ketone and cyclohexanone so that the mixture would account for 60% by mass (solid content concentration) of the coating slurry.
• the resulting slurry-like thermosetting composition was applied to a PET substrate by a doctor blade method and then dried by heating at 60°C (heating atmosphere temperature) for 120 minutes to obtain a sheet-like thermosetting composition.
• the total content of methyl ethyl ketone and cyclohexanone in the sheet-like thermosetting composition was 1 mass% or less.
• thermosetting composition was then placed in a vacuum-packed bag, the air inside the bag was removed, and the opening of the bag was heat-sealed.
• the bag was then stored in a -20°C freezer for 72 hours to perform low-temperature aging, yielding a sheet-shaped thermosetting composition (sample).
• the prepared sheet-like thermosetting composition (sample) was cut into a piece 2 cm wide and 15 cm long or longer, and the bending resistance was evaluated according to the test method of JIS K5600-5-1.
• ⁇ (pass) The diameter of the jig where the sheet broke was less than 10 mm.
• ⁇ (fail) The diameter of the jig where the sheet broke was 10 mm or more.
• the breaking energy value obtained by three-point bending measurement at 190°C of a cured product of a thermosetting composition containing an inorganic filler and a thermosetting compound is 55 kPa or more, as obtained by three-point bending measurement at 150°C, and the breaking energy value obtained by three-point bending measurement is 80 kPa or more, the dielectric strength voltage can be maintained even after the reflow process, and further, even when bonded to a substrate under conditions in which an external force is applied at high temperatures, such as sinter bonding, the cured product will have such high temperature resistance that cracks will not occur in the cured product or the bond will not peel off.
• thermosetting composition containing an inorganic filler and a thermosetting compound
• the ratio (x/y) of the breaking energy x at 190°C to the breaking energy y at 150°C obtained by three-point bending measurement is 0.7 or more and 1.15 or less, and the value of x is 55 kPa or more
• the dielectric strength voltage can be maintained even after being exposed to a state in which internal stress is applied at high temperatures, such as in a reflow process, and further, high temperature resistance can be obtained such that the cured product does not crack or the bond does not peel off even when bonded to a substrate under conditions in which external force is applied at high temperatures, such as in sinter bonding.
• Thermosetting compositions tend to accumulate strain during curing, and stress due to strain tends to accumulate at temperatures around the curing temperature.
• stress due to strain tends to accumulate at 120 to 200°C. Therefore, by measuring the fracture energy at 150°C and 190°C in a three-point bending test and ensuring that these fracture energies are of a consistent magnitude, the composition can be made resistant to reflow conditions, which impose internal stress at temperatures above 200°C, and sintering conditions, which impose external forces. This not only improves insulation resistance, but also reduces the risk of cracking in the sheet and peeling at the interface with the substrate.
• breaking energy at 190°C remains at a certain level or above and the difference in breaking energy between 150°C and 190°C is small, even when internal stress or external force is applied at temperatures above 200°C or when the temperature is subsequently lowered, stress is dispersed, and it is thought that not only is the insulation resistance improved during the reflow process and sinter bonding, but the sheet is also less likely to crack or peel at the interface with the substrate.
• Comparative Example 1 and Comparative Example 2 the amount of polymer with a mass average molecular weight (Mw) of 5,000 or more per 100% by mass of solid content excluding inorganic filler is high, resulting in a small breaking energy at 190°C and a small value of x/y.
• Comparative Example 3 the amount of polymer with a mass average molecular weight (Mw) of 5,000 or more per 100% by mass of solid content excluding inorganic filler is high, and it does not contain a multifunctional epoxy compound with three or more epoxy groups in one molecule, resulting in a small breaking energy at 150°C and a small value of x/y.
• Comparative Example 4 contains a polyfunctional epoxy compound having three or more epoxy groups in one molecule but does not contain a polymer with a mass average molecular weight (Mw) of 5,000 or more, and therefore has a high storage modulus at 200°C but insufficient toughness, resulting in a small breaking energy at 150°C and a large value of x/y.
• Comparative Example 5 does not undergo low-temperature aging, which prevents freezing and dispersion of water, resulting in the formation of voids, which are thought to be the reasons for the small breaking energy and x/y values at 150°C and 190°C.
• the breaking energy value obtained by three-point bending measurement at 190°C and/or the breaking energy value obtained by three-point bending measurement at 150°C no longer satisfied the specified range, or the ratio (x/y) of the breaking energy x obtained by three-point bending measurement at 190°C to the breaking energy y obtained by three-point bending measurement at 150°C and/or the value of x no longer satisfied the specified range, which is thought to have resulted in the dielectric strength being unable to be maintained when exposed to conditions in which internal stress is applied at high temperatures, such as in a reflow process, or in the occurrence of cracks in the cured product or peeling when bonded to a substrate under conditions in which further external force is applied at high temperatures, such as in sinter bonding.
• the factors that contribute to the effects of the examples are thought to be that by incorporating a curing agent that acts on the epoxy compound, and further adjusting the amount of polymer, such as epoxy polymer, to adjust the WPE of the resin component within a specified range, adjusting the amount of polyfunctional epoxy compound to adjust the number of functional groups and molecular weight of the resin component, selecting the skeletal structure, adjusting the low-temperature aging conditions, etc., the crosslink density and cohesive strength of the cured product are increased, and elasticity and breaking energy at high temperatures are increased, providing insulation resistance when exposed to high temperatures and sintering resistance under high-temperature conditions.
• a curing agent that acts on the epoxy compound
• the amount of polymer such as epoxy polymer
• thermosetting composition of the present invention it is even more preferable to increase the content of polyfunctional epoxy compounds as thermosetting compounds, reduce the content of polymers such as epoxy polymers, use a phenolic resin-based curing agent as a curing agent to increase the crosslink density of the cured product, and perform low-temperature aging to prepare the composition of the present invention.
• Example 1 provided better handling characteristics for the sheet-shaped thermosetting composition
• Example 2 showed even less decrease in thermal conductivity at high temperatures. This is presumably because Example 1 contains a smaller amount of epoxy polymer than Example 2, allowing the flexibility of the sheet-shaped thermosetting composition in an uncured state to be maintained, while Example 2 contains a benzoxazine compound in addition to the phenolic resin, which prevents a decrease in thermal conductivity at high temperatures compared to Example 1, resulting in less change in physical properties at high temperatures.

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