JP2018095541A - Graphite resin composite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a graphite resin composite which is excellent in mass productivity and product characteristics (heat dissipation, adhesiveness, and conductivity) and with which especially heat dissipation of an electronic device is drastically improved.SOLUTION: A graphite resin composite is formed by impregnating a graphite sintered body having an integral structure of graphite primary particles continuous in three dimensions with a thermosetting resin composition and has at least one heat-conducting surface, in which the content of the graphite sintered body based on the total amount of the graphite sintered body and the thermosetting resin composition is 70 to 80 vol.%, the content of the thermosetting resin composition based on the total amount of the graphite sintered body and the thermosetting resin composition is 20 to 30 vol.%, and in an X-ray diffraction pattern obtained by making the heat-conducting surface irradiated with X-ray, the value of diffraction peak intensity corresponding to the (002) face of the graphite primary particles divided by diffraction peak intensity corresponding to the (100) face of the graphite primary particles is less than 30.SELECTED DRAWING: None

Description

  The present invention relates to a graphite resin composite and a heat conductive adhesive sheet using the same. Moreover, this invention relates also to the vehicle-mounted power module or semiconductor device obtained using the said heat conductive adhesive sheet.

  In recent years, with the improvement in performance and miniaturization of electronic devices typified by mobile phones, LED lighting devices, in-vehicle power modules, etc., mounting technology has rapidly advanced at each level of semiconductor device, printed wiring board mounting, and device mounting. doing. Therefore, the heat generation density inside the electronic device is increasing year by year, and how to efficiently dissipate the heat generated during use is an important issue.

  Also, in these electronic devices, particularly power modules or semiconductor devices, the lower surface of an insulating substrate having a semiconductor chip on the upper surface is joined to a metal base plate such as copper by soldering, and the metal base plate further serves as a heat sink or cooler. It is configured to be joined with solder. Here, a plurality of fins are generally formed in the cooler, and solder made of an alloy mainly composed of Sn is generally used as bonding solder. However, there is room for further improvement with respect to thermal shock in joining by soldering, and there is a risk of destruction of the joining material (crack) or destruction of the joining interface (shear failure) due to the thermal stress due to the difference in thermal expansion coefficient of the constituent materials. There is. In general, the thermal expansion coefficient of a cooler (mainly a metal having high thermal conductivity is used as a material) is significantly higher than that of a semiconductor and an insulating substrate directly bonded to the semiconductor device. high. For example, the thermal expansion of a semiconductor chip is generally 3 ppm, the thermal expansion of an insulating substrate is 4 to 5 ppm, and the thermal expansion coefficient of an aluminum cooler is about 23 ppm. Since the thermal stress generated by such a large difference in thermal expansion coefficient in the semiconductor device is large, it has been difficult to resist by conventional techniques such as solder.

  In order to satisfy the high requirements for thermal conductivity and thermal stress, a thermally conductive adhesive sheet may be prepared instead of solder to fix the electronic member.

  Conventionally, in the above heat conductive adhesive sheet, ceramic powder having high thermal conductivity such as aluminum oxide, silicon nitride, boron nitride, aluminum nitride is dispersed in an uncured (A stage) thermosetting resin. After that, a thermosetting resin composition that has been molded into a sheet shape by coating with various coaters, etc., and has been made into a semi-cured state (B stage) by heating has been used.

  The heat conductive adhesive sheet is adhered to an electronic member such as a metal circuit or a metal plate, and then heated to melt the semi-cured (B stage) thermosetting resin and bond it to the surface of the electronic member. In this way, the adhesiveness of the thermally conductive adhesive sheet to the electronic member is expressed, and further, the thermosetting resin is completely cured by heating (C stage), and the adhesion between the electronic member is strengthened. .

  The above heat conductive adhesive sheet is an adhesive layer (an uncured state (A stage) thermosetting resin or an uncured state (A stage) thermosetting between an electronic member such as a metal circuit or a metal plate. It is not necessary to form a ceramic resin dispersed in a functional resin), so there is no need for coating work or the introduction of precision coating equipment, and the user's work becomes very simple and widely used. Yes.

  In Patent Document 1, in a metal base circuit board, in a state where a metal foil is arranged on a heat conductive adhesive sheet in which ceramic powder is dispersed in a thermosetting resin in a semi-cured state (B stage), heat conductive bonding is performed. By curing the thermosetting resin contained in the sheet to form a C stage, it is possible to obtain a metal base circuit board with excellent heat dissipation by a simple method.

  Moreover, as a method for increasing the thermal conductivity of the above-mentioned thermally conductive adhesive sheet, (1) increasing the thermal conductivity of a completely cured thermosetting resin (C stage), (2) ceramic powder (3) Enlarging the particle diameter of the ceramic powder, and (4) Highly filling the ceramic powder. In Patent Document 2, it is possible to obtain a heat conductive adhesive sheet having high heat conductivity by the method (1). Further, in Patent Document 3, by using boron nitride having high thermal conductivity as the ceramic powder, it is possible to obtain a heat conductive adhesive sheet having high thermal conductivity by the method (2). Moreover, in patent document 4, it is possible to obtain the heat conductive adhesive sheet of high heat conductivity by the method of (2) and (4). Furthermore, in patent document 5, the heat conductive adhesive sheet of high heat conductivity is obtained by the method of (2), (3), and (4) by combining the aluminum nitride powder of various particle diameters by a specific ratio. Making it possible.

  However, in the inventions of Patent Documents 1 and 3 to 5 described above, since there is a thermosetting resin layer having a low thermal conductivity between the particles of the ceramic powder, the thermal conductivity is at most 16 W / (m · K) (see Patent Document 5, Table 2, Synthesis Example 7), and there was a limit to obtaining high thermal conductivity. Also in Patent Document 2, there is a limit to increasing the thermal conductivity of the thermosetting resin, and the thermal conductivity is 10.5 W / (m · K) at the maximum (see Table 1, Example 6 of Patent Document 2). )Met. For this reason, there has been a problem in terms of heat dissipation in the thermal design requirements of electronic devices that have become increasingly difficult in recent years.

  Therefore, in Patent Documents 6 to 9, ceramics in which ceramic primary particles having high thermal conductivity are sintered and a thermosetting resin is filled in the pores of a ceramic sintered body having a three-dimensional continuous integrated structure. A product obtained by processing a resin composite into a plate shape has been proposed. In these inventions, since the thermal conductivity of the plate-like ceramic resin composite (thermally conductive adhesive sheet) is determined by the ceramic sintered body, high thermal conductivity can be obtained.

  In Patent Document 10, a buffer material having an intermediate thermal expansion coefficient between a semiconductor chip typified by silicon and a cooler typified by aluminum or copper is appropriately interposed to relax the difference in thermal expansion coefficient. Has been proposed. In Patent Document 10, as a basic configuration, a power module substrate is interposed between a semiconductor chip and a cooler, and this power module substrate is formed with metal layers above and below a ceramic insulating substrate. In order to alleviate the difference in expansion coefficient, a laminated substrate in which three layers of copper-molybdenum-copper are laminated by brazing is used.

JP 2009-049062 A JP 2006-063315 A JP 2014-196403 A JP 2011-184507 A JP 2014-189701 A JP 62-126694 A International Publication WO2014 / 196696A1 International Publication WO2015 / 022956A1 Japanese Patent Laid-Open No. 08-244163 JP 2007-335795 A

  Some electronic members used in in-vehicle power module structures such as semiconductor devices do not require electrical insulation, and examples thereof include heat-dissipating grease and heat-dissipating sheets.

  In some cases, the above-described ceramic resin composites as described above have been tried to be used for electronic members that do not require electrical insulation, aiming at thermal conductivity. However, thermal conductivity is low and satisfactory results are not obtained. That is, such ceramic resin composites are known to have the following problems in terms of heat dissipation / thermal conductivity.

  When two or more plate-shaped ceramic resin composites are laminated according to the invention described in Patent Document 6, an adhesive layer (thermosetting resin or thermosetting resin having a low thermal conductivity is provided between the plate-shaped ceramic resin composites. (A ceramic powder dispersed in a resin) is required (see FIG. 4 of Patent Document 6), and there is a problem in terms of heat dissipation.

  Also in Patent Document 7, when a plate-shaped ceramic resin composite is bonded to an electronic member such as a metal circuit or a metal plate, an adhesive layer having a low thermal conductivity (a ceramic powder in a thermosetting resin or a thermosetting resin). ) Is necessary, and there is a problem in terms of heat dissipation.

  Also in Patent Document 8, when bonding to a metal circuit and a metal plate, an adhesive layer having a low thermal conductivity (a ceramic powder dispersed in a thermosetting resin or a thermosetting resin, paragraph 0056 of Patent Document 8). , 0057) is required. For this reason, the thermal resistance of the adhesive layer between the metal circuit and the plate-like ceramic resin composite is increased, which causes a problem in terms of heat dissipation.

  Patent Document 9 proposes a plate-shaped ceramic resin composite (thermally conductive adhesive sheet) having an adhesive function, and a circuit board excellent in heat dissipation can be obtained. However, according to Patent Document 9, the cured state of the thermosetting resin before being bonded to the metal circuit is an uncured state (A stage) (see Paragraph 0053 of Patent Document 9). If the cured state of the thermosetting resin contained in the ceramic resin composite is an uncured state (A stage), the heat at the time of cutting the ceramic resin composite into a plate-like thermally conductive adhesive sheet is not sufficient. The cured thermosetting resin melts and thickness variation occurs, and a desired heat conductive adhesive sheet cannot be obtained. Furthermore, the heat conductive adhesive sheet cannot withstand the impact at the time of cutting and cracks occur. Therefore, in order to reinforce the ceramic sintered body in the cutting process, after impregnating a liquid organic material such as TMP (trimethylolpropane), the plate is cut into a plate shape, and after removing the liquid organic material by heat treatment or the like, It is necessary to impregnate a ceramic sintered body with a thermosetting resin to obtain a heat conductive adhesive sheet. Therefore, the process becomes complicated (the impregnation process is required twice (impregnation of liquid organic substance and thermosetting resin), and the impregnation of the thermosetting resin is plate-like and needs to be processed in large quantities for each sheet. ) And an increase in cost, which has been an obstacle to mass production (see paragraphs 0036 to 0045 of Patent Document 9). In addition, since the cured state of the thermosetting resin contained in the thin thermally conductive adhesive sheet is an uncured state (A stage), the reinforcing effect is small, and cracking is likely to occur when a metal circuit is bonded (patent) (See paragraph 0063 of Document 9), it is difficult to obtain desired characteristics. Furthermore, if the thermosetting resin is in an uncured state (A stage) in which the fluidity is too high, a thermosetting resin layer having a low thermal conductivity is formed on the unevenness of the surface of the electronic member, and the thermal conductivity decreases. There was also a problem to say.

  In addition, ceramic sintered bodies such as boron nitride usually have a high elastic modulus, so although they have a high thermal conductivity as a material, an electronic member such as a metal circuit or a metal plate is bonded to a heat conductive adhesive sheet by heating and pressing. In this case, the ceramic sintered body contained in the heat conductive adhesive sheet hardly follows the shape of the surface of the electronic member that is generally flat (fine irregular shape), and the air layer is likely to be caught. As a result, the high thermal conductivity is not exhibited. Furthermore, even when a ceramic sintered body having a low elastic modulus is used, if the thermosetting resin contained in the heat conductive adhesive sheet is in a completely cured state (C stage) with low fluidity, the surface of the electronic member Furthermore, since it is difficult to bond the ceramic sintered body and the thermosetting resin, high thermal conductivity is not exhibited.

  In the first place, when a ceramic sintered body is used even for an electronic member that does not require electrical insulation, there is a problem that the cost is increased and the manufacturing process becomes complicated, so that there are few advantages.

  Moreover, if the fluidity of the thermosetting resin contained in the heat conductive adhesive sheet is too high (viscosity is too low) and is in an uncured state (A stage), problems are likely to occur in the cutting process and the bonding process. In some cases, the process becomes complicated, and the characteristics such as thermal conductivity may deteriorate.

  In addition, regarding the use for the power module substrate, in the method described in Patent Document 10, the laminated structure becomes very complicated and the product cost is increased, and the overall thermal resistance is increased because of the multilayer structure, There was a problem that sufficient cooling performance could not be obtained.

  In the prior art as described above, there is no technology that can provide sufficient heat conductivity (heat dissipation) and adhesiveness in the heat-dissipating adhesive sheet. The technology that can be solved is not seen until now.

  In view of the background art as described above, the present invention is excellent in mass productivity and product characteristics (heat dissipation and adhesiveness), and in particular, can greatly improve the heat dissipation of electronic devices, and in particular has electrical insulation. An object is to provide a graphite resin composite that is not necessary or that is suitable for use as an electronic member for the purpose of positively imparting conductivity. Another object of the present invention is to provide a heat conductive adhesive sheet made of the graphite resin composite according to the present invention.

  In view of the said subject, the following can be provided in embodiment of this invention.

[1]
A graphite resin composite comprising a graphite sintered body having a monolithic structure in which graphite primary particles are three-dimensionally continuous, impregnated with a thermosetting resin composition, and having at least one heat conducting surface,
The ratio of the graphite sintered body to the total amount of the graphite sintered body and the thermosetting resin composition is 70% by volume or more and 80% by volume or less,
The ratio of the thermosetting resin composition to the total amount of the graphite sintered body and the thermosetting resin composition is 20 vol% or more and 30 vol% or less,
In the X-ray diffraction pattern obtained by irradiating the heat conducting surface with X-rays, the diffraction peak intensity corresponding to the (002) plane of the graphite primary particles is the diffraction peak intensity corresponding to the (100) plane of the graphite primary particles. A graphite resin composite, wherein the value divided by is less than 30.

[2]
In the X-ray diffraction pattern obtained by irradiating the heat conducting surface with X-rays, the diffraction peak intensity corresponding to the (002) plane of the graphite primary particles is the diffraction peak intensity corresponding to the (100) plane of the graphite primary particles. The graphite resin composite according to [1], wherein the value divided by is from 0.01 to 25.

[3]
The thermosetting resin composition is a combination of any one or both of a substance having an epoxy group and a substance having a cyanate group and one or both of a substance having a hydroxyl group and a substance having a maleimide group. The graphite resin composite according to [1] or [2].

[4]
The graphite resin composite according to [3], wherein the thermosetting resin composition is a bismaleimide triazine resin.

[5]
The heat generation starting temperature measured by a differential scanning calorimeter of the thermosetting resin composition is in the range of 180 ° C. or higher and 300 ° C. or lower, the curing rate is in the range of 5% or higher and 60% or lower, and several The graphite resin composite according to any one of [1] to [4], wherein the average molecular weight is in the range of 450 to 4800.

[6]
The heat conductive adhesive sheet which processes the graphite resin composite in any one of [1]-[5], and has a heat conductive surface on both surfaces.

[7]
The vehicle-mounted power module structure provided with the 2 or more electronic member each adhere | attached on the heat conductive surface of both surfaces of the heat conductive adhesive sheet as described in [6].

[8]
The in-vehicle power module structure according to [7], wherein the electronic member is at least one selected from a metal base plate for a substrate, a heat sink for cooling the substrate, and a heat exchange cooler.

[9]
The in-vehicle power module structure according to [7] or [8], which is a semiconductor device.

  Since the heat conductive adhesive sheet obtained by processing the graphite resin composite according to the present invention is excellent in adhesiveness and exhibits high thermal conductivity (low thermal resistance), the heat conductive adhesive sheet of the present invention was used. Electronic equipment exhibits excellent reliability and heat dissipation, and also exhibits high resistance to heat stress and electrical conductivity. Furthermore, since it is possible to arbitrarily control the thermal expansion coefficient by controlling the volume content of the thermosetting resin and graphite, it is possible to relieve stress during the thermal cycle and obtain high reliability.

It is the figure which modeled the shape of the graphite primary particle. It is a schematic diagram showing the prediction of the ideal orientation of the graphite primary particle which concerns on embodiment of this invention. It is a schematic diagram which shows the structural example of the vehicle-mounted power module structure which concerns on embodiment of this invention.

  Hereinafter, the present invention will be described in more detail. In the present specification, a numerical range indicated by using a tilde symbol “˜” means a numerical range including both a lower limit value and an upper limit value of a certain range unless otherwise specified.

  In the present invention, a graphite sintered body controlled within a range of specific physical properties is impregnated with an appropriate amount of a predetermined thermosetting resin composition, so that it has an unprecedented high mass productivity and adhesiveness. One of the features is that the thermal conductivity has been achieved. Although it is not intended that the present invention be limited by theory, it was possible to achieve high thermal conductivity because the graphite sintered body and the thermosetting resin were formed into fine irregularities on the surface of an electronic member such as a metal plate. It is considered that the composition is capable of following up effectively and that the air for heat insulation hardly penetrates. Such a high thermal conductivity cannot be realized by a combination of a conventional general ceramic sintered body and a thermosetting resin composition, and can be provided for the first time by the present invention. That is, the present inventor has developed an unprecedented innovative heat conductive adhesive sheet. Hereinafter, definitions of terms used in the present specification and materials used in the present invention will be described.

<Sintered graphite, graphite resin composite, thermally conductive adhesive sheet>
In the present invention, a state in which two or more graphite primary particles are aggregated in a state where they are bonded together by sintering is defined as a “graphite sintered body” having a three-dimensional continuous structure. Furthermore, in the present invention, a composite composed of a graphite sintered body and a thermosetting resin composition is defined as a “graphite resin composite”. In addition, a product obtained by processing a graphite resin composite into a sheet is defined as a “thermal conductive adhesive sheet”.

  Bonding of graphite primary particles by sintering is evaluated by observing a bonded portion of primary particles of a cross section of the graphite primary particles using a scanning electron microscope (for example, “JSM-6010LA” manufactured by JEOL Ltd.). can do. As pretreatment for observation, the graphite particles are embedded with a resin, processed by a CP (cross section polisher) method, fixed on a sample stage, and then coated with osmium. The observation magnification is 1500 times. Moreover, the graphite sintered compact for evaluation can be obtained by ashing the thermosetting resin composition which comprises a graphite resin composite at 500-900 degreeC in air | atmosphere. If there is no bonding between the graphite primary particles by sintering, the shape cannot be maintained during ashing.

<Ratio of sintered graphite>
The graphite sintered body in the graphite resin composite is preferably in the range of 70 to 80% by volume (the thermosetting resin composition is 20 to 30% by volume), more preferably 71 to 79% by volume. . When the amount of the graphite sintered body is smaller than 70% by volume, the ratio of the thermosetting resin composition having a low thermal conductivity increases, so that the thermal conductivity decreases. When the amount of the sintered graphite is larger than 80% by volume, the thermosetting resin composition conforms to the shape of the surface of the electronic member when the electronic member such as a metal plate is bonded to the heat conductive adhesive sheet by heating and pressing. As a result, the tensile shear bond strength and the thermal conductivity may be reduced. The ratio (volume%) of the graphite sintered body in the ceramic resin composite can be obtained by measuring the bulk density and porosity of the graphite sintered body shown below.
Graphite sintered body bulk density (D) = mass / volume (1)
Graphite sintered body porosity (%) = (1- (D / graphite sintered body true density)) × 100 = ratio of thermosetting resin composition (%) (2)
Ratio of sintered graphite (%) = 100-ratio of thermosetting resin composition (3)

<Method for producing sintered graphite>
The sintered graphite is obtained, for example, by coking and molding coke and tar pitch, first firing at approximately 1000 ° C., and then graphitizing at approximately 3000 ° C. Examples of the molding method include CIP molding, extrusion molding, and mold molding.

<Composite of sintered graphite and thermosetting resin composition>
The graphite sintered body and the thermosetting resin composition of the present invention can be combined, for example, by impregnating the graphite sintered body with the thermosetting resin composition. The impregnation of the thermosetting resin composition can be performed by vacuum impregnation, pressure impregnation at 1 to 300 MPa (G), or impregnation thereof. The pressure during vacuum impregnation is preferably 1000 Pa (abs) or less, and more preferably 100 Pa (abs) or less. In the pressure impregnation step, if the pressure is less than 1 MPa (G), there is a possibility that the thermosetting resin composition cannot be sufficiently impregnated to the inside of the graphite sintered body, and if it exceeds 300 MPa (G), the facility becomes large and costly. Disadvantageous. In order to easily impregnate the thermosetting resin composition inside the graphite sintered body, it is more preferable to heat to 100 to 180 ° C. during vacuum impregnation and pressure impregnation to reduce the viscosity of the thermosetting resin composition. It can be carried out.

<Orientation of graphite primary particles in graphite resin composite>
The graphite resin composite of the present invention has a heat conducting surface on at least one surface, preferably both surfaces, and is configured to adhere the heat conducting surface to a heat conducting object. This heat conducting surface is characterized in that the orientation of the primary graphite particles is controlled.

  The graphite primary particles generally have a scaly shape, and it is preferable to orient the graphite primary particles so that the in-plane direction ((100) direction) is along the heat conduction direction. This means an orientation in which the thickness direction ((002) direction) of the primary graphite particles is perpendicular to the heat conduction direction. The orientation of the primary graphite particles can be confirmed by an X-ray diffraction pattern, and can be measured by a method based on JIS K0131: 1996 or JIS R7651: 2007. FIG. 1 is a diagram schematically showing the shape of graphite primary particles, and FIG. 2 is a schematic diagram showing an outline of the orientation of graphite primary particles according to an embodiment of the present invention.

  The primary graphite particles that can be used in the embodiment of the present invention can have any shape (average major axis, aspect ratio). Although there is no particular limitation, for example, graphite primary particles having an average major axis in the range of 1 μm to 800 μm and an aspect ratio in the range of 5 to 30 can be used. The average major axis and the aspect ratio can be calculated by observing the graphite sintered body with the above-described scanning electron microscope and calculating, for example, from 100 graphite primary particles in the measurement visual field.

<Thermosetting resin composition>
The thermosetting resin composition is a combination of one or both of a substance having an epoxy group and a substance having a cyanate group and one or both of a substance having a hydroxyl group and a substance having a maleimide group. Is preferred. Among these, a combination of a substance having a cyanate group and a substance having a maleimide group is more preferable. Substances having an epoxy group include bisphenol A type epoxy resins, bisphenol F type epoxy resins, polyfunctional epoxy resins (cresol borac epoxy resins, dicyclopentadiene type epoxy resins, etc.), phenol novolac type epoxy resins, cyclic Examples of the epoxy resin include aliphatic epoxy resins, glycidyl ester type epoxy resins, and glycidyl amine type epoxy resins. Examples of the substance having a cyanate group include 2,2′-bis (4-cyanatophenyl) propane and bis (4 -Cyanato-3,5-dimethylphenyl) methane, 2,2'-bis (4-cyanatophenyl) hexafluoropropane, 1,1'-bis (4-cyanatophenyl) ethane, 1,3-bis ( Cyanate resins such as 2- (4-cyanatophenyl) isopropyl) benzene Examples of the substance having a hydroxyl group include phenol novolac resins, phenols such as 4,4 ′-(dimethylmethylene) bis [2- (2-propenyl) phenol], and examples of the substance having a maleimide group include 4,4′-diphenylmethane bismaleimide, m-phenylene bismaleimide, bisphenol A diphenyl ether bismaleimide, 3,3′-dimethyl-5,5′-diethyl-4,4′-diphenylmethane bismaleimide, 4-methyl-1, 3-phenylene bismaleimide, 1,6′-bismaleimide- (2,2,4-trimethyl) hexane, 4,4′-diphenyl ether bismaleimide, 4,4′-diphenylsulfone bismaleimide, 1,3-bis ( 3-maleimidophenoxy) benzene, 1,3-bis (4-maleimidophenoxy) benzene And maleimide resins such as bis- (3-ethyl-5-methyl-4-maleimidophenyl) methane and 2,2′-bis [4- (4-maleimidophenoxy) phenyl] propane. Particularly preferably, a bismaleimide triazine resin can be used as the thermosetting resin composition in view of excellent properties obtained.

  The thermosetting resin composition is appropriately impregnated with a silane coupling agent for improving the adhesion between the graphite sintered body and the thermosetting resin composition, improving wettability and leveling properties, and promoting viscosity reduction. An antifoaming agent, a surface conditioner, and a wetting and dispersing agent for reducing the occurrence of defects during curing can be contained. Further, a curing accelerator may be added in order to control the curing rate and the heat generation start temperature. Curing accelerators include imidazoles such as 2-ethyl-4-methylimidazole and 2-phenylimidazole, organophosphorus compounds such as triphenylphosphine and tetraphenylphosphonium tetra-p-tolylborate, acetylacetone copper (II), zinc (II) Metal catalysts such as acetylacetonate can be mentioned.

<Semi-curing of thermosetting resin composition>
A graphite resin composite can be obtained by semi-curing (B-stage) the thermosetting resin composition combined with the graphite sintered body. As the heating method, infrared heating, hot air circulation, oil heating method, hot plate heating method or a combination thereof can be used. The semi-curing may be performed as it is using the heating function of the impregnation apparatus after completion of the impregnation, or may be separately performed using a known apparatus such as a hot air circulating conveyor furnace after taking out from the impregnation apparatus.

<Heat generation start temperature of thermosetting resin composition>
The heat generation starting temperature measured with a differential scanning calorimeter of the thermosetting resin composition contained in the graphite resin composite is preferably 180 ° C or higher, more preferably 190 ° C or higher, and 200 ° C or higher. Even more preferably. When the heat generation start temperature is lower than 180 ° C., when the thermosetting resin composition is heated during vacuum impregnation and pressure impregnation, the curing reaction of the thermosetting resin composition proceeds and the viscosity of the thermosetting resin composition is increased. As a result, the thermosetting resin composition cannot be impregnated in the pores of the graphite sintered body. For this reason, the adhesiveness of a graphite resin composite falls. Although there is no restriction | limiting in particular about the upper limit of the said heat_generation | fever starting temperature, 300 degrees C or less is practical when the productivity at the time of adhere | attaching on a heat conductive adhesive sheet by heating and pressurization, and the heat resistance of an apparatus component are considered. The heat generation start temperature can be controlled by a curing accelerator or the like.

<Curing temperature and curing time of thermosetting resin composition>
The curing temperature of the thermosetting resin composition contained in the graphite resin composite is preferably 180 ° C. or less, and more preferably 160 ° C. or less. Further, the curing time of the thermosetting resin composition is preferably about 10 to 15 hours.

<Evaluation method of heat generation start temperature of thermosetting resin composition>
The exothermic start temperature is a heat generation curve obtained when the thermosetting resin composition is heated and cured with a differential scanning calorimeter, with the horizontal axis representing temperature (° C.) and the vertical axis representing heat flow (mW). This is the temperature at the intersection of the tangent and the base line at the inflection point on the curve from the exothermic peak to the rise of the exothermic curve.

<Curing rate of thermosetting resin composition>
The “semi-cured (B stage) state”, which is a term indicating the cured state of the thermosetting resin composition contained in the graphite resin composite, is a cure rate obtained from the following formula using differential scanning calorimetry. The state of 5-60% is said. If the curing rate is less than 5%, the heat at the time of cutting the graphite resin composite into a plate-like thermally conductive adhesive sheet melts the uncured thermosetting resin composition, resulting in variations in thickness. To do. In addition, the graphite resin composite cannot withstand the impact at the time of cutting, cracks occur, and sheet molding becomes difficult. Furthermore, when the thermally conductive adhesive sheet is adhered by heating and pressing, an adhesive (thermosetting resin composition) layer having low thermal conductivity is formed on the surface of the electronic member, and the thermal conductivity is lowered. If the curing rate is greater than 90%, the thermosetting resin composition does not melt when bonded to the heat conductive adhesive sheet by heating and pressurization, and thus the heat conductive adhesive sheet cannot be bonded. The curing rate of the thermosetting resin composition in the graphite resin composite is preferably 10 to 90%, more preferably 12 to 40%, and even more preferably 15 to 30%.

<Evaluation method of curing rate of thermosetting resin composition>
Curing rate (%) = [(X−Y) / X] × 100
X: The amount of heat generated when the thermosetting resin composition in a state before being cured by heating was cured using a differential scanning calorimeter.
Y: When the thermosetting resin composition (thermosetting resin composition to be evaluated for curing rate) in a semi-cured state (B stage) by heating is cured using a differential scanning calorimeter The amount of heat generated.

The state of “cured” in the above X and Y can be identified from the peak of the exothermic curve obtained. In this technical field, “C stage state” refers to a state in which the thermosetting resin composition is almost completely cured and does not melt again even when heated to a high temperature. Specifically, it refers to a state where the curing rate described in the “B stage state” column exceeds 60%. Furthermore, the “A stage state” refers to a state in which curing by heating has not progressed at all or has progressed only slightly and is liquid at 20 ° C. at room temperature. Specifically, it means a state where the curing rate described in the “B stage state” column is smaller than 5.0%.

<Number average molecular weight and evaluation method of thermosetting resin composition>
The number average molecular weight of the thermosetting resin composition contained in the graphite resin composite in the present invention is an average molecular weight expressed in terms of polystyrene measured by size exclusion chromatography (hereinafter abbreviated as SEC) (JIS K). 7252-1: 2016 Section 3.4.1 (according to formula (1)). The number average molecular weight is preferably in the range of 450 to 4800, more preferably in the range of 500 to 4000, and still more preferably in the range of 550 to 3500. When the number average molecular weight is smaller than 450, the thermosetting resin composition is melted by the heat generated when the graphite resin composite is cut into a plate-like thermally conductive adhesive sheet, resulting in variation in thickness. Further, the graphite resin composite cannot withstand the impact at the time of cutting, and cracks occur. Furthermore, when it adheres to a heat conductive adhesive sheet by heating and pressurizing, an adhesive (thermosetting resin composition) layer having low heat conductivity is formed at the interface, and the heat conductivity is lowered. When the number average molecular weight is larger than 4800, the melt viscosity of the thermosetting resin composition when bonded to the heat conductive adhesive sheet by heating and pressurization is high, so that the adhesive strength with the electronic member is lowered. Moreover, when it adheres to a heat conductive adhesive sheet by heating and pressurization, since a graphite sintered compact and a thermosetting resin composition become difficult to couple | bond with the surface of an electronic member, heat conductivity falls.

<Melt temperature and evaluation method of thermosetting resin composition>
The melting temperature of the thermosetting resin composition contained in the graphite resin composite in the present invention is preferably 70 ° C. or higher, more preferably 80 ° C. or higher, and even more preferably 95 ° C. or higher. preferable. When the melting temperature is lower than 70 ° C., the thermosetting resin composition is melted by heat at the time of cutting the graphite resin composite into a plate-like thermally conductive adhesive sheet, and thickness variation occurs. The upper limit of the melting temperature is not particularly limited, but it is necessary to suppress an increase in viscosity due to the progress of the curing reaction of the thermosetting resin composition when bonded to the heat conductive adhesive sheet by heating and pressing. The melting temperature is practically 180 ° C. or lower, typically 150 ° C. or lower, and more typically 120 ° C. or lower. The melting temperature of the present invention is the temperature of the endothermic peak when the thermosetting resin composition is heated by differential scanning calorimetry.

<Configuration of heat conductive adhesive sheet>
The thermally conductive adhesive sheet according to the embodiment of the present invention has a thermally conductive surface on at least one side, preferably on both sides. This heat conducting surface is configured to adhere to a heat conducting object such as a heat exchange cooler (heat sink) or a heat sink (such as a copper base). As described above, the orientation of the primary graphite particles is controlled on the heat conducting surface. The usage example of a heat conductive adhesive sheet is mentioned later.

<Thickness of heat conductive adhesive sheet>
The thickness of the heat conductive adhesive sheet can be changed according to required characteristics. For example, when thermal resistance is important, a thin one of 0.1 mm to 0.35 mm can be used.

<In-vehicle power module structure>
The heat conductive adhesive sheet which concerns on embodiment of this invention can be included in a vehicle-mounted power module structure. The in-vehicle power module structure can be manufactured by using the thermally conductive adhesive sheet for bonding two or more electronic members. With two or more electronic members, for example, one electronic member is an aluminum heat exchange cooler (heat sink), and the other electronic member is a copper plate (heat radiating plate) on the bottom of the power module. In the prior art, by fixing the thermal interface material (TIM) such as a heat-dissipating sheet with screws, the heat of the heat generating electronic components of the power module is released from the copper heat-dissipating plate to the aluminum cooler via the heat-dissipating sheet. However, since the heat conductive adhesive sheet according to the embodiment of the present invention has an adhesive function as well as high thermal conductivity, screwing is unnecessary, and the heat conductive adhesive sheet is suitable as a constituent member of an in-vehicle power module structure. In a preferred embodiment, the in-vehicle power module structure may be a semiconductor device.

  An in-vehicle power module structure according to an embodiment of the present invention includes a heat conductive adhesive sheet, a heating element or a semiconductor element (hereinafter also abbreviated as “substrate” as included in “substrate”), and heat dissipation. A plate and a heat exchange cooler can be included. In FIG. 3, the structural example of the vehicle-mounted power module structure which concerns on embodiment of this invention was shown as a schematic diagram. The in-vehicle power module structure 30 shown in FIG. 3 includes, in order from the top, a substrate 32, a heat radiating plate 34, a heat conductive adhesive sheet 36 (shown by a wavy pattern), and a heat exchange cooler 38. It is. Further, the substrate 32 includes a heating element or semiconductor element 33a, solder 33b (shown with a right oblique line) for joining the heating element or semiconductor element 33a to the copper circuit 33c, a copper circuit 33c, a copper circuit 33c, and a heat dissipation plate. And an insulating layer 33d (shown by a left oblique line pattern) that are bonded to each other with a gap 34 interposed therebetween. Here, for the sake of simplicity, each component is drawn one by one, but it goes without saying that a plurality of components may be included.

  The substrate (including a heating element or a semiconductor element) can include a power element such as an IGBT (insulated gate bipolar transistor) or a thyristor. Further, in the present specification, the substrate may include a copper circuit or an insulating layer (for example, as in the above-described embodiment in which the substrate 32 in FIG. 3 includes the copper circuit 33c and the insulating layer 33d). As such an insulating layer, a ceramic resin composite having excellent insulating properties may be used. Here, it should be noted that the ceramic resin composite having insulating properties and the graphite resin composite having thermal conductivity according to the embodiment of the present invention are clearly different in use particularly in an in-vehicle power module structure. .

  The heat radiating plate also functions as an electrode and a heat radiating body, and is usually composed of a metal having good thermal conductivity and electrical conductivity. Examples of the heat sink include a copper base, an aluminum base, or a base made of an alloy thereof.

  The heat exchange cooler may be a general solid heat sink (made of aluminum or the like), or may be a water cooling type in which cooling water flows inside or an air cooling type having fins.

<Adhesion method using a thermally conductive adhesive sheet for manufacturing an in-vehicle power module structure>
In manufacturing the vehicle-mounted power module structure according to the embodiment of the present invention, the heat conductive adhesive sheet can be used for bonding between the heat sink and the heat exchange cooler. In this bonding, the graphite resin composite contained in the heat conductive adhesive sheet is heated to melt the semi-cured (B stage) thermosetting resin, and the shape follows the shape of the adherend surface. It is possible to develop adhesiveness and further heat the thermosetting resin to a completely cured state (C stage), thereby strengthening the adhesion with the adherend. In the case of bonding in a shorter time, a method of applying a thermosetting resin in a C-stage state and heating and curing is also possible. As the heating method, infrared heating, hot air circulation, oil heating method, hot plate heating method or a combination thereof can be used. The semi-curing may be performed as it is using the heating function of the impregnation apparatus after completion of the impregnation, or may be separately performed using a known apparatus such as a hot air circulating conveyor furnace after taking out from the impregnation apparatus. In addition, it is preferable to adhere to a to-be-adhered body to the heat conductive surface of a heat conductive adhesive sheet.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but these are provided for better understanding of the present invention and its advantages, and are intended to limit the present invention. Not what you want.

<Examples 1-3>
As a graphite sintered body, graphite (G100 (Examples 1 and 3), G159 (Example 2)) manufactured by Tokai Carbon Co., Ltd. was used. Further, as the thermosetting resin composition, bismaleimide triazine resin (“BT2160” manufactured by Mitsubishi Gas Chemical Company) was used. The blending ratio and the like are shown together with comparative examples in the following table.

<Impregnation, semi-curing and sheet-like processing of a thermosetting resin composition into a graphite sintered body>
The graphite sintered body was impregnated with the thermosetting resin composition. Using a vacuum warming impregnation apparatus (“G-555AT-R” manufactured by Kyoshin Engineering Co., Ltd.), the graphite sintered body and the thermosetting resin composition are vacuumed at a temperature of 145 ° C. and a pressure of 15 Pa (abs). After deaeration for 10 minutes each, the graphite sintered body was subsequently immersed in the thermosetting resin composition for 10 minutes in the same apparatus under the heating vacuum. Furthermore, using a pressure heating and impregnation apparatus (“HP-4030AA-H45” manufactured by Kyoshin Engineering Co., Ltd.), the graphite sintered body was impregnated for 120 minutes at a temperature of 145 ° C. and a pressure of 3.5 MPa. A thermosetting resin composition was combined. Then, it heated at 160 degreeC under atmospheric pressure on the time conditions shown in the following table | surface, the thermosetting resin composition was semi-hardened (B-staged), and it was set as the graphite resin composite.

<Proportion of graphite sintered body and proportion of thermosetting resin composition>
The ratio of the graphite sintered body in the graphite resin composite was determined from the bulk density and the true density of the graphite sintered body according to the method described above. The bulk density was determined by measuring the volume of each graphite sintered body measured with a vernier caliper (“CD67-SPS” manufactured by Mitutoyo Corporation) and an electronic balance (“MC-1000” manufactured by A & D Corporation) according to the method described above. Calculated from the length of the side) and the mass. The true density was obtained from the volume and mass of graphite obtained by a dry automatic densimeter (“AccuPyc II 1340” manufactured by Micromeritics) according to the method described above. The calculation results are shown in the following table.

  Subsequently, 26 types of ceramic resin composites were processed into a sheet having a thickness of 320 μm using a multi-wire saw (“MWS-32N” manufactured by Takatori) to obtain a heat conductive adhesive sheet.

<Measurement of thickness and thickness standard deviation of heat conductive adhesive sheet>
The thickness of the heat conductive adhesive sheet was measured based on A method of JIS K 7130: 1999. The width of the measured heat conductive adhesive sheet × length = 50 mm × 50 mm, and 10 types per sheet were measured for each type, and the average was calculated. The evaluation result about the thickness of the obtained heat conductive adhesive sheet is shown in the following table.

<Thermal conductivity>
In the present invention, the thermal conductivity to be evaluated is the thermal conductivity of the thermally conductive adhesive sheet that has been almost cured and is in the C-stage state. A “resin material thermal resistance measuring device” manufactured by Hitachi Techno & Service Co., Ltd. was used as the measuring device. The evaluation results of the obtained thermal conductivity are shown in the following table.

<Tensile shear bond strength>
Laminated copper plates of width x length x thickness = 25 mm x 100 mm x 1.0 mm on both sides of a thermally conductive adhesive sheet of width x length x thickness = 25 mm x 12.5 mm x 320 μm (sample size and lamination method are JIS K 6850: 1999 (see Figure 1) and press-bonded using a vacuum heating press machine under the conditions of a pressure of 5 MPa, a heating temperature of 240 ° C., and a heating time of 5 hours to obtain a sample for measuring shear bond strength. The measurement apparatus is an autograph (“AG-100kN” manufactured by Shimadzu Corporation), and the measurement conditions are a measurement temperature of 25 ° C. and a crosshead speed of 5.0 mm / min, in accordance with JIS K 6850: 1999. Measurements were performed. The evaluation results of the obtained tensile shear bond strength are shown in the following table.

<X-ray diffraction pattern analysis of heat conductive surface of heat conductive adhesive sheet>
As an X-ray diffraction method of the heat conductive surface of the heat conductive adhesive sheet, a sample is fixed to a resin holder, and measured using a 3 kW-X-ray diffractometer (D8ADVANCE manufactured by Bruker) at 2θ = 10 to 70 °. And the peak intensities of the (002) plane and (100) plane were measured.

<Comparative Examples 1-2>
The graphite sintered body was prepared and evaluated in the same manner as in the above example except that products manufactured by Tokai Carbon Co., Ltd. (G535 (Comparative Example 1), G348 (Comparative Example 2)) were used. The blending ratio and the like are shown together with examples in the following table. In Comparative Example 2, the composite could not be produced because the resin could not be impregnated. About the result of this comparative example 2, since the porosity of a graphite is small, it is estimated that resin impregnation was not able to be performed.

  The heat conductive adhesive sheet of the present invention can be used for general industrial and in-vehicle power semiconductor modules.

Claims (9)

A graphite resin composite in which a graphite sintered body having a three-dimensional continuous structure of graphite primary particles is impregnated with a thermosetting resin composition and has at least one heat conductive surface,
The ratio of the graphite sintered body to the total amount of the graphite sintered body and the thermosetting resin composition is 70% by volume or more and 80% by volume or less,
The ratio of the thermosetting resin composition to the total amount of the graphite sintered body and the thermosetting resin composition is 20 vol% or more and 30 vol% or less,
In the X-ray diffraction pattern obtained by irradiating the heat conducting surface with X-rays, the diffraction peak intensity corresponding to the (002) plane of the graphite primary particles is the diffraction peak intensity corresponding to the (100) plane of the graphite primary particles. A graphite resin composite, wherein the value divided by is less than 30.   In the X-ray diffraction pattern obtained by irradiating the heat conducting surface with X-rays, the diffraction peak intensity corresponding to the (002) plane of the graphite primary particles is the diffraction peak intensity corresponding to the (100) plane of the graphite primary particles. The graphite resin composite according to claim 1, wherein the value divided by is from 0.01 to 25.   The thermosetting resin composition is a combination of any one or both of a substance having an epoxy group and a substance having a cyanate group and one or both of a substance having a hydroxyl group and a substance having a maleimide group. The graphite resin composite according to claim 1 or 2.   The graphite resin composite according to claim 3, wherein the thermosetting resin composition is a bismaleimide triazine resin.   The heat generation starting temperature measured by a differential scanning calorimeter of the thermosetting resin composition is in the range of 180 ° C. or higher and 300 ° C. or lower, the curing rate is in the range of 5% or higher and 60% or lower, and several The graphite resin composite according to any one of claims 1 to 4, wherein the average molecular weight is in the range of 450 to 4800.   The heat conductive adhesive sheet which processes the graphite resin composite as described in any one of Claims 1-5, and has a heat conductive surface on both surfaces.   An in-vehicle power module structure comprising two or more electronic members respectively bonded to heat conductive surfaces on both sides of the heat conductive adhesive sheet according to claim 6.   The in-vehicle power module structure according to claim 7, wherein the electronic member is at least one selected from a metal base plate for a substrate, a heat radiating plate for cooling the substrate, and a heat exchanger.   The in-vehicle power module structure according to claim 7 or 8, which is a semiconductor device.