Thermally conductive sheet and semiconductor module having the same

Abstract

The thermally conductive sheet according to the present invention is a thermally conductive sheet comprising a resin layer composed of a resin composition containing a thermosetting resin, a specific curing agent, and an inorganic filler.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of Japanese Patent Application No. 2020-101163, which is incorporated herein by reference. Technical Field

[0003] The present invention relates to a thermally conductive sheet and a semiconductor module including the thermally conductive sheet. Background Art

[0004] Conventionally, in the field of electronics, a thermally conductive sheet including a resin layer composed of a resin composition containing a thermosetting resin, a curing agent, and an inorganic filler is known (for example, Patent Document 1).

[0005] Patent Document 1 listed below discloses a thermally conductive sheet formed by supporting the resin layer with a metal foil.

[0006] In a semiconductor module including a semiconductor element, such a thermally conductive sheet is used to conduct heat generated by the semiconductor element to a heat dissipation surface for dissipating the heat.

[0007] More specifically, in a semiconductor module including a semiconductor element, a heat sink, and a heat radiator, the thermally conductive sheet is interposed between the heat sink and the heat radiator to conduct the heat conducted from the heat sink to the heat dissipation surface of the heat radiator. The heat sink supports the semiconductor element and conducts heat generated by the semiconductor element. The heat radiator is located at a position overlapping the heat sink on the side opposite to the side supporting the semiconductor element and is spaced apart from the heat sink at this position.

[0008] Furthermore, the thermally conductive sheet is interposed between the heat absorbing member and the radiator so that the resin layer is bonded to the heat absorbing member and the metal foil is in contact with the radiator.

[0009] This thermally conductive sheet is bonded to the heat absorbing member by bringing the resin layer into contact with the heat absorbing member before the thermosetting resin in the resin layer is cured and curing the thermosetting resin.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-32496 Summary of the Invention

[0013] Problems to be solved by the invention

[0014] In the aforementioned thermally conductive sheet, the inorganic filler content in the resin layer is relatively increased to improve thermal conductivity. However, as the inorganic filler content in the resin layer increases, the thermosetting resin content in the resin layer decreases. In this case, if the surface of an adherend, such as a heat-absorbing component, is not sufficiently flat, sufficient adhesion between the adherend and the resin layer may be impaired.

[0015] Furthermore, when the thermally conductive sheet is interposed between the heat absorbing member and the heat radiator, there is a problem in that it is difficult to achieve both high heat dissipation and high dielectric breakdown strength (BDV). In other words, it is difficult to achieve both improved heat dissipation and improved dielectric breakdown strength in the thermally conductive sheet.

[0016] Therefore, an object of the present invention is to provide a thermally conductive sheet that can ensure more sufficient adhesion to an adherend even if the adherend's surface is not sufficiently smooth, and can achieve both improved heat dissipation and improved dielectric breakdown strength; and a semiconductor module including the thermally conductive sheet.

[0017] Solutions for solving problems

[0018] The thermally conductive sheet of the present invention comprises a resin layer composed of a resin composition containing a thermosetting resin, a curing agent, and an inorganic filler.

[0019] The curing agent contains a benzoxazine derivative represented by the following formula (1).

[0020]

[0021] (Wherein, in the above formula (1), X represents any of -CH2-, -C(CH3)2- or -SO2-, and R1 and R2 represent -H, -C n H 2n+1 Any of an alkyl group (wherein n is an integer of 1 to 10) or an aryl group represented by

[0022] The semiconductor module of the present invention comprises:

[0023] semiconductor components;

[0024] a heat dissipation surface for dissipating heat generated by the semiconductor element; and

[0025] a thermally conductive sheet for conducting the heat to the heat dissipation surface;

[0026] The thermally conductive sheet is the thermally conductive sheet described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1This is a cross-sectional view showing the structure of a thermally conductive sheet according to one embodiment of the present invention.

[0028] Figure 2 This is a cross-sectional view schematically showing a semiconductor module according to one embodiment of the present invention.

[0029] Figure 3 It is a top view showing the etched laminated body.

[0030] Figure 4 It is a cross-sectional view showing the arrangement in the measurement of dielectric breakdown strength. DETAILED DESCRIPTION

[0031] Hereinafter, one embodiment of the present invention will be described.

[0032] (Thermal conductive sheet)

[0033] The thermally conductive sheet according to this embodiment includes a resin layer formed of a resin composition containing a thermosetting resin, a curing agent, and an inorganic filler.

[0034] Among the components contained in the resin composition, the thermosetting resin and the curing agent are the components that ultimately form a cured product. Specifically, the thermosetting resin and the curing agent are polymerizable components that form a cured resin upon polymerization. More specifically, in the resin composition, the thermosetting resin forms the cured resin upon curing together with the curing agent.

[0035] Among the components contained in the resin composition, the inorganic filler is a component that imparts good thermal conductivity to the cured product by being contained in the cured product together with the curable resin.

[0036] The resin composition may contain, in addition to the thermosetting resin, the curing agent, and the inorganic filler, additives commonly used as plastic compounding chemicals within a range that does not impair the effects of the present invention.

[0037] In the thermally conductive sheet according to this embodiment, the content of the polymerizable components (the thermosetting resin and the curing agent) in 100 parts by mass of the cured product is preferably 5 parts by mass or more and 70 parts by mass or less, more preferably 10 parts by mass or more and 40 parts by mass or less.

[0038] In the thermally conductive sheet according to this embodiment, the content of the inorganic filler is preferably 50% to 90% by volume relative to the total solid volume of the cured resin composition. This allows the thermally conductive sheet according to this embodiment to have more adequate heat dissipation (thermal conductivity).

[0039] In addition, showing sufficient heat dissipation (thermal conductivity) means that the thermal conductivity of the thermally conductive sheet is 10 W / m·K or more. The thermal conductivity can be measured by the method described below.

[0040] Furthermore, the resin composition preferably contains 0.005 parts by mass or more and 0.05 parts by mass or less of the additive relative to 100 parts by mass of the inorganic filler, and more preferably contains 0.01 parts by mass or more and 0.03 parts by mass or less.

[0041] Examples of the thermosetting resin include epoxy resins, phenolic resins, melamine resins, urea-formaldehyde resins, unsaturated polyester resins, alkyd resins, polyurethane resins, polyimide resins, silicone resins, modified acrylic resins, and diallyl phthalate resins. Among these, epoxy resins are preferably used, and among epoxy resins, at least one of a bisphenol A-type epoxy resin represented by the following formula (2) and a bisphenol F-type epoxy resin represented by the following formula (3) is preferably used.

[0042] As the bisphenol A type epoxy resin, a resin in which n=0 in the following formula (2) is preferred, and as the bisphenol F type epoxy resin, a resin in which n=0 in the following formula (3) is preferred.

[0043] It should be noted that in the following general formulas (2) and (3), Ra, Rb, Rc, Rd, Re, Rf, Rg and Rh represent 0 to 4 monovalent groups possessed by each benzene ring, which are -H or -C n H 2n+1 The alkyl group represented by (wherein n is an integer of 1 to 10).

[0044] Examples of commercially available bisphenol A epoxy resins include "JER828" manufactured by Mitsubishi Chemical Corporation, and examples of commercially available bisphenol F epoxy resins include "YSLV-80XY" manufactured by Nippon Steel Chemicals & Materials Co., Ltd., which is a tetramethylbisphenol F epoxy resin.

[0045]

[0046] Here, n is an integer greater than or equal to 0.

[0047]

[0048] Here, n is an integer greater than or equal to 0.

[0049] When the thermosetting resin is an epoxy resin, the ratio of the total amount of the epoxy resin and the curing agent in the polymerizable component is preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less.

[0050] The curing agent contains a benzoxazine derivative represented by the following formula (1).

[0051]

[0052] (Wherein, in the above formula (1), X represents any of -CH2-, -C(CH3)2- or -SO2-, and R1 and R2 represent -H, -C n H 2n+1 Any of an alkyl group (wherein n is an integer of 1 to 10) or an aryl group represented by

[0053] The benzoxazine derivative represented by formula (1) is called a Pd-type. When the thermosetting resin is crosslinked with the benzoxazine derivative in a rigid structure to form a cured structure, the cured structure exhibits a small free volume and, therefore, excellent thermal and mechanical properties. Therefore, it is suitable for use as a curing agent in resin compositions for thermally conductive sheets.

[0054] The curing agent is preferably a compound among the benzoxazine derivatives represented by the above formula (1) in which X is represented by -CH2- and R1 and R2 are represented by -H, that is, a Pd-type benzoxazine represented by the following formula (1a).

[0055]

[0056] When the thermosetting resin is an epoxy resin, the molar ratio of the epoxy groups in the epoxy resin to the benzoxazine rings in the curing agent is preferably 0.8 to 1.2. Thus, the thermally conductive sheet according to this embodiment can more fully ensure adhesion to an adherend.

[0057] Examples of the inorganic filler include boron nitride fillers, aluminum nitride fillers, silicon nitride fillers, gallium nitride fillers, aluminum oxide fillers, silicon carbide fillers, silicon dioxide fillers, magnesium oxide fillers, and diamond fillers. Among these, boron nitride fillers are preferred.

[0058] The inorganic filler is preferably dispersed in the thermosetting resin.

[0059] The inorganic filler preferably includes aggregated particles formed by aggregating a plurality of primary particles. By including the aggregated particles, the distance between the particles in the thermosetting resin can be reduced, thereby improving the thermal conductivity between the particles.

[0060] The present inventors speculate as follows as to why the thermally conductive sheet according to this embodiment comprises a resin layer composed of a resin composition comprising a thermosetting resin, a curing agent, and an inorganic filler, wherein the curing agent is a benzoxazine derivative represented by the above formula (1). This allows for more adequate adhesion to the adherend even if the surface of the adherend is not sufficiently smooth, and allows for both improved heat dissipation (thermal conductivity) and improved dielectric breakdown strength.

[0061] As described in Example 1 below, the resin layer of the thermally conductive sheet according to this embodiment is composed of a resin composition as described above, resulting in excellent flexibility evaluation in the pre-cured state (B-stage state). Therefore, it is believed that even if the surface of an adherend, such as a heat-absorbing component, is not sufficiently smooth, the thermosetting resin in the resin layer can fully penetrate into the recesses of the adherend, thereby further ensuring the close adhesion between the resin layer and the adherend. It is believed that since the close adhesion between the resin layer and the adherend is further ensured in the pre-cured state, it is believed that when the thermosetting resin is cured (in the C-stage state), the resin layer is bonded to the adherend in a state in which the close adhesion between the resin layer and the adherend is further ensured.

[0062] Furthermore, as described above, the resin layer of the thermally conductive sheet according to this embodiment exhibits excellent flexibility before curing, resulting in excellent conformability to the surface of the inorganic filler contained in the resin layer, and more fully adhering to the surface of the inorganic filler. Therefore, when the thermosetting resin is cured to form a cured resin, it is believed that the cured resin and the surface of the inorganic filler can maintain a relatively close contact state. As a result, it is believed that the gaps formed at the interface between the cured resin and the inorganic filler due to separation of the cured resin from the inorganic filler can be reduced, thereby improving the dielectric breakdown strength of the resin layer.

[0063] It is further believed that: in the aforementioned resin layer, the surfaces of the aforementioned cured resin and the aforementioned inorganic filler can maintain a relatively close contact state, and therefore it is believed that: the reduction in the dielectric breakdown strength of the aforementioned resin layer can be suppressed, and the aforementioned resin layer contains a relatively large amount of inorganic filler, thereby improving the heat dissipation of the aforementioned resin layer.

[0064] In addition, when the thermosetting resin includes an epoxy resin, the adhesive force generated at the interface between the thermosetting resin and the inorganic filler can be further enhanced, thereby further improving the heat dissipation property of the thermally conductive sheet.

[0065] Furthermore, when the thermosetting resin comprises an epoxy resin, the adhesion between the thermally conductive sheet and the adherend can be improved. This reduces the thermal resistance generated at the interface between the thermally conductive sheet and the adherend, thereby further improving the heat dissipation of the thermally conductive sheet.

[0066] Furthermore, to further enhance the heat dissipation of the resin layer, sufficient heat conduction through lattice vibrations generated within the crystal structure of the inorganic filler is required within the resin layer. Furthermore, to further enhance heat conduction through lattice vibrations, it is preferable to further fully cure the thermosetting resin, thereby imparting sufficient hardness to the resin layer.

[0067] Here, it is believed that when at least one of the bisphenol A epoxy resin represented by formula (2) and the bisphenol F epoxy resin represented by formula (3) is used as the thermosetting resin, these epoxy resins have a common structural unit with the benzoxazine derivative represented by formula (1) in their structure, and therefore have a higher affinity with the benzoxazine derivative represented by formula (1). Therefore, it is believed that when at least one of the bisphenol A epoxy resin and the bisphenol F epoxy resin is used as the thermosetting resin, the curing reaction of the thermosetting resin can proceed more fully, the resin layer can have a more sufficient hardness, and thus heat conduction by lattice vibration can be more fully performed.

[0068] It is therefore considered that when at least one of the bisphenol A epoxy resin represented by the above formula (2) and the bisphenol F epoxy resin represented by the above formula (3) is used as the above thermosetting resin, the above resin layer has more sufficient heat dissipation properties.

[0069] Examples of the additives include curing accelerators that accelerate the curing reaction between the thermosetting resin and the curing agent. Examples of the additives include dispersants, adhesion-imparting agents, antioxidants, antioxidants, processing aids, stabilizers, defoaming agents, flame retardants, thickeners, pigments, and the like.

[0070] Examples of the curing accelerator include tetraphenylphosphonium tetraphenylborate, imidazoles, triphenyl phosphate (TPP), amine curing accelerators, and protonic acids. Examples of the amine curing accelerator include boron trifluoride monoethylamine, and examples of the protonic acid include p-toluenesulfonic acid.

[0071] In the thermally conductive sheet according to this embodiment, the resin composition preferably contains 0.5 to 5.0 parts by mass of the curing accelerator, more preferably 0.5 to 3.0 parts by mass, based on 100 parts by mass of the total of the thermosetting resin and the curing agent.

[0072] In the thermally conductive sheet according to this embodiment, the resin composition may be in a state where a certain degree of curing reaction has occurred but the resin composition is not completely cured. In other words, the resin composition may be in a state where a portion of the resin composition has undergone a curing reaction, that is, a state where both a B-stage state and a C-stage state coexist.

[0073] For example, the resin composition may be applied to a sheet in a fluid state and then partially cured. Even in a state where a partial curing reaction has occurred, the resin composition still contains the thermosetting resin, the curing agent, and the inorganic filler.

[0074] On the other hand, from the viewpoint of adhesion to an adherend and adhesion to the surface of an inorganic filler, it is preferred that the entire resin composition be in a state before curing (B-stage state).

[0075] The material of the adherend of the thermally conductive sheet is preferably metal, more specifically, preferably a metal containing copper or aluminum.

[0076] The thermally conductive sheet described in this embodiment can be used in a metal base circuit board. This metal base circuit board is constructed, for example, by bonding a circuit layer to a thermally conductive sheet. A metal base circuit board having this configuration, including the thermally conductive sheet described in this embodiment, also improves heat dissipation.

[0077] Furthermore, the thermally conductive sheet described in this embodiment can be used, for example, in a power module. This power module is constructed by mounting heat-dissipating components such as semiconductor chips and power ICs on the circuit layer of the aforementioned metal-based circuit board. These components are temporarily sealed with silicone rubber, and then resin molded onto the silicone rubber. A power module having this configuration, incorporating the thermally conductive sheet described in this embodiment, improves heat dissipation.

[0078] (Semiconductor Module)

[0079] The semiconductor module according to this embodiment includes a semiconductor element, a heat dissipation surface for dissipating heat generated by the semiconductor element, and a thermally conductive sheet for conducting the heat to the heat dissipation surface.

[0080] In the semiconductor module according to this embodiment, the thermally conductive sheet described in the above embodiment can be used as the thermally conductive sheet.

[0081] The thermally conductive sheet forms at least a portion of a path for conducting heat generated by the semiconductor element.

[0082] The thermally conductive sheet conducts heat in the thickness direction.

[0083] Below, refer to Figure 1 and Figure 2 , the semiconductor module described in this embodiment is described.

[0084] like Figure 2 As shown, the semiconductor module 2 according to the present embodiment has a flat box shape, and its four peripheral walls are formed by a rectangular plastic case 80 opened at the top and bottom.

[0085] Furthermore, in the semiconductor module 2 , the semiconductor element 50 and the heat absorbing member 30 are housed inside the plastic case 80 .

[0086] In order to quickly remove heat from the semiconductor element 50 , the heat absorbing member 30 is formed of a metal block that is sufficiently larger than the semiconductor element 50 and is connected to the semiconductor element 50 via the solder 40 .

[0087] More specifically, the heat absorbing component 30 has a thickness approximately half the height of the surrounding walls formed by the plastic case 80 and is in the shape of a rectangular plate that is slightly smaller than the opening area of the plastic case 80. The semiconductor element 50 is mounted in the center of its upper surface and housed inside the plastic case 80.

[0088] In addition, one end portion of the first terminal 70 a that passes through the plastic case 80 in the horizontal direction is welded to the upper surface of the heat absorbing member 30 .

[0089] Furthermore, in heat-absorbing member 30, second terminals 70b, which extend horizontally through plastic case 80 at positions opposite to the penetration points of first terminals 70a, are electrically connected to semiconductor element 50 via bonding wires 60, forming a current path between these terminals. In other words, when power is supplied to semiconductor module 2, current flows through heat-absorbing member 30.

[0090] Therefore, in the semiconductor module 2 according to the present embodiment, in addition to the heat dissipated by the semiconductor element 50 , the temperature rises due to Joule heat associated with the current flowing through the heat absorbing member 30 .

[0091] In semiconductor module 2 , the interior of plastic case 80 is filled with molding resin 90 , leaving the lower surface of heat absorbing member 30 , and semiconductor element 50 and the like are embedded in the molding resin.

[0092] In the semiconductor module 2 according to this embodiment, as the thermally conductive sheet, Figure 1 The thermally conductive sheet 1 shown.

[0093] like Figure 1 As shown, the thermally conductive sheet 1 is configured as a thermally conductive sheet with metal foil in which a resin layer 1 a is supported by a metal foil layer 1 b .

[0094] Generally, the resin layer 1 a is preferably thin because it can reduce the thermal resistance from the heat absorbing member 30 described later toward the metal foil layer 1 b , and is therefore advantageous for heat dissipation.

[0095] On the other hand, if the thickness of the resin layer 1 a is too thin, the reliability of the electrical insulation may be reduced.

[0096] Therefore, usually, the volume resistivity after thermal curing is 1×10 14 The resin composition having a thickness of Ω·cm or greater forms the resin layer 1 a so as to have a thickness of 100 μm to 300 μm.

[0097] In the semiconductor module 2 according to this embodiment, the thermally conductive sheet 1 has an area larger than the lower surface of the heat absorbing member 30 and smaller than the opening of the plastic case 80. The resin layer 1a is adhered to the lower surface of the heat absorbing member 30 so as to cover the entire lower surface of the heat absorbing member 30 and is present in the semiconductor module 2.

[0098] The semiconductor module 2 according to this embodiment includes the thermally conductive sheet 1 so that the surface of the metal foil layer 1 b is exposed on the lower surface of the semiconductor module 2 and the surface 1 bA of the metal foil layer 1 b can be used as a heat dissipation surface of the semiconductor module 2 .

[0099] That is, in the lower surface of the semiconductor module 2 according to this embodiment, the surface 1bA of the metal foil layer 1b is exposed in the center, and the mold resin 90 is exposed between the lower end surface of the plastic case 80 constituting the outer edge thereof and the surface 1bA of the metal foil layer 1b.

[0100] It should be noted that the exposed surface of the molded resin 90, the surface 1bA of the metal foil layer 1b, and the lower end surface of the plastic box 80 are roughly formed into a single surface, and a heat radiator is installed on the lower surface so that the surface of the heat radiator is in surface contact with the surface 1bA of the metal foil 1b. The semiconductor module 2 described in this embodiment is formed by dissipating the heat generated by the semiconductor element 50 with the help of the thermally conductive sheet 1.

[0101] Matters disclosed in this specification include the following matters.

[0102] (1) A thermally conductive sheet comprising a resin layer composed of a resin composition containing a thermosetting resin, a curing agent, and an inorganic filler,

[0103] The curing agent contains a benzoxazine derivative represented by the following formula (1).

[0104]

[0105] (Wherein, in the above formula (1), X represents any of -CH2-, -C(CH3)2- or -SO2-, and R1 and R2 represent -H, -C n H 2n+1 Any of an alkyl group (wherein n is an integer of 1 to 10) or an aryl group represented by

[0106] According to this configuration, even if the surface of the adherend is not sufficiently smooth, it is possible to more fully ensure adhesion to the adherend, and it is possible to achieve both improvement in heat dissipation and improvement in dielectric breakdown strength.

[0107] (2) The thermally conductive sheet according to (1) above, wherein the thermosetting resin includes an epoxy resin.

[0108] According to this configuration, the adhesive force generated at the interface between the thermosetting resin and the inorganic filler can be further enhanced.

[0109] This can further improve the heat dissipation performance of the thermally conductive sheet.

[0110] Furthermore, by including an epoxy resin in the thermosetting resin, the thermally conductive sheet can exhibit excellent adhesion to an adherend. This reduces thermal resistance at the interface between the thermally conductive sheet and the adherend, further improving the heat dissipation of the thermally conductive sheet.

[0111] Furthermore, by including an epoxy resin in the thermosetting resin, the resin layer can have a more sufficient hardness, and from this point of view, the heat dissipation property of the thermally conductive sheet can be further improved.

[0112] (3) The thermally conductive sheet according to (2) above, wherein a molar ratio of the epoxy group of the epoxy resin to the benzoxazine ring of the curing agent is 0.8 or more and 1.2 or less.

[0113] According to this configuration, it is possible to further sufficiently ensure adhesion to an adherend.

[0114] (4) The thermally conductive sheet according to any one of (1) to (3) above, wherein the content of the inorganic filler is 50% by volume or more and 90% by volume or less relative to the total volume of the solid content of the cured resin composition.

[0115] According to this configuration, heat dissipation can be further improved.

[0116] (5) A semiconductor module comprising:

[0117] semiconductor components;

[0118] a heat dissipation surface for dissipating heat generated by the semiconductor element; and

[0119] a thermally conductive sheet for conducting the heat to the heat dissipation surface;

[0120] The thermally conductive sheet is the thermally conductive sheet according to any one of (1) to (4) above.

[0121] According to this configuration, the semiconductor module can more fully ensure adhesion to the adherend even if the surface of the adherend is not sufficiently smooth, and can also achieve both improved heat dissipation and improved dielectric breakdown strength.

[0122] It should be noted that the thermally conductive sheet and semiconductor module of the present invention are not limited to the aforementioned embodiments. Furthermore, the thermally conductive sheet and semiconductor module of the present invention are not limited to the aforementioned functions and effects. Various modifications may be made to the thermally conductive sheet and semiconductor module of the present invention without departing from the spirit of the present invention.

[0123] Example

[0124] Next, the present invention will be described in more detail with reference to Examples and Comparative Examples.

[0125] (Example 1)

[0126] The following thermosetting resin and the following curing agent were dissolved in methyl ethyl ketone at an equivalent ratio of 1:1 to prepare a varnish. The following inorganic filler was added to the varnish and kneaded to obtain the resin composition described in Example 1.

[0127] The inorganic filler described below was contained in the varnish so that the content of the inorganic filler described below was 63% by volume relative to the total volume of the solid content of the resin composition after curing.

[0128] Thermosetting resin: Epoxy resin A (bisphenol F epoxy resin, YSLV-80XY, manufactured by Nippon Steel Chemicals & Materials Co., Ltd.)

[0129] Curing agent: benzoxazine derivative of the following formula (1a) (Pd-type benzoxazine manufactured by Shikoku Chemicals Co., Ltd.)

[0130] Inorganic filler: Boron nitride filler (BN filler (h-BN filler))

[0131]

[0132] Thermal conductivity

[0133] In the evaluation of thermal conductivity, a laminated sheet with metal foil was prepared as follows.

[0134] First, on a copper foil substrate (area: 2500 cm 2 ) was coated with the resin composition described in Example 1 to a thickness of approximately 200 μm. A roll-to-roll coating method was used, and drying conditions were 120°C for 5 minutes. This produced a first laminate sheet having a resin layer made from the resin composition described in Example 1.

[0135] Next, for the first laminate sheet described in Example 1, two first laminate sheets are overlapped with their surfaces opposite to the substrate facing each other, and hot pressing is performed at a temperature of 100°C, a pressure of 8 MPa, and a time of 20 minutes to produce a laminate sheet with a metal foil having a resin layer thickness of 0.22±0.04 mm.

[0136] The copper foil, which served as the metal foil, was removed from both sides of the metal-foil laminate by etching. The resin laminate was then removed and, to allow for thermal conductivity evaluation, the resin laminate was stacked to a thickness of 1.00 mm ± 0.15 mm and thermocompression bonded. The resin laminate was then exposed to a temperature of 200°C and a pressure of 5 MPa for 4 hours to cure.

[0137] A rectangular cured resin body was cut out from the cured resin laminate sheet so that one side had a size of 10 mm ± 0.5 mm. An antireflection agent (manufactured by Fine Chemicals Japan Co., Ltd., model: FC-153) was applied to both sides of the cut cured resin body. The resulting sample was used as a thermal diffusivity measurement sample.

[0138] The thermal conductivity value was calculated by multiplying the thermal diffusivity value obtained by measuring the thermal diffusivity measurement sample using a xenon flash analyzer (manufactured by NETZSCH, Model LFA-447) by the specific heat value measured by heat flow DSC in accordance with JIS 7123:1987 and the density value measured by the water displacement method in accordance with JIS K 7122:1999. The thermal diffusivity value was calculated by taking the arithmetic average of the thermal diffusivity values measured for three measurement samples.

[0139] The thermal diffusivity was measured at five locations on one measurement sample, and the arithmetic mean of three values excluding the maximum value and the minimum value for each measurement sample was used as the measured value.

[0140] <Dielectric Breakdown Strength>

[0141] The dielectric breakdown strength is measured using a dielectric breakdown device with a crest factor between 1.34 and 1.48, capable of applying a voltage at a frequency of 50 Hz or 60 Hz, and a maximum voltage of AC10 kV (effective value). For details on the measurement method, see Figure 3 and Figure 4 Provide explanation.

[0142] The copper foil on one side of a 75±1mm×65±1mm laminate with metal foil is peeled off to obtain a second laminate. An aluminum plate 13 is laminated on the surface of the second laminate after the copper foil 13 is peeled off and heated to obtain a third laminate in which the second laminate and the aluminum plate are integrated. Next, the third laminate is further heated to completely cure the resin layer to obtain Figure 1 The dielectric breakdown strength measurement sample 14 is shown. Note that the resin layer was produced using the resin composition described in Example 1.

[0143] Then, if Figure 4 As shown, a dielectric breakdown strength test specimen 14 was placed with the aluminum plate side facing downward on a brass disc electrode 17 (Ø: 40 mm) in insulating oil 16 (JIS C2320:1999) in an oil tank 15. A brass spherical electrode 18 (Ø: 15 mm, weight: 50 g) was placed on the dielectric breakdown strength test specimen 14 so as to contact the substantially central portion of the dielectric breakdown strength test specimen 14. The insulating oil 16 was maintained at 20±10°C, and AC 3.0 kV (effective value) was applied to the dielectric breakdown strength test specimen 14 for one minute.

[0144] Furthermore, if insulation breakdown did not occur, the voltage was rapidly increased to 0.5 kV AC (effective value) and applied for 1 minute, and the voltage was increased in steps of 0.5 kV AC (effective value) (0.5 kV (effective value) steps, applied for 1 minute) until insulation breakdown occurred.

[0145] It should be noted that as a criterion for determining dielectric breakdown, the cutoff current was set to 10 mA. Furthermore, the dielectric breakdown strength was determined by dividing the applied voltage (unit: kV) that was 0.5 kV (effective value) lower than the voltage at which dielectric breakdown occurred by the thickness (unit: mm) of the dielectric breakdown strength measurement sample 14.

[0146] <Peel Strength>

[0147] The resin composition described in Example 1 was applied to one surface of an electrolytic copper foil (thickness: 35 μm) to prepare two sheets having a resin layer (thickness: 145 μm).

[0148] Next, the two sheets were heat-pressed (3.0 MPa, 120° C., 20 minutes) to adhere the resin layers to each other, and one copper foil was peeled off from the back surface of the sheet.

[0149] An aluminum plate was placed on the surface from which the copper foil was peeled, and hot pressing (2.0 MPa, 120° C., 20 min) was performed to transfer the sheet to the aluminum plate. The copper foil was then peeled from the sheet to obtain a semi-cured sheet.

[0150] Next, an adherend (1 oz copper foil) was laminated on the semi-cured sheet and heat-pressed (2.0 MPa, 180°C, 120 min) to integrate the resin layer and the adherend. After the resin layer was fully cured, a 20 mm x 100 mm piece was cut out. The adherend of the cut sample was processed (etched) to a width of 10 mm to prepare a test piece for the peel test.

[0151] The test piece was subjected to a 90° peel test at a peel strength of 50 mm / min, and the adhesive strength between the adherend and the resin layer was evaluated based on the peel strength.

[0152] <Flexibility>

[0153] Flexibility was evaluated by a method based on JIS A6909:2014.

[0154] The test piece for flexibility evaluation was prepared as follows.

[0155] First, on a copper foil substrate (area: 2500 cm 2 ) was coated with the resin composition described in Example 1 to a thickness of approximately 200 μm. A roll-to-roll coater was used for coating, and drying conditions were 120°C for 5 minutes. In this manner, a thermally conductive sheet with metal foil (a thermally conductive sheet having a metal foil substrate disposed on one side of the resin layer) was produced using the resin composition described in Example 1.

[0156] Next, two of the aforementioned thermally conductive sheets with metal foil were stacked with their surfaces without a substrate facing each other, and then hot-pressed at a temperature of 100°C and a pressure of 8 MPa for 2 hours to produce a laminated thermally conductive sheet with metal foil having a resin layer thickness of 0.22±0.04 mm (a thermally conductive sheet having metal foil as a substrate disposed on both sides of the resin layer).

[0157] Next, the copper foil serving as the metal foil was removed from both sides of the thermally conductive laminated sheet with metal foil by etching, and the resin laminate was taken out. A resin laminate having a side size of 10 mm ± 0.5 mm was cut out from the resin laminate to prepare a test piece for flexibility evaluation.

[0158] Flexibility was evaluated by placing a 10 mm Φ metal rod in contact with the approximate center of one surface of the flexibility evaluation test body. The test body was then bent 90° along the curved surface of the metal rod. The other surface of the test body was then visually observed for cracks. Flexibility was evaluated by testing three specimens of the flexibility evaluation test body.

[0159] Furthermore, if no cracks were observed in any of the three specimens, the evaluation was excellent, and if cracks were observed in even one of the three specimens, the evaluation was unacceptable.

[0160] In addition, the flexibility was evaluated in the state before the test body for flexibility evaluation was cured (B-stage state).

[0161] The measurement results of thermal conductivity, dielectric breakdown strength, and peel strength, and the evaluation results of flexibility are shown in Table 1 below.

[0162] (Example 2)

[0163] The resin composition described in Example 2 was obtained in the same manner as in Example 1, except that epoxy resin B (bisphenol A-type epoxy resin, manufactured by Mitsubishi Chemical Corporation, JER828) was used instead of epoxy resin A as the thermosetting resin, and an inorganic filler was contained in the varnish so as to provide 64 volume % relative to the total volume of the solid content of the cured resin composition.

[0164] The resin composition described in Example 2 was also measured for thermal conductivity, dielectric breakdown strength, and peel strength by the same method as described in Example 1, and flexibility was also evaluated. The results are shown in Table 1 below.

[0165] (Example 3)

[0166] The resin composition described in Example 3 was obtained in the same manner as in Example 1 except that the varnish contained an inorganic filler so as to have an amount of 73% by volume relative to the total volume of the solid content of the cured resin composition.

[0167] The resin composition described in Example 3 was also measured for thermal conductivity, dielectric breakdown strength, and peel strength by the same method as described in Example 1, and flexibility was also evaluated. The results are shown in Table 1 below.

[0168] (Comparative Example 1)

[0169] The resin composition described in Comparative Example 1 was obtained in the same manner as in Example 1, except that epoxy resin C (manufactured by Nippon Kayaku Co., Ltd., EPPN501HY) was used as the thermosetting resin instead of epoxy resin A, DL-92 (manufactured by Meiwa Chemicals Co., Ltd.) was used as the curing agent instead of the benzoxazine derivative represented by formula (1a), tetraphenylphosphonium tetraphenylborate (TPP-K (registered trademark), manufactured by Hokko Chemical Industry Co., Ltd.) was used as the curing accelerator, and an inorganic filler was added to the varnish so as to provide 67% by volume of the total volume of the solid content of the cured resin composition.

[0170] The resin composition contains the curing accelerator in an amount of 0.01 parts by mass based on 100 parts by mass of the total of the thermosetting resin and the curing agent.

[0171] The resin composition described in Comparative Example 1 was also measured for thermal conductivity, dielectric breakdown strength, and peel strength, and its flexibility was also evaluated by the same method as described in Example 1. The results are shown in Table 1 below.

[0172] In addition, the glass transition temperature Tg is also described in Table 1. This glass transition temperature Tg refers to the midpoint glass transition temperature in JIS K7121:2012.

[0173] [Table 1]

[0174]

[0175] As shown in Table 1, when the resin compositions described in Examples 1 to 3 were used, the thermal conductivity showed a high value of 14 W / (m·K) and the dielectric breakdown strength also showed a high value of 40 kV / mm or more.

[0176] Furthermore, it was found that when the resin compositions described in Examples 1 to 3 were used, the flexibility evaluation was excellent in all cases, indicating that the flexibility was good.

[0177] In contrast, when the resin composition described in Comparative Example 1 was used, it was found that although the thermal conductivity showed a high value of 14 W / (m·K) or more, the dielectric breakdown strength showed a low value of less than 40 kV / mm.

[0178] Furthermore, it was found that when the resin composition described in Comparative Example 1 was used, the flexibility was evaluated as unacceptable, indicating that the flexibility was deteriorated.

[0179] The above results indicate that, in a thermally conductive sheet having a resin layer composed of a resin composition comprising a thermosetting resin, a curing agent, and an inorganic filler, by using the benzoxazine derivative represented by the above formula (1) as the curing agent, a thermally conductive sheet can be obtained that achieves both thermal conductivity and dielectric breakdown properties and can more fully ensure adhesion to the adherend even if the surface of the adherend is not sufficiently smooth.

[0180] Description of Reference Numerals

[0181] 1. Thermally conductive sheet, 2. Semiconductor module, 3. Heat absorbing component, 4. Solder, 5. Semiconductor element, 6. Bonding wire, 8. Plastic case, 9. Molding resin,

[0182] 1a resin layer, 1b metal foil layer, 70a first terminal, 70b second terminal, 1bA surface.

Claims

1. A thermally conductive sheet comprising a resin layer composed of a resin composition comprising a thermosetting resin, a curing agent, and an inorganic filler, wherein the thermosetting resin comprises an epoxy resin. The curing agent is a benzoxazine derivative represented by the following formula (1): The molar ratio of the epoxy group of the epoxy resin to the benzoxazine ring of the curing agent is 0.8 or more and 1.2 or less, in, In the above formula (1), X represents any of -CH2-, -C(CH3)2- or -SO2-, and R1 and R2 represent -H, -C n H 2n+1 Any of the alkyl or aryl groups shown, wherein the -C n H 2n+1 Here, n is an integer of 1 to 10.

2. The thermally conductive sheet according to claim 1, wherein The content of the inorganic filler is 50% by volume or more and 90% by volume or less relative to the total volume of the solid content of the resin composition after curing.

3. A semiconductor module comprising: semiconductor components; a heat dissipation surface for dissipating heat generated by the semiconductor element; and a thermally conductive sheet for conducting the heat to the heat dissipation surface; The thermally conductive sheet is the thermally conductive sheet according to claim 1 or 2.

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