Insulation heat dissipation sheet

Abstract

Provided is an insulating heat dissipation sheet comprising at least an insulating layer containing a thermosetting resin and a boron nitride filler, wherein, when the particle size distribution of the boron nitride filler is measured, D70, which is the value of 70% of the cumulative distribution function of the particle size distribution, is 40 µm or more.

Description

Insulating heat dissipation sheet Cross-reference to related applications

[0001] This application claims the priority of Japanese Patent Application No. 2024-196096 and Japanese Patent Application No. 2025-187504, and these applications are incorporated by reference into the description of this application specification.

[0002] The present invention relates to an insulating heat dissipation sheet used, for example, as a member in a semiconductor device.

[0003] Conventionally, for example, an insulating heat dissipation sheet that is a member constituting a semiconductor device having a semiconductor element and that transfers heat generated in the semiconductor element to the outside of the device is known. This type of insulating heat dissipation sheet has both electrical insulation (hereinafter also simply referred to as insulation) and thermal conductivity. Therefore, while maintaining electrical insulation between the insulating heat dissipation sheet and the adjacent member in the device, the heat generated in the semiconductor element is transferred to the outside of the device, suppressing an excessive temperature rise of the semiconductor element.

[0004] As this type of insulating heat dissipation sheet, for example, an insulating heat dissipation sheet including an insulating layer formed of a resin composition, the insulating layer containing an alumina filler as a thermal conductivity filler, a phenolic curing agent as a curing agent, and a specific curing accelerator as a curing accelerator is known (for example, Patent Document 1).

[0005] In the insulating heat dissipation sheet described in Patent Document 1, since the insulating layer contains an epoxy resin, an alumina filler, a phenolic curing agent, and a specific curing accelerator, the adhesiveness after adhering the insulating layer to the adherend can be improved.

[0006] Japanese Patent Application Laid-Open No. 2018-070687

[0007] However, although the insulating layer of the conventional insulating heat dissipation sheet described in Patent Document 1 and the like has relatively good adhesiveness, the thermal conductivity may not always be good. Although it is known to blend a boron nitride filler into the insulating layer to improve the thermal conductivity, problems such as a decrease in the adhesive force to the adherend may occur when a large amount of the boron nitride filler is blended. Therefore, the blending amount of the boron nitride filler into the insulating layer is limited to a certain extent.

[0008] Therefore, there is a demand for insulating heat dissipation sheets that have an insulating layer with improved thermal conductivity, even when incorporating the same amount of boron nitride filler.

[0009] In view of the above-mentioned problems and requirements, the present invention aims to provide an insulating heat dissipation sheet having an insulating layer that can improve thermal conductivity even when containing boron nitride filler at the same concentration.

[0010] To solve the above problems, the insulating heat dissipation sheet according to the present invention comprises at least an insulating layer containing a thermosetting resin and a boron nitride filler, wherein when the particle size distribution of the boron nitride filler is measured, D70, which is the 70% value of the cumulative distribution function of the particle size distribution, is 40 μm or more.

[0011] Figure 1A is a schematic cross-sectional view showing a cross-section of an example of the insulating heat dissipation sheet of this embodiment, cut in the thickness direction. Figure 1B is a schematic cross-sectional view showing a cross-section of another example of the insulating heat dissipation sheet of this embodiment, cut in the thickness direction. Figure 2 is a schematic diagram showing an example of how the insulating layer of the insulating heat dissipation sheet is manufactured. Figure 3 is a schematic front view of the semiconductor device of this embodiment. Figure 4A is a schematic cross-sectional view showing the internal structure of an example of the semiconductor device. Figure 4B is a schematic cross-sectional view showing the internal structure of another example of the semiconductor device. Figure 5 is a schematic cross-sectional view partially showing the internal structure of yet another example of the semiconductor device. Figure 6 is a schematic cross-sectional view partially showing the internal structure of yet another example of the semiconductor device.

[0012] Hereinafter, one embodiment of the insulating heat dissipation sheet according to the present invention will be described with reference to the drawings. Note that the following description illustrates preferred embodiments of the present invention, and the present invention is not limited thereto.

[0013] The insulating heat dissipation sheet 10 of this embodiment is in the form of a sheet, as shown in Figures 1A and 1B, respectively. The insulating heat dissipation sheet 10 of this embodiment may be formed in a rectangular shape, or in a strip shape (long sheet shape).

[0014] The insulating heat dissipation sheet 10 of this embodiment may have a single-layer structure or a laminated structure. For example, the insulating heat dissipation sheet 10 of this embodiment may have only an insulating layer 11 as shown in Figure 1A, or it may have an insulating layer 11 and a base material 12 overlapping one side of the insulating layer 11 as shown in Figure 1B. The base material 12 is, for example, a metal foil or a metal plate. The type of metal contained in the base material 12 is not particularly limited, but for example, it may be copper or aluminum. In other words, the base material 12 may be copper foil, aluminum foil, aluminum foil, or an aluminum plate.

[0015] The insulating layer 11 described above contains boron nitride filler as an inorganic filler. The insulating layer 11 also contains, for example, epoxy resin as a thermosetting resin. The insulating layer 11 may also contain inorganic fillers other than boron nitride filler, and curing accelerators, etc. The insulating layer 11 is in the B stage state. Before reaching the fully cured state (C stage state), the insulating layer 11 can be used in applications as a pressure-sensitive adhesive sheet.

[0016] The insulating layer 11 described above contains an epoxy resin as a thermosetting resin (thermosetting binder resin) that binds inorganic filler particles such as boron nitride filler to each other. The insulating layer 11 may also contain thermosetting resins other than epoxy resin (thermosetting binder resins), and may further contain a curing agent. The insulating layer 11 described above may further contain a curing accelerator, an antioxidant, and the like.

[0017] The insulating layer 11 may be a single layer or a laminate of multiple layers. The thickness (total thickness) of the insulating layer 11 is not particularly limited and may be, for example, 50 μm or more, preferably 100 μm or more. The thickness (total thickness) of the insulating layer 11 may be 300 μm or less, preferably 200 μm or less. If the insulating layer 11 is a laminate of multiple layers, the thickness of each layer constituting the laminate may be, for example, 20 μm or more. The thicknesses of each layer may differ from each other.

[0018] The proportion of boron nitride filler to the total volume of the insulating layer 11 is preferably 45% to 60% by volume, more preferably 50% to 60% by volume, and even more preferably 55% to 60% by volume. This allows the insulating layer 11 to have good thermal conductivity while maintaining the adhesive strength of the insulating layer 11 to the adherend. In terms of further improving the adhesive strength of the insulating layer 11 to the adherend, the proportion of boron nitride filler is preferably 45% to 55% by volume. The above volume percentages are calculated based on the specific gravity and mass ratio of each material blended into the insulating layer 11. Alternatively, the above volume percentages are calculated based on the mass difference of the insulating layer 11 before and after combustion and the specific gravity of each blended material. The temperature used for combustion is above the ignition point of the thermosetting resin and below the melting point of the inorganic filler such as boron nitride filler.

[0019] The ratio of the total mass of inorganic fillers such as boron nitride fillers and thermosetting resins to the total mass of the insulating layer 11 may be 95% by mass or more, 98% by mass or more, or 99% by mass or more.

[0020] The insulating layer 11 may contain less than 45 parts by mass of thermosetting resin, or 40 parts by mass or less, per 100 parts by mass of the total of inorganic fillers such as boron nitride filler and thermosetting resin (when the total is 100 parts by mass). The insulating layer 11 may contain 10 parts by mass or more, 15 parts by mass or more, or 20 parts by mass or more of thermosetting resin per 100 parts by mass of the above total.

[0021] In the insulating layer 11, the content of the curing accelerator may be 0.005 parts by mass or more and 1.50 parts by mass or less per 100 parts by mass of the thermosetting resin.

[0022] (Inorganic filler) The inorganic filler is in powder form before being incorporated into the insulating layer 11. The inorganic filler contains at least boron nitride filler.

[0023] When the particle size distribution of the boron nitride filler contained in the insulating layer 11 is measured, D70, which is the 70% value of the cumulative distribution function of the particle size distribution, is 40 μm or more. Such D70 may be 60 μm or less, and is preferably in the range of 40 μm or more and 45 μm or less.

[0024] Since the insulating heat dissipation sheet 10 of this embodiment is configured as described above, the insulating layer 11 in the fully cured C-stage state can have better thermal conductivity if the amount of boron nitride filler is the same.

[0025] The particle size distribution of boron nitride filler is measured by the following method: Measurement device: Laser diffraction particle size distribution analyzer (e.g., device name: Mastersizer 3000 (Malvern Panalytical)) Feed rate: 40 Sample input: High-energy type venturi Measurement time: Background measurement 5 seconds, sample measurement 3 seconds Particle size type: Non-spherical Particle size reference: Volume reference Refractive index: 1.74 Absorption rate: 0.01 Analysis model: General-purpose Dispersion pressure: 3.0 bar Sample pretreatment: None

[0026] This document describes a method for producing hexagonal boron nitride powder used as a boron nitride filler. Note that the following description is merely one example of a method for producing hexagonal boron nitride powder, and the present invention is not limited thereto. First, hexagonal boron nitride is produced from boron carbide (B4C) as a raw material. The boron carbide is not particularly limited and can be produced by any method. While the method for producing hexagonal boron nitride from boron carbide is not particularly limited, typically, hexagonal boron nitride can be obtained by subjecting boron carbide to nitriding and decarburization treatments. The nitriding treatment can be performed by calcining boron carbide in a nitrogen atmosphere. This nitriding treatment requires sufficient nitrogen partial pressure and temperature. If the nitrogen partial pressure is less than 5 kPa, the nitriding reaction will proceed slowly and require a long time. Therefore, it is preferable to set the nitrogen partial pressure to 5 kPa or higher when performing the nitriding treatment. On the other hand, from the viewpoint of high-pressure gas safety, it is preferable to set the nitrogen partial pressure to 1000 kPa or less. Furthermore, if the temperature during the nitriding treatment is lower than 1800°C, the nitriding reaction will proceed slowly and require a long time. For this reason, the firing temperature is preferably 1800°C or higher, and more preferably 1900°C or higher. On the other hand, if the firing temperature exceeds 2200°C, the reverse reaction will occur, which will ultimately hinder the progress of the reaction. For this reason, the firing temperature is preferably 2200°C or lower, and more preferably 2100°C or lower. The boron nitride obtained by the above nitriding treatment contains carbon (C) as a by-product. Therefore, the boron nitride is subjected to a decarburization treatment to remove the C contained in the boron nitride. Specifically, one or both of diboron trioxide and its precursors (hereinafter referred to as diboron trioxide, etc.) are mixed with the boron nitride and heated in a non-oxidizing atmosphere. This makes it possible to remove the C mixed in the boron nitride as CO (gas). Furthermore, the non-oxidizing atmosphere is preferably an inert gas atmosphere, and more preferably a nitrogen atmosphere. The amounts of boron nitride, diboron trioxide, etc., are not particularly limited.However, from the viewpoint of increasing the efficiency of carbon removal and sufficiently reducing the amount of carbon contained in boron nitride, it is preferable to add more diboron trioxide or the like than the amount necessary to remove all the carbon contained in the boron nitride. Furthermore, in order to sufficiently reduce the amount of carbon contained in the boron nitride, it is preferable to set the temperature during the above decarburization treatment to 1500°C or higher, and more preferably to 1800°C or higher. On the other hand, it is preferable that the temperature be 2200°C or lower. The time for the above decarburization treatment is not particularly limited, but a certain amount of treatment time is required to ensure that the decarburization reaction proceeds reliably. Also, by extending the decarburization treatment time, it is possible to evaporate and remove to some extent any excess diboron trioxide that remains without being consumed by the decarburization reaction. For this reason, the decarburization treatment time is preferably 1 hour or more, more preferably 3 hours or more, and even more preferably 6 hours or more. On the other hand, it is preferable that the decarburization treatment time be 30 hours or less. The boron nitride after the decarburization treatment is not in powder form, but in block form in which particles are bonded together. Therefore, the boron nitride after the decarburization treatment is crushed to obtain hexagonal boron nitride powder.

[0027] Boron nitride fillers with a D70 of 40 μm or more can be obtained, for example, as described below. Specifically, crude boron nitride fillers synthesized by a general method are crushed (disintegrated), classified, and separated according to particle size. The large particle group and the small particle group are then mixed. By making the proportion of the large particle group relatively large during the mixing process, boron nitride fillers with a D70 of 40 μm or more can be obtained.

[0028] Examples of inorganic filler materials other than boron nitride include inorganic nitrides such as aluminum nitride or silicon nitride, inorganic oxides such as silicon oxide (silica), aluminum oxide (alumina), titanium oxide (titania), magnesium oxide (magnesia), and zirconium oxide (zirconia), as well as diamond, silicon carbide, talc, clay, and calcium carbonate. The insulating layer 11 may also contain particulate aluminum oxide and particulate silicon oxide in addition to particulate boron nitride.

[0029] In this embodiment, the thermal conductivity of the insulating layer 11 can be improved by including at least boron nitride in the insulating layer 11. In the insulating layer 11, the proportion of boron nitride among the inorganic fillers may be 95% by mass or more, or 98% by mass or more.

[0030] (Thermosetting resin) Examples of thermosetting resins include epoxy resins or curing agents (polymer-type curing agents). It is preferable that the thermosetting resin contains both epoxy resin and a curing agent (polymer-type curing agent).

[0031] Epoxy resins used as thermosetting resins include, for example, bisphenol A type epoxy resin, modified bisphenol A type epoxy resin, bisphenol F type epoxy resin, modified bisphenol F type epoxy resin, trisphenolmethane type (triphenylmethane type) epoxy resin, cresol novolac type epoxy resin, biphenyl type epoxy resin, dicyclopentadiene type epoxy resin, or phenol novolac type epoxy resin. One of these epoxy resins can be used alone, or two or more can be used in combination.

[0032] The epoxy equivalent [g / eq] of the epoxy resin may be between 100 and 200. The above epoxy equivalent is measured according to JIS K7236-2001.

[0033] As a curing agent, a polymer-type curing agent such as a phenol resin can be used. Examples of phenol resins include phenol resins having a novolac structure (novolac-type phenol resin), aralkyl-type phenol resin, dicyclopentadiene-modified phenol resin, naphthalene-type phenol resin, or bisphenol-based phenol resin. A phenol resin having a novolac structure has at least a structure in which phenol structures are linked together in the molecule. A typical example of a phenol resin having a novolac structure is a phenol novolac resin. A phenol resin having a novolac structure may also be, for example, a xylene novolac resin (phenol-modified) that further has a xylene structure. The curing agent may contain multiple types of phenol resins.

[0034] The hydroxyl equivalent [g / eq] of the phenolic resin may be between 50 and 150. The above hydroxyl value is measured according to the acetylation method in JIS K0070-1992.

[0035] In this embodiment, the proportion of thermosetting resins, such as epoxy resins, and curing agents, such as phenolic resins, in the thermosetting resin may be 95% by mass or more, or 99% by mass or more.

[0036] Commercially available products can be used as the thermosetting resin and curing agent. Epoxy resins, used as thermosetting resins, can be obtained from companies such as Mitsubishi Chemical Corporation, Shin-Nippon Chemical Epoxy Manufacturing Co., Ltd., DIC Corporation, ADEKA Corporation, or Nippon Kayaku Co., Ltd. Phenolic resins, used as curing agents, can be obtained from companies such as Sumitomo Bakelite Corporation, DIC Corporation, or UBE Corporation.

[0037] (Curing accelerators) Examples of curing accelerators include thiol-based curing accelerators, imidazole-based curing accelerators, phosphorus-based curing accelerators such as triphenylphosphine (TPP) or tetraphenylphosphonium tetraphenylborate (TPP-K), or amine-based curing accelerators such as boron trifluoride monoethylamine.

[0038] Commercially available products can be used as the curing accelerators mentioned above. Such products can be obtained from companies such as Sunapro and Hokko Chemical.

[0039] The insulating layer 11 may further contain, for example, a silane coupling agent, in addition to the above-mentioned components.

[0040] In this embodiment, when the insulating layer 11 is sufficiently cured (C-stage state), the thermal conductivity of the insulating layer 11 is, for example, 5 W / m·K or higher. However, the above thermal conductivity may be 35 W / m·K or lower.

[0041] Next, the manufacturing method for the insulating heat dissipation sheet of this embodiment will be described.

[0042] The insulating and heat-dissipating sheet of the present embodiment is manufactured, for example, by performing the following steps. The manufacturing method of the insulating and heat-dissipating sheet of the present embodiment includes, for example, a step of forming a pre-cured insulating layer by volatilizing the organic solvent from a coating liquid containing a boron nitride filler as an inorganic filler, an epoxy resin as a thermosetting resin, and an organic solvent (pre-cured insulating layer forming step), and a step of producing an insulating layer in a B-stage state by B-staging the pre-cured insulating layer (B-staging step).

[0043] In the above pre-cured insulating layer forming step, first, a coating liquid containing the compounding components and the organic solvent that will constitute the insulating layer 11 and a coating sheet are prepared. As the coating sheet, a transfer sheet Z or a base material 12 is adopted. As the transfer sheet Z, a general one such as a resin film with a release-treated surface is used. The base material 12 is as described above. Next, in the above pre-cured insulating layer forming step, a coating liquid is applied to the surface of the transfer sheet Z or the base material 12 (coating sheet) to form a film on the transfer sheet Z or the base material 12. Further, the organic solvent is volatilized from the film to form a pre-cured insulating layer 11a, and for example, two laminated sheets W in a state where the dried film (pre-cured insulating layer) overlaps one side of the transfer sheet Z or the base material 12 are produced (see FIG. 2).

[0044] Subsequently, in the above B-staging step, two of the above laminated sheets W are prepared, and for example, as shown in FIG. 2, the two laminated sheets W, W are overlapped so that the two pre-cured insulating layers 11a contact each other, and a heat and pressure treatment (hereinafter also referred to as a hot press treatment) is performed. Thereby, the curing reactions in the two pre-cured insulating layers 11a are advanced and integrated respectively. In this way, the insulating layer 11 in the B-stage state is produced by integration.

[0045] Incidentally, two laminated sheets W having the pre-curing insulating layer 11a and the transfer sheet Z may be prepared, and these may be overlapped with each other and subjected to a hot press treatment. Alternatively, two laminated sheets W having the pre-curing insulating layer 11a and the base material 12 may be prepared, and these may be overlapped with each other and subjected to a hot press treatment. In the latter case, the materials of the two base materials 12 may be the same or different. On the other hand, one laminated sheet W has the pre-curing insulating layer 11a and the transfer sheet Z, and the other laminated sheet W has the pre-curing insulating layer 11a and the base material 12, and these two laminated sheets may be overlapped with each other and subjected to a hot press treatment. Also, in the above example, two pre-curing insulating layers 11a are overlapped, but for example, a plurality of pre-curing insulating layers 11a may be overlapped on the pre-curing insulating layer 11a of one laminated sheet W as described above to produce the insulating layer 11. As a result, the number of pre-curing insulating layers 11a to be overlapped may be three or more.

[0046] In the preparation of the above coating liquid, for example, boron nitride filler, thermosetting resin, etc. are mixed with an organic solvent. As a mixing method, a general method can be adopted.

[0047] As the above organic solvent, for example, ethyl acetate, methyl ethyl ketone (MEK), toluene, etc. can be used.

[0048] When coating the coating liquid on the transfer sheet Z or the base material 12 (coating sheet), general coating methods such as die coating method, reverse coating method, etc. can be adopted. The temperature in coating is usually room temperature (15 to 25°C).

[0049] The temperature for volatilizing the organic solvent in the coating liquid may be, for example, 60°C to 150°C.

[0050] The hot press treatment is carried out, for example, under temperature conditions, pressure conditions, and time such that defects (such as voids) inside the pre-curing insulating layer 11a can be removed. The conditions of the hot press treatment are, for example, a temperature of 80°C or higher and 150°C or lower, a pressure of 2 MPa or higher and 10 MPa or higher, and 5 minutes or more and 60 minutes or less. By carrying out the hot press treatment, the insulating layer 11 becomes a B-stage state.

[0051] Next, we will explain how to use the insulating heat dissipation sheet (insulating layer) manufactured as described above.

[0052] The insulating layer 11 manufactured as described above can be heated and pressurized for, for example, 140°C to 200°C, 2 MPa to 15 MPa, and for a processing time of 30 minutes to 3 hours to reach a sufficiently hardened state (C-stage state).

[0053] The insulating heat dissipation sheet 10 manufactured as described above may be used, for example, as a component of a semiconductor device. Examples of semiconductor devices that can be manufactured include so-called power semiconductor devices that include power diodes for rectification and power transistors for switching and amplification. Examples of power transistors include thyristors, power MOSFETs (metal-oxide-semiconductor field-effect transistors), and IGBTs (isolated gate bipolar transistors).

[0054] The insulating layer 11 of the insulating heat dissipation sheet 10 manufactured as described above can be used in the manufacture of semiconductor devices using a so-called transfer molding method, which involves a process in which the insulating layer 11 is subjected to a heat treatment followed by a pressurizing treatment to ensure sufficient hardening.

[0055] <Semiconductor Device> The semiconductor device 100 is rectangular in shape, as shown in Figures 3, 4A, and 4B, and includes an insulating heat dissipation sheet 10 inside. The following description will detail the state in which the insulating heat dissipation sheet 10 of this embodiment is arranged so that its thickness direction is the vertical direction. In the following description, the thickness direction of the semiconductor device may be referred to as the "vertical direction," "up and down direction," or "perpendicular direction," and the direction perpendicular to the "thickness direction" may be referred to as the "horizontal direction," "horizontal direction," or "surface direction."

[0056] In a semiconductor device, for example, the heat dissipation member 20, lead frame 40, semiconductor element 30, and the insulating heat dissipation sheet 10 manufactured as described above are arranged in the positions shown in Figure 4A. The insulating heat dissipation sheet 10 may consist only of an insulating layer 11, or it may consist of an insulating layer 11 and a substrate 12.

[0057] The semiconductor device 100 has a rectangular parallelepiped body and two terminals T, T protruding upward from the top surface of the body. The semiconductor device 100 of this embodiment has a semiconductor element 30 in the center of the thickness direction and in the center of the planar direction. The semiconductor device 100 further includes two lead frames 40 which are conductive paths connected to the semiconductor element 30, a metal plate-shaped heat dissipation member 20, and an insulating heat dissipation sheet 10 (for example, an insulating layer 11 in the C-stage state described later) disposed between the heat dissipation member 20 and the semiconductor element 30.

[0058] The main body of the semiconductor device 100 further comprises a rectangular frame-shaped case 50 and a molded resin 60 that fills the inside of the case 50 and in which semiconductor elements 30 and the like are embedded. The upper surface of the molded resin 60 forms the upper surface of the main body.

[0059] The semiconductor element 30 may be a packaged element or a bare chip.

[0060] Each of the two lead frames 40 is formed by bending a strip-shaped metal plate at approximately a right angle at one point along its length. Each lead frame 40 has a portion extending horizontally from the bent portion and a portion extending upward. A semiconductor element 30 is positioned on the upper surface of the horizontally extending portion of one lead frame 40a. The upper end of the vertically extending portion of one lead frame 40a protrudes above the upper surface of the molded resin 60, forming one terminal T. This lead frame 40a forms a conductive path in the semiconductor device 100 and is configured to transmit the heat generated by the semiconductor element 30 to the outside of the semiconductor element 30. The other lead frame 40b is similar to the one lead frame 40a in that the upper end of the vertically extending portion forms the other terminal T.

[0061] Each lead frame 40 is formed from a general-purpose metal such as iron, copper, aluminum, or nickel. Each lead frame is preferably made of copper because it has good conductivity and a relatively high specific heat. The copper lead frame 40 may be made of pure copper or a copper alloy. Each lead frame 40 may also be surface-treated, such as by plating.

[0062] The heat dissipation member 20 is located at the bottom of the semiconductor device 100. An insulating heat dissipation sheet 10 (for example, an insulating layer 11 in the C-stage state, described later) is placed between the heat dissipation member 20 and the horizontally extending portion of one of the lead frames 40. The outer surface of the heat dissipation member 20 is exposed at the bottom of the semiconductor device 100.

[0063] The semiconductor device 100 described above is configured to dissipate heat from the semiconductor element 30 to the outside through the heat dissipation member 20. In other words, the semiconductor device 100 described above is configured so that the heat generated in the internal semiconductor element 30 is mainly transferred to the outside via the lower surface of the heat dissipation member 20. The semiconductor device 100 described above may also be used with a refrigerant-circulating heat sink or heat dissipation fins for atmospheric heat dissipation in contact with the lower surface of the heat dissipation member 20. Furthermore, the semiconductor device 100 described above may also be used with a component with a relatively large heat capacity (for example, a housing) in contact with the lower surface of the heat dissipation member 20.

[0064] The heat dissipation member 20 has good thermal conductivity. It is preferable that the heat dissipation member 20 is made of a material with high surface hardness and resistance to scratches, in order to ensure good adhesion when in contact with the heat sink or heat sink fins. Furthermore, it is preferable that the heat dissipation member 20 is made of a material with relatively high rigidity, in order to resist deformation when in contact with the heat sink or heat sink fins. From the above viewpoint, it is preferable that the heat dissipation member 20 is made of aluminum. The aluminum heat dissipation member 20 may be made of pure aluminum or an alloy containing aluminum (aluminum alloy).

[0065] The insulating layer 11 of the insulating heat dissipation sheet 10 described above is placed, for example, between a horizontally extending portion of one lead frame 40 and the heat dissipation member 20, and is bonded to the heat dissipation member 20 in a C-stage state (sufficiently cured state).

[0066] As the heat dissipation member 20, for example, an aluminum plate made of A1100, A1050, or A5052 with a thickness of 0.1 mm to 10 mm can be used.

[0067] The insulating layer 11 of the insulating heat dissipation sheet 10 is placed inside the semiconductor device 100 to electrically insulate the lead frame 40 from the heat dissipation member 20. The heat dissipation member 20 and the lead frame 40 are bonded together by the insulating layer 11 of the insulating heat dissipation sheet 10. The semiconductor device 100, for example, has a lead frame 40, the insulating layer 11 of the insulating heat dissipation sheet 10, and the heat dissipation member 20, and is configured to transfer heat from one lead frame 40a on the upstream side of the heat dissipation path, through the insulating layer 11 of the insulating heat dissipation sheet 10, to the heat dissipation member 20 on the downstream side of the heat dissipation path.

[0068] Although Figure 4A uses a plate-shaped heat dissipation member as an example, the heat dissipation member 20 in the semiconductor device 100 of this embodiment may be, for example, a heat dissipation fin 20x as shown in Figure 4B.

[0069] Figures 4A and 4B show a state in which only the insulating layer 11 of the insulating heat dissipation sheet 10 is placed between the semiconductor element 30 and the heat dissipation member 20. However, the insulating layer 11 and the base material 12 may also be placed between the semiconductor element 30 and the heat dissipation member 20. For example, as shown in Figure 5, the insulating heat dissipation sheet 10 may be positioned so that the insulating layer 11 of the insulating heat dissipation sheet 10 is closer to the lead frame 40, and a heat transfer material (generally called TIM) may be placed between the insulating heat dissipation sheet 10 and the heat dissipation member 20. A general commercially available product can be used as such a heat transfer material. On the other hand, as shown in Figure 6, for example, the insulating heat dissipation sheet 10 may be positioned so that the base material 12 of the insulating heat dissipation sheet 10 is closer to the lead frame 40, and a heat transfer material (TIM) may be placed between the insulating heat dissipation sheet 10 and the lead frame 40.

[0070] In the semiconductor device, the insulating heat dissipation sheet 10 (specifically, the insulating layer 11 in the C-stage state) is well adhered to the substrate between the lead frame 40 and the heat dissipation member 20.

[0071] The insulating heat dissipation sheet of this embodiment is as illustrated above, but the present invention is not limited to the insulating heat dissipation sheet illustrated above. That is, various forms used in general insulating heat dissipation sheets can be adopted as long as they do not impair the effects of the present invention.

[0072] The matters disclosed herein include: (1) an insulating heat dissipation sheet comprising at least an insulating layer containing a thermosetting resin and a boron nitride filler, wherein when the particle size distribution of the boron nitride filler is measured, the D70, which is the 70% value of the cumulative distribution function of the particle size distribution, is 40 μm or more. The insulating layer of such an insulating heat dissipation sheet may have improved thermal conductivity even if it contains the same concentration of boron nitride filler. (2) the insulating heat dissipation sheet according to (1) above, wherein the insulating layer contains 45 volume% to 60 volume% of the boron nitride filler. (3) the insulating heat dissipation sheet according to (1) or (2) above, wherein the thermosetting resin contains an epoxy resin and a phenolic resin.

[0073] The present invention will be further explained with experimental examples, but the present invention is not limited to these.

[0074] An insulating heat dissipation sheet consisting solely of an insulating layer was manufactured in the following manner.

[0075] <Raw materials for insulating heat dissipation sheet (insulating layer)> [Thermosetting resin (epoxy resin A)] ・Trisphenolmethane type epoxy resin: 100 parts by mass (commercial product) Epoxy equivalent: approximately 163-175 [g / eq], softening point: 57-63 [°C] [Thermosetting resin polymer type curing agent (phenol resin)] ・Phenol novolac resin: 62.1 parts by mass (commercial product) Hydroxyl group equivalent: 103-107 [g / eq], softening point: 94-98 [°C] [Curing accelerator] (TPP-K) Tetraphenylphosphonium tetraphenylborate: 1.0 part by mass, average particle size: 1.80-2.88 [μm] [Inorganic filler (production method is as follows)] The amount of each filler is as shown in Table 1 (BN filler 1) Boron nitride filler (D70 = 42.8 μm) Used in Example 1 (BN Filler 2) Boron nitride filler (D70 = 41.0 μm) Used in Examples 2 and 3 (BN Filler 3) Boron nitride filler (D70 = 39.2 μm) Used in Comparative Example 1 (BN Filler 4) Boron nitride filler (D70 = 37.1 μm) Used in Comparative Example 2 [Thermosetting resin (epoxy resin B)] The amount of bisphenol A type epoxy resin is as shown in Table 1 (Commercial product) Polymer obtained by polycondensation of bisphenol A and epichlorohydrin, epoxy equivalent 184-194 [g / eq] [Coupling agent] The amount of silane coupling agent having an epoxy group is as shown in Table 1 (Commercial product) Silane coupling agent having an epoxy group (3-glycidoxypropyltrimethoxysilane) Molecular weight 236.3 [g / eq] [Other inorganic fillers] Silica powder 4.8 parts by mass (Commercial product) Specific surface area 270-330 [m ２ [Solvent] Methyl ethyl ketone (MEK)

[0076] (Method for preparing boron nitride filler) Hexagonal boron nitride powder was prepared using the following procedure to obtain boron nitride filler. First, commercially available boron carbide powder was nitrided by firing in a nitrogen atmosphere while maintaining furnace pressure. The firing was carried out under conditions of nitrogen partial pressure of 800 kPa, 2000°C, and 10 hours. Next, the firing product was mixed with commercially available diboron trioxide to obtain a powder mixture. The amount of diboron trioxide added at this time was twice the amount (2 equivalents) required to remove all the carbon contained in the firing product (1 equivalent). The mixing was carried out using a V-blender, rotating at 1 Hz for 30 minutes. The obtained powder mixture was subjected to a decarburization treatment to obtain a second firing product. The decarburization treatment was carried out under conditions of 2000°C and 10 hours in a nitrogen atmosphere. The second firing product was crushed to obtain hexagonal boron nitride powder. For the crushing process, a crusher that crushes using impact and shear forces was used. Next, the crushed powder was classified into first sieve-up powder and first sieve-down powder. For the classification, an air-powered classifier equipped with a screen with a mesh size of 106 μm was used. Subsequently, the first sieve-up powder was crushed a second time and classified under the same conditions as the first time to separate it into second sieve-up powder and second sieve-down powder. It is presumed that this crushes some of the high-hardness particles that were not crushed in the first time, and that the second sieve-down powder contains a large number of relatively large particles with a particle size close to the mesh size of the screen. After the two classification processes, the first sieve-down powder and the second sieve-down powder were mixed. At this time, the D70 of the boron nitride filler was adjusted by adjusting the ratio of each sieve-down powder to obtain BN filler 1 to BN filler 4.

[0077] (Measurement of particle size distribution of boron nitride filler) The particle size distribution of BN filler 1 to BN filler 4 was measured according to the measurement method described above. The D70 values ​​are shown in Table 2.

[0078] <Manufacturing of insulating heat dissipation sheet (insulating layer)> (Example 1) The above-mentioned amounts of raw materials and organic solvent (methyl ethyl ketone MEK) were mixed at 23°C to prepare a coating solution. Furthermore, each of the prepared coating solutions was applied to a transfer sheet (PET film) by die coating. It was left to stand at 80-120°C for 3 minutes to evaporate the organic solvent and form a pre-curing insulating layer. In this way, two laminated sheets were made by laminating the transfer sheet and the pre-curing insulating layer. The two laminated sheets were stacked so that the pre-curing insulating layers were in contact with each other, and then a hot press treatment was performed. The conditions for the hot press treatment were a temperature of 120°C, a pressure of 5 MPa or more, and a duration of 50 minutes. By performing the hot press treatment, an insulating layer with a thickness of 120 μm and in the B-stage state was manufactured. The volume ratio of boron nitride filler was calculated using the method described above.

[0079]

[0080] (Examples 2 and 3) Except for using BN filler 2 instead of BN filler 1 and changing the amount of raw materials to the amounts shown in Table 1, the above raw materials and organic solvent (MEK) were mixed at 23°C to produce an insulating layer in the same manner as in Example 1.

[0081] (Comparative Example 1) An insulating layer was manufactured in the same manner as in Example 1, except that BN filler 3 was used instead of BN filler 1, and the amount of raw materials was changed to the amount shown in Table 1, by mixing the above-mentioned amount of raw materials and organic solvent (MEK) at 23°C.

[0082] (Comparative Example 2) An insulating layer was manufactured in the same manner as in Example 1, except that BN filler 4 was used instead of BN filler 1, and the amount of raw materials was changed to the amount shown in Table 1, by mixing the above-mentioned amount of raw materials and organic solvent (MEK) at 23°C.

[0083] <Evaluation of Physical Properties and Performance of Insulating Layers> For the insulating layers manufactured in each example and comparative example, various physical properties were measured and various performance aspects were evaluated as follows. The results are shown in Table 2.

[0084]

[0085] (Thermal diffusivity of the insulating layer) Four insulating layers with a thickness of 120 μm (B-stage state) were laminated and cured at 180°C for 2 hours under a pressure of 5 MPa to produce a laminate (cured body) with a thickness of 480 μm in the C-stage state. From this laminate, square sheet-shaped test pieces were cut out so that each side was 10 mm ± 0.5 mm. Anti-reflective agent (Fine Chemical Japan Co., Ltd., part number: FC-153) was applied to both sides of the cut test pieces to prepare samples for thermal diffusivity measurement. Thermal diffusivity was measured using a xenon flash analyzer (NETZSCH, LFA-447). The thermal diffusivity was calculated by taking the arithmetic mean of the measured values ​​of the four test samples.

[0086] (Measurement of Peel Strength (90° Peel)) The peel strength of the copper foil was measured by performing a 90° peel test using the following method. Sample: A 2 mm thick anodized aluminum plate was prepared as the substrate. On one side of the insulating layer, the glossy side of a 1 oz copper foil was bonded to one side. The other side of the insulating layer was attached to the substrate, and the insulating layer was cured by applying a pressure of 5 MPa at 180°C for 2 hours to reach the C stage. After that, a portion of the copper foil was removed by etching it in a 10 mm width. Measurement device: 90° peel test machine Measurement environment: Room temperature (23°C) Measurement method: In accordance with JIS C6481 5.7. Using the 90° peel test device, the exposed insulating layer was continuously peeled off by approximately 50 mm at a speed of 50 mm / min, so that the tensile direction was perpendicular (90°) to the substrate. The average value of the peeling load during the peeling process (over four trials) was defined as the 90° copper foil peel strength.

[0087] As can be seen from Table 2, the insulating layers of each example after sufficient curing were able to exhibit better thermal conductivity (thermal diffusivity) than the insulating layers of the comparative examples, even with the same boron nitride filler content.

[0088] The insulating heat dissipation sheet of the present invention is suitably used, for example, by being attached (bonded) to two adherends that should be electrically insulated from each other. Moreover, it is used to transfer heat from one of the two adherends to the other. The insulating heat dissipation sheet of the present invention is suitably used, for example, by being placed between a conductive member such as a lead frame in contact with a semiconductor element in a semiconductor device and a heat dissipation member, and being bonded to both, in order to transfer heat generated in the semiconductor element to the heat dissipation member, and to electrically insulate the conductive member and the heat dissipation member.

[0089] 100: Semiconductor device, 10: Insulating heat dissipation sheet, 11: Insulating layer, 12: Substrate, 20: Heat dissipation component, 30: Semiconductor element, 40: Lead frame, 50: Case, 60: Molding resin.

Claims

1. An insulating heat dissipation sheet comprising at least an insulating layer containing a thermosetting resin and a boron nitride filler, wherein when the particle size distribution of the boron nitride filler is measured, D70, which is the 70% value of the cumulative distribution function of the particle size distribution, is 40 μm or more.

2. The insulating heat dissipation sheet according to claim 1, wherein the insulating layer contains 45% to 60% by volume of the boron nitride filler.

3. The insulating heat dissipation sheet according to claim 1 or 2, wherein the thermosetting resin comprises an epoxy resin and a phenolic resin.

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