Insulating heat dissipation sheet

Abstract

The objective is to provide an insulating heat dissipation sheet equipped with an insulating layer that can improve thermal conductivity even when containing boron nitride filler at the same concentration. [Solution] An insulating heat dissipation sheet is provided, 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 value, which is the 70% value of the cumulative distribution function of the particle size distribution, is 40 μm or more.

Description

Technical Field

[0001] The present invention relates to an insulating heat dissipation sheet used, for example, as a member in a semiconductor device.

Background Art

[0002] Conventionally, for example, an insulating heat dissipation sheet, which is a member constituting a semiconductor device having a semiconductor element and is a member for transferring heat generated in the semiconductor element to the outside of the device, is known. Since this type of insulating heat dissipation sheet has electrical insulation (hereinafter, also simply referred to as insulation) and also has heat conductivity, while maintaining electrical insulation between the insulating heat dissipation sheet and an adjacent member in the device, the heat generated in the semiconductor element can be transferred to the outside of the device, suppressing an excessive temperature rise of the semiconductor element.

[0003] 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 including an alumina filler as a heat conductive 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).

[0004] In the insulating heat dissipation sheet described in Patent Document 1, since the insulating layer includes an epoxy resin, an alumina filler, a phenolic curing agent, and a specific curing accelerator, the adhesiveness after adhering the insulating layer to an adherend can be improved.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, while the insulating layer of conventional insulating heat dissipation sheets described in Patent Document 1 and others has relatively good adhesion, its thermal conductivity is not always good. It is known that boron nitride filler can be incorporated into the insulating layer to improve thermal conductivity, but if a large amount of boron nitride filler is incorporated, problems such as a decrease in adhesion to the substrate may occur. Therefore, the amount of boron nitride filler incorporated into the insulating layer is limited to some extent.

[0007] 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.

[0008] 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. [Means for solving the problem]

[0009] To solve the above problems, the insulating heat dissipation sheet according to the present invention is The device comprises at least an insulating layer containing a thermosetting resin and a boron nitride filler, 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 larger. [Effects of the Invention]

[0010] The insulating heat dissipation sheet according to the present invention comprises an insulating layer that can improve thermal conductivity even when containing boron nitride filler at the same concentration. [Brief explanation of the drawing]

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

[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 that overlaps 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 may be, for example, copper or aluminum. In other words, the base material 12 may be copper foil, aluminum foil, aluminum foil, or an aluminum plate.

[0015] The above-mentioned insulating layer 11 contains boron nitride filler as an inorganic filler. Also, the above-mentioned insulating layer 11 contains, for example, an epoxy resin as a thermosetting resin. The above-mentioned insulating layer 11 may contain inorganic fillers other than boron nitride filler, a curing accelerator, etc. The above-mentioned insulating layer 11 is in a B-stage state. The above-mentioned insulating layer 11 can be used in the application of a pressure-sensitive adhesive sheet before it reaches the fully cured state (C-stage state).

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

[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. When 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 be different from each other.

[0018] The ratio of the boron nitride filler to the total volume of the insulating layer 11 is preferably 45% by volume or more and 60% by volume or less, more preferably 50% by volume or more and 60% by volume or less, and still more preferably 55% by volume or more and 60% by volume or less. Thereby, while maintaining the adhesive force of the insulating layer 11 to the adherend, the insulating layer 11 can have good thermal conductivity. In terms of further improving the adhesive force of the insulating layer 11 to the adherend, the ratio of the above-mentioned boron nitride filler is preferably 45% by volume or more and 55% by volume or less. The above volume percentage is calculated based on the specific gravity and mass ratio of each material blended into the insulating layer 11. Alternatively, the above volume percentage is calculated based on the mass difference of the insulating layer 11 before and after combustion and the specific gravity of each blended material. The combustion temperature used is one that 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 includes 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 to 45 μm.

[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 fillers is measured by the following method. Measurement device: Laser diffraction particle size distribution analyzer (For example, device name: Mastersizer 3000 (manufactured by Malvern Panalytical)) Feed rate speed: 40 Sample input section: High-energy type venturi Measurement time: Background measurement 5 seconds, sample measurement 3 seconds Particle size type: Non-spherical Particle size standard: Volume standard Refractive index: 1.74 Absorption rate: 0.01 Analysis model: General purpose Dispersion pressure: 3.0 bar Sample pretreatment: None

[0026] This section 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. The method for producing hexagonal boron nitride from boron carbide is not particularly limited, but typically, hexagonal boron nitride can be obtained by subjecting boron carbide to nitriding and decarburization treatments. Nitriding can be performed by calcining boron carbide in a nitrogen atmosphere. This nitriding process requires sufficient nitrogen partial pressure and temperature. If the nitrogen partial pressure is less than 5 kPa, the nitriding reaction will proceed slowly and take a long time. Therefore, it is preferable to maintain a nitrogen partial pressure of 5 kPa or higher when performing nitriding. On the other hand, from the viewpoint of high-pressure gas safety, it is preferable to maintain a nitrogen partial pressure of 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 byproduct. 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 present 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 and diboron trioxide 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 than is necessary to remove all of 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 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 duration of the decarburization treatment is not particularly limited, but a certain amount of treatment time is required to ensure that the decarburization reaction proceeds reliably. Furthermore, by extending the decarburization treatment time, it is possible to evaporate and remove to some extent any excess niboron trioxide that remains unconsumed 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, the decarburization treatment time is preferably 30 hours or less. After decarburization, boron nitride is not in powder form, but rather in block-like structures where particles are bonded together. Therefore, the decarburized boron nitride 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 follows. 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). Preferably, the thermosetting resin contains both an 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 phenolic resin can be used. Examples of phenolic resins include phenolic resins having a novolac structure (novolac-type phenolic resins), aralkyl-type phenolic resins, dicyclopentadiene-modified phenolic resins, naphthalene-type phenolic resins, or bisphenol-based phenolic resins. Phenolic resins having a novolac structure have at least one structure consisting of linked phenolic structures within their molecules. A typical example of a phenolic resin having a novolac structure is a phenol novolac resin. A phenolic resin having a novolac structure may also be, for example, a xylene novolac resin (phenol-modified) that further contains xylene structures. The curing agent may contain multiple types of phenolic 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 accelerator) 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 heat dissipation sheet of this embodiment is manufactured, for example, by carrying out the following steps. The method for manufacturing the insulating heat dissipation sheet of this embodiment includes, for example, a step of forming a pre-curing insulating layer (pre-curing insulating layer formation step) 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, The process includes a step of producing an insulating layer in a B-stage state by B-stage the aforementioned insulating layer before curing (B-stage stage step).

[0043] In the pre-curing insulating layer formation process described above, first, a coating liquid containing the compounding components and 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 substrate 12 is used. As the transfer sheet Z, a general material such as a resin film with a release treatment on its surface is used. The substrate 12 is as described above. Next, in the pre-curing insulating layer formation step described above, a coating liquid is applied to the surface of the transfer sheet Z or the substrate 12 (coating sheet) to form a film on the transfer sheet Z or the substrate 12. Furthermore, the organic solvent is evaporated from the film to form a pre-curing insulating layer 11a, and two laminated sheets W are prepared, for example, in which the dried film (pre-curing insulating layer) overlaps one side of the transfer sheet Z or the substrate 12 (see Figure 2).

[0044] Next, in the B-stage process described above, two laminated sheets W are prepared, and the two laminated sheets W, W are stacked on top of each other so that the two pre-cured insulating layers 11a are in contact with each other, as shown in Figure 2, and then subjected to a heat and pressure treatment (hereinafter also referred to as a heat press treatment). This causes the curing reactions in the two pre-cured insulating layers 11a to proceed separately while they are integrated. In this way, an insulating layer 11 in the B-stage state is produced.

[0045] Alternatively, two laminated sheets W, each having a pre-curing insulating layer 11a and a transfer sheet Z, may be prepared and stacked on top of each other before heat pressing. Alternatively, two laminated sheets W, each having a pre-curing insulating layer 11a and a base material 12, may be prepared and stacked on top of each other before heat pressing. In the latter case, the materials of the two base materials 12 may be the same or different. Alternatively, one laminated sheet W may have a pre-curing insulating layer 11a and a transfer sheet Z, and the other laminated sheet W may have a pre-curing insulating layer 11a and a base material 12, and these two laminated sheets may be stacked on top of each other and subjected to a heat press treatment. Furthermore, although two pre-curing insulating layers 11a are superimposed in the above example, an insulating layer 11 may also be created by superimposing multiple pre-curing insulating layers 11a onto a single pre-curing insulating layer 11a of a single laminated sheet W as described above. As a result, the number of superimposed pre-curing insulating layers 11a may be three or more.

[0046] In preparing the coating solution described above, for example, boron nitride filler and thermosetting resin are mixed with an organic solvent. A general method can be used for mixing.

[0047] Examples of organic solvents that can be used include ethyl acetate, methyl ethyl ketone (MEK), and toluene.

[0048] When applying the coating solution to the transfer sheet Z or substrate 12 (coating sheet), general coating methods such as die coating and reverse coating can be used. The temperature during coating is usually room temperature (15-25°C).

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

[0050] The hot pressing treatment is carried out under temperature, pressure, and time conditions that can remove defects (e.g., voids) within the pre-curing insulating layer 11a. The conditions for the hot pressing treatment are, for example, a temperature of 80°C to 150°C, a pressure of 2 MPa to 10 MPa, and a duration of 5 minutes to 60 minutes. By performing the hot pressing treatment, the insulating layer 11 enters the 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 will reach a sufficiently hardened state (C-stage state) by heating and pressurizing it for, for example, at a temperature of 140°C to 200°C, a pressure of 2 MPa to 15 MPa, and a processing time of 30 minutes to 3 hours.

[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 are manufactured include so-called power semiconductor devices, which are equipped with 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 pressure treatment after a heat treatment to ensure sufficient curing.

[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 will describe in detail the state in which the insulating heat dissipation sheet 10 of this embodiment is arranged so that its thickness direction is in the vertical direction. In the following explanation, the thickness direction of a semiconductor device may be referred to as the "vertical direction," "up-down direction," or "perpendicular direction," and the direction perpendicular to the "thickness direction" may be referred to as the "lateral direction," "horizontal direction," or "plane 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 base material 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. Furthermore, the semiconductor device 100 further comprises 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 of 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 the one lead frame 40a protrudes above the upper surface of the molded resin 60 to form one terminal T. This one lead frame 40a forms a conductive path in the semiconductor device 100 and is configured to transfer the heat generated by the semiconductor element 30 to the outside of the semiconductor element 30. The other lead frame 40b, like the first lead frame 40a, has the upper end of its vertically extending portion forming the other terminal T.

[0061] Each lead frame 40 is formed from a common 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 an alloy containing copper (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. Furthermore, the semiconductor device 100 described above may 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. Also, the semiconductor device 100 described above may 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 it comes into contact with the heat sink or heat sink fins. It is also preferable that the heat dissipation member 20 is made of a material with relatively high rigidity, in order to prevent deformation when it comes into contact with the heat sink or heat sink fins. From the above viewpoint, it is preferable that the heat dissipation member 20 be 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 component 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. Furthermore, 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, as described above, includes a lead frame 40, an insulating layer 11 of the insulating heat dissipation sheet 10, and a 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) adheres well 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 as illustrated above. In other words, 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 the following: (1) The device comprises at least an insulating layer containing a thermosetting resin and a boron nitride filler, An insulating heat dissipation sheet 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. The insulating layer of an insulating heat dissipation sheet with such a configuration may exhibit improved thermal conductivity even if it contains boron nitride filler at the same concentration. (2) The insulating heat dissipation sheet according to (1) above, wherein the insulating layer contains 45% to 60% by volume of the boron nitride filler. (3) The insulating heat dissipation sheet according to (1) or (2) above, wherein the thermosetting resin comprises an epoxy resin and a phenolic resin. [Examples]

[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 sheets (insulating layers)> [Thermosetting resin (epoxy resin A)] Trisphenolmethane-type epoxy resin: 100 parts by mass (commercial product) Epoxy equivalent: 163~175[g / eq], softening point: 57~63[℃] [Thermosetting resin polymer-type curing agent (phenol resin)] • Phenolic novolac resin 62.1 parts by mass (commercial product) Hydroxyl equivalent: 103~107[g / eq], Softening point: 94~98[℃] [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 to be added 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 epoxy resin used is as shown in Table 1 (commercial product). A polymer obtained by polycondensation of bisphenol A and epichlorohydrin, Epoxy equivalent weight 184-194 [g / eq] [Coupling agent] The amount of silane coupling agent containing 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 / g] [solvent] Methyl ethyl ketone (MEK)

[0076] (Method for preparing boron nitride fillers) Hexagonal boron nitride powder was prepared using the following procedure and used as a 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 a nitrogen partial pressure of 800 kPa, 2000°C, and 10 hours. Next, the calcined product was mixed with commercially available diboron trioxide to form a powdered mixture. The amount of diboron trioxide added was twice the amount (2 equivalents) needed to remove all the carbon contained in the calcined product (1 equivalent). The mixing was performed using a V-blender, rotating at 1 Hz for 30 minutes. The obtained powdered mixture was subjected to a decarburization treatment to obtain a second calcined product. The decarburization treatment was carried out in a nitrogen atmosphere at 2000°C for 10 hours. The second calcined product was crushed to obtain hexagonal boron nitride powder. A pulverizer that uses impact and shear forces was used for the crushing. Next, the crushed powder was classified into first-sieve-up powder and first-sieve-down powder. For this classification, an air-powered classifier equipped with a screen with a mesh size of 106 μm was used. Next, the flour from the first sieve was crushed a second time and classified under the same conditions as the first time, separating it into flour from the second sieve and flour from the second sieve. It is presumed that this crushes some of the high-hardness particles that were not crushed in the first time, and that the flour from the second sieve contains a large number of relatively large particles with a particle size close to the screen opening. After the two classification processes described above, the first sieved powder and the second sieved powder were mixed. At this time, the D70 of the boron nitride filler was adjusted by adjusting the ratio of each sieved powder, thereby obtaining 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 sheets (insulating layers)> (Example 1) The coating solution was prepared by mixing the above-mentioned amounts of raw materials with an organic solvent (methyl ethyl ketone MEK) at 23°C. Furthermore, each of the prepared coating solutions was applied to a transfer sheet (PET film) by die coating. The sheets were left to stand at 80-120°C for 3 minutes to allow the organic solvent to evaporate and form a pre-curing insulating layer. In this way, two laminated sheets were prepared by stacking a transfer sheet and a pre-curing insulating layer. Two laminated sheets were stacked so that the pre-curing insulating layers were in contact with each other, and then subjected to a hot press treatment. 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 produced. Furthermore, the volume percentage of boron nitride filler was calculated using the method described above.

[0079] [Table 1]

[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 insulating layer was manufactured in the same manner as in Example 1 by mixing the above raw materials with an organic solvent (MEK) at 23°C.

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

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

[0083] <Evaluation of the physical properties and performance of the insulating layer> For the insulating layers produced in each example and comparative example, various physical properties were measured and various performance characteristics were evaluated as follows. The results are shown in Table 2.

[0084] [Table 2]

[0085] (Thermal diffusivity of the insulating layer) Four insulating layers with a thickness of 120 μm (B-stage state) were laminated together, and a laminated body (cured body) with a thickness of 480 μm in the C-stage state was fabricated by applying a pressure of 5 MPa at 180°C for 2 hours. From this laminate, square sheet-shaped test pieces were cut out with sides measuring 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-out test pieces to prepare samples for measuring thermal diffusivity. 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 four samples.

[0086] (Measurement of peel strength (90° peel)) The peel strength of copper foil at 90° was measured using the following method. Measurement sample: A 2mm thick anodized aluminum plate was prepared as the substrate. One side of the insulating layer was bonded to the glossy side of a 1oz copper foil. The other side of the insulating layer was attached to the substrate, and the insulating layer was cured at 180°C for 2 hours under a pressure of 5MPa to reach the C stage. Subsequently, a portion of the copper foil was removed by etching it in 10mm widths. Measurement device: 90° peel test machine Measurement environment: Room temperature (23℃) Measurement method: In accordance with JIS C6481, 5.7. Using a 90° peel test apparatus, the exposed insulating layer was continuously peeled off by approximately 50 mm at a speed of 50 mm / min, with the tensile direction perpendicular (90°) to the adherend. The average value of the peel load during peeling (4 tests performed) 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. [Industrial applicability]

[0088] The insulating heat dissipation sheet of the present invention is preferably used, for example, by being attached (adhered) 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, in semiconductor devices, to transfer heat generated by the semiconductor element to the heat dissipation member while being placed between a conductive member, such as a lead frame in contact with a semiconductor element, and a heat dissipation member, and while being adhered to both. It is also suitable for electrically insulating the conductive member from the heat dissipation member. [Explanation of Symbols]

[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: Molded resin.

Claims

1. The device comprises at least an insulating layer containing a thermosetting resin and a boron nitride filler, An insulating heat dissipation sheet 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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