Insulating sheet, method for manufacturing insulating sheet, and semiconductor device

Abstract

Provided is an insulating sheet and so on including at least an insulating layer that includes an inorganic filler and an epoxy resin and is in a B-stage state. One of one surface portion of the insulating layer in a thickness direction, the other surface portion thereof, and an inner portion sandwiched between both of the surface portions, has a higher degree of curing than any of the other portions.

Description

Insulating sheet, method for manufacturing insulating sheet, and semiconductor device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application No. 2024-028369, which is incorporated herein by reference.

[0002] The present invention relates to an insulating sheet used as a component in, for example, a semiconductor device, a method for manufacturing the insulating sheet, and a semiconductor device including the insulating sheet.

[0003] Conventionally, insulating sheets have been known as components constituting semiconductor devices having semiconductor elements, for example, for conducting heat generated in the semiconductor elements to the outside of the device. This type of insulating sheet can have both electrical insulation and thermal conductivity, and therefore can conduct heat generated in the semiconductor elements to the outside of the device while maintaining electrical insulation between the insulating sheet and components adjacent to it, thereby suppressing excessive temperature rise in the semiconductor elements.

[0004] Known examples of this type of insulating sheet include an insulating sheet that is a laminate having two polymer layers formed by stacking and hot pressing at least two polymer sheets containing an inorganic filler and a polymer component (see, for example, Patent Document 1).

[0005] In detail, the insulating sheet described in Patent Document 1 is produced by using an inorganic filler whose maximum particle size is larger than the thickness of a polymer layer, causing the inorganic filler to protrude from one polymer layer by hot pressing, and then inserting the inorganic filler into the other polymer layer.

[0006] Japanese Patent Application Publication No. 2010-094887

[0007] However, while the conventional insulating sheets described in Patent Document 1 and elsewhere have relatively good electrical insulation properties, they may not necessarily have good adhesion to an adherend. If an insulating sheet is simply made of an inorganic filler and a curable resin, it is difficult to achieve both good electrical insulation properties and good adhesion.

[0008] In view of the above problems, an object of the present invention is to provide an insulating sheet having an insulating layer that has both good electrical insulation properties and good adhesive properties.

[0009] In order to solve the above problem, the insulating sheet of the present invention comprises at least an insulating layer that contains an inorganic filler and an epoxy resin and is in a B-stage state, and the degree of hardening of any one of one surface portion, the other surface portion, and an inner portion sandwiched between both surface portions in the thickness direction of the insulating layer is higher than the degree of hardening of any of the other portions.

[0010] The semiconductor device according to the present invention comprises at least the insulating layer of the insulating sheet, a semiconductor element, and a heat dissipation member that dissipates heat generated by the semiconductor element to the outside, and the insulating layer arranged between the semiconductor element and the heat dissipation member is in a C-stage state.

[0011] The method for manufacturing an insulating sheet according to the present invention is a method for manufacturing an insulating sheet having at least an insulating layer that contains an inorganic filler and an epoxy resin and is in a B-stage state, and comprises the steps of: forming a pre-cured insulating layer by volatilizing an organic solvent from a coating liquid containing the inorganic filler, the epoxy resin, and the organic solvent; and producing an insulating layer in a B-stage state by bringing the pre-cured insulating layer to a B-stage; wherein the degree of curing of any one portion of the insulating layer is made higher than the degree of curing of any one of the other portions by producing the pre-cured insulating layer by stacking multiple layers containing different types or amounts of components, or by promoting a curing reaction more in one surface portion, the other surface portion, and the inner portion sandwiched between both surface portions in the thickness direction of the pre-cured insulating layer than in the other portions.

[0012] FIG. 1 is a schematic front view of a semiconductor device according to this embodiment. FIG. 2A is a schematic cross-sectional view showing the internal structure of an example of a semiconductor device according to this embodiment. FIG. 2B is a schematic cross-sectional view showing the internal structure of another example of a semiconductor device according to this embodiment. FIG. 3 is a schematic cross-sectional view showing a portion of the internal structure of another example of a semiconductor device according to this embodiment. FIG. 4 is a schematic cross-sectional view showing a portion of the internal structure of yet another example of a semiconductor device according to this embodiment. FIG. 5A is a schematic cross-sectional view showing a cross-section of an example of an insulating sheet according to this embodiment cut in the thickness direction. FIG. 5B is a schematic cross-sectional view showing a cross-section of another example of an insulating sheet according to this embodiment cut in the thickness direction. FIG. 6 is a schematic view showing an example of how an insulating layer of an insulating sheet is produced. FIG. 7 is an analysis chart obtained by analyzing the insulating layers of multiple types of insulating sheets by near-infrared (NIR) spectroscopy. FIG. 8A is a schematic view of two copper plates stacked together with an insulating layer interposed therebetween when performing a shear strength test, viewed from one side of the copper plates in the thickness direction. Fig. 8B is a schematic diagram showing a cross section of two copper plates stacked together with an insulating layer interposed therebetween when a shear strength test is carried out, cut in the thickness direction along the longitudinal direction of the copper plates. Fig. 9 is a schematic diagram showing the state of measurement of dielectric breakdown strength.

[0013] Hereinafter, embodiments of a semiconductor device and an insulating sheet according to the present invention will be described with reference to the drawings.

[0014] <Semiconductor Device> The semiconductor device 100 of this embodiment has a rectangular parallelepiped shape, as shown in, for example, Figures 1, 2A, and 2B, and includes an insulating sheet 10 therein. A state in which the insulating sheet 10 of this embodiment is arranged so that its thickness direction is the up-down direction will be described in detail below. In the following description, the thickness direction of the semiconductor device may be referred to as the "longitudinal direction," "up-down direction," or "vertical direction," and the direction perpendicular to the "thickness direction" may be referred to as the "lateral direction," "horizontal direction," or "surface direction."

[0015] The semiconductor device 100 of this embodiment has a rectangular parallelepiped main body and two terminals T, T protruding upward from the top surface of the main body. The semiconductor device 100 of this embodiment has a semiconductor element 30 at the center in the thickness direction and the center in the planar direction. The semiconductor device 100 of this embodiment also includes two lead frames 40 that are conductive paths connecting to the semiconductor element 30, a metal plate-shaped heat dissipation member 20, and an insulating sheet 10 (for example, an insulating layer 11 in a C-stage state, which will be described later) arranged between the heat dissipation member 20 and the semiconductor element 30.

[0016] The main body of the semiconductor device 100 of this embodiment further includes a rectangular frame-shaped case 50 and a molding resin 60 that fills the inside of the case 50 and embeds the semiconductor element 30 and the like. The upper surface of the molding resin 60 forms the upper surface of the main body.

[0017] The semiconductor device 30 may be a packaged device or may be something like a bare chip.

[0018] Each of the two lead frames 40 is formed by bending a rectangular metal plate at a single point in the lengthwise direction at a substantially right angle. Each lead frame 40 has a portion extending horizontally from the bent portion and a portion extending upward. The semiconductor element 30 is disposed 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 to form one terminal T. This one lead frame 40a forms a conductive path in the semiconductor device 100 and is configured to conduct heat generated by the semiconductor element 30 to the outside of the semiconductor element 30. Similar to the one lead frame 40a, the upper end of the vertically extending portion of the other lead frame 40b also forms the other terminal T.

[0019] Each lead frame 40 is formed of a general-purpose metal such as iron, copper, aluminum, or nickel. Each lead frame is preferably made of copper because of its good electrical conductivity and 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 be subjected to a surface treatment such as plating.

[0020] The heat dissipation member 20 is disposed on the bottom of the semiconductor device 100. An insulating sheet 10 (e.g., an insulating layer 11 in a C-stage state, which will be described later) is disposed between the heat dissipation member 20 and a horizontally extending portion of one of the lead frames 40. The lower surface of the heat dissipation member 20 is exposed at the bottom of the semiconductor device 100.

[0021] The semiconductor device 100 as 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 as described above is configured so that heat generated in the internal semiconductor element 30 is transferred to the outside mainly via the lower surface of the heat dissipation member 20. The semiconductor device 100 as described above may be used with a refrigerant circulating radiator or heat dissipation fins for atmospheric heat dissipation in contact with the lower surface of the heat dissipation member 20. The semiconductor device 100 as described above may also be used with a member with a relatively large heat capacity (for example, a housing) in contact with the lower surface of the heat dissipation member 20.

[0022] The heat dissipation member 20 has good thermal conductivity. The heat dissipation member 20 is preferably formed of a material with high surface hardness and scratch resistance, which can provide good adhesion when it comes into contact with a heat sink or a heat dissipation fin. The heat dissipation member 20 is also preferably formed of a material with relatively high rigidity, which makes it less likely to deform when it comes into contact with a heat sink or a heat dissipation fin. From the above-mentioned viewpoints, the heat dissipation member 20 is preferably made of aluminum. The aluminum heat dissipation member 20 may be made of pure aluminum or an alloy containing aluminum (aluminum alloy).

[0023] In one example of this embodiment, the insulating layer 11 of the insulating sheet 10, which will be described in detail later, is arranged, for example, between a horizontally extending portion of one lead frame 40 and the heat dissipation member 20, and is adhered to the heat dissipation member 20, etc. in a C-stage state (fully cured state).

[0024] The heat dissipation member 20 may be, for example, an aluminum plate made of A1100, A1050, or A5052 and having a thickness of 0.1 mm to 10 mm.

[0025] The insulating layer 11 of the insulating sheet 10 is disposed within 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 sheet 10. The semiconductor device 100 of this embodiment includes, for example, the lead frame 40, the insulating layer 11 of the insulating sheet 10, and the heat dissipation member 20 as described above, and is configured to conduct heat from one lead frame 40a located upstream of the heat dissipation path, through the insulating layer 11 of the insulating sheet 10, to the heat dissipation member 20 located downstream of the heat dissipation path.

[0026] Although the heat dissipation member 20 in FIG. 2A is illustrated as a plate-shaped member, 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 FIG. 2B.

[0027] 2A and 2B show a state in which only the insulating layer 11 of the insulating sheet 10 is disposed between the semiconductor element 30 and the heat dissipation member 20. However, as shown in FIG. 3, for example, the insulating sheet 10 may be disposed so that the insulating layer 11 of the insulating sheet 10 is closer to the lead frame 40, and a heat transfer material (commonly referred to as a TIM) may be disposed between the insulating sheet 10 and the heat dissipation member 20. A typical commercially available product may be used as such a heat transfer material. On the other hand, as shown in FIG. 4, for example, the insulating sheet 10 may be disposed so that the base material 12 of the insulating sheet 10 is closer to the lead frame 40, and a heat transfer material (TIM) may be disposed between the insulating sheet 10 and the lead frame 40.

[0028] In the semiconductor device of this embodiment, the insulating sheet 10 (specifically, the insulating layer 11 in a C-stage state) is well adhered to the adherend between the lead frame 40 and the heat dissipation member 20 .

[0029] Next, the insulating sheet 10 of this embodiment will be described in detail.

[0030] <Insulating Sheet> The insulating sheet 10 of this embodiment is in a sheet shape as shown in Figures 5A and 5B, etc. The insulating sheet 10 of this embodiment may be formed in, for example, a rectangular shape or a strip shape (long sheet shape).

[0031] The insulating sheet 10 of this embodiment may have a single-layer structure or a laminated structure. For example, the insulating sheet 10 of this embodiment may have only an insulating layer 11 as shown in FIG. 5A , or may have an insulating layer 11 and a substrate 12 overlapping one side of the insulating layer 11 as shown in FIG. 5B . The substrate 12 is, for example, a metal foil or a metal plate. The type of metal contained in the substrate 12 is not particularly limited, but may be, for example, copper or aluminum. In other words, the substrate 12 may be copper foil, aluminum foil, aluminum foil, aluminum plate, or the like.

[0032] The insulating layer 11 contains at least an inorganic filler and an epoxy resin as a curable resin, and is in a B-stage state (semi-cured state). The insulating layer 11 may also contain a curing accelerator. Before reaching a C-stage state (fully cured state), the insulating layer 11 can be used as a pressure-sensitive adhesive sheet.

[0033] The insulating layer 11 contains an epoxy resin as a curable resin (curable binder resin) that binds inorganic filler particles together. The insulating layer 11 may contain a curable resin (curable binder resin) other than the epoxy resin, and may further contain a curing agent. The insulating layer 11 may further contain an antioxidant, etc.

[0034] The insulating layer 11 may be a single layer or a laminate of multiple layers. The insulating layer 11 may be, for example, a two-layer laminate or a three-layer laminate. The thickness (total thickness) of the insulating layer 11 is not particularly limited and may be, for example, 20 μm or more, 50 μm or more, and preferably 100 μm or more. The thickness (total thickness) of the insulating layer 11 may be 300 μm or less, and 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 the layers may be different from each other.

[0035] In the insulating sheet 10 of this embodiment, the degree of hardening of any one of the surface portions, the other surface portion, and the inner portion sandwiched between the surface portions in the thickness direction of the insulating layer 11 is higher than the degree of hardening of any of the other portions. For example, the degree of hardening of the inner portion in the thickness direction of the insulating layer 11 may be higher than the degree of hardening of the surface portions on both sides. Note that the surface portion is, for example, a portion extending from the surface of the insulating layer 11 to a specific depth of 1 / 5 or more and 2 / 5 or less of the thickness in the thickness direction of the insulating layer 11. The inner portion is a portion other than the surface portion that includes at least half the depth of the insulating layer 11 in the thickness direction.

[0036] Preferably, in the insulating sheet 10 of this embodiment, one of the surface portions on both sides of the insulating layer 11 has a higher degree of hardening than the other surface portion. In other words, the hardening degrees of one surface portion and the other surface portion of the insulating layer 11 are different from each other. Hereinafter, the insulating layer 11 having such an aspect will be mainly described in detail.

[0037] The method for producing the insulating layer 11 having different degrees of hardness on one surface portion and the other surface portion as described above will be described in detail later.

[0038] As an index of the degree of curing, for example, a degree of curing progress calculated from the ratio of the absorption peak intensities of specific functional groups by near-infrared (NIR) spectroscopy (described in detail later) can be used. For example, when one surface portion and the other surface portion of the insulating layer 11 are measured by near-infrared (NIR) spectroscopy, the ratio of the absorption peak intensity of the functional group that decreases as the curing reaction progresses to the absorption peak intensity of the functional group not involved in the curing reaction is determined, and the degree of curing progress calculated from this ratio of absorption peak intensities is used as an index of the degree of curing. The difference in the degree of curing progress between one surface portion and the other surface portion (maximum difference in the degree of curing progress) is, for example, 15% or more.

[0039] The difference in the degree of curing progress is preferably 10% or more, more preferably 15% or more, even more preferably 20% or more, and even more preferably 45% or more. The difference in the degree of curing progress may be 100% or less, or may be 90% or less. For example, if the higher degree of curing progress is 50% and the lower degree of curing progress is 30%, the difference in the degree of curing progress is 20%.

[0040] Near-infrared (NIR) spectroscopy is carried out as follows: Measurement equipment: wave number 4000-8000 cm －１ The ratio of the absorption peak intensity (peak height) of a functional group (e.g., an epoxy group) that decreases as the curing reaction progresses to the absorption peak intensity (peak height) of a functional group (e.g., a benzene ring) that is not involved in the curing reaction is calculated. The absorption peak intensity ratio before B-staging (before curing treatment by heating and pressurizing) is set to 0. In contrast, the absorption peak intensity ratio after complete curing is set to 100. For example, if the insulating layer contains an epoxy resin that has a benzene ring structure in its molecule, the target peaks are those with peak apexes at the following fractions: Peak I: 4556 cm －１ (Benzene ring) Peak II: 4464 cm －１(Epoxy group) With the absorption intensity as the vertical axis of the chart after measurement, the height from absorption intensity 0 to the peak is calculated. The ratio of the height before B-staging (uncured state) to the height after complete curing is taken as the absorption peak intensity ratio, which is calculated using the following formula. Absorption peak intensity ratio before B-staging α: (peak II height / peak I height) Absorption peak intensity ratio after complete curing β: (peak II height / peak I height) Absorption peak intensity ratio of each surface portion γ: (peak II height / peak I height) The value calculated using the following formula is taken as the degree of curing progress (index of degree of curing). Degree of curing progress (index of absorption peak intensity ratio): [(α-γ) / (α-β)] x 100

[0041] The degree of curing (one of the indicators of the degree of curing) can be adjusted, for example, by changing the type of curable resin or curing accelerator, or by changing the amount of curing accelerator. Furthermore, as described below, the degree of curing can also be adjusted by the method for producing the insulating layer 11. In other words, the degree of curing can be adjusted in one surface side portion and the other surface side portion of the insulating layer 11 by changing the amount and type of components contained in the insulating layer 11 or the method for producing the insulating layer 11. Note that, for example, even when the degree of curing is low in both surface portions of the insulating layer and high in the inner portion, the degree of curing can be adjusted in a similar manner.

[0042] The proportion of the inorganic filler to the total volume of the insulating layer 11 is, for example, 50% by volume or more. This proportion may be 60% by volume or more, or even 65% by volume. It is also possible for this proportion to be 90% by volume or less. The above volume percentages are calculated based on the specific gravity and blending mass ratio of each material blended in the insulating layer 11. Alternatively, the above volume percentages are calculated based on the mass difference between the insulating layer 11 before and after combustion and the specific gravity of each blended material. The temperature used for the combustion is a temperature equal to or higher than the ignition point of the curable resin and lower than the melting point of the inorganic filler.

[0043] In one specific example of the present embodiment, the insulating layer 11 is configured so that one of the two surface portions has a higher degree of cure than the other. If the degree of cure is relatively high throughout the insulating layer, the fluidity of both surfaces of the insulating layer will be low, potentially resulting in poor adhesion on both surfaces. On the other hand, if the degree of cure is relatively low throughout the insulating layer, the internal cohesive force will be relatively low, potentially resulting in defects such as voids and poor electrical insulation. Thus, the degree of cure has a trade-off relationship between adhesiveness and electrical insulation. In contrast, the insulating layer 11 in the above specific example is configured so that the degree of cure is higher on one surface portion than on the other surface portion, thereby exhibiting good adhesiveness in the B-stage state and good electrical insulation in the C-stage state after sufficient curing. That is, the insulating layer 11 can have both good electrical insulation and good adhesiveness in both the B-stage and C-stage states. The same applies, for example, to a case where the degree of cure is low on both surface portions of the insulating layer and high on the inner portion.

[0044] The proportion of the total mass of the inorganic filler and the curable resin to the total mass of the insulating layer 11 may be 95 mass % or more, 98 mass % or more, or 99 mass % or more.

[0045] The insulating layer 11 may contain less than 45 parts by mass, or 40 parts by mass or less of the curable resin per 100 parts by mass of the inorganic filler and the curable resin combined (assuming the total is 100 parts by mass). The insulating layer 11 may contain 10 parts by mass or more, or 15 parts by mass or more of the curable resin per 100 parts by mass of the inorganic filler and the curable resin combined.

[0046] 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 with respect to 100 parts by mass of the curable resin.

[0047] (Inorganic Filler) The inorganic filler is in a powder state before being mixed into the insulating layer 11 .

[0048] Examples of inorganic fillers include inorganic nitrides such as boron nitride, aluminum nitride, and silicon nitride; inorganic oxides such as silicon oxide (silica), aluminum oxide (alumina), titanium oxide (titania), magnesium oxide (magnesia), and zirconium oxide (zirconia); diamond, silicon carbide, talc, clay, and calcium carbonate. The inorganic filler preferably contains at least one of boron nitride, aluminum oxide, and silicon oxide, and more preferably contains at least boron nitride. In other words, the insulating layer 11 more preferably contains at least particulate boron nitride. In addition to particulate boron nitride, the insulating layer 11 may also contain particulate aluminum oxide and particulate silicon oxide.

[0049] In the present embodiment, the insulating layer 11 contains at least boron nitride, which can improve the thermal conductivity of the insulating layer 11. In the insulating layer 11, the proportion of boron nitride in the inorganic filler may be 95 mass % or more, or may be 99 mass % or more.

[0050] Commercially available products can be used as the inorganic filler, such as boron nitride fillers manufactured by Tokuyama Corporation, 3M Company, Denka Company, and JFE Mineral Co., Ltd.

[0051] (Curable Resin) Examples of the curable resin include a thermosetting resin, a curing agent (polymer curing agent), etc. The curable resin includes at least an epoxy resin.

[0052] The curable resin preferably contains a thermosetting resin and a curing agent (polymer curing agent). The thermosetting resin and the curing agent will be described in detail later.

[0053] Examples of epoxy resins as thermosetting resins include bisphenol A type epoxy resins, modified bisphenol A type epoxy resins, bisphenol F type epoxy resins, modified bisphenol F type epoxy resins, trisphenolmethane type (triphenylmethane type) epoxy resins, cresol novolac type epoxy resins, biphenyl type epoxy resins, dicyclopentadiene type epoxy resins, and phenol novolac type epoxy resins. One of these epoxy resins can be used alone, or two or more can be used in combination.

[0054] The epoxy equivalent [g / eq] of the epoxy resin may be 100 or more and 200 or less. The epoxy equivalent is measured in accordance with JIS K7236-2001.

[0055] As the curing agent, for example, a polymeric 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, and bisphenol-based phenolic resins. A phenolic resin having a novolac structure has at least a structure in which phenol structures are linked together in the molecule. A representative example of a phenolic resin having a novolac structure is a phenol novolac resin. A phenolic resin having a novolac structure may be, for example, a xylene novolac resin (phenol-modified) that further has a xylene structure. The curing agent may contain multiple types of phenolic resins.

[0056] The hydroxyl equivalent [g / eq] of the phenolic resin may be from 50 to 150. The hydroxyl value is measured according to the acetylation method in JIS K0070-1992.

[0057] In this embodiment, the proportion of the thermosetting resin such as epoxy resin and the curing agent such as phenol resin in the curable resin may be 95% by mass or more, or may be 99% by mass or more.

[0058] As the thermosetting resin and curing agent, commercially available products can be used. Epoxy resin products as thermosetting resins are available from, for example, Mitsubishi Chemical Corporation, Shin-Nichika Epoxy Manufacturing Co., Ltd., DIC Corporation, ADEKA Corporation, or Nippon Kayaku Co., Ltd. Phenolic resin products as curing agents are available from, for example, Sumitomo Bakelite Co., Ltd., DIC Corporation, or UBE Corporation.

[0059] (Curing Accelerator) Examples of the curing accelerator include thiol-based curing accelerators, imidazole-based curing accelerators, phosphorus-based curing accelerators such as triphenylphosphine (TPP) or tetraphenylphosphonium tetraphenylborate (TPP-K), and amine-based curing accelerators such as boron trifluoride monoethylamine.

[0060] As the curing accelerator, commercially available products can be used, such as those available from San-Apro Co., Ltd. and Hokko Chemical Co., Ltd.

[0061] Since the insulating sheet 10 of this embodiment is configured as described above, the insulating layer 11 in a fully cured C-stage state can have both good electrical insulation properties and good adhesive properties.

[0062] In this embodiment, when the insulating layer 11 is fully cured (C-stage state), the dielectric breakdown strength (BDS) of the insulating layer 11 may be, for example, 5 kVrms or more and 200 kVrms or less. The dielectric breakdown strength (BDS) is a value measured by a measurement method conforming to the Japanese Industrial Standards (JIS C2110-1:2016 "Solid Electrical Insulating Materials - Test Method for Dielectric Breakdown Strength - Part 1: Test by Application of Power Frequency AC Voltage"). In this embodiment, when the insulating layer 11 is fully cured (C-stage state), the thermal conductivity of the insulating layer 11 is, for example, 5 W / m·K or more. Note that the thermal conductivity may be 35 W / m·K or less.

[0063] Next, a method for manufacturing the insulating sheet of this embodiment will be described.

[0064] <Method for Manufacturing Insulating Sheet> The method for manufacturing an insulating sheet according to this embodiment is a method for manufacturing an insulating sheet (the insulating sheet 10 described above) that includes at least an insulating layer that contains an inorganic filler and an epoxy resin and is in a B-stage state. The method includes: a step of forming a pre-cured insulating layer by volatilizing an organic solvent from a coating liquid containing the inorganic filler, the epoxy 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). Furthermore, the degree of cure of any one portion of the insulating layer is made higher than the degree of cure of any one of the other portions by stacking multiple layers containing different types or amounts of components to form the pre-cured insulating layer, or by promoting a curing reaction more rapidly in one surface portion, the other surface portion, or an inner portion sandwiched between the two surface portions in the thickness direction of the pre-cured insulating layer than in the other portions.

[0065] The following mainly describes a method for promoting the curing reaction more in one surface portion of the pre-cured insulating layer than in the other surface portion of the pre-cured insulating layer.

[0066] (Example of Manufacturing Method) In one example of a manufacturing method for the insulating sheet 10 of this embodiment, first, a coating liquid containing the ingredients and organic solvent that will form the insulating layer 11 and a coating sheet are prepared. A transfer sheet Z or a substrate 12 is used as the coating sheet. A typical transfer sheet Z, such as a resin film with a release-treated surface, is used. The substrate 12 is as described above. Next, in the pre-cured insulating layer forming step, a coating liquid is applied to the surface of the coating sheet (transfer sheet Z or substrate 12) to form a coating on the coating sheet. Furthermore, the organic solvent is volatilized from the coating to form a pre-cured insulating layer 11a, and two laminated sheets W, for example, are prepared in a state in which the dried coating (pre-cured insulating layer) is superimposed on one side of the coating sheet (transfer sheet Z or substrate 12) (see FIG. 6 ).

[0067] Next, in the B-staging step, before the two laminate sheets W are stacked, one of the two laminate sheets W is subjected to at least one of a longer heating time and a higher heating temperature than the other (one pre-cured insulating layer is subjected to at least one of the pre-cured insulating layers than the other pre-cured insulating layer). This results in a higher degree of curing of one laminate sheet W. Note that there may be cases where the other laminate sheet W is not subjected to heat treatment. The above-mentioned heat treatment can be carried out, for example, by subjecting one coating sheet (one transfer sheet Z or substrate 12) to a longer heating time or a higher heating temperature than the other coating sheet.

[0068] Furthermore, in the B-stage process, two of the laminate sheets W are prepared, and the two laminate sheets W, W are stacked together so that the two pre-curing insulating layers 11a are in contact with each other, as shown in Figure 6, and then subjected to a heat and pressure treatment (hereinafter also referred to as a heat press treatment). This allows the curing reactions in the two pre-curing insulating layers 11a to progress and integrate them. By integrating them in this way, an insulating layer 11 in a B-stage state is produced.

[0069] Two laminate sheets W each having a pre-cured insulating layer 11a and a transfer sheet Z may be prepared and then stacked on top of each other for heat pressing. Alternatively, two laminate sheets W each having a pre-cured insulating layer 11a and a substrate 12 may be prepared and then stacked on top of each other for heat pressing. In the latter case, the materials of the two substrates 12 may be the same or different. Alternatively, one laminate sheet W may have a pre-cured insulating layer 11a and a transfer sheet Z, and the other laminate sheet W may have a pre-cured insulating layer 11a and a substrate 12, and these two laminate sheets may be stacked on top of each other for heat pressing. In the above example, two pre-cured insulating layers 11a are stacked on top of each other. However, for example, the insulating layer 11 may be produced by stacking multiple pre-cured insulating layers 11a on the pre-cured insulating layer 11a of a single laminate sheet W. As a result, the number of stacked pre-cured insulating layers 11a may be three or more.

[0070] In preparing the coating liquid, for example, the inorganic filler, the curable resin, and the like are mixed with an organic solvent. A general method can be used as the mixing method.

[0071] Examples of the organic solvent that can be used include ethyl acetate, methyl ethyl ketone (MEK), and toluene.

[0072] When applying the coating liquid to the coating sheet (transfer sheet Z or substrate 12), a general coating method such as die coating or reverse coating can be used. The temperature during coating is usually room temperature (15 to 25°C).

[0073] The temperature for volatilizing the organic solvent in the coating liquid may be, for example, 60°C to 150°C.

[0074] The heat press treatment is performed under temperature, pressure, and time conditions that can remove defects (e.g., voids) inside the pre-cured insulating layer 11a. The heat press treatment conditions are, for example, a temperature of 80°C to 150°C, a pressure of 2 MPa to 50 MPa, and a time of 5 minutes to 60 minutes. By performing the heat press treatment, the insulating layer 11 is put into a B-stage state.

[0075] (Another Example of Manufacturing Method) In another example of the manufacturing method of the insulating sheet 10 of this embodiment, when the two laminate sheets W, W are overlapped and then hot-pressed in the B-staging step, one of the coating sheets (transfer sheet Z or substrate 12) can be heated for a longer time or at a higher temperature than the other coating sheet (transfer sheet Z or substrate 12). This results in a higher degree of hardening of the surface portion of the insulating layer on the one laminate sheet W side.

[0076] (Another Example of Manufacturing Method) In another example of the manufacturing method of the insulating sheet 10 of this embodiment, in the above-mentioned pre-curing insulating layer forming step, for example, two coating liquids with different curing accelerator contents are prepared. Then, one insulating layer is formed using one coating liquid with a higher curing accelerator content, and the other insulating layer is formed using the other coating liquid with a lower curing accelerator content. Furthermore, an insulating layer 11 in a B-stage state is manufactured using a method similar to the above-mentioned manufacturing method. However, the heat treatment conditions for one laminate sheet and the other laminate sheet do not need to be different from each other. This results in a higher degree of curing of the surface portion of the insulating layer 11 on the one laminate sheet W side. It should be noted that the higher degree of curing of the surface portion of the insulating layer 11 on the one laminate sheet W side can also be achieved by using two or more curing accelerators with different curing accelerator performance on one and the other laminate sheets, rather than by different curing accelerator contents.

[0077] (Another Example of the Manufacturing Method) In yet another example of the manufacturing method for the insulating sheet 10 of this embodiment, one of the two laminate sheets W (the coating sheet Z or the substrate 12) does not contain a curing reaction inhibitor, and the other coating sheet (the transfer sheet Z or the substrate 12) contains a curing reaction inhibitor. After the two laminate sheets W are stacked, a heat press treatment can be simply performed. Alternatively, one of the two laminate sheets W (the coating sheet Z or the substrate 12) contains a curing reaction accelerator, and the other coating sheet (the transfer sheet Z or the substrate 12) does not contain a curing reaction accelerator. After the two laminate sheets W are stacked, a heat press treatment can be simply performed. This results in a higher degree of curing of the surface portion of the insulating layer 11 on the side of one of the laminate sheets W. When the pre-cured insulating layer contains a thiol-based curing accelerator, examples of the curing reaction inhibitor include oxides. Furthermore, when the pre-cured insulating layer contains an imidazole-based curing accelerator, examples of the curing reaction inhibitor include phosphate ester compounds. Examples of the curing reaction accelerator include the curing accelerators described above. Note that the transfer sheet Z may have the curing reaction inhibitor or curing reaction inhibitor uniformly dispersed or dissolved therein. On the other hand, the transfer sheet Z may have the curing reaction inhibitor or curing reaction inhibitor applied to the surface portion on the side in contact with the pre-cured insulating layer. The same applies to the substrate 12.

[0078] However, the manufacturing method of this embodiment is not limited to the above-described manufacturing method. For example, it is also possible to employ formulations in which the ease with which the curing reaction progresses differs between one pre-cured insulating layer and the other pre-cured insulating layer, and then simply perform the above-described heat press treatment. The formulation of the pre-cured insulating layer can be changed by changing the type or amount of the resin, curing accelerator, additive, or other component contained therein. For example, even when an insulating layer having a higher degree of curing in the inner portion than in both surface portions is produced, an insulating sheet can be manufactured using the same manufacturing method as described above.

[0079] Alternatively, for example, in the B-staging process, a transfer sheet Z or substrate 12 (e.g., made of resin) with a smaller heat capacity is used in one of the laminate sheets, and a transfer sheet Z or substrate 12 (made of metal, such as copper foil) with a larger heat capacity is used in the other laminate sheet. Then, after the two laminate sheets W are stacked, the two laminate sheets W are subjected to a heat treatment under the same conditions. This results in a higher degree of hardness in the surface portion of the insulating layer 11 in the other laminate sheet W.

[0080] In the method for manufacturing a semiconductor device according to the present embodiment, for example, the heat dissipation member 20, the lead frame 40, the semiconductor element 30, and the insulating sheet 10 manufactured as described above are arranged in the positions shown in Fig. 2A. The insulating sheet 10 may include only the insulating layer 11, or may include the insulating layer 11 and the base material 12.

[0081] In one specific example of the semiconductor device of this embodiment, the insulating layer 11 is positioned so that the surface portion of the insulating layer 11 with a lower degree of hardness adheres to the adherend at a position closer to the semiconductor element 30. The surface portion with a lower degree of hardness has relatively high fluidity, allowing it to adhere sufficiently to the surface of the adherend, and therefore has better adhesive properties than the surface portion with a higher degree of hardness. On the other hand, the surface portion with a higher degree of hardness has relatively high cohesive strength, making it less likely to develop defects such as voids internally, and therefore has better electrical insulation properties than the surface portion with a lower degree of hardness. Thus, an insulating layer having different electrical insulation and adhesive properties on one surface portion and the other surface portion can, as a whole, possess both good electrical insulation and good adhesive properties. Even in a semiconductor device having an insulating layer with a higher degree of hardness in the inner portion than both surface portions, the insulating layer can, for the same reasons as above, possess both good electrical insulation and good adhesive properties overall. Note that the specific example of the semiconductor device described above is merely an example. The adherend to which the insulating layer 11 is to be attached is not particularly limited. More specifically, the surface portion of the insulating layer 11 having a lower degree of cure can be bonded to a variety of adherends. Similarly, the surface portion of the insulating layer 11 having a higher degree of cure can be bonded to a variety of adherends.

[0082] <Method of using the insulating sheet (method of manufacturing a semiconductor device)> The insulating layer 11 manufactured as described above is brought into a sufficiently hardened state (C-stage state) by being subjected to a heating and pressurizing treatment, for example, at a temperature of 140°C or higher and 200°C or lower, a pressure of 0.1 MPa or higher and 15 MPa or lower, and a treatment time of 3 minutes or higher and 3 hours or lower.

[0083] The insulating sheet 10 manufactured as described above may be used, for example, as a component of a semiconductor device. Examples of the semiconductor device to be manufactured include so-called power semiconductor devices 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 (insulated gate bipolar transistors).

[0084] The insulating layer 11 of the insulating sheet 10 manufactured as described above is particularly useful in a semiconductor device manufacturing method involving a so-called transfer molding method, in which the insulating layer 11 is subjected to a heat treatment followed by a pressure treatment to be fully cured.

[0085] The semiconductor device, insulating sheet, and insulating sheet manufacturing method of this embodiment are as exemplified above, but the present invention is not limited to the semiconductor device, insulating sheet, and insulating sheet manufacturing method exemplified above. In other words, various forms used in general semiconductor devices, insulating sheets, and insulating sheet manufacturing methods can be adopted within the scope that does not impair the effects of the present invention.

[0086] The present specification discloses the following: (1) An insulating sheet comprising at least an insulating layer containing an inorganic filler and an epoxy resin in a B-stage state, wherein the degree of cure of any one of one surface portion, the other surface portion, and an inner portion sandwiched between both surface portions in the thickness direction of the insulating layer is higher than the degree of cure of any of the other portions. An insulating sheet having such a configuration allows the insulating layer to have both good electrical insulation and good adhesiveness. (2) An insulating sheet according to (1) above, wherein the degree of cure of the insulating layer is higher in the one surface portion than in the other surface portion. (3) The insulating sheet according to (1) or (2) above, wherein the index of the degree of cure is a degree of cure calculated from a ratio of absorption peak intensities measured by near-infrared (NIR) spectroscopy, the ratio of absorption peak intensities being a ratio of the absorption peak intensity of a functional group that decreases as the curing reaction progresses to the absorption peak intensity of a functional group not involved in the curing reaction, and a difference between the maximum and minimum values ​​of the degree of cure progress in the one surface portion, the other surface portion, and an inner portion sandwiched between both surface portions is 15% or more. (4) The insulating sheet according to any of (1) to (3) above, wherein the insulating layer contains 50% by volume or more and 80% by volume or less of the inorganic filler. (5) A semiconductor device comprising at least the insulating layer of the insulating sheet according to any of (1) to (4) above, a semiconductor element, and a heat dissipation member that dissipates heat generated by the semiconductor element to the outside, wherein the insulating layer disposed between the semiconductor element and the heat dissipation member is in a C-stage state.(6) A method for producing an insulating sheet having at least an insulating layer that contains an inorganic filler and an epoxy resin and is in a B-stage state, the method comprising: forming a pre-cured insulating layer by volatilizing an organic solvent from a coating liquid containing the inorganic filler, the epoxy resin, and an organic solvent; and producing an insulating layer in a B-stage state by bringing the pre-cured insulating layer to a B-stage, wherein the pre-cured insulating layer is formed by stacking multiple layers containing different types or amounts of components, or by promoting a curing reaction in any one of one surface portion, the other surface portion, and an inner portion sandwiched between both surface portions in the thickness direction of the pre-cured insulating layer more than in the other portions, thereby making the degree of curing of any one portion of the insulating layer higher than the degree of curing of any one of the other portions. A method for producing an insulating sheet having such a configuration can obtain an insulating layer that has both good electrical insulation and good adhesion.

[0087] The present invention will now be described in more detail with reference to experimental examples, but the present invention is not limited to these examples.

[0088] Insulating sheets composed only of an insulating layer were manufactured as follows. The raw materials and compounding compositions for manufacturing the insulating sheets of each Example and Comparative Example are shown below. An outline of the configuration of the insulating sheets of each Example and Comparative Example is shown in Table 1.

[0089] <Ingredients for insulating layer> (A) Curable resin (epoxy resin) Trisphenolmethane type epoxy resin Product name "EPPN-502H" (manufactured by Nippon Kayaku Co., Ltd.) (B) Curing agent (phenolic resin) Phenol novolac resin Product name "HF-1M" (manufactured by UBE Co., Ltd.) (C) Curing accelerator (TPP-K) Tetraphenylphosphonium tetraphenylborate (TPP-MK) Tetraphenylphosphonium tetrakis(4-methylphenyl)borate (D) Inorganic filler (BN filler) Boron nitride filler Commercially available product (SiO ２ Filler) Silica filler Commercially available products

[0090] <Composition of coating liquid for producing insulating layer> The composition of each coating liquid is shown below. As shown in Table 1, the type of curing accelerator was changed for each insulating layer. Each coating liquid was prepared by mixing the following raw materials and an organic solvent (methyl ethyl ketone (MEK)) at 23°C. (A) Curable resin (epoxy resin): 100 parts by mass (B) Curing agent (phenolic resin): 62 parts by mass (C) Curing accelerator: 1 part by mass (type as described below) (D) Inorganic filler: (BN filler) 428 parts by mass and (SiO ２ Filler) 5 parts by mass

[0091] <Production of Insulating Sheet (Insulating Layer)> (Example 1) Layers a and b were prepared, and an insulating layer was fabricated using these layers a and b. Specifically, as shown in Table 1, two types of coating liquids (for layer a and layer b) were prepared. - Coating liquid for layer a: Contains 1 part by mass of TPP-K. - Coating liquid for layer b: Contains 1 part by mass of TPP-MK. Each prepared coating liquid was applied to a transfer sheet (PET film) by die coating. The resulting mixture was left at 80 to 120°C for 3 minutes to volatilize the organic solvent, forming a pre-cured insulating layer. In this way, a laminate sheet was prepared by laminating the pre-cured insulating layer for layer a and the transfer sheet, and a laminate sheet was prepared by laminating the pre-cured insulating layer for layer b and the transfer sheet. Note that both pre-cured insulating layers had approximately the same thickness. The two laminate sheets were stacked so that the pre-cured insulating layers were in contact with each other, and then subjected to a heat press treatment. Heat pressing conditions: 120°C, 5-50 MPa pressure, 50 minutes. In this way, an insulating layer in a B-stage state with a thickness of 120 μm was produced. The volume fraction of the inorganic filler was calculated using the method described above.

[0092] Example 2: An insulating layer composed of a c layer and a d layer was prepared using a single coating liquid. Coating liquid: 1 part by mass of TPP-K. Specifically, the prepared coating liquid was applied to a transfer sheet (PET film) by die coating. The resulting mixture was left at 80-120°C for 3 minutes to volatilize the organic solvent, forming a pre-cured insulating layer. In this manner, a laminate sheet was prepared by laminating a pre-cured insulating layer for the c layer and a transfer sheet, and a laminate sheet was prepared by laminating a pre-cured insulating layer for the d layer and a transfer sheet. Note that both pre-cured insulating layers had approximately the same thickness. The pre-cured insulating layer for the d layer was subjected to a pre-heat press treatment, while the pre-cured insulating layer for the c layer was not. Pre-heat press treatment conditions: 130°C, 5-50 MPa (predetermined pressure), 35 minutes. The two laminate sheets were then stacked so that the pre-cured insulating layers were in contact with each other, and then further heat pressed. Heat press treatment conditions: 100°C, the above-mentioned predetermined pressure of 5 to 50 MPa, 30 minutes. In this way, an insulating layer in a B-stage state with a thickness of 120 μm was produced. The volume fraction of the inorganic filler was calculated by the above-mentioned method.

[0093] Example 3: An e layer and an f layer were prepared, and an insulating layer was fabricated using the e layer and the f layer. Specifically, as shown in Table 1, two types of coating liquid (for the e layer and the f layer) were prepared. - Coating liquid for the e layer: Contains 1 part by mass of TPP-K. - Coating liquid for the f layer: Contains 1 part by mass of TPP-MK. Each prepared coating liquid was applied to a transfer sheet (PET film) by die coating. The mixture was left at 80 to 120°C for 3 minutes to volatilize the organic solvent and form a pre-cured insulating layer. In this way, a laminate sheet was prepared by laminating the pre-cured insulating layer for the e layer and the transfer sheet, and a laminate sheet was prepared by laminating the pre-cured insulating layer for the f layer and the transfer sheet. Note that both pre-cured insulating layers had approximately the same thickness. The two laminate sheets were overlapped so that the pre-cured insulating layers were in contact with each other, and then subjected to a heat press treatment. Heat pressing conditions: 120°C, 5 to 50 MPa, 50 minutes. In this way, an insulating layer in a B-stage state with a thickness of 120 μm was produced. The volume fraction of the inorganic filler was calculated by the method described above.

[0094] Example 4: A g-layer, an h-layer, and an i-layer were prepared, and an insulating layer was fabricated from the g-layer, the h-layer, and the i-layer. Specifically, as shown in Table 1, two types of coating liquid (one for the g-layer and the i-layer, and one for the h-layer) were prepared. - Coating liquid for the g-layer and the i-layer: Contains 1 part by mass of TPP-K. - Coating liquid for the h-layer: Contains 1 part by mass of TPP-MK. Each prepared coating liquid was applied to a transfer sheet (PET film) by die coating. The resulting mixture was left at 80 to 120°C for 3 minutes to volatilize the organic solvent, forming a pre-cured insulating layer. In this way, two laminate sheets for the g-layer and the i-layer, each consisting of a pre-cured insulating layer and a transfer sheet, and one laminate sheet for the h-layer, each consisting of a pre-cured insulating layer and a transfer sheet, were prepared. Note that all pre-cured insulating layers had approximately the same thickness. Two laminated sheets were bonded together so that the pre-cured insulating layer for the g layer and the pre-cured insulating layer for the h layer were overlapped, and the transfer sheet overlapping the pre-cured insulating layer for the h layer was removed to expose one side of the pre-cured insulating layer for the h layer. The pre-cured insulating layer for the i layer was then overlapped on this exposed surface, resulting in a laminate in which the pre-cured insulating layer for the g layer, the pre-cured insulating layer for the h layer, and the pre-cured insulating layer for the i layer were stacked in this order between the two transfer sheets. This laminate was then subjected to a heat press treatment. Heat press treatment conditions: temperature of 120°C, the above-mentioned specified pressure of 5 to 50 MPa, for 50 minutes. In this way, an insulating layer with a thickness of 120 μm and in a B-stage state was produced. The volume fraction of the inorganic filler was calculated using the method described above.

[0095] Example 5: An insulating layer composed of a j layer, a k layer, and an l layer was prepared from a single coating liquid. Coating liquid: 1 part by mass of TPP-K. Specifically, the prepared coating liquid was applied to a transfer sheet (PET film) by die coating. The resulting mixture was left at 80-120°C for 3 minutes to volatilize the organic solvent and form a pre-cured insulating layer. In this manner, two laminated sheets for the j layer and the l layer, each consisting of a pre-cured insulating layer and a transfer sheet, and one laminated sheet for the k layer, each consisting of a pre-cured insulating layer and a transfer sheet, were prepared. Note that all pre-cured insulating layers had approximately the same thickness. The pre-cured insulating layer for the k layer was subjected to a pre-heat press treatment, while the two pre-cured insulating layers for the j layer and the l layer were not. - Conditions for preliminary hot pressing: 130°C, the above-mentioned specified pressure of 5 to 50 MPa, 35 minutes. Two laminated sheets were attached together so that the pre-cured insulating layer for the j layer and the pre-cured insulating layer for the k layer were overlapped, and the transfer sheet overlapping the pre-cured insulating layer for the k layer was removed to expose one side of the pre-cured insulating layer for the k layer. The pre-cured insulating layer for the l layer was overlapped on this exposed surface, yielding a laminate in which the pre-cured insulating layer for the j layer, the pre-cured insulating layer for the k layer, and the pre-cured insulating layer for the l layer were stacked in this order between the two transfer sheets. This laminate was further subjected to hot pressing. - Conditions for hot pressing: Temperature of 100°C, the above-mentioned specified pressure of 5 to 50 MPa, 30 minutes

[0096] Comparative Example 1: An insulating layer was prepared using one type of coating liquid. - Coating liquid: Contains 1 part by mass of TPP-K. Specifically, the prepared coating liquid was applied to a transfer sheet (PET film) by die coating. The resulting mixture was left at 80-120°C for 3 minutes to volatilize the organic solvent and form a pre-cured insulating layer. In this manner, two laminated sheets were prepared, each consisting of a pre-cured insulating layer and a transfer sheet. Both pre-cured insulating layers had approximately the same thickness. The two laminated sheets were stacked so that the pre-cured insulating layers were in contact with each other, and then subjected to a heat press treatment. - Heat press treatment conditions: Temperature: 120°C, pressure: 5-50 MPa, for 50 minutes. In this manner, an insulating layer with a thickness of 120 μm and in a B-stage state was prepared. The volume fraction of the inorganic filler was calculated using the method described above.

[0097] (Comparative Example 2) An insulating layer was produced from one type of coating liquid. Coating liquid: containing 1 part by mass of TPP-MK. Except for using this coating liquid, an insulating layer in a B-stage state was produced in the same manner as in Comparative Example 1. The volume fraction of the inorganic filler was calculated using the method described above.

[0098]

[0099] (Near-infrared (NIR) Spectroscopic Analysis of Insulating Layer in B-Stage State) Near-infrared (NIR) spectroscopic analysis was performed on the insulating layer after the heat press treatment (B-stage state) as described above. When performing this analysis, in order to reliably collect each test sample from the surface and inner portions of the insulating layer, the heat press treatment was not performed after bonding multiple layers together, but rather, the heat press treatment was performed on each layer (in Example 1, layer a and layer b were performed separately) under the same conditions as the heat press treatment performed in each Example and Comparative Example. Then, using the method described above, the ratio of the absorption peak intensities of the portions corresponding to the surface and inner portions of the insulating layer was determined. When an insulating layer was prepared by bonding two layers together, a portion of each layer was collected as a test sample, and the ratio of the absorption peak intensities of each test sample was determined. In the above analysis, each layer was further subjected to an after-cure treatment (post-curing treatment) at 180°C, a pressure of 5 MPa, and for 5 minutes to completely cure each layer. The absorption peak intensity ratio was calculated based on the absorption peak intensity of the benzene ring (height of peak I / 4556 cm). －１ ) relative to the absorption peak intensity of the epoxy group (height of peak II / 4464 cm －１ ) is the ratio of the absorption peak intensities. The degree of curing progress (used as an index of the degree of curing) calculated from the ratio of the absorption peak intensities is shown in Table 1. The method for calculating the degree of curing progress is as described above. FIG. 7 shows a near-infrared (NIR) spectroscopic analysis chart of each layer (layers a, b, c, and d) of the insulating layer in Examples 1 and 2.

[0100] <Performance Evaluation of Insulating Layer> The insulating layers produced in each of the examples and comparative examples were evaluated for various performances as follows.

[0101] (Shear Strength (Adhesion)) As shown in Figures 8A and 8B, two copper plates G (length: 70 mm, width: 25 mm, thickness: 3.0 mm) were overlapped with an insulating layer 11 (thickness: 0.120 mm) interposed therebetween (adhesion area: 15 mm x 25 mm). Next, the overlapping portion was preheated (heated at 180°C for 20 seconds or more), and then the two copper plates were heated at 180°C for 5 minutes while applying a pressure of 5 MPa. After that, after-curing (180°C x 2 hours) was performed to fully harden the insulating layers (pseudo-transfer molding method). The two insulating layers were then pulled apart in the longitudinal direction, and a shear strength test (adhesion test) was performed under the following test conditions. The results are shown in Table 1. Note that "cohesive failure" in Table 1 indicates that the insulating layers were destroyed, indicating very high adhesive strength. Note that "unattached" indicates that the two copper plates were not adhered. If it is judged as "interfacial failure", it means that the copper plate and the insulating layer have peeled off at the interface, and the adhesive strength is not very strong. Shear strength test conditions Load measurement tester: AUTOGRAPH AG-X plus / 100kN (manufactured by SHIMADZU) Load cell: SLFL-100kN / MWG-100kNA (manufactured by SHIMADZU) Tensile speed: 5.0mm / min Chuck distance: 12.5cm Environmental temperature: Room temperature (25°C)

[0102] (Breakdown Strength (Electrical Insulation)) The breakdown strength (BDS) was measured using a breakdown tester capable of applying a voltage at a frequency of 50 Hz or 60 Hz and a maximum voltage of AC 100 kVrms. Copper foil was attached to one side of an insulating layer (thickness: 0.120 mm), and the layer was preheated (heated at 180°C for 20 seconds or more), followed by application of a pressure of 5 MPa at 180°C for 5 minutes. After that, after-curing (180°C x 2 hours) was performed to fully harden the insulating layer (pseudo-transfer molding method). An insulating layer with copper foil (indicated by J) was placed in the apparatus shown in FIG. 9 . Specifically, the insulating layer with copper foil was placed on a brass disk electrode M (diameter 40 mm) in insulating oil L (JIS C2320:1999) in an oil tank K, with the copper foil facing downward. A brass spherical electrode N (15 mm diameter, 50 g weight) was placed above the approximate center of the insulating layer. The insulating oil L was kept at 20±10°C, and an alternating current (AC) of 0.2 kVrms / sec was applied to the insulating layer. A cutoff current of 10 mA was used as the criterion for determining dielectric breakdown. The voltage at which dielectric breakdown occurred was divided by the thickness of the insulating layer (unit: mm) to determine the dielectric breakdown strength (BDS).

[0103] As can be seen from Table 1, the insulating layers of the Examples, after being fully cured, were able to combine both better electrical insulation and better adhesion than the insulating layers of the Comparative Examples. Specifically, some of the insulating sheets in the Examples had insulating layers configured such that one of the two surface portions had a higher degree of cure than the other surface portion. The shear strength results above indicate that such insulating layers were able to adhere sufficiently to the adherend at their interface. Furthermore, since high electrical insulation was demonstrated in the dielectric breakdown strength evaluation, it can be said that the occurrence of voids and the like within the insulating layer was suppressed, resulting in fewer internal defects. For these reasons, it can be said that the insulating layers, after being fully cured, exhibited both good electrical insulation and good adhesion. For the same reasons as above, it can be said that the insulating layers of the Examples, which had a higher degree of cure in their inner portions than in the two surface portions, also exhibited both good electrical insulation and good adhesion after being fully cured.

[0104] The insulating sheet of the present invention is preferably used, for example, by being attached to two adherends that should be electrically insulated from each other. Furthermore, it is used as an insulating and heat-dissipating sheet to transfer heat from one of the two adherends to the other. For example, the insulating sheet of the present invention is preferably placed between a conductive member, such as a lead frame, that is in contact with a semiconductor element in a semiconductor device and a heat-dissipating member to transfer heat generated by the semiconductor element to the heat-dissipating member and to electrically insulate the conductive member from the heat-dissipating member.

[0105] 100: Semiconductor device, 10: Insulating sheet, 11: Insulating layer, 12: Base material, 20: Heat dissipation member, 30: Semiconductor element, 40: Lead frame, 50: Case, 60: Molding resin.

Claims

1. An insulating sheet comprising at least an insulating layer that contains an inorganic filler and an epoxy resin and is in a B-stage state, wherein the degree of hardening of any one of the surface portions, the other surface portion, and the inner portion sandwiched between both surface portions in the thickness direction of the insulating layer is higher than the degree of hardening of any of the other portions.

2. The insulating sheet according to claim 1, wherein the degree of hardness of the insulating layer is higher in the one surface portion than in the other surface portion.

3. An insulating sheet according to claim 1 or 2, wherein the index of the degree of curing is a degree of curing progress calculated from the ratio of absorption peak intensities measured by near-infrared (NIR) spectroscopy, wherein the ratio of absorption peak intensities is the ratio of the absorption peak intensity of a functional group that decreases as the curing reaction progresses to the absorption peak intensity of a functional group not involved in the curing reaction, and wherein the difference between the maximum and minimum values ​​of the degree of curing progress in the one surface portion, the other surface portion, and an inner portion sandwiched between both surface portions is 15% or more.

4. The insulating sheet according to claim 1 or 2, wherein the insulating layer contains 50% by volume or more and 80% by volume or less of the inorganic filler.

5. A semiconductor device comprising at least the insulating layer of the insulating sheet according to claim 1 or 2, a semiconductor element, and a heat dissipation member that dissipates heat generated by the semiconductor element to the outside, wherein the insulating layer disposed between the semiconductor element and the heat dissipation member is in a C-stage state.

6. A method for manufacturing an insulating sheet having at least an insulating layer that contains an inorganic filler and an epoxy resin and is in a B-stage state, comprising: a step of forming a pre-cured insulating layer by volatilizing an organic solvent from a coating liquid containing the inorganic filler, the epoxy resin, and an organic solvent; and a step of producing an insulating layer in a B-stage state by bringing the pre-cured insulating layer to a B-stage; wherein the method for manufacturing an insulating sheet has a higher degree of hardening in any one portion of the insulating layer than in any of the other portions by forming the pre-cured insulating layer by stacking a plurality of layers that contain components that are different from each other in type or amount, or by promoting a hardening reaction more in one surface portion, the other surface portion, and an inner portion sandwiched between both surface portions in the thickness direction of the pre-cured insulating layer than in the other portions.

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