Semiconductor device

Abstract

To provide a highly reliable semiconductor device which suppresses a potential difference between a rear surface conductive plate of a power semiconductor module and a cooler and achieves miniaturization.SOLUTION: A semiconductor device includes a laminated substrate 2 in which conductive plates 21a, 21b, and 23 are arranged on both surfaces of an insulating substrate 22 having a relative dielectric constant ε 0, a semiconductor element 1 mounted on the laminated substrate 2, a sealing material 6 for insulating and sealing the laminated substrate 2 and the semiconductor element 1, an adhesive layer 11 including an epoxy resin and a filler including first particles having a relative dielectric constant ε 1 exceeding 10, and a cooler 12 arranged on the semiconductor module by the adhesive layer, wherein ε 0 1 is satisfied SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a semiconductor device, and more particularly to a semiconductor device that is excellent in discharge resistance characteristics (voltage resistance characteristics) and highly reliable. [Background technology]

[0002] Power semiconductor modules are widely used in fields requiring efficient power conversion. Examples include renewable energy fields such as solar power generation and wind power generation, which have been attracting attention in recent years, automotive fields such as hybrid vehicles and electric vehicles, and railway fields such as rolling stock. These power semiconductor modules contain semiconductor elements and diodes, and the semiconductor elements are insulated and sealed with a thermosetting resin such as silicone gel or epoxy resin. The power semiconductor module is then installed in a cooler via a thermal compound and used as a power semiconductor device.

[0003] Conventionally, a semiconductor device has been known that includes a semiconductor module having a laminated substrate on which a semiconductor element is mounted and a sealing material, and a cooler disposed on the semiconductor module via a thermal compound containing a filler containing high-dielectric-constant particles with a relative dielectric constant of 10 or more and a base oil (see, for example, Patent Document 1).

[0004] A semiconductor device is known that includes a semiconductor module portion, an insulating resin layer bonded to the semiconductor module portion and containing a first resin, a frame material arranged to surround the insulating resin layer and containing a porous body, and a heat sink that sandwiches the insulating resin layer and the frame material with the semiconductor module portion, wherein the frame material is compressed while sandwiched between the semiconductor module portion and the heat sink, the insulating resin layer is filled in the area surrounded by the semiconductor module portion, the heat sink, and the frame material, and the first resin penetrates into the pores of the porous body (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-041013 [Patent Document 2] International Publication WO2021 / 019614 A1 Summary of the Invention [Problem to be solved by the invention]

[0006] In the invention disclosed in Patent Document 1, a semiconductor module and a cooler are fixed with screws, and a thermal compound is filled between the semiconductor module and the cooler to form a semiconductor device. Further miniaturization of semiconductor devices is required, and a configuration that does not require the cooler to be fixed with screws is desirable. However, in such a configuration, a fluid thermal compound may not be suitable as a cooling structure.

[0007] Furthermore, the invention disclosed in Patent Document 2 requires a configuration in which the insulating resin layer is surrounded by a frame material. Furthermore, since the dielectric constant is not taken into consideration, if the dielectric constant of the insulating resin layer is small, there is a risk of discharge occurring due to a decrease in the withstand voltage characteristics when a voltage is applied to operate the semiconductor module. [Means for solving the problem]

[0008] As a result of extensive research, the inventors came up with the idea of ​​using a resin layer as an adhesive layer between the semiconductor module and the cooler, and containing particles with a high dielectric constant in this resin layer, thereby completing the present invention.

[0009] That is, according to one embodiment, the present invention relates to a semiconductor device comprising: a laminated substrate having conductive plates arranged on both sides of an insulating substrate having a relative dielectric constant ε0; a semiconductor element mounted on the laminated substrate; and a sealing material that insulates and seals the laminated substrate and the semiconductor element; an adhesive layer containing an epoxy resin and a filler including first particles having a relative dielectric constant ε1 of greater than 10; and a cooler disposed on the semiconductor module by the adhesive layer, wherein ε0<ε1.

[0010] In the semiconductor device, ε1 is preferably 30 or more.

[0011] In the semiconductor device, it is preferable that the filler further contains second particles having a relative dielectric constant ε2 of 10 or less and a thermal conductivity λ2 of 10 or more.

[0012] In the semiconductor device, the second particles are preferably oxide particles.

[0013] In the semiconductor device, the content of the first particles is preferably 30 to 80 mass % of the total mass of the adhesive layer. Here, the total mass of the adhesive layer refers to the mass of all components constituting the adhesive layer, including the epoxy resin and the filler, and may further include optional components. The epoxy resin may include an epoxy resin base and, optionally, a curing agent, a curing accelerator, an additive, etc.

[0014] In the semiconductor device in which the adhesive layer contains second particles, the content of the second particles is preferably 6 to 64 mass % with respect to the total mass of the adhesive layer.

[0015] In the semiconductor device in which the adhesive layer contains second particles, the content of the first particles is preferably 20 to 80 mass % with respect to the total mass of the first particles and the second particles.

[0016] In the semiconductor device, the first particles are preferably one or more inorganic particles selected from barium titanate, titanium (IV) oxide, and zirconia.

[0017] In the semiconductor device in which the adhesive layer contains second particles, the second particles are preferably alumina.

[0018] In the semiconductor device, the adhesive layer is preferably formed to a thickness of 20 μm or more and 300 μm or less.

[0019] According to another aspect, the present invention relates to a cooling structure for use in being adhered to a semiconductor module, the cooling structure comprising: an adhesive layer containing an epoxy resin and a filler including first particles having a relative dielectric constant ε1 of greater than 10; and a cooler adhered to one surface of the adhesive layer, wherein the semiconductor module comprises a laminated substrate having conductive plates disposed on both surfaces of an insulating substrate having a relative dielectric constant ε0, and ε0<ε1. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a small semiconductor device that does not require a screw fastening portion, that suppresses the potential difference between the conductive plate on the back surface of the semiconductor module and the cooler, and that eliminates malfunction of the drive circuit due to discharge, and that has excellent voltage resistance characteristics and high reliability. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a conceptual diagram showing a cross-sectional structure of a semiconductor device according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments described below.

[0023] According to one embodiment, the present invention is a semiconductor device, which includes the following (a), (b), and (c): (a) A semiconductor module comprising a laminated substrate in which conductive plates are arranged on both sides of an insulating substrate having a relative dielectric constant of ε0, a semiconductor element mounted on the laminated substrate, and a sealing material that insulates and seals the laminated substrate and the semiconductor element. (b) an adhesive layer including an epoxy resin and a filler including first particles having a relative dielectric constant ε1 of greater than 10; (c) a cooler disposed on the semiconductor module by the adhesive layer; In this semiconductor device, ε0<ε1.

[0024] FIG. 1 is a conceptual diagram showing an example of a semiconductor device according to an embodiment of the present invention. In FIG. 1, a semiconductor element 1 is mounted on a second conductive plate 21a constituting a laminated substrate 2 via a bonding layer 3a such as solder. A terminal 4a is attached to the second conductive plate 21a via a bonding layer 3b. Furthermore, a terminal 4b is attached to another second conductive plate 21b constituting the laminated substrate 2 via a bonding layer 3c. Wiring members 7 such as bonding wires are attached to the upper surface of the semiconductor element 1 and the second conductive plate 21b, electrically connecting the upper surface of the semiconductor element 1 and the second conductive plate 21b. These members are encapsulated with an encapsulant 6.

[0025] A component obtained by sealing a sealed component including at least the laminated substrate 2 on which the semiconductor element 1 is mounted with the sealing material 6 is referred to as a semiconductor module 10. The semiconductor module 10 is primarily used for power conversion and can also be referred to as a power semiconductor module. In the illustrated embodiment, a heat dissipation base is not provided on the back surface of the laminated substrate 2 of the semiconductor module 10, i.e., the surface opposite to the surface on which the semiconductor element 1 is mounted. Also, FIG. 1 does not include a case for holding the sealing material 6 and accommodating the semiconductor element, etc. However, such a case may be provided for appropriate terminal arrangement. The semiconductor module 10 and the cooler 12 are arranged via an adhesive layer 11, and no screws or the like are used to attach them. Note that in this specification, the terms "top surface" and "bottom surface" are relative terms referring to the top and bottom in the drawings for the purpose of explanation, and do not limit the top and bottom in relation to the manner of use of the semiconductor device, etc. In the following specification, a component including the semiconductor element 1 and the laminated substrate 2 and insulated and sealed with a sealing material in a typical sealing manner is referred to as a sealed component. In the illustrated embodiment, the sealed components include a semiconductor element 1, a laminated substrate 2, bonding layers 3a, 3b, and 3c, terminals 4a and 4b, and a wiring member 7. If the semiconductor device has a metal heat dissipation base, the semiconductor module 10 and the heat dissipation base are bonded together with a thermally conductive bonding material such as solder or sintered silver to form a bonded assembly. This bonded assembly is then placed on a cooler via an adhesive layer 11. In this case, too, it is preferable that screws or the like for fastening the cooler and the bonded assembly are not used in order to miniaturize the module.

[0026] The semiconductor element 1 may be a power chip such as an IGBT or diode chip, and various Si devices, SiC devices, GaN devices, etc. may be used. A combination of these devices may also be used. For example, a hybrid module using a Si-IGBT and a SiC-SBD may be used. The number of semiconductor elements 1 mounted is not limited to that shown in the figure, and multiple semiconductor elements 1 may also be mounted.

[0027] The laminated substrate 2 is composed of an insulating substrate 22, second conductive plates 21a and 21b formed on one surface thereof, and a first conductive plate 23 formed on the other surface thereof. The insulating substrate 22 can be made of a material with excellent electrical insulation and thermal conductivity. Examples of materials for the insulating substrate 22 include inorganic materials such as Al2O3, AlN, and SiN, and resins such as epoxy resin, polyimide resin, and liquid crystal polymer. The material for the insulating substrate 22 can be selected so that its relative dielectric constant ε0 is smaller than the relative dielectric constant ε1 of the first particles contained in the adhesive layer, which will be described later. The relative dielectric constant ε0 of the insulating substrate 22 is the relative dielectric constant ε0 of the material that constitutes it, and is approximately 10 for Al2O3, approximately 8 for AlN and SiN, and approximately 4 to 5 for resin.

[0028] Metal materials such as Cu and Al, which are easy to process, can be used for the second conductive plates 21a, 21b and the first conductive plate 23. In this specification, the first conductive plate 23 made of Cu is sometimes referred to as backside copper foil. The first conductive plate 23 may be Cu or Al that has been treated with Ni plating or the like for the purpose of rust prevention. Methods for disposing the second conductive plates 21a, 21b and the first conductive plate 23 on the insulating substrate 22 include a direct copper bonding method and an active metal brazing method.

[0029] The bonding layers 3a, 3b, and 3c can be formed using lead-free solder, such as, but not limited to, Sn-Ag-Cu, Sn-Sb, Sn-Sb-Ag, Sn-Cu, Sn-Sb-Ag-Cu, Sn-Cu-Ni, and Sn-Ag solders.

[0030] In this embodiment, the members to be sealed, including the semiconductor element 1, the laminated substrate 2, the bonding layers 3a, 3b, and 3c, the terminals 4a and 4b, and the wiring member 7, and possibly other terminals (not shown), are insulated and sealed with a sealing material 6. The sealing material 6 may be a resin sealing material containing a thermosetting resin or a silicone gel. In the illustrated embodiment, a resin sealing material that does not require a case or the like is preferred. In another embodiment, the resin sealing material containing a thermosetting resin is preferably, for example, an epoxy resin, a maleimide resin, a cyanate resin, or a mixture thereof, and particularly preferably contains an epoxy resin. In the most preferred embodiment, the sealing material 6 can be formed from an epoxy resin composition containing an epoxy resin base and a curing agent, and optionally containing inorganic fillers and other additives. The epoxy resin base can be an aliphatic epoxy or an alicyclic epoxy.

[0031] Aliphatic epoxy refers to an epoxy compound in which the carbon atom directly bonded to the epoxy group is a carbon atom constituting an aliphatic hydrocarbon. Therefore, even if the main skeleton contains an aromatic ring, if it satisfies the above conditions, it is classified as an aliphatic epoxy. Aliphatic epoxy resins include, but are not limited to, bisphenol A type epoxy, bisphenol F type epoxy, bisphenol AD ​​type epoxy, biphenyl type epoxy, cresol novolac type epoxy, and trifunctional or higher multifunctional epoxy. These can be used alone or in combination.

[0032] Alicyclic epoxy resins are epoxy compounds in which the two carbon atoms constituting the epoxy group constitute an alicyclic compound. Examples of alicyclic epoxy resins include, but are not limited to, monofunctional epoxy resins, bifunctional epoxy resins, and trifunctional or higher polyfunctional epoxy resins. Alicyclic epoxy resins can be used alone or in combination of two or more different alicyclic epoxy resins.

[0033] A mixture of an aliphatic epoxy and an alicyclic epoxy may be used, and in this case the mixing ratio may be any ratio, for example, 1:4 to 4:1, and preferably 1:1 to 1:4, but is not limited to a specific mixing ratio.

[0034] The curing agent is not particularly limited as long as it can react with the epoxy resin base and harden, but it is preferable to use an acid anhydride curing agent. Examples of acid anhydride curing agents include aromatic acid anhydrides, specifically phthalic anhydride, pyromellitic anhydride, and trimellitic anhydride. Alternatively, examples include cyclic aliphatic acid anhydrides, specifically tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methylnadic anhydride, or aliphatic acid anhydrides, specifically succinic anhydride, polyadipic anhydride, polysebacic anhydride, and polyazelaic anhydride. The amount of curing agent added is preferably about 50 to 170 parts by weight, more preferably about 80 to 150 parts by weight, per 100 parts by weight of the epoxy resin base. If the amount of curing agent is less than 50 parts by mass, the glass transition temperature may decrease due to insufficient crosslinking, while if it is more than 170 parts by mass, the moisture resistance, high heat distortion temperature, and heat resistance stability may decrease.

[0035] A curing accelerator may be added to the epoxy resin composition as an optional component. Examples of the curing accelerator include imidazole or its derivatives, tertiary amines, boric acid esters, Lewis acids, organometallic compounds, and organic acid metal salts. The amount of the curing accelerator added is preferably 0.01 to 50 parts by mass, more preferably 0.1 to 20 parts by mass, per 100 parts by mass of the epoxy resin base.

[0036] In addition, inorganic fillers that may be optionally contained in the epoxy resin composition include, but are not limited to, fused silica, silica, alumina, aluminum hydroxide, titania, zirconia, aluminum nitride, talc, clay, mica, and glass fiber. These inorganic fillers can increase the thermal conductivity and reduce the thermal expansion coefficient of the cured product. These inorganic fillers may be used alone or in combination of two or more. These inorganic fillers may be microfillers or nanofillers, and two or more inorganic fillers with different particle sizes and / or types may be mixed and used. In particular, inorganic fillers with an average particle size of approximately 0.2 μm or more and 20 μm or less are preferred. The amount of inorganic filler added is preferably 100 parts by mass or more and 600 parts by mass or less, and more preferably 200 parts by mass or more and 400 parts by mass or less, based on 100 parts by mass of the total mass of the epoxy resin base and curing agent. If the amount of inorganic filler is less than 100 parts by mass, the thermal expansion coefficient of the encapsulant may become high, which may lead to peeling or cracking, whereas if the amount is more than 600 parts by mass, the viscosity of the composition may increase, which may lead to poor extrusion moldability.

[0037] The epoxy resin composition may also contain optional additives to the extent that the properties of the composition are not impaired. Examples of additives include, but are not limited to, flame retardants, pigments for coloring the resin, and plasticizers and silicone elastomers for improving crack resistance. These optional components and their amounts can be determined by those skilled in the art according to the specifications required for the semiconductor device and / or encapsulant.

[0038] A semiconductor module 10 not including a heat dissipation base as shown in the figure can be manufactured by placing the members to be sealed in an appropriate mold, filling the mold with the sealing material 6, and heat-curing the material. Examples of molding methods for such a sealed body include vacuum casting, transfer molding, and liquid transfer molding, but the molding method is not limited to a specific one. By using such a molding method, a semiconductor module 10 can be manufactured in which one surface of the first conductive plate 23 (rear copper foil) and necessary external terminals of the members to be sealed are exposed, and the other members are insulated and sealed with the sealing material 6.

[0039] The adhesive layer 11 is made of a composition containing an epoxy resin and a filler containing first particles having a relative dielectric constant ε1 of more than 10. The adhesive layer 11 bonds the semiconductor module 10 and the cooler 12 together, and functions as a heat dissipation layer for heat generated by the semiconductor module 10. As for the properties of the adhesive layer 11, the glass transition temperature does not need to be as high as that of the sealing material, but it is preferable that the glass transition temperature be at least 125°C.

[0040] The adhesive layer 11 can be applied to the back surface of the semiconductor module 10, including the first conductive plate 23 exposed from the sealing material 6, to a thickness of, for example, about 20 μm or more and 300 μm or less. The thickness of the adhesive layer 11 is more preferably 50 μm or more and 150 μm or less, and a thickness in this range is preferable from the viewpoint of capacitance. The adhesive layer 11 is also required to be insulating, because if it were conductive, it could cause a short circuit if it were separated. Therefore, it is preferable that the adhesive layer 11 does not contain a conductive material.

[0041] Next, the composition constituting the adhesive layer 11 will be described in detail. The adhesive layer 11 contains an epoxy resin and a filler. The term "epoxy resin" refers to a material that contains an epoxy resin base as an essential component and optionally includes a curing agent, a curing accelerator, and additives. The epoxy resin base can be selected from the same options as for the encapsulant. Preferably, the base is an aliphatic epoxy resin system that has both insulating and adhesive properties, such as, but not limited to, bisphenol A epoxy, bisphenol F epoxy, biphenyl epoxy, and cresol novolac epoxy. These can be used alone or in combination. Optionally, an epoxy resin other than an aliphatic epoxy resin may be mixed with the aliphatic epoxy resin. In this case, the aliphatic epoxy resin preferably accounts for 60% by mass or more, and more preferably 80% by mass or more, of the base. Epoxy resins other than an aliphatic epoxy resin that may be mixed include, but are not limited to, alicyclic epoxy resins.

[0042] The epoxy resin may contain a curing agent as an optional component. The curing agent is not particularly limited as long as it can react with the epoxy resin base and harden, but preferably, a phenol-based curing agent or an amine-based curing agent, which has good adhesion to the first conductive plate and the heat dissipation base, can be used. Specific examples that can be used include, but are not limited to, phenol novolac resin, polyaromatic novolac resin, polyamide polyamine, aliphatic polyamine, and aromatic polyamine. A curing accelerator can also be added to the epoxy resin as an optional component. Examples of the curing accelerator include imidazole.

[0043] In this embodiment, the filler contained in the composition constituting the adhesive layer 11 contains first particles as an essential component. The first particles are particles having a relative dielectric constant ε1 greater than the relative dielectric constant ε0 of the insulating substrate 22 and having a relative dielectric constant value exceeding 10. In this specification, particles having a relative dielectric constant value exceeding 10 are referred to as high-dielectric-constant particles. The high-dielectric-constant particles may be organic or inorganic particles as long as they maintain their particle shape in the adhesive layer 11 and do not chemically react with the epoxy resin.

[0044] Examples of organic particles that can be used as high-dielectric-constant particles include powdered polyvinylidene fluoride (PVDF particles, with a relative dielectric constant of ε r PVDF particles have a high relative dielectric constant and high heat resistance, and are therefore suitable as a filler that is dispersed in the adhesive layer 11 in the particle form before addition.

[0045] Inorganic particles that can be used as high dielectric constant particles include barium titanate (BaTiO3, with a relative dielectric constant of ε r =1450), strontium titanate (SrTiO3, relative dielectric constant ε r =330), lithium titanate (Li2TiO3, relative dielectric constant ε r =40), lead titanate (PbTiO3, relative dielectric constant ε r =250). These have a perovskite crystal structure with a composition formula of ABO3, where the A element is Ba, Pb, La, etc., and the B element is Ti, Zr, etc., but are not limited to these. In addition, lead zirconate titanate (PZT, Pb(Zr,Ti)O3, relative dielectric constant ε r =1300~2100), lead niobate (PbNb2O6, ε r =370), hafnium(IV) oxide (HfO2, relative dielectric constant ε r =15), tantalum pentoxide (Ta2O5, relative dielectric constant ε r =22), titanium(IV) oxide (TiO2, anatase type TiO2) r =48), zirconium oxide (ZrO2, relative dielectric constant ε r=33), yttria (Y2O3, relative dielectric constant ε r =11), chromium oxide (Cr2O3, relative dielectric constant ε r =13.3), copper oxide (CuO, relative dielectric constant ε r =18.1), nickel oxide (NiO, relative dielectric constant ε r =11.9), lithium niobate (LiNbO3, relative dielectric constant ε r =29), silicon (Si, relative dielectric constant ε r =12), barium magnesium niobate (Ba(Mg 1 / 3 Nb 2 / 3 )O3, relative permittivity ε r =25), barium neodymium titanate (Ba3Nd 9.3 Ti 18 O 54 , relative permittivity ε r =85, diamond (relative dielectric constant ε r =26) and the like. One or more inorganic particles selected from these may be included in the filler according to the present embodiment, but the filler is not limited to these.

[0046] The first particles may be a mixture of multiple different types of high-dielectric-constant particles. In this case, the relative dielectric constant ε1 of the mixture should be greater than the relative dielectric constant ε0 of insulating substrate 22. The relative dielectric constant ε1 of a mixture of multiple different first particles can be obtained by measuring the dielectric constant of a sample made of the mixture using a dielectric constant measuring device and calculating the relative dielectric constant.

[0047] The particle shape of the first particles is not particularly limited and may be spherical, needle-like, foil-like, fibrous, or the like, with spherical particles being particularly preferred. The average particle size of the first particles is, for example, approximately 1 μm or more and 50 μm or less, preferably approximately 1 μm or more and 10 μm or less, and more preferably approximately 5 μm or more and 10 μm or less. The particle size of the first particles is also determined in relation to the thickness of the adhesive layer 11, and is preferably smaller than the thickness of the adhesive layer 11.

[0048] The filler is preferably contained in an amount of 30 to 80 mass % when the total mass of the resin composition constituting the adhesive layer 11 is taken as 100%, and 100% of that may be the first particles. The resin composition constituting the adhesive layer 11 refers to a composition containing all of the components constituting the adhesive layer 1, including the epoxy resin and filler defined above, and possibly other optional components. When the adhesive layer 11 contains the first particles in an amount within this range, the capacitance of the adhesive layer 11 can be increased and the voltage applied to the insulating substrate in the semiconductor module can be reduced. The first particles are more preferably contained in an amount of 60 to 80 mass % when the total mass of the resin composition is taken as 100%. When a relatively large amount of first particles having a high relative dielectric constant is contained, the capacitance of the adhesive layer 11 can be increased and dielectric breakdown can be suppressed.

[0049] In addition to the first particles, the filler may optionally contain second particles. The second particles are particles having a thermal conductivity λ2 of 10 W / m·K or more and a relative dielectric constant ε2 of 10 or less. Examples of second particles include, but are not limited to, alumina (Al2O3, ε2=10, λ2=20), aluminum nitride (AlN, ε2=8, λ2=180), and boron nitride (BN, ε2=4, λ2=50). The inclusion of these highly thermally conductive second particles can improve the heat dissipation characteristics of the adhesive layer 11. The second particles may also be a mixture of two or more different types of particles. The shape and particle size of the second particles may be within the range of options described for the first particles. Therefore, the shape of the second particles may be the same as or different from the shape of the first particles, and the particle size of the second particles may be the same as or different from the particle size of the first particles.

[0050] The second particles are more preferably oxide particles, and in some embodiments may preferably be free of nitride particles, since nitride particles have a slightly lower partial discharge inception voltage than oxide particles.

[0051] The content of the second particles may be 6 to 64% by mass, where the total mass of the resin composition constituting the adhesive layer 11 is taken as 100%. Furthermore, the content of the second particles is preferably 20 to 80% by mass, where the total mass of the first particles and the second particles is taken as 100%. However, the total mass of the first particles and the second particles is within a preferred range for the content of the filler, and is preferably 30 to 80% by mass, where the total mass of the resin composition is taken as 100%.

[0052] In some cases, the filler may contain particles that do not fall into the category of either the first particles or the second particles.

[0053] The composition constituting the adhesive layer 11 may optionally contain a silane coupling agent in addition to the epoxy resin and filler. The silane coupling agent may be preferable because it improves the adhesion between the epoxy resin and the filler and can contribute to suppressing dielectric breakdown in the adhesive layer 11. The type of silane coupling agent may vary depending on the types of epoxy resin, first particles, and optionally second particles contained in the adhesive layer 11, but for example, a trialkoxy silane coupling agent may be used. The content of the silane coupling agent may be 0.1 to 5 mass %, preferably 1 to 3 mass %, when the total mass of the resin composition constituting the adhesive layer 11 is taken as 100%.

[0054] The composition constituting the adhesive layer 11 may contain optional additives to the extent that the properties of the adhesive layer 11 are not impaired. Examples of additives include, but are not limited to, antioxidants and modifiers. The adhesive layer 11 is preferably insulating and preferably does not contain conductive materials such as metal particles. This is because, if the adhesive layer 11 were to scatter, it could short-circuit the wiring of the semiconductor device. Furthermore, to reduce the elastic modulus of the adhesive layer, for example, nylon, nitrile rubber (also known as NBR rubber, a copolymer of acrylonitrile and butadiene), acrylic resin, etc. may be added. This can give the adhesive layer greater rigidity and strength, reducing peeling, etc. In this case, the amount added is preferably about 1 to 10 mass % of the total mass of the epoxy resin.

[0055] The adhesive layer 11 can be prepared by mixing a filler containing first particles and optionally second particles into an epoxy resin, preferably dispersing the mixture uniformly, and applying the mixture to the back surface of the first conductive plate 23 of the semiconductor module. The adhesive layer 11 can be heated and cured when adhering to the cooler 12, or can be allowed to cure naturally without heating.

[0056] The cooler 12 can be made of a material with excellent thermal conductivity and electrical conductivity. For example, metal materials such as Cu and Al are used, and Al is preferred when lighter weight is also required. Furthermore, the cooler 12 made of an Al material can be plated with Ni, Cr, or the like as needed to provide electrical conductivity at least at the area in contact with the adhesive layer 11. The shape and specifications of the cooler 12 can be selected arbitrarily to suit the intended use of the semiconductor module, and are not limited to specific ones. In other words, the cooler may be plate-shaped, or may have an air-cooling mechanism such as fins or a water-cooling mechanism.

[0057] According to the semiconductor device of this embodiment, by providing an adhesive layer 11 containing high-dielectric-constant particles and having a high dielectric constant, the potential difference between the cooler 12 and the first conductive plate 23 of the semiconductor module 10 is reduced, partial discharges are suppressed, and malfunctions of the semiconductor device's drive circuit are eliminated, resulting in a highly reliable, high-voltage semiconductor device. In particular, adding particles with a higher dielectric constant than that of the insulating substrate 22 further reduces the potential difference with the first conductive plate 23. In other words, bonding an electrically insulated conductive plate and a conductive material such as the cooler with the adhesive layer 11 having a high dielectric constant suppresses partial discharges and promotes heat dissipation. Furthermore, by using the adhesive layer 11 instead of a thermal compound, a small-sized semiconductor device can be obtained with high manufacturing efficiency, without the need for a screw-fastening structure or manufacturing process.

[0058] The present invention is not limited to the semiconductor module shown in the drawings, but includes any semiconductor device in which the conductive plate and cooler of the semiconductor module are insulated by an adhesive layer. For example, a semiconductor module using conductive connecting members such as copper pins or lead frames instead of wire bonding as shown in FIG. 1, or a semiconductor module in which a printed circuit board connected to a semiconductor element by copper pins is provided inside or outside the sealing material, can also be provided with a cooler attached via an adhesive layer to the surface of the first conductive plate exposed from the sealing material, thereby forming a semiconductor device according to the present invention. Furthermore, instead of the caseless semiconductor module shown in FIG. 1, a semiconductor module may be provided in which a case made of polyphenylene sulfide (PPS) or the like is fixed to a laminated substrate and filled with silicone gel for insulating and sealing. In this case, too, by fixing the case in a manner that exposes the surface of the first conductive plate, a cooler can be attached via an adhesive layer to the surface of the first conductive plate, thereby forming a semiconductor device according to the present invention.

[0059] According to one aspect, the present invention relates to a cooling structure for use in being adhered to a semiconductor module. The cooling structure includes the following (A) and (B): (A) An adhesive layer including an epoxy resin and a filler including first particles having a relative dielectric constant ε1 of more than 10 (B) A cooler bonded to one side of the adhesive layer The semiconductor module to be bonded includes a laminated substrate in which conductive plates are arranged on both sides of an insulating substrate having a relative dielectric constant of ε0, and is characterized in that ε0<ε1.

[0060] The adhesive layer and cooler that constitute the cooling structure may be similar to the adhesive layer 11 and cooler 12 described with reference to Fig. 1. The semiconductor module to be bonded may also have the same configuration as the semiconductor module 10 described with reference to Fig. 1, and has a semiconductor element that constitutes the semiconductor module, and a laminated substrate that has an insulating substrate.

[0061] The cooling structure can be held on the cooler with the adhesive layer provided, and can be attached to a semiconductor module during the manufacture of a semiconductor device. The cooling structure has the advantage that it can be processed separately from the semiconductor module and can be applied regardless of the type of semiconductor module. [Example]

[0062] The present invention will be described in more detail below with reference to examples of the present invention, but the present invention is not limited to the scope of the following examples.

[0063] Power semiconductor devices of the examples and comparative examples were fabricated. The laminated substrate used was an alumina substrate (manufactured by Rogers) with a Cu conductive plate thickness of 0.3 mm and an insulating substrate thickness of 0.38 mm. The insulating substrate material was Al2O3. Solder and Si power semiconductor elements, solder and copper pins, and a printed circuit board were arranged on the laminated substrate by soldering in an N2 reflow furnace to obtain a sealed component. The sealed component was then set in a mold. The sealing material used was a mixture of aliphatic epoxy resin base: jER630 (manufactured by Mitsubishi Chemical), curing agent: jER Cure 113 (manufactured by Mitsubishi Chemical), and inorganic filler (silica): Exelica (average particle size: several μm to several tens of μm) (Tokuyama) in a mass ratio of 10:5:50. This sealing material was vacuum degassed and injected into a mold. It was primarily cured at 100°C for 1 hour, and then secondary cured at 150°C for 3 hours to obtain a power semiconductor module.

[0064] The adhesive layer was prepared by mixing barium titanate (TiBaO) particles (relative dielectric constant ε1 = 1450, average particle diameter 5 μm) as the first particles with an epoxy resin containing a predetermined amount of alumina (Al2O3) as the second particles. The epoxy resin consisted of bisphenol A epoxy as the base resin, phenol novolac curing agent, acrylic resin as an additive, and imidazole as a curing accelerator, with a mass ratio of 10:5:1:0.1. The combined content of alumina and barium titanate was 80 mass% based on the total mass of the adhesive layer. This mixture was uniformly dispersed to obtain a resin composition for the adhesive layer. An adhesive layer approximately 100 μm thick was applied to the exposed surface of the conductive plate of the power semiconductor module laminate substrate, bonded to an aluminum cooler, and heat-cured at 150°C for 1 hour to obtain the semiconductor device of Example 1.

[0065] The semiconductor devices of Examples 2 to 5 were obtained by changing the compound species of the first particles and the contents of the first particles and second particles as shown in Table 1. The semiconductor devices of Examples 6 and 7 were obtained by changing the second particles to aluminum nitride (AlN) and the contents of the first particles and second particles as shown in Table 1. The semiconductor devices of Examples 8 to 11 were obtained by not including the second particles and changing the compound species and content of the first particles as shown in Table 1. On the other hand, the semiconductor devices of Comparative Examples 1 to 5 were obtained by not including the first particles and changing the compound species and content of the second particles as shown in Table 2.

[0066] In Tables 1 and 2, the filler content (%) refers to the mass percent of the filler when the total mass of the resin composition constituting the adhesive layer (i.e., the epoxy resin base, curing agent, curing accelerator, additives, and filler) is taken as 100%. The first particle content (%) refers to the mass percent of the first particles when the total mass of the resin composition constituting the adhesive layer is taken as 100%. The filler proportion (%) refers to the mass percent of the first particles when the total mass of the filler is taken as 100%. The second particle content (%) refers to the mass percent of the second particles when the total mass of the resin composition constituting the adhesive layer is taken as 100%. ε0 represents the dielectric constant of the insulating substrate, ε1 represents the dielectric constant of the first particles, ε2 represents the dielectric constant of the second particles, λ1 represents the thermal conductivity of the first particles, and λ2 represents the thermal conductivity of the second particles.

[0067] [Partial discharge evaluation] The partial discharge susceptibility of the semiconductor devices of Examples 1 to 11 and Comparative Examples 1 to 5 before and after moisture absorption was evaluated using a partial discharge detector (voltage resistance characteristic evaluation). "Before moisture absorption" refers to the semiconductor device immediately after manufacture. "After moisture absorption" refers to the semiconductor device after it was left standing for 300 hours under conditions of 85°C and 85% relative humidity after manufacture. For the partial discharge evaluation, the power supply voltage was gradually applied up to 2.5 kV, and the voltage at which a signal of 10 pC or more was detected was defined as the partial discharge inception voltage. On the other hand, if the power supply voltage was increased to 2.5 kV and the discharge charge amount after 60 seconds was less than 10 pC, it was determined that no partial discharge was observed. The partial discharge inception voltages are shown in Tables 1 and 2. If no partial discharge was observed, it was indicated that the partial discharge inception voltage was greater than 2.5 kV, and if partial discharge was observed, the voltage in that case was also displayed.

[0068] [Power cycle test evaluation] A ΔTc power cycle (P / C) test was conducted on the semiconductor device after moisture absorption. The P / C test after moisture absorption can evaluate the reliability of the semiconductor device, including its heat dissipation performance. The test conditions were a case temperature (Tc) of Δ=80°C (25°C to 105°C). For the semiconductor devices of the example and comparative examples, the thermal resistance Rth (K / W) between the temperature of the rear surface of the first conductive plate 23 and the surface temperature of the heat dissipation base was measured, and the number of cycles at which the thermal resistance Rth (K / W) increased by 20% from the initial state was evaluated. The "P / C after moisture absorption" values ​​in Tables 1 and 2 are shown relative to the number of cycles (5 kilocycles) for Comparative Example 1, which is set to 1. It has been confirmed that when the number of P / C cycles after moisture absorption is 1.5 times or more the standard (Comparative Example 1), a similar number of cycles can be obtained even with a temperature change Δ of 100°C. Therefore, it is more preferable for the relative value of P / C after moisture absorption to be 1.8 times or more.

[0069] [comprehensive evaluation] The overall evaluation is the result of a comprehensive evaluation of the semiconductor device based on the results of both the partial discharge evaluation and the power cycle test evaluation, and the semiconductor device was given a "◎" when the insulation was good and the heat dissipation was even better, a "◯" when the insulation was good, and an "×" when there was a problem with the insulation.

[0070] [Table 1]

[0071] [Table 2]

[0072] Tables 1 and 2 confirm that an adhesive layer containing at least first particles prevents partial discharges both before and after moisture absorption, and provides sufficient reliability in power cycle tests after moisture absorption. It was also confirmed that heat dissipation characteristics are improved when the thermal conductivity λ1 of the first particles is at least 6 or higher. Furthermore, comparing Examples 1 to 7 with Examples 8 to 11, adhesive layers containing second particles with high thermal conductivity, oxide-based, in addition to the first particles exhibited higher P / C resistance in power cycle tests after moisture absorption, resulting in more reliable results. This is presumably due to the contribution of the second particles to heat dissipation characteristics. Specifically, when second particles were added, it was confirmed that Al2O3 as the second particles had slightly better voltage resistance characteristics than AlN (Examples 6 and 7). This is presumably due to slightly poorer adhesion between AlN, a nitride, and the resin in the adhesive layer compared to oxides. Therefore, oxides are more preferable than nitrides for the second particles. On the other hand, as shown in Comparative Examples 1 to 5, it was confirmed that when only a filler with ε2 of less than 10 was used, the voltage resistance characteristics were poor. When the rated voltage is 1.2 kV or more, the modules of Comparative Examples 1 to 5 discharge during operation, which may cause dielectric breakdown and may destroy the module.

[0073] Although there is no intention to be bound by theory, it is believed that the results of the Examples are due to the fact that the relative dielectric constant of the ceramic insulating substrate and the relative dielectric constant of the adhesive layer became closer, which increased the capacitance and reduced the voltage distribution on the adhesive layer, preventing discharge.In the Comparative Examples, it is believed that the large difference in relative dielectric constant between the ceramic insulating substrate and the adhesive layer caused discharge of 1.2 kV and 10 pC or more.

[0074] The examples of the present invention have confirmed that the use of an adhesive layer containing high dielectric constant particles can suppress partial discharge in a semiconductor device, and that the addition of highly thermally conductive particles can also ensure heat dissipation. According to the present invention, a highly reliable power semiconductor device can be provided. [Explanation of symbols]

[0075] REFERENCE SIGNS LIST 1 semiconductor element, 2 laminated substrate, 21 second conductive plate, 22 insulating substrate, 23a, 23b first conductive plate, 3a, 3b, 3c bonding layer, 6 sealing material, 10 semiconductor module, 11 adhesive layer, 12 cooler

Claims

1. Relative permittivity ε ０ a semiconductor module including a laminated substrate in which conductive plates are arranged on both sides of the insulating substrate, a semiconductor element mounted on the laminated substrate, and a sealing material that insulates and seals the laminated substrate and the semiconductor element; Epoxy resin and relative dielectric constant ε １ an adhesive layer comprising a filler comprising first particles having a particle size greater than 10; a cooler disposed on the semiconductor module by the adhesive layer; A semiconductor device comprising: ε ０ <ε １ This is a semiconductor device.

2. ε １ The semiconductor device according to claim 1 , wherein the value of the saturation voltage is 30 or more.

3. The filler has a relative dielectric constant ε ２ is 10 or less, and the thermal conductivity λ ２ The semiconductor device according to claim 1 , further comprising 10 or more second particles.

4. The semiconductor device according to claim 3 , wherein the second particles are oxide particles.

5. 2. The semiconductor device according to claim 1, wherein the content of said first particles is 30 to 80 mass % with respect to the total mass of said adhesive layer.

6. 4. The semiconductor device according to claim 3, wherein the content of the second particles is 6 to 64 mass % with respect to the total mass of the adhesive layer.

7. 4. The semiconductor device according to claim 3, wherein the content of said first particles is 20 to 80 mass % with respect to the total mass of said first particles and said second particles.

8. The semiconductor device according to claim 5 , wherein the first particles are inorganic particles of one or more kinds selected from the group consisting of barium titanate, titanium (IV) oxide, and zirconia.

9. The semiconductor device according to claim 3 , wherein the second particles are alumina.

10. 2. The semiconductor device according to claim 1, wherein the adhesive layer is formed to a thickness of 20 [mu]m or more and 300 [mu]m or less.

11. A cooling structure for use by adhering to a semiconductor module, comprising: Epoxy resin and relative dielectric constant ε １ an adhesive layer comprising a filler comprising first particles having a particle size greater than 10; a cooler bonded to one surface of the adhesive layer; Including, The semiconductor module has a relative dielectric constant ε ０ The laminated substrate includes an insulating substrate having conductive plates on both sides thereof, and ０ <ε １ That is, the cooling structure.

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