Semiconductor device and method for manufacturing a semiconductor device

Abstract

To provide a highly reliable semiconductor device and a method for manufacturing the same. [Solution] A semiconductor device comprising a semiconductor element 1 mounted on a laminated substrate 2 comprising an insulating substrate 22 and a conductive plate 21, and a cured silicone gel encapsulation layer 9 that encapsulates the semiconductor element 1, wherein the semiconductor device comprises a rust inhibitor film 12 in contact with the laminated substrate 2 or the semiconductor element 1, and a rust inhibitor 11 diffused into the silicone gel encapsulation layer 9. A method for manufacturing the semiconductor device, comprising the steps of mounting the semiconductor element on the laminated substrate, encapsulating the laminated substrate and the semiconductor element with a silicone gel encapsulant to obtain a cured silicone gel encapsulation layer, and forming a coating layer containing a rust inhibitor on the cured silicone gel encapsulation layer.

Description

[Technical Field]

[0001] This invention relates to semiconductor devices and methods for manufacturing semiconductor devices. In particular, this invention relates to semiconductor devices with excellent corrosion resistance and high reliability, and methods for manufacturing the same. [Background technology]

[0002] Power semiconductor modules are widely used in fields where efficient power conversion is required. For example, their application is expanding in the power electronics field, including industrial equipment, electric vehicles, and home appliances. These power semiconductor modules incorporate switching elements and diodes, and the elements use silicon (Si) semiconductors or silicon carbide (SiC) semiconductors.

[0003] A silicone resin composition for encapsulation is known, characterized in that, after curing, the penetration degree becomes 35 to 70 and the adhesive strength to an insulating circuit board with a Cu layer on its surface becomes 50 kPa to 180 kPa, and a power semiconductor module encapsulated by curing the resin composition is also known (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-213336 [Overview of the project] [Problems that the invention aims to solve]

[0005] In recent years, with the changing operating environments of power semiconductor modules, the increasing temperatures of semiconductor elements, and the narrowing of the pitch of metal components such as conductive plates, there has been a growing demand for the development of highly reliable semiconductor devices. [Means for solving the problem]

[0006] As a result of diligent research, the inventors have solved the problem by constructing a semiconductor device in a predetermined manner and forming a rust-preventive coating on the surface of a metal component sealed with a sealing material, thereby completing the present invention.

[0007] According to one embodiment, the present invention relates to a semiconductor device comprising a semiconductor element mounted on a laminated substrate having an insulating substrate and a conductive plate, a cured silicone gel encapsulation layer that encapsulates the semiconductor element, a rust inhibitor film in contact with the laminated substrate or the semiconductor element, and a rust inhibitor dispersed in the silicone gel encapsulation layer.

[0008] In the semiconductor device described above, it is preferable that the rust inhibitor includes benzotriazole or a derivative thereof.

[0009] In the semiconductor device described above, it is preferable that the conductive plate contains copper or a copper alloy.

[0010] In the semiconductor device described above, it is preferable that the laminated substrate includes a conductive bonding layer containing silver that bonds the insulating substrate and the conductive plate.

[0011] According to another embodiment, the present invention relates to a method for manufacturing the aforementioned semiconductor device, comprising the steps of: mounting the semiconductor element on the laminated substrate; sealing the laminated substrate and the semiconductor element with a silicone gel encapsulant to obtain the cured silicone gel encapsulation layer; and forming a coating layer containing the rust inhibitor on the cured silicone gel encapsulation layer.

[0012] In the method for manufacturing the semiconductor device, it is preferable that the step of forming the coating layer includes the step of applying an aqueous solution containing the rust inhibitor onto the cured silicone gel encapsulation layer and drying it. Alternatively, in the method for manufacturing the semiconductor device, it is preferable that the step of forming the coating layer includes the step of applying a silicone resin composition containing the rust inhibitor onto the cured silicone gel encapsulation layer.

[0013] In the method for manufacturing the semiconductor device, it is further preferable to include a step of diffusing the rust preventive agent from the coating layer into the cured silicone gel sealing layer to form the rust preventive agent film.

Advantages of the Invention

[0014] According to the present invention, a highly reliable semiconductor device excellent in corrosion resistance against corrosive gases containing hydrogen sulfide, chlorine, etc. and moisture can be provided, in which a rust preventive agent film is formed on the surface of a metal member including a conductive plate.

Brief Description of the Drawings

[0015] [Figure 1] FIG. 1 is a conceptual cross-sectional view showing a cross-sectional structure of a semiconductor device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a conceptual cross-sectional view showing a cross-sectional structure in a coating layer formation stage in a method for manufacturing a semiconductor device according to an embodiment of the present invention. [Figure 3] FIG. 3 is a diagram for explaining sample preparation for X-ray photoelectron spectroscopy.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments described below. Also, in the drawings, there are parts where members constituting the device are described enlarged or reduced for the purpose of explanation, and the dimensions of each member and the relative dimensional relationship between a plurality of members do not limit the present invention.

[0017] [First Embodiment: Semiconductor Device] According to the first embodiment, the present invention relates to a semiconductor device. The semiconductor device according to the present embodiment includes a semiconductor element mounted on a laminated substrate including an insulating substrate and a conductive plate, and a cured silicone gel sealing layer for sealing the semiconductor element, and includes a rust preventive agent film in contact with the laminated substrate or the semiconductor element, and a rust preventive agent dispersed in the silicone gel sealing layer.

[0018] The configuration of the semiconductor device will be described with reference to FIG. 1. FIG. 1 is a conceptual cross-sectional view of a power semiconductor module, which is an example of a semiconductor device according to the first embodiment of the present invention. Referring to FIG. 1, in the power semiconductor module, a stacked substrate 2 is joined on a heat sink 3, and a semiconductor element 1 is mounted on the stacked substrate 2. A metal wire 7, which is an example of a conductive connection member, is joined to the semiconductor element 1 and is connected to an external terminal 6, a wiring terminal on the stacked substrate, and the like. A case 4 incorporating the external terminal 6 is adhered to the heat sink 3 with an adhesive 8, and the inside of the case 4 is filled with a silicone gel sealing material to form a silicone gel sealing layer 9. An anti-rust agent film 12 is formed so as to cover the exposed portions of the semiconductor element 1, the conductive plates 21a and 21b constituting the stacked substrate 2, and the heat sink 3. Further, an anti-rust agent 11 is distributed in the silicone gel sealing layer 9. The anti-rust agent film 12 and the anti-rust agent 11 in the silicone gel sealing layer 9 are added from above the silicone gel sealing layer 9 and diffused after the sealing and curing by the silicone gel sealing material, resulting in the illustrated configuration. Details will be described later in the explanation of the manufacturing method.

[0019] The semiconductor element 1 is a power chip such as an IGBT (Insulated Gate Bipolar Transistor) or a diode chip, and may be a Si device, or may be a wide-gap semiconductor device such as a SiC device, a GaN device, a diamond device, or a ZnO device. Further, these devices may be used in combination. For example, a hybrid module using a Si-IGBT and a SiC-SBD can be used. The number of semiconductor elements 1 mounted may be one, or a plurality of them may be mounted. The semiconductor element 1 includes a back surface electrode and a front surface electrode (both not shown) that are joined to the stacked substrate 2.

[0020] The laminated substrate 2 can be composed of an insulating substrate 22, first conductive plates 21a and 21b joined to one main surface of the insulating substrate 22 by a conductive bonding layer or the like (not shown), and a second conductive plate 23 joined to the other main surface of the insulating substrate 22 by a conductive bonding layer or the like (not shown). The conductive bonding layer preferably contains silver. As the insulating substrate 22, a material with excellent electrical insulation and thermal conductivity can be used. Examples of materials for the insulating substrate 22 include Al2O3, AlN, and SiN. In particular for high-voltage applications, a material that balances electrical insulation and thermal conductivity is preferred, and AlN and SiN can be used, but the material is not limited to these. As the first conductive plates 21a and 21b and the second conductive plate 23, metallic materials such as Cu and Al with excellent processability can be used. Furthermore, the first conductive plates 21a and 21b and the second conductive plate 23 may be Cu or Al that have been treated with Ni plating or the like for purposes such as rust prevention. The first conductive plates 21a, 21b and the second conductive plate 23 are generally used with a thickness of approximately 0.15 to 0.8 mm. Methods for arranging the first conductive plates 21a, 21b and the second conductive plate 23 on the insulating substrate 22 include direct copper bonding and active metal brazing. A typical brazing material is an Ag alloy. An Ag alloy may be an alloy containing 50% by mass or more of Ag, and specifically, Ag-Cu-Zn alloys are examples, but it is not limited to a specific composition. The brazing material has an exposed portion and a portion that is in contact with the silicone gel encapsulation layer 9. In laminated substrates manufactured by direct bonding, there may be no conductive bonding layer (not shown).

[0021] In the illustrated embodiment, two first conductive plates 21a and 21b are bonded discontinuously on an insulating substrate 22. Specifically, the two first conductive plates 21a and 21b are arranged separately in such a manner that the insulating substrate 22 is exposed. The distance (pitch) between the two first conductive plates 21a and 21b may be, for example, about 0.5 to 1.5 mm, but is not limited to a specific distance depending on the specifications of the semiconductor device. Generally, the narrower the pitch, the greater the risk of short circuits due to corrosion. However, according to this embodiment, even in semiconductor devices with a relatively narrow pitch, the corrosion prevention effect can be achieved by forming a rust-preventive coating 12. In other embodiments, there may be cases where only one first conductive plate is bonded to the insulating substrate, or where three or more first conductive plates are bonded.

[0022] In the illustrated embodiment, a metal wire 7, serving as a conductive connecting member, is joined to the front electrode of the semiconductor element 1. Aluminum wire can be used as the metal wire. Depending on the specifications of the semiconductor device, the metal wire may not be present, and other conductive connecting members such as lead frames or metal pins (implant pins) may function similarly (not shown). In some cases, lead frames or metal pins may be joined in addition to the metal wire. The lead frame may be made of a metal such as copper or a copper-containing alloy. A Ni or Ni alloy layer, or a Cr or Cr alloy layer, may be formed on the surface of the lead frame by a plating method, and it may also have a rust-preventive coating applied during the manufacturing process. In this case, the thickness of the Ni or Ni alloy layer, or the Cr or Cr alloy layer, can be approximately 20 μm or less. The lead frame can be joined to the front electrode of the semiconductor element 1 by a bonding material layer made of sintered material or solder material.

[0023] The heat sink 3 is bonded to the second conductive plate 23 by a bonding material layer (not shown). The heat sink 3 is made of a metal with excellent thermal conductivity, such as copper or aluminum. Furthermore, the heat sink 3 can be coated with Ni or a Ni alloy to prevent corrosion. The heat sink 3 conducts heat generated by the semiconductor element 1 and transmitted through the laminated substrate 2 to the cooling device. The heat sink 3 itself may also be the cooling device. There may also be embodiments in which the heat sink is absent and the case is directly bonded to the laminated substrate.

[0024] Case 4 houses the silicone gel encapsulant and constitutes the outer surface of the semiconductor device. Case 4 may be made of a thermoplastic resin such as polyphenylene sulfide (PPS) or polybutylene terephthalate (PBT), and can be insert-molded to fix the external terminals 6. The lid 5 is located on the opposite side of the heat sink 3 from the semiconductor element 1 and the silicone gel encapsulant layer 9, and can be fitted into the case without contacting the silicone gel encapsulant layer 9. The lid 5 has the function of preventing the ingress of foreign matter, preventing damage, and protecting components such as wires inside the module. The lid 5 may be made of a thermoplastic resin such as polyphenylene sulfide (PPS) or polybutylene terephthalate (PBT), similar to case 4.

[0025] Case 4 is filled with a silicone gel encapsulant to form a silicone gel encapsulation layer 9. The silicone gel encapsulation layer 9 insulates and encapsulates the components of a semiconductor device, including the semiconductor element 1, metal wire 7, laminated substrate 2, external terminals 6, and heat sink 3, which may include metal components. Silicone gel encapsulants are preferred because they have a stress-relieving effect against vibration and thermal stress, and they have high insulating properties. However, compared to encapsulants made of thermosetting resins such as epoxy resin, they have a tendency to permeate sulfur-containing gases such as H2S and moisture, which can cause corrosion of metal components including Cu and Ag. Therefore, corrosion is a significant problem in semiconductor devices encapsulated with silicone gel encapsulants. In this embodiment, corrosion is suppressed by a rust-preventive coating, realizing a semiconductor device that combines the advantages of silicone gel encapsulants with corrosion resistance.

[0026] The silicone gel encapsulant constituting the silicone gel encapsulant layer 9 comprises a silicone gel and optionally an inorganic filler. The thickness of the silicone gel encapsulant layer 9 is generally 20 mm or less, and may be, for example, 3 mm to 15 mm. If it is too thick, it may take a long time to form the rust inhibitor film, and if it is too thin, sufficient insulating sealing may not be possible.

[0027] The silicone gel (cured product) is an organosilicon polymer whose main chain is composed of siloxane bonds. A silicone polymer with an elastic modulus of 100 MPa or less and a penetration degree (1 / 10 mm) of 15 to 150 is preferably used. More preferably, the penetration degree is 30 to 110. The silicone gel generally contains a main component (A) and a crosslinking agent (B), and may optionally contain a catalyst, additives, and an organic solvent. In some embodiments, the crosslinking agent (B) may be present in an amount of 5 to 20 parts by mass per 100 parts by mass of the main component (A). Both a one-component type containing both the main component (A) and the crosslinking agent (B), and a two-component type containing the main component (A) and the crosslinking agent (B) separately, can be used.

[0028] The main component (A) is composed of the following units (CH2=CH)SiO 1.5 , R(CH2=CH)SiO, R2(CH2=CH)SiO 0.5 , and RH(CH2=CH)SiO 0.5 It comprises one or more structural units selected from the group consisting of (where R is a hydrocarbon group bonded to Si), and further RSiO 1.5 , R2SiO, R3SiO 0.5It may be an organopolysiloxane that may contain one or more structural units selected from the group consisting of (where R is a hydrocarbon group bonded to Si). In certain embodiments, the main agent may comprise one or more of the same or different types of the above structural units such that, on average, each molecule of the main agent contains, for example, 1.5 or more, preferably 2 to 5 vinyl groups bonded to Si atoms. The molecular structure of the polysiloxane may be linear, branched, or cyclic, but is more preferably linear in order to smoothly proceed with the curing reaction by addition polymerization. The hydrocarbon group R bonded to Si is not particularly limited and can be independently selected from aliphatic saturated hydrocarbon groups such as methyl and ethyl groups, aromatic hydrocarbon groups such as phenyl groups, etc. Particularly, methyl and phenyl groups are preferred for R. This is because methylphenyl silicone is less likely to be affected by re-crosslinking caused by the rust inhibitor after curing, and there is little risk of reducing the heat resistance of the silicone gel sealing layer 9 due to re-crosslinking. It is speculated that the re-crosslinking after curing is due to the action of the rust inhibitor on the methyl groups present in the side chains of the silicone gel molecular structure at high temperatures, promoting re-crosslinking. It is not preferable to make all R phenyl groups because the dielectric breakdown voltage of the silicone gel obtained by curing the organopolysiloxane decreases.

[0029] The crosslinking agent (B) contains one or more structural units selected from the group consisting of the following units HSiO 1.5 , RHSiO, RH2SiO 0.5 , R2HSiO 0.5 (where R is a hydrocarbon group bonded to Si), and further 、 RSiO 1.5 , R2SiO, and R3SiO 0.5The organic polysiloxane may contain one or more structural units selected from the group consisting of (where R is a hydrocarbon group that is independently bonded to Si). In one embodiment, the crosslinking agent may contain one or more identical or different types of the above structural units such that each molecule of the crosslinking agent contains an average of, for example, 1.5 or more, preferably 2 to 5, H groups bonded to Si atoms. The molecular structure may be linear, branched, or cyclic, but a linear structure is more preferable for smooth curing reactions by addition polymerization. The hydrocarbon group R that is bonded to Si is not particularly limited and can be independently selected from aliphatic saturated hydrocarbon groups such as methyl groups and ethyl groups, aromatic hydrocarbon groups such as phenyl groups, etc. Methyl groups and phenyl groups are particularly preferred for R. This is because methylphenyl silicone is less susceptible to re-crosslinking caused by rust inhibitors after curing, and there is less risk of reducing the heat resistance of the silicone gel sealing layer 9 due to re-crosslinking. Furthermore, it is presumed that the re-crosslinking after curing is due to the action of a rust inhibitor on the methyl groups present in the side chains of the silicone gel molecular structure at high temperatures, thereby promoting re-crosslinking. Replacing all R groups with phenyl groups is undesirable because it lowers the dielectric strength of the silicone gel cured from organic polysiloxane.

[0030] The catalyst used in the present invention is not particularly limited, and conventionally known platinum compounds or rhodium compounds soluble in organic solvents can be used. Specifically, examples include, but are not limited to, chloroplatinic acid, alcohol-modified chloroplatinic acid, and chloroplatinic acid-vinylsiloxane complexes.

[0031] As additives used in the present invention, metal oxides can be used to improve heat resistance. Specifically, examples include, but are not limited to, titanium oxide, iron oxide, hydrated cerium oxide, and hydrated zirconium oxide.

[0032] Examples of organic solvents used in the present invention include aliphatic alcohols such as methanol, ethanol, 2-propanol, and butanol; aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic or alicyclic hydrocarbons such as n-pentane, n-hexane, and cyclohexane; and halogenated hydrocarbons such as dichloromethane, chloroform, carbon tetrachloride, trichloroethane, trichloroethylene, and fluorinated hydrocarbons.

[0033] It is preferable to use an addition-type silicone gel for the silicone gel encapsulation layer 9. An addition-type silicone gel is a silicone resin obtained by an addition reaction between an unsaturated hydrocarbon group bonded to a silicon atom and a hydrosilyl group in the presence of a catalyst. The platinum catalyst used in addition-type silicones can have its curing stopped or inhibited by compounds containing nitrogen, sulfur, tin, phosphorus, etc. For example, benzotriazole (BTA), a well-known rust inhibitor, is a nitrogen compound and acts as a curing inhibitor. In addition, tin catalysts are sometimes used as curing catalysts for condensation-type silicones, and condensation-type silicones using these catalysts will have their curing inhibited compared to addition-type silicones.

[0034] The silicone gel is preferably hard with a high degree of crosslinking from the viewpoint of stress relaxation and insulation. This is because re-crosslinking by rust inhibitors is less likely to occur. Specifically, a penetration degree of 100 [1 / 10 mm] or less is preferred, and a penetration degree of 60 [1 / 10 mm] or less is more preferred in order to protect wiring members such as wires from vibration, etc. However, if it is too hard, the impact resistance of the silicone gel sealing layer 9 will be impaired, so the lower limit of the penetration degree is preferably 20 [1 / 10 mm] or more. The degree of crosslinking of the silicone gel can be adjusted as appropriate by selecting the starting material, adjusting the mixing ratio of the main agent and the crosslinking agent, etc.

[0035] Generally, it is not advisable to use one-component condensation reaction type silicones as silicone gel encapsulants. Condensation reaction type silicones may include one-component curable resins obtained by a condensation reaction between a compound having hydrolyzable groups such as alkoxy or acetoxy groups bonded to silicon atoms and water in the atmosphere, or two-component curable resins obtained by a condensation reaction between a compound having hydrolyzable groups such as alkoxy or acetoxy groups bonded to silicon atoms and a compound having a silanol group. The curing reaction of one-component curable resins generally requires moisture in the air, and in the formation of relatively thick layers that do not come into contact with air, the curing reaction may not proceed sufficiently. As described above, the internal encapsulation structure of power semiconductor modules is generally about 10 mm deep, and when the thickness of the silicone gel encapsulation layer 9 is 3 mm or more, it may be difficult to achieve internal curing with condensation reaction type silicones. Therefore, one-component condensation reaction type silicones may not be advisable from the viewpoint of curability. Two-component condensation reaction type silicones can be used without problems from the viewpoint of curability. Furthermore, condensation-type silicones may have inferior heat resistance compared to addition-type silicones. This is because, in condensation-type silicones, if condensation reaction by-products such as alcohols and oximes generated during curing remain in the cured product, the active hydrogen of these compounds cleaves the main chain siloxane bonds in the presence of the condensation catalyst. This phenomenon is due to the ionic properties of siloxane bonds. On the other hand, addition-type silicones do not generate by-products during the curing process, so they are less prone to polysiloxane chain cleavage and show less change in physical properties. Also, condensation-type silicones have high hardness, which can put stress on the wires and may be undesirable. Therefore, it is undesirable to use condensation-type silicone in the sealing layer portion that comes into contact with the semiconductor element 1, the laminated substrate 2, the heat sink 3, and the metal wire 7. However, in semiconductor devices manufactured by the second method described later, a layer of condensation-type silicone about 10 μm to 500 μm thick may be formed on the outermost surface of the silicone gel sealing layer 9 that comes into contact with the air.

[0036] The inorganic filler that may be optionally included in the silicone gel encapsulant may be a metal oxide or metal nitride with high thermal conductivity, and examples include, but are not limited to, fumed silica, crystalline silica, precipitated silica, hollow filler, silsesquioxane, fumed titanium dioxide, magnesium oxide, zinc oxide, iron oxide, aluminum hydroxide, magnesium carbonate, calcium carbonate, zinc carbonate, layered mica, carbon black, diatomaceous earth, and glass fiber.

[0037] Silicone gel encapsulants may contain optional additives, provided they do not impair their properties. Examples of additives include heat-resistant additives, flame retardants, pigments for coloring the encapsulant, plasticizers or silicone elastomers to improve crack resistance, etc., which can be added as appropriate depending on the type of encapsulant, but the types of additives are not limited to these. These optional components and their amounts can be appropriately determined by a person skilled in the art according to the specifications required for the semiconductor device and / or encapsulant.

[0038] The rust inhibitor film 12 is a coating layer derived from a rust inhibitor. The rust inhibitor film 12 is formed on the contact surfaces of the semiconductor element 1, the laminated substrate 2, and optionally on conductive connecting members such as a heat sink 3, metal wires 7, solder joint layers, and brazing materials with the silicone gel encapsulation layer 9. The rust inhibitor film 12 may be a discrete layer as shown in the figure, and depending on the manufacturing method described later, there may be areas where the layer is not partially formed. On the surface of metal members such as conductive plates and heat sinks, the rust inhibitor film 12 may be a layer formed by partially chemical bonding between the metal constituting the metal member and the rust inhibitor. Although not shown in the figure, in semiconductor devices provided with conductive connecting members such as lead frames and metal pins, the rust inhibitor film is similarly formed on the contact surfaces between these and the silicone gel encapsulation layer 9.

[0039] As a rust inhibitor, commercially available volatile rust inhibitors for metals such as copper and silver may be used. For example, benzotriazole (BTA) or its derivatives are examples, but are not limited to these. Specifically, dicyclohexylammonium nitride (DICHAN), diisopropylammonium benzoate (DIPA·BA), cyclohexylamine benzoate (CHA·BA), dicyclohexylammonium cyclohexane carboxylate (DICHA·CHC), dicyclohexylammonium benzoate (DICHA·BA), monoethanolamine benzoate (MEA·BA), cyclohexylamine cyclohexane carboxylate (CHA·CHC), dicyclohexylammonium acrylate (DICHA·AA), cyclohexylamine acrylate (CHA·AA), and dicyclohexylammonium salicylate (DICHA·SA) can be used, but are not limited to these. Any commercially available and known rust inhibitor with rust-preventive properties can be used.

[0040] For example, if a metal component such as a conductive plate contains copper or a copper alloy, and the rust inhibitor is BTA or a derivative thereof, the rust inhibitor coating 12 is a benzotriazole copper salt coating, and benzotriazole and Cu 1+ , or benzotriazole and Cu 2+ This forms a polymer compound. The presence of such a polymer compound can be confirmed by measuring the amount of nitrogen atoms in a survey scan spectrum of the surface of the first conductive plate 21a, 21b, the second conductive plate 23, or the heat sink plate 3 using X-ray photoelectron spectroscopy. Alternatively, it can be confirmed by measuring the amount of decomposition products (fragments) caused by the rust inhibitor film using time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0041] The rust inhibitor 11 exists as a rust inhibitor film 12 at the interface between the silicone gel encapsulation layer 9 and the metal component, as well as dispersed within the silicone gel encapsulation layer 9. The rust inhibitor 11 in the silicone gel encapsulation layer 9 usually does not form polymer compounds and does not react with the silicone gel, existing as a single compound. The rust inhibitor 11 may be dispersed almost uniformly throughout the silicone gel encapsulation layer 9, or it may not be present in certain locations. Although the concentration of the rust inhibitor may be high near the coating layer described later, after diffusion equilibrium, the rust inhibitor is generally not localized at the contact surface between the silicone gel encapsulation layer 9 and the atmosphere.

[0042] With the miniaturization of semiconductor devices in recent years, for example, in the semiconductor device shown in Figure 1, the first conductive plate 21a and the first conductive plate 21b are sometimes placed in close proximity, which has led to the problem of migration due to corrosion. Here, "close proximity" refers to a case where the distance between the first conductive plate 21a and the first conductive plate 21b is approximately 1.0 mm or less. With this embodiment, the formation of a rust-preventive coating 12 can suppress corrosion in the vicinity between closely spaced metal components. More specifically, when sulfur-containing gases or water reach metal components containing silver or copper, needle-shaped compounds mainly composed of sulfides such as silver sulfide (AgS) or copper sulfide (CuS) may be formed. For example, in Figure 1, sulfides may be formed at the right end of the first conductive plate 21a, and these sulfides may grow further to the right along the insulating substrate 22, reaching the left end of the first conductive plate 21b. Since sulfides are conductive, a short circuit may occur between the first conductive plates 21a and 21b, leading to dielectric breakdown. According to this embodiment, it is possible to prevent such dielectric breakdown.

[0043] In this embodiment, the semiconductor device can improve the reliability of the semiconductor device by suppressing oxidation and corrosion of the metal component through the rust-preventive coating 12 formed at the interface between the silicone gel encapsulation layer 9 and the metal component.

[0044] [Second Embodiment: Method for Manufacturing a Semiconductor Device] The present invention relates to a method for manufacturing a semiconductor device, according to a second embodiment. The method for manufacturing a semiconductor device according to this embodiment is the method for manufacturing a semiconductor device according to the first embodiment, and includes the following steps. (a) Process of mounting semiconductor elements on a multilayer substrate (b) A step of sealing the laminated substrate and the semiconductor element with a silicone gel encapsulant to obtain a cured silicone gel encapsulant layer. (c) A step of forming a coating layer containing a rust inhibitor on a cured silicone gel encapsulation layer.

[0045] The method for manufacturing a semiconductor device according to this embodiment will now be described with reference to Figure 2. Figure 2 is a diagram illustrating the method for manufacturing a semiconductor device, and shows the apparatus at the stage when step (c) described above has been completed.

[0046] In step (a), the semiconductor element 1 is bonded to the laminated substrate 2. The laminated substrate 2 and the heat sink 3 are also bonded, and the case 4 is attached to the heat sink 3 with adhesive 8. Conductive bonding materials such as sintered material or solder can be used for bonding. Furthermore, wiring is performed using metal wire 7. In this step, each component can be assembled using a standard method, employing appropriate conditions depending on the specifications of the semiconductor element 1 and the laminated substrate 2.

[0047] In step (b), the laminated substrate and semiconductor elements are sealed with a silicone gel encapsulant, and the silicone gel encapsulant is cured to obtain a cured silicone gel encapsulant layer 9. The silicone gel encapsulant used in step (b) preferably contains an addition reaction type silicone gel starting material (e.g., a main component and a crosslinking agent), optionally an inorganic filler, and optionally various additives. The reaction conditions for the silicone gel can be appropriately adjusted depending on the specifications of the starting material compound. Generally, the starting material compound and catalyst are injected into a case and then degassed under reduced pressure. Then, they can be cured by heating at 80°C to 150°C for about 1 to 2 hours. However, the degassing and curing reactions are not limited to these conditions.

[0048] In step (c), a coating layer 10 containing a rust inhibitor is formed on the cured silicone gel encapsulating layer 9. In step (c), there may be two embodiments depending on the composition of the coating layer 10. The first and second embodiments will be described below.

[0049] [First aspect] The coating layer 10 of the first embodiment typically consists substantially of a rust inhibitor. The coating layer 10 of the first embodiment is formed using an aqueous solution in which the rust inhibitor is dissolved in a solvent such as distilled water. By applying the aqueous solution onto the cured silicone gel sealing layer 9 and drying it, a coating layer 10 consisting substantially of a rust inhibitor can be formed. The concentration of the rust inhibitor when dissolved in the solvent is not particularly limited, but it can be determined so that the coating layer after the solvent has evaporated is about 10 μm to 500 μm thick. The application method is not particularly limited, but examples include application using a dispenser or spraying.

[0050] The coating layer 10 can be formed in such a manner that it substantially covers the entire surface of the cured silicone gel encapsulation layer 9. Alternatively, although not shown in the figures, it can be partially arranged in such a manner that it does not cover the entire surface of the silicone gel encapsulation layer 9, leaving the silicone gel encapsulation layer 9 exposed. In this case, it can be placed on the surface portion of the silicone gel encapsulation layer 9 that is closest in straight line to the location of the metal member on which the rust-preventive coating 12 is desired. This is because the rust-preventive compound constituting the coating layer 10 diffuses through the interior of the silicone gel encapsulation layer 9 and reaches the surface of the metal members constituting the semiconductor element 1, the laminated substrate 2, and the heat sink 3. The metal members on which the rust-preventive coating 12 is desired may be, for example, the semiconductor element 1, the first conductive plates 21a and 21b, the second conductive plate 23, and the heat sink 3, or they may be brazing materials or solder materials used to join them. Therefore, for example, when the semiconductor device in the manufacturing process shown in Figure 2 is viewed from the direction of the lid 5 with the heat sink 3 as the bottom surface, the coating layer 10 can be partially placed on the surface of the silicone gel encapsulation layer 9 in areas that overlap with the arrangement of the semiconductor element 1, and / or areas that overlap with the arrangement of the first conductive plates 21a, 21b and the second conductive plate 23, and / or areas that overlap with the arrangement of the heat sink 3.

[0051] The formation of the coating layer 10 according to the first embodiment has the advantage that, in particular, because the coating layer is thin, thermal stress is less likely to occur between it and the silicone gel sealing layer 9. In addition, the rust inhibitor has the advantage of diffusing easily because it is in direct contact with the silicone gel sealing layer.

[0052] [Second aspect] The coating layer 10 of the second embodiment is formed from a silicone resin composition containing a rust inhibitor and a silicone gel. The coating layer 10 of the second embodiment can be formed by mixing a rust inhibitor with a matrix resin containing a silicone gel before curing, applying it onto the silicone gel sealing layer 9 cured in step (b), and then heat curing it.

[0053] It is preferable to use a condensation reaction type silicone for the matrix resin. This is because condensation reaction type silicones are less affected by curing inhibition by rust inhibitors. The condensation reaction type silicone may be a one-component curing type resin or a two-component curing type resin, but it is preferable that the resin undergoes curing reaction at room temperature. In the case of a two-component curing type resin, it is preferable to use acetoxy groups, alkoxy groups, ketoxime groups, etc., as the hydrolyzable groups. Furthermore, it is preferable that the siloxane skeleton after curing contains methylphenyl silicone, similar to the siloxane skeleton constituting the silicone gel encapsulation layer 9. The content of the rust inhibitor is preferably 0.02% to 0.2% by mass, when the total mass of the rust inhibitor and the matrix resin is taken as 100%. If the content of the rust inhibitor is less than 0.02% by mass, it may be difficult to form a rust inhibitor film 12 of sufficient thickness to prevent corrosion in the next step, and if it exceeds 0.2% by mass, it may promote the re-crosslinking of the silicone gel encapsulation layer 9 after curing. Furthermore, the cured coating layer 10 of the second embodiment preferably has a rubber hardness of 30 to 50, as measured using a durometer type A according to JIS K 6253 (ISO 7619). Additionally, using an addition-reaction type silicone gel as the matrix resin also provides corrosion protection. However, the coating layer 10 does not harden and remains fluid. Therefore, when semiconductor devices are arranged vertically, components constituting the coating layer may leak to the outside. Vertical arrangement refers to arranging semiconductor elements or laminated substrates so that their main surfaces are parallel to the vertical direction.

[0054] In the second embodiment, the coating layer 10 is preferably formed to a thickness of about 0.1 mm to 0.3 mm. Here, thickness refers to the thickness after the curing reaction. The curing reaction can be carried out at room temperature and atmospheric pressure.

[0055] In the second embodiment, the placement of the coating layer 10 on the cured silicone gel encapsulation layer 9 can be the same as in the first embodiment. In the formation of the coating layer 10 according to the second embodiment, because the silicone resin composition is viscous, the coating layer 10 can be placed even on the uneven surface. Therefore, it is preferable to use the second embodiment when the upper surface of the silicone gel encapsulation layer 9 has an uneven surface. In addition, there is the advantage that the amount of rust inhibitor supplied can be adjusted by adjusting the film thickness of the coating layer 10.

[0056] By forming the coating layer 10 of the first or second embodiment in step (c), the rust inhibitor can be diffused into the cured silicone gel sealing layer 9, thereby forming a rust inhibitor film.

[0057] After the completion of step (c), an optional step may be performed to diffuse the rust inhibitor and form a rust inhibitor film. In this step, the entire apparatus, including the coat layer 10 obtained in step (c) and the silicone gel sealing layer 9, is left to stand for a predetermined time in order to diffuse the rust inhibitor in the coat layer 10 and to more reliably form a rust inhibitor film. The standing conditions can be 5°C to 150°C, preferably 20°C to 80°C, for at least 48 hours, preferably 5 to 10 days. The rust inhibitor can also diffuse and form a rust inhibitor film even at around room temperature of 20 to 30°C. The relative humidity (RH) can be, for example, 45% to 85%, preferably 45% to 55%, but is not particularly limited. By allowing the device to stand under these conditions, the rust inhibitor in the coating layer 10 diffuses from the coating layer 10 through the cured silicone gel encapsulation layer 9, reaching the semiconductor element 1, the laminated substrate 2, or the metal component including the heat sink 3, thereby forming the rust inhibitor film 12 shown in Figure 1. When diffusion equilibrium is reached, the rust inhibitor 11 is also distributed within the cured silicone gel encapsulation layer 9. Note that if the standing temperature is too high, deterioration of the encapsulating material may occur, so the above range is preferable.

[0058] In the manufacturing method according to the first embodiment, after step (c), or after the execution of an optional step, the coating layer 10 consisting of the rust inhibitor has substantially disappeared from the surface of the cured silicone gel encapsulation layer 9 and no residue remains. The rust inhibitor that constituted the coating layer 10 in step (c) has diffused into the silicone gel encapsulation layer 9 and has reached approximately diffusion equilibrium. Therefore, the concentration of the rust inhibitor on the outermost surface of the silicone gel encapsulation layer 9 is substantially the same as the concentration of the rust inhibitor in the silicone gel encapsulation layer 9.

[0059] On the other hand, in the manufacturing method according to the second embodiment, after the execution of step (c), a silicone resin layer derived from the coating layer 10 remains on the surface of the cured silicone gel encapsulation layer 9, and this layer may contain a rust inhibitor, but the concentration of the rust inhibitor is lower compared to when the coating layer 10 was first formed. The silicone resin layer derived from the coating layer 10 refers to a resin layer that, after being formed as a coating layer containing a predetermined amount of rust inhibitor in step (c), has generally decreased in composition due to the diffusion of the rust inhibitor. Similar to the first embodiment, the rust inhibitor contained in the coating layer 10 diffuses into the silicone gel encapsulation layer 9 and has reached approximately diffusion equilibrium. Therefore, the concentrations of rust inhibitor in the silicone gel encapsulation layer 9 and the silicone resin layer derived from the coating layer 10 are about the same, although the concentration of rust inhibitor in the silicone resin layer derived from the coating layer 10 may be higher. When an addition-reaction type silicone gel is used to form the silicone gel encapsulation layer 9 and a condensation-reaction type silicone gel is used to form the coating layer 10, the catalyst is present only in the layer portion derived from the addition-reaction type silicone gel, which may allow for the identification of each layer.

[0060] Conventionally, benzotriazole-based rust inhibitors have been used in the manufacture of semiconductor components by directly applying them to the surface of laminated substrates and lead frames that contain copper or copper alloys as part of the material. However, when these components are sealed with addition-reaction type silicone gels, which are commonly used as encapsulants, there is a problem that the rust inhibitor re-diffuses into the silicone gel, inhibiting the curing of the silicone gel. In contrast, according to the semiconductor device manufacturing method of the present invention, a metal component including a semiconductor element 1, a laminated substrate 2, or a heat sink 3 comes into contact with a silicone gel encapsulant, and a rust inhibitor can be added after the silicone gel encapsulant layer 9 has cured to form a rust inhibitor film 12. Therefore, a rust inhibitor film 12 can be formed on the surface of the metal component without inhibiting the curing characteristics of the silicone gel encapsulant, and corrosion of the metal component can be prevented. [Examples]

[0061] The present invention will be described in more detail below with reference to examples of the present invention. However, the present invention is not limited to the scope of the following examples.

[0062] (1) Manufacturing of power semiconductor test modules A power semiconductor test module, as shown in Figure 1, was manufactured, and high-temperature storage tests and corrosive gas tests were conducted to investigate the heat resistance and corrosion resistance of the silicone gel encapsulation layer 9. The power module used for evaluation was free of internal obstacles such as case beams, and the silicone gel encapsulation layer 9 was exposed flat across its entire surface (silicone gel encapsulation layer 9 surface: 100 × 52 mm). The spacing between the two first conductive plates 21a and 21b (insulation pattern width) was 800 μm. The composition and preparation methods of the silicone gel encapsulation layer 9 and coating layer 10 for each example and comparative example are as follows.

[0063] [Example 1] The silicone gel encapsulation layer 9 was made using a one-component addition-reaction type silicone (dimethyl silicone, 100 parts by mass of main component, 8 parts by mass of crosslinking agent). The penetration was 55 [1 / 10 mm]. The silicone gel encapsulation layer 9 was formed by injecting 26 ml of the starting material for the silicone gel encapsulant into case 4, degassing under reduced pressure of 0.2 atm for 3 minutes, and then heat curing at 125°C for 2 hours (thickness 6.3 mm).

[0064] The coating layer 10 was formed using a one-component curing condensation reaction type silicone containing BTA at a concentration of 0.1% by mass. After forming the silicone gel sealing layer 9, it was applied to the entire surface of the silicone gel sealing layer 9 using a dispenser device (application amount: 2 ml). It was left to stand for 1 hour at 25°C and 50% RH to cure. The thickness of the coating layer 10 after curing was 0.2 mm. Next, to allow the rust inhibitor to diffuse, it was left to stand for another week in an atmospheric environment at a temperature of 25°C and a relative humidity of 50%.

[0065] [Example 2] The silicone gel encapsulation layer 9 was formed in the same manner as in Example 1. For the coating layer 10, a BTA aqueous solution, prepared by dissolving 5% by mass of BTA in distilled water, was applied to the entire surface of the silicone gel encapsulation layer 9 using a dispenser device (application amount: 2 ml). To evaporate the distilled water and diffuse the rust inhibitor, the mixture was left to stand for one week in an atmospheric environment at a temperature of 25°C and a relative humidity of 50%.

[0066] [Example 3] The silicone gel encapsulation layer 9 was formed in the same manner as in Example 1. The coating layer 10 was formed in the same manner as in Example 2, except that the rust inhibitor was changed to DIPA·BA.

[0067] [Example 4] The silicone gel encapsulation layer 9 was formed in the same manner as in Example 1. The coating layer 10 was formed in the same manner as in Example 2, except that the rust inhibitor was changed to DICHA·CHC.

[0068] [Example 5] In the production of the dimethyl silicone for the silicone gel encapsulation layer 9, the silicone gel encapsulation layer 9 and the coating layer 10 were formed in the same manner as in Example 1, except that the degree of crosslinking was changed to set the penetration depth to 40 [1 / 10 mm]. The degree of crosslinking of the silicone gel was adjusted by increasing the proportion of the crosslinking agent relative to the proportion of the main component. In this example, 15 parts by mass of crosslinking agent were used for every 100 parts by mass of the main component.

[0069] [Example 6] The silicone gel encapsulation layer 9 and the coating layer 10 were formed in the same manner as in Example 1, except that a two-component addition-reaction type silicone (methylphenyl silicone) was used in the silicone gel encapsulation layer 9. In preparing the methylphenyl silicone gel, the main component and curing agent were mixed in a mass ratio of 1:1, and the curing conditions were 80°C for 1 hour. The penetration of the methylphenyl silicone gel was 55 [1 / 10 mm].

[0070] [Example 7] The specifications and preparation method for the silicone gel encapsulation layer 9 of the test module in Example 7 were the same as in Example 1. The coating layer used the same one-component addition-reaction type silicone (dimethyl silicone) as the silicone gel encapsulation layer 9. 5% by mass of BTA was added to the silicone gel before curing, and 2 ml was injected into case 4. After degassing under reduced pressure at 0.2 atm for 3 minutes, it was heated at 125°C for 2 hours. The thickness could not be measured because the coating layer did not cure.

[0071] [Comparative Example 1] The test module of Comparative Example 1 had only a single layer of silicone gel encapsulation formed, and no coating layer was formed. In other words, no rust inhibitor was used. The specifications and preparation method of the silicone gel encapsulation layer were the same as in Example 1.

[0072] [Comparative Example 2] The test module in Comparative Example 2 had only a single layer of silicone gel encapsulation formed, and no coating layer was formed. In other words, no rust inhibitor was used. The specifications and preparation method of the silicone gel encapsulation layer were the same as in Example 6.

[0073] [Comparative Example 3] The silicone gel encapsulation layer of the test module in Comparative Example 3 was formed using a condensation-type silicone containing a rust inhibitor. No coating layer was formed. The same condensation-type silicone used for the coating layer in Example 1 was used. BTA was added to the silicone gel before curing at a concentration of 0.1% by mass, and 26 ml was injected into Case 4. It was allowed to stand for 1 hour at 25°C and 50% RH to cure. Then, it was left to stand for another week at 25°C and 50% RH to allow the rust inhibitor to diffuse. The thickness of the silicone gel encapsulation layer could not be measured because it was not sufficiently cured.

[0074] [Comparative Example 4] In the test module of Comparative Example 4, a coating layer (substrate coating layer) was formed in contact with and covering the semiconductor element, the laminated substrate, and the heat sink, and a silicone gel encapsulation layer was formed on the substrate coating layer. The substrate coating layer was applied by adding BTA at a concentration of 0.1 mass% to condensation reaction type silicone before curing, and applying it using a dispenser device to cover the exposed surfaces of the semiconductor element 1, the laminated substrate 2, and the heat sink 3 (application amount: 2 ml). After application, it was left to stand at 25°C under 50% RH for 1 hour to obtain a cured state (thickness 0.2 mm (after curing)). On the cured substrate coating layer, a silicone gel encapsulation layer was formed using the same addition reaction type silicone (dimethyl silicone) with a penetration degree of 55 [1 / 10 mm] as in Comparative Example 1. 26 ml of dimethyl silicone before curing was injected into the case, degassed under reduced pressure at 0.2 atm for 3 minutes, and then heat curing was performed at 125°C for 2 hours. The thickness could not be measured because the upper silicone gel encapsulation layer had not cured sufficiently.

[0075] [Comparative Example 5] In the test module of Comparative Example 5, the procedure was the same as in Comparative Example 4, except that the coating layer on the substrate was formed with an aqueous solution containing BTA. An aqueous BTA solution, prepared by dissolving 5% by mass of BTA in distilled water, was applied using a dispenser device to cover the exposed surfaces of the semiconductor element, laminated substrate, and heat sink (application amount: 2 ml). The distilled water was allowed to stand for 1 hour at 25°C and 50% RH to dry. The thickness after drying was 20 μm. A silicone gel encapsulation layer was formed on the substrate coating layer in the same manner as in Comparative Example 4. The thickness could not be measured because the upper silicone gel encapsulation layer was not sufficiently cured.

[0076] The test module was evaluated as follows: (1) Corrosion resistance evaluation: Measurement of corrosion growth in corrosion gas tests A DC voltage of 1000V was applied to the test module for 2000 hours in an environment with 0.005% hydrogen sulfide by mass, a temperature of 85°C, and a humidity of 85% RH. After the voltage was applied, corrosion growth between the first conductive plates 21a and 21b (copper circuit board patterns) on the laminated substrate of the test module was observed with an optical microscope, and the length of the corrosion growth was measured. The evaluation criterion was that the corrosion growth was less than or equal to half the pattern width of the first conductive plate (less than or equal to 400 μm).

[0077] (2) Evaluation of high-temperature degradation of the silicone gel encapsulation layer High-temperature degradation was evaluated by the retention rate of the hardness (penetration) of the silicone gel encapsulation layer after the high-temperature storage test. The high-temperature storage conditions were 200°C for 1000 hours. A sample was considered acceptable if the penetration after the high-temperature storage test was 50% or more of the initial penetration before the test (penetration retention rate of 50% or more). This standard is based on the UL (Underwriters Laboratories Inc.) standard UL746B "Long-term characterization of polymer materials," which determines material degradation when the material properties fall to half or less of the initial values. Penetration D is an evaluation value based on JIS K2207, where a needle of a specified weight is inserted perpendicularly into the sample, and the depth of penetration represents the hardness of the sample. A penetration value of 1 / 10 mm is considered to be 1. The retention rate can be expressed by the following formula. In the formula, D0 represents the initial value of the penetration, and Dx represents the penetration after the high-temperature storage test; a larger number indicates a softer material. Retention rate=(D0-D x ) / D0×100

[0078] (3) Evaluation of the insulating properties of the sealing layer The following conditions were used to determine whether the silicone gel encapsulation layer maintained its insulating properties. After the high-temperature storage test described above, an insulation withstand voltage test was performed to check for short circuits, thereby determining whether the silicone gel encapsulation layer maintained its insulation properties. The insulation withstand voltage test conditions involved applying AC 4.0kV between conductive plates 21a and 21b and heat sink 3 for 1 minute while measuring the current value. If the current value exceeded 5mA even once, it was determined to be a short circuit (insulation failure). If the current value was 5mA or less, it was determined that the insulation properties were maintained and the test was deemed to pass.

[0079] Tables 1 and 2 show the evaluation results for the examples and comparative examples. Note that in the manufacturing of the comparative example apparatus, some do not have the silicone gel encapsulation layer and coating layer configuration shown in Figure 2; therefore, the layer in contact with the semiconductor element and multilayer substrate is referred to as the lower layer, and the layer in contact with the atmosphere is referred to as the upper layer.

[0080] [Table 1]

[0081] [Table 2]

[0082] (4) Reference example, analysis by X-ray photoelectron spectroscopy To confirm the presence of a rust inhibitor on the conductive plate constituting the laminated substrate, surface analysis of a conductive plate formed to mimic the semiconductor device of the embodiment of the present invention was performed using X-ray photoelectron spectroscopy. Figure 3 is a diagram illustrating the sample preparation method using X-ray photoelectron spectroscopy. A copper plate 121 was embedded in epoxy resin 100, and the surface of the copper plate 121 was polished with #1000 abrasive paper. Tape 104 was wrapped around the outer circumference of the epoxy resin 100, and silicone gel (dimethyl silicone) was injected and cured to form a silicone gel encapsulation layer 109. The thickness of the cured silicone gel encapsulation layer 109 was 6.3 mm. Next, a condensation reaction type silicone resin composition containing 0.1 mass% of BTA was applied to the cured silicone gel encapsulation layer 109 to form a coat layer 110. The thickness of the cured coat layer 110 was 0.2 mm (Figure 3(a)). This was cured at 25°C and 50% RH for 1 hour. To allow the cured BTA111 to diffuse, the sample was left to stand for another week at 25°C and 50% RH (Figure 3(b)). Next, the silicone gel encapsulation layer 109 and the coating layer 110 were removed with tweezers to obtain a sample for measurement (with BTA) (Figure 3(c)). In the preparation of the sample corresponding to the comparative example (without BTA), no coating layer was formed.

[0083] Component analysis of the copper plate surface was performed on the two types of samples obtained. Specifically, analysis was performed using X-ray photoelectron spectroscopy (XPS) with a Thermo Fisher Scientific K-Alpha+. The irradiation X-rays were single-crystal spectrometer Al Kα, with an X-ray spot diameter of 400 μm and a neutralization electron gun. Survey scan spectra were obtained for the sample prepared under the conditions of the example (with BTA) and the sample prepared under the conditions of the comparative example (without BTA) (not shown). Table 3 shows the estimated state ratios and assignment results of photoelectrons on the copper plate surface based on these survey scan spectra. The binding energies are shown normalized to 284.6 eV for CC and CH. In the table below, - means not detected, and * means trace detection (not calculated as a state ratio). State ratios are expressed as atomic percentages (Atomic%).

[0084] [Table 3]

[0085] Compared to the comparative example sample (without BTA) in which no coating layer was formed on the silicone gel encapsulation layer, the sample corresponding to the example (with BTA) in which a coating layer was formed showed a higher level of nitrogen detection. This is thought to be due to the nitrogen contained in BTA, and as mentioned above, it suggests that the rust inhibitor BTA reacted with the copper plate surface to form a metal-BTA protective film.

[0086] [Evaluation results of the examples] In Examples 1-7, the penetration retention rate after high-temperature storage tests was above the acceptable standard in all cases. However, compared to Comparative Examples 1 and 2, which did not have a coating layer, the penetration retention rate was lower in all cases. This is presumed to be due to the re-crosslinking effect of the rust inhibitor diffused into the silicone gel encapsulation layer 9, as mentioned above. This effect could be reduced by increasing the degree of crosslinking (lowering the penetration) of the encapsulation gel applied, thereby reducing the opportunity for re-crosslinking (Example 5). Furthermore, in Example 6, adopting a methylphenyl structure as the main chain structure of the encapsulation gel reduced high-temperature degradation. In Example 7, the coating layer did not harden and remained fluid. Therefore, when semiconductor devices are arranged vertically, there is a possibility that the coating layer may leak to the outside, which may limit the methods of use.

[0087] Furthermore, in the examples, observations of the laminated substrate after the corrosion gas test showed that the length of the corrosion growth was below the judgment criterion. This effect is thought to be due to the rust inhibitor diffusing from the coating layer 10 formed on the silicone gel sealing layer 9, reaching the laminated substrate 2, and reacting with the silver and copper of the laminated substrate 2 to form a protective film. In the high-temperature and high-humidity test at 85°C and 85%RH, Examples 1 to 7 showed approximately 30% improved reliability compared to Comparative Example 1 of the conventional example, and also showed improved moisture resistance. The reliability was evaluated by applying 2kV under the above conditions and measuring the time until the leakage current exceeded the specified current.

[0088] In all of Examples 1 to 7, the coating layer 10 is applied on the silicone gel encapsulation layer 9 during manufacturing. With this method, the coating layer 10 does not come into direct contact with the laminated substrate 2 on which the semiconductor element 1 is mounted or the heat sink 3, and therefore does not reach high temperatures. As a result, the required mechanical properties and heat resistance levels for the coating layer 10 material are reduced. Furthermore, since it is formed on a generally flat surface on the silicone gel encapsulation layer 9, the process is simpler than directly applying the coating layer to the laminated substrate 2 on which the semiconductor element 1 is mounted or the heat sink 3.

[0089] [Evaluation results of comparative examples] In Comparative Examples 1 and 2, the penetration retention rate after high-temperature storage tests was above the acceptable standard in both cases. However, in the corrosion gas test, a short-circuit failure occurred before 2000 hours were reached, and the test was interrupted. Observation of the conductive plate revealed corrosion growth traversing the insulating pattern, and traces of burning were observed. In Comparative Example 3, hardening was not achieved inside the silicone gel encapsulation layer, and the test was stopped. In many power semiconductor modules, a film thickness of 5 mm or more is sometimes required to form the silicone gel encapsulation layer necessary for reliability. Condensation reaction type silicone reacts with moisture in the air, and hardening progresses from the surface exposed to the air. However, if the layer is thick, moisture cannot penetrate into the interior, and hardening does not occur. Therefore, it is difficult to use condensation reaction type silicone containing rust inhibitors as an encapsulation layer. In Comparative Example 3, the film thickness was too thick, and the condensation reaction type silicone did not harden. On the other hand, it is possible to form a 2 mm encapsulation layer by repeating the process of forming and hardening a thin layer of about 0.2 mm 10 times, but this is not practical in terms of manufacturing costs due to the increased time and man-hours. Furthermore, bubbles and other particles tend to form between each layer, which is undesirable from an insulating standpoint. In Comparative Example 4, the silicone gel formed on the coating layer containing BTA did not harden sufficiently, remaining fluid, and the test was stopped. It is presumed that even without direct addition of BTA, BTA diffused from the coating layer to the sealing layer, causing the silicone gel to harden, similar to Comparative Example 1. In Comparative Example 5, water containing BTA was applied to the substrate, and an attempt was made to harden the silicone gel on top, but hardening was not achieved, and the test was stopped. It is presumed that BTA diffused into the sealing layer, causing hardening inhibition. Comparative Examples 3 to 5 showed corrosion suppression, but the sealing layer did not harden and therefore did not have a stress-relieving effect against vibration and thermal stress. Also, because it was fluid, the silicone gel of the sealing layer leaked out to the outside, such as when the module was installed vertically, making it impractical. [Explanation of symbols]

[0090] 1 Semiconductor element, 2 Multilayer substrate, 21a, 21b First conductive plate, 22 Insulating substrate, 23 Second conductive plate, 3 Heat sink, 4 Case, 5 Lid, 6 External terminals, 7 Metal wire, 8 Adhesive, 9 Silicone gel sealing layer, 10 Coating layer, 11 Rust inhibitor, 12 Rust inhibitor film

Claims

1. A semiconductor device comprising a semiconductor element mounted on a laminated substrate having an insulating substrate and a conductive plate, and a cured silicone gel encapsulation layer that encapsulates the semiconductor element, A semiconductor device comprising a rust inhibitor coating in contact with the laminated substrate or the semiconductor element, and a rust inhibitor dispersed in the silicone gel encapsulation layer.

2. The semiconductor device according to claim 1, wherein the rust inhibitor comprises benzotriazole or a derivative thereof.

3. The semiconductor device according to claim 1, wherein the conductive plate includes copper or a copper alloy.

4. The semiconductor device according to claim 1, wherein the laminated substrate includes a conductive bonding layer containing silver that bonds the insulating substrate and the conductive plate.

5. A method for manufacturing a semiconductor device according to claim 1, A step of mounting the semiconductor element on the laminated substrate, The process involves sealing the laminated substrate and the semiconductor element with a silicone gel encapsulant to obtain the cured silicone gel encapsulant layer, A method comprising the step of forming a coating layer containing the rust inhibitor on the cured silicone gel encapsulating layer.

6. The method according to claim 5, wherein the step of forming the coating layer includes applying an aqueous solution containing the rust inhibitor onto the cured silicone gel sealing layer and drying it.

7. The method according to claim 5, wherein the step of forming the coating layer includes the step of applying the silicone resin composition containing the rust inhibitor onto the cured silicone gel encapsulating layer.

8. The method according to claim 5, comprising the step of diffusing the rust inhibitor from the coating layer into the cured silicone gel sealing layer to form the rust inhibitor film.

Images