Semiconductor Device

Abstract

To provide a semiconductor device capable of preventing penetration of moisture through cracks even when cracks are generated in a sealing material.SOLUTION: In a semiconductor device in which a semiconductor element 11 mounted on a laminated substrate 12 and a conductive connecting member are sealed with a sealing material, the sealing material includes a sealing layer 20 including a thermosetting resin, which seals a member to be sealed including the laminated substrate 12, the semiconductor element 11, and the conductive connection member, and a protective layer 21 covering the sealing layer and containing silicone rubber, and a value A1 of tensile strength×elongation at break of the sealing layer 20 is smaller than a value A2 of tensile strength×elongation at break of the protective layer 21, and A2 is 1600 MPa or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a semiconductor device, and more particularly to a highly reliable semiconductor device in which peeling or cracking of a sealing material is prevented. [Background technology]

[0002] Power semiconductor modules are widely used in fields that require efficient power conversion. For example, their application is expanding to the power electronics field, such as industrial equipment, electric vehicles, and home appliances. These power semiconductor modules contain switching elements and diodes, and the elements are made of Si (silicon) semiconductors and SiC (silicon carbide) semiconductors. stomach D) Semiconductors are used.

[0003] A power semiconductor module is manufactured by encapsulating a chip made of a semiconductor element and conductive connection members such as a lead frame connected to the chip with an insulating resin encapsulant. The resin encapsulant contains a thermosetting resin and an inorganic filler as main components. The linear expansion coefficient of the resin itself is larger than that of metal members such as the lead frame. Therefore, when the semiconductor module is subjected to a heat cycle or the like, high thermal stress is generated.

[0004] A semiconductor device is known that includes a first sealing material for sealing a semiconductor element and a second sealing material for sealing a wiring member, where the second sealing material is made of silicone gel that is softer than the first sealing material (see Patent Document 1). Patent Document 1 discloses that the semiconductor element is sealed with a hard first sealing material to prevent the semiconductor element from peeling off, and the soft second sealing material reduces thermal stress on the wiring member.

[0005] There is known a semiconductor device in which a semiconductor element is covered with a first sealing resin, and the outside of the first sealing resin is covered with a second sealing resin (see Patent Documents 2 and 3). Patent Documents 2 and 3 disclose that the second sealing resin is made of a silicone resin, an acrylic resin, or the like, which has a smaller elastic modulus than the first sealing resin, thereby preventing peeling between the sealing resin and the member to be sealed, and preventing cracks from occurring in the sealing resin. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication WO2018 / 159678 [Patent Document 2] International Publication WO2013 / 111276 [Patent Document 3] JP 2013-4766 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the sealing structure of conventional power semiconductor modules, when thermal stress is repeatedly applied, the module itself may repeatedly deform (warp, twist, etc.), causing cracks in the sealing resin. When cracks occur near the electrodes, the electrical insulation decreases, and the T j This leads to a problem of reduced power cycle resistance. [Means for solving the problem]

[0008] When the sealing resin itself deteriorates due to heat cycles or moisture absorption, or when cracks or the like occur in the sealing resin due to thermal stress due to heat cycles or power cycles, moisture or corrosive gases that penetrate from the outside through the cracks or the like accelerate peeling or deterioration of the chip and its surroundings, wire breakage due to crack propagation, etc. In particular, when a primer layer is provided on wiring members such as lead frames and wires, or on the surface of a laminated substrate on which a chip is mounted, there are cases in which moisture reacts with the primer, causing problems such as peeling of the primer and poor insulation.

[0009] As a result of extensive research, the inventors have come to the conclusion that by providing a sealing structure with a protective layer having specific physical properties that can prevent moisture from entering through cracks even if cracks occur in the sealing material, it is possible to prevent a decrease in reliability due to peeling, which was not possible with conventional sealing structures, and have completed the present invention.

[0010] That is, according to one embodiment, the present invention provides a semiconductor device in which a semiconductor element and a conductive connection member mounted on a laminated substrate are sealed with a sealing material, the sealing material seals the laminated substrate, the semiconductor element, and the conductive connection member, and includes a sealing layer containing a thermosetting resin, and a protective layer covering the sealing layer and containing a silicone rubber; The present invention relates to a semiconductor device, wherein a value A1 of the tensile strength x elongation at break of the sealing layer is smaller than a value A2 of the tensile strength x elongation at break of the protective layer, and A2 is 1600 MPa or less.

[0011] In the semiconductor device, A1 and A2 have the following relationship: A1 <A2<A1*25 It is preferable that the following is satisfied.

[0012] In the semiconductor device, it is preferable that the protective layer contains an inorganic filler.

[0013] In the semiconductor device, the inorganic filler is preferably a plate-like or flaky inorganic filler.

[0014] In the semiconductor device, the protective layer preferably has a thickness of 20 μm to 1000 μm.

[0015] In the semiconductor device, it is preferable that the thermosetting resin contained in the sealing layer is an epoxy resin, the sealing layer further contains a curing agent for the epoxy resin, and the curing agent is an acid anhydride-based curing agent.

[0016] In the semiconductor device, it is preferable that a primer layer is provided at the interface between the sealing layer and a member to be sealed, which member includes the laminated substrate, the semiconductor element, and the conductive connecting member.

[0017] In the semiconductor device, the primer layer is preferably made of a resin selected from the group consisting of polyamide resin, polyimide resin, and polyamideimide resin. Effect of the Invention

[0018] According to the present invention, a highly reliable semiconductor device can be provided in which, even if a crack occurs in a sealing layer containing a thermosetting resin, the protective layer prevents the intrusion of moisture and suppresses peeling between the sealing layer and the sealed component. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a conceptual cross-sectional view showing a cross-sectional structure of a semiconductor device according to the present invention. [Diagram 2] FIG. 2 is a graph in which the elastic modulus of the protective layer is plotted on the horizontal axis and the power cycle resistance (P / C resistance) of the power semiconductor module after moisture absorption treatment is plotted on the vertical axis. [Diagram 3] FIG. 3 is a graph showing an expanded range of elastic modulus on the horizontal axis up to 400 MPa from FIG. 2, excluding the epoxy resin of Comparative Example 2, Comparative Example 4, and Example 6. [Figure 4] FIG. 4 is a graph in which the tensile strength T2 of the protective layer is plotted on the horizontal axis and the P / C resistance of the power semiconductor module after moisture absorption treatment is plotted on the vertical axis. [Diagram 5]FIG. 5 is a graph showing an expanded range of tensile strength on the horizontal axis up to 15 MPa from FIG. 4, excluding the epoxy resin of Comparative Example 2. [Figure 6] FIG. 6 is a graph in which the elongation at break E2 of the protective layer is plotted on the horizontal axis and the P / C resistance of the power semiconductor module after moisture absorption treatment is plotted on the vertical axis. [Figure 7] FIG. 7 is a graph in which the tensile strength x elongation at break A2 of the protective layer is plotted on the horizontal axis, and the P / C resistance of the power semiconductor module after moisture absorption treatment is plotted on the vertical axis. [Figure 8] FIG. 8 shows the results of evaluating the tensile strength × elongation at break A2 and P / C resistance after moisture absorption treatment of the protective layer when the amount of mica (muscovite) added to the protective layer was changed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiment described below.

[0021] According to one embodiment, the present invention relates to a semiconductor device, in which a semiconductor element mounted on a laminated substrate and an output terminal are connected to each other by a conductive connecting member and sealed with a sealing material, and the sealing material includes a sealing layer and a protective layer.

[0022] FIG. 1 shows a conceptual cross-sectional view of a power semiconductor module, which is an example of the semiconductor device according to this embodiment. The power semiconductor module shown in the figure has a laminated structure in which a semiconductor element 11 and a laminated substrate 12 are bonded to a heat sink 13 by a bonding layer 17. A case 16 incorporating an external terminal 15 is bonded to the heat sink 13. The electrodes of the semiconductor element 11 and the laminated substrate 12 are connected by a lead frame 18, which is a conductive connecting member, and the semiconductor element 11 and the external terminal 15 are connected by an aluminum wire 14. A sealing layer 20 is filled in contact with the semiconductor element 11, the laminated substrate 12, the lead frame 18, the aluminum wire 14, and other members to be sealed. Furthermore, a protective layer 21 is provided in contact with the sealing layer 20.

[0023] The semiconductor element 11 is a power chip such as an IGBT (Insulated Gate Bipolar Transistor) or a diode chip, and may be a Si device or a wide-gap semiconductor device such as a SiC device, a GaN device, a diamond device, or a ZnO device. These devices may also be used in combination. For example, a hybrid module using a Si-IGBT and a SiC-SBD may be used. The number of semiconductor elements mounted may be one or more.

[0024] The laminated substrate 12 can be composed of an insulating substrate 122, a first conductive plate 121 formed on one of its main surfaces, and second conductive plates 123a, b formed on the other main surface. The insulating substrate 122 can be made of a material having excellent electrical insulation and thermal conductivity. Examples of the material for the insulating substrate 122 include Al2O3, AlN, and SiN. In particular, for high-voltage applications, a material having both electrical insulation and thermal conductivity is preferable, and AlN and SiN can be used, but are not limited to these. The first conductive plate 121 and the second conductive plates 123a, b can be made of metal materials such as Cu and Al that are excellent in workability. The conductive plates may be Cu or Al that have been treated with Ni plating or the like for the purpose of rust prevention or the like. Methods for disposing the conductive plates 121, 123a, and b on the insulating substrate 122 include a direct copper bonding method and an active metal brazing method. In the illustrated embodiment, two second conductive plates 123a, b are discontinuously provided on an insulating substrate 122, with one 123a functioning as an electrode to be joined to the semiconductor element 11 and the other 123b functioning as an electrode to be connected to a lead frame 18.

[0025] The lead frame 18 is a conductive connection member that connects the semiconductor element 11 and the second conductive plate 123b and the like. Specifically, it is joined to the electrode (front electrode) of the semiconductor element 11 with a bonding layer 17 of a solder material or the like. It is also joined to the wiring parts of the second conductive plate 123b and the like with a bonding layer 17 of a solder material or the like. The lead frame 18 may be made of a metal such as copper or an alloy containing copper. A Ni or Ni alloy layer, or a Cr or Cr alloy layer may be formed on the surface of the lead frame 18 by a plating method or the like. In this case, the film thickness of the Ni or Ni alloy layer, or the Cr or Cr alloy layer may be about 20 μm or less.

[0026] Metals such as copper and aluminum, which have excellent thermal conductivity, are used for the heat sink 13. The heat sink 13 may be coated with Ni or a Ni alloy to prevent corrosion. The heat sink may be a cooler having a function of water cooling or air cooling.

[0027] The bonding layer 17 can be formed using lead-free solder. For example, Sn-Ag-Cu, Sn-Sb, Sn-Sb-Ag, Sn-Cu, Sn-Sb-Ag-Cu, Sn-Cu-Ni, Sn-Ag, etc. can be used, but are not limited to these. Alternatively, the bonding layer can be formed using a connecting material containing fine metal particles, such as a sintered body of nano-silver particles.

[0028] The case 16 may be made of a thermoplastic resin such as polyphenylene sulfide (PPS) or polybutylene terephthalate (PBT).

[0029] In this embodiment, the members including the semiconductor element 11, the laminated substrate 12, and the conductive connecting members such as the lead frame 18 and the aluminum wire 14 are also referred to as the members to be sealed. A sealing material is filled onto the members to be sealed. The sealing material includes at least a sealing layer 20 and a protective layer 21.

[0030] The sealing layer 20 contacts the semiconductor element 11, the laminated substrate 12, and the conductive connecting member, or covers the periphery of these members to be sealed via a primer layer (not shown). The protective layer 21 is provided so as to contact the sealing layer 20 and cover the sealing layer 20. The protective layer 21 has a function of repairing defects in the sealing layer 20 and preventing moisture from penetrating into the sealing layer 20. In general, the protective layer 21 does not contact the members to be sealed, such as the semiconductor element 11, the laminated substrate 12, and the conductive connecting member. In an embodiment in which the sealing material is filled in the case as in the illustrated embodiment, the protective layer 21 constitutes the surface that contacts the atmosphere. It is preferable that the sealing layer 20 does not contact the atmosphere. The protective layer may cover the entire surface of the sealing layer 20, but is preferably disposed at least at the boundary with the case and / or the upper part of the semiconductor element 11. This is because the boundary with the case is the part where thermal stress is highest, and the upper part of the semiconductor element 11 is the part that is easily heated to high temperatures. The upper part of the semiconductor element 11 refers to a portion of the surface of the sealing layer 20 that generally faces the upper electrode of the semiconductor element 11. 11 The upper surface electrode refers to one of the electrodes of the semiconductor element 11 that is not in contact with the laminated substrate 12 .

[0031] The sealing layer 20 is a cured product of a thermosetting resin composition, preferably an epoxy resin composition. The protective layer 21 is a cured product of a composition containing silicone rubber. The sealing layer 20 and the protective layer 21, when in a cured state containing each of the components described below, satisfy the relationship between physical properties expressed by the following formula (1). If the parameter expressed by the product (T1×E1) of the tensile strength T1 (MPa) of the sealing layer 20 and the elongation at break E1 (%) is A1 (MPa), and the parameter expressed by the product (T2×E2) of the tensile strength T2 (MPa) of the protective layer 21 and the elongation at break E2 (%) is A2 (MPa), A1 <A2(1) and A2 is 1600 MPa or less. By providing the sealing layer 20 and the protective layer 21 that satisfy such physical property values, even if the sealing layer 20 is cracked, the protective layer 21 can prevent moisture from penetrating into the sealing layer 20 and prevent dielectric breakdown, thereby ensuring the reliability of the semiconductor device. The lower limit of A1 is not particularly limited, but is generally 10 to 150 MPa. For example, when A1 is 80 to 150 MPa, the upper limit of A2 may be 200 to 1600 MPa, and is more preferably 200 to 1000 MPa.

[0032] The tensile strength T1 (MPa) and elongation at break E1 (%) of the sealing layer 20 can be measured according to JIS K 7161, JIS K 7162, and ASTM D 638 (tensile strength of plastic materials). The tensile strength T2 (MPa) and elongation at break E2 (%) of the protective layer 21 can be measured according to JIS K 6251 or ASTM D 412 (tensile strength of rubber materials).

[0033] It is more preferable that the sealing layer 20 and the protective layer 21 satisfy the relational expression of the physical properties expressed by the following formula (2). A1 <A2<A1*25 (2) By setting the value of A2 to less than 25 times the value of A1, peeling at the interface between sealing layer 20 and protective layer 21 can be reduced. More preferably, by setting the value of A2 to less than 15 times the value of A1, peeling can be further reduced. That is, even if cracks occur in sealing layer 20, protective layer 21 stretches following sealing layer 20, and adhesion between protective layer 21 and sealing layer 20 can be ensured, and penetration of moisture from outside protective layer 21 can be prevented.

[0034] The thickness of the sealing layer 20 is preferably a thickness that can encapsulate at least the semiconductor element 11, the laminated substrate 12, and the members to be sealed, including the conductive connection member, and can be insulated and sealed. Depending on the aspect of the semiconductor device, it may be desirable to configure the conductive connection member or a part of the printed circuit board not to be sealed. The thickness of the protective layer 21 is preferably 20 μm to 1000 μm, and more preferably 100 μm to 500 μm. If it is thinner than 20 μm, it may not be able to fully function as the protective layer 21, such as not being able to cover cracks in the sealing layer 20. If it is thicker than 1000 μm, it may be easy for peeling to occur between the sealing layer 20 and the protective layer 21 due to thermal stress. There may be a plurality of layers that function as the protective layer 21, and in that case, it is preferable that the total film thickness is within the above range.

[0035] The sealing layer 20 and the protective layer 21 that satisfy the above-mentioned relational expressions of the physical properties can be selected from among cured resins that can be obtained by curing a resin composition having the following composition.

[0036] The sealing layer 20 may be a cured thermosetting resin obtained by curing a thermosetting resin composition that contains a thermosetting resin base and an inorganic filler, and may optionally contain a curing agent, a curing accelerator, and additives.

[0037] The thermosetting resin base is not particularly limited, and examples thereof include epoxy resin, phenol resin, maleimide resin, etc. Among them, epoxy resin having at least two epoxy groups in one molecule is particularly preferred because of its high dimensional stability, water resistance, chemical resistance, and electrical insulation. Specifically, it is preferred to use an aliphatic epoxy resin, an alicyclic epoxy resin, or a mixture thereof. As the sealing resin, a thermosetting resin is preferred because it requires heat resistance and high insulation, and epoxy resin is particularly preferred because of its high elasticity.

[0038] Aliphatic epoxy resin refers to an epoxy compound in which the carbon to which the epoxy group is directly bonded is a carbon that constitutes an aliphatic hydrocarbon. Therefore, even if the main skeleton contains an aromatic ring, if the above condition is satisfied, it is classified as an aliphatic epoxy resin. Examples of aliphatic epoxy resins include, but are not limited to, bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AD ​​type epoxy resins, biphenyl type epoxy resins, naphthalene type epoxy resins, cresol novolac type epoxy resins, and polyfunctional epoxy resins having three or more functional groups. These can be used alone or in combination of two or more types. In addition, naphthalene type epoxy resins and polyfunctional epoxy resins having three or more functional groups have high glass transition temperatures, and are therefore also referred to as high heat resistant epoxy resins. By including these high heat resistant epoxy resins, heat resistance can be improved.

[0039] The term "alicyclic epoxy resin" refers to an epoxy compound in which the two carbon atoms constituting the epoxy group constitute an alicyclic compound. Examples of alicyclic epoxy resins include monofunctional epoxy resins, bifunctional epoxy resins, and trifunctional or higher polyfunctional epoxy resins, but are not limited thereto. The alicyclic epoxy resins can be used alone or in combination of two or more different alicyclic epoxy resins. Alicyclic epoxy resin When mixed with an acid anhydride curing agent and cured, the glass transition temperature increases, so mixing an alicyclic epoxy resin with an aliphatic epoxy resin can improve heat resistance.

[0040] The thermosetting resin base material used in the sealing layer 20 may be a mixture of the above-mentioned aliphatic epoxy resin and alicyclic epoxy resin. The mixing ratio when mixing may be any, and the mass ratio of the aliphatic epoxy resin to the alicyclic epoxy resin may be about 2:8 to 8:2, or may be about 3:7 to 7:3, and is not limited to a specific mass ratio. In a preferred embodiment, the thermosetting resin base material used in the sealing layer 20 is a mixture of a bisphenol A type epoxy resin and an alicyclic epoxy resin in a mass ratio of 1:1 to 1:4.

[0041] The inorganic filler may be a metal oxide or a metal nitride, and examples thereof include, but are not limited to, fused silica, silica (silicon oxide), alumina, aluminum hydroxide, titania, zirconia, aluminum nitride, talc, clay, mica, and glass fiber. These inorganic fillers can increase the thermal conductivity of the sealing layer 20 and reduce the thermal expansion coefficient. These inorganic fillers may be used alone or in combination of two or more. The inorganic filler may be a microfiller or a nanofiller, and two or more inorganic fillers having different particle sizes and / or types may be used in combination. In particular, it is preferable to use an inorganic filler having an average particle size of about 0.2 to 20 μm. The amount of the inorganic filler added to the sealing layer 20 is preferably 100 to 600 parts by mass, and more preferably 200 to 400 parts by mass, when the total mass of the thermosetting resin base agent and the curing agent that may be optionally contained is 100 parts by mass. If the amount of the inorganic filler is less than 100 parts by mass, the thermal expansion coefficient of the encapsulant may become high, which may cause peeling or cracking, whereas if the amount is more than 600 parts by mass, the viscosity of the composition may increase, which may cause poor extrusion moldability.

[0042] The thermosetting resin composition constituting the sealing layer 20 may contain a curing agent as an optional component. The curing agent is not particularly limited as long as it reacts with the thermosetting resin base, preferably the epoxy resin base, and can be cured, but it is preferable to use an acid anhydride-based curing agent. Examples of the acid anhydride-based curing agent include aromatic acid anhydrides, specifically phthalic anhydride, pyromellitic anhydride, trimellitic anhydride, etc. Alternatively, examples of the acid anhydride include cyclic aliphatic acid anhydrides, specifically tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, etc., or aliphatic acid anhydrides, specifically succinic anhydride, polyadipic anhydride, polysebacic anhydride, polyazelaic anhydride, etc. The amount of the curing agent is preferably 50 parts by mass or more and 170 parts by mass or less, and more preferably 80 parts by mass or more and 150 parts by mass or less, relative to 100 parts by mass of the epoxy resin base. If the amount of the curing agent is less than 50 parts by mass, the glass transition temperature may decrease due to insufficient crosslinking, and if it is more than 170 parts by mass, the moisture resistance, high heat distortion temperature, and heat resistance stability may decrease. In addition, when a bisphenol A type epoxy resin is used alone or a mixture of a bisphenol A type epoxy resin and a high heat resistant epoxy resin exemplified above is used as the thermosetting resin base, it may be preferable not to use a curing agent because heat resistance is improved. The compounding ratio of the high heat resistant epoxy resin may be, for example, 10% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 25% by mass or less, when the total mass of the thermosetting resin base is 100%. This range is preferable because heat resistance is improved and viscosity does not increase.

[0043] A curing accelerator may be added as an optional component to the thermosetting resin composition constituting the sealing layer 20. As the curing accelerator, imidazole or its derivatives, tertiary amines, boric acid esters, Lewis acids, organometallic compounds, organic acid metal salts, etc. may be appropriately blended. The amount of the curing accelerator added is preferably 0.01 parts by mass or more and 50 parts by mass or less, more preferably 0.1 parts by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the thermosetting resin base.

[0044] The thermosetting resin composition constituting the encapsulating layer 20 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 the amounts of them to be added can be appropriately determined by those skilled in the art according to the specifications required for the semiconductor device and / or the encapsulating material.

[0045] The protective layer 21 is a silicone rubber cured product that contains silicone rubber and may optionally contain inorganic fillers and additives. Silicone rubber is an organosilicon polymer whose main chain is composed of siloxane bonds, and has higher heat resistance, weather resistance, and chemical resistance than conventional rubber (organic rubber) whose main chain contains C-C bonds. Silicone rubber is also preferable as a protective layer for semiconductor modules because it has good elastic fatigue resistance and generates little dust. Silicone rubber is also preferable because it has good adhesion to the thermosetting resin used in the above-mentioned sealing layer. Silicone rubber may be a molecule with a linear structure with 5,000 to 10,000 siloxane bonds in one molecule after thermal curing. Silicone rubber has an elastic modulus of about 10 after thermal curing. 5It is preferable that the thermal resistance is more than 10000 MPa (0.1 MPa) and less than 10000 MPa. More preferably, it is more than 1 MPa and less than 5000 MPa in order to maintain the rigidity of the protective film. It is also preferable that the silicone rubber has a heat resistance of 175°C or more. The heat resistance here means a temperature at which the rubber does not decompose, and here means that the dielectric breakdown voltage does not decrease after being left at a predetermined temperature for 6000 hours when the rubber is used as a semiconductor module. Silicone rubbers are mainly classified into room temperature curing types by condensation reaction, heat curing types by addition reaction, and UV curing types depending on the curing process, but as long as the rubber has a predetermined physical property value, the type of the curing process is not important. Silicone rubbers are classified into several types depending on the type and structure of the side chain, but in order to obtain the effect of the present invention, the type and structure of the side chain are not particularly limited, and it is sufficient to satisfy the condition of the predetermined physical property value A2.

[0046] The protective layer 21 preferably contains an inorganic filler as an optional component. By containing an inorganic filler, the value of A2 increases, and the power cycle resistance of the semiconductor device can be increased. The amount of inorganic filler added is preferably 50 parts by mass to 200 parts by mass, and more preferably 50 parts by mass to 150 parts by mass, per 100 parts by mass of silicone rubber. When the amount of inorganic filler added is less than 50 parts by mass or more than 200 parts by mass, the effect of increasing the value of A2 is small, and may not contribute to an increase in the P / C resistance.

[0047] The compound species constituting the inorganic filler added to the protective layer 21 can be selected from the same range of options as the inorganic filler added to the sealing layer 20, and is not particularly limited. Two or more different compound species can also be mixed and used. The shape of the inorganic filler is not particularly limited, and inorganic fillers such as spherical, crushed, fibrous, and plate-shaped can be used. Among them, plate-shaped inorganic fillers with a large aspect ratio are preferred. This is because plate-shaped inorganic fillers with a large aspect ratio are less likely to cause cracks in the protective layer, and have the effect of improving the reliability of the semiconductor module. Even if a crack occurs, it stops at the main surface of the inorganic filler, and there is an effect of preventing further growth and extension of the crack. In this specification, the aspect ratio of the plate-like inorganic filler can be defined by the values ​​of b / a and a / c, where a is the length of the long diameter or long side constituting the main surface of the plate-like body, b is the length of the short diameter or short side, c is the length of the shortest side corresponding to the plate thickness, and b≧a>c. b / a may be 1 to 100, and preferably 1 to 20. And a / c may be 10 to 100, and preferably 20 to 50. A more preferable embodiment of the plate-like inorganic filler is a scale-like inorganic filler. The scale-like inorganic filler can refer to a filler having a shape in which at least a part of the outer shape is formed by a curve, such as an ellipse, a circle, a sector, or a shape formed by curving these. In the scale-like inorganic filler, when the longest diameter on the main surface is A and the length of the shortest side corresponding to the thickness is C, A / C may be 10 to 10,000, and preferably 100 to 2,000. A specific example of the scale-like inorganic filler is mica.

[0048] The average particle size or major axis of the inorganic filler is, for example, preferably about 1 μm to 50 μm, more preferably about 10 μm to 40 μm, from the viewpoint of dispersibility. Note that the major axis of a plate-like or scale-like inorganic filler may be the longest diameter a or A of the main surface.

[0049] The protective layer 21 may also contain optional additives as long as the additives do not impair the properties of the protective layer 21. Examples of the additives include flame retardants, ArrivalExamples of the pigment and the like for coloring include, but are not limited to, these.

[0050] The encapsulant only needs to be arranged such that the encapsulation layer 20 and the protection layer 21 that satisfy the conditions of the above parameters A1 and A2 are in contact with each other. The protection layer 21 may include a silicone rubber and may include a plurality of layers having physical property values that satisfy the relational expressions of the above parameters A1 and A2. For example, a second protection layer may be provided on the outer side (the main surface opposite to the encapsulation layer 20) of the illustrated protection layer 21, and a third protection layer may be provided on the outer side of the second protection layer. Then, the material compositions of the second protection layer and the third protection layer both satisfy the material composition of the protection layer 21, and when the parameter of the second protection layer is A3 and the parameter of the third protection layer is A4, it is preferable to satisfy the relational expression of A2 < A3 < A4, and it is more preferable to satisfy the relational expression of A2 < A3 < A4 < A1 * 25. For example, the protection layer 21 can be a cured silicone rubber product that does not contain an inorganic filler, and the second and third protection layers can be cured silicone rubber products that contain an inorganic filler, but it is not limited to a specific composition. Also, the encapsulation layer 20 may also be a cured thermosetting resin defined above and may include a plurality of layers having physical property values that satisfy the relational expressions of the above parameters A1 and A2.

[0051] Next, the manufacturing of the illustrated power semiconductor module will be described. After joining the heat sink 13, the laminated substrate 12, and Bihan the conductor element 11, attaching the case 16 to the heat sink 13, joining the lead frame 18, and performing wire bonding with the aluminum wire 14. Next, a thermosetting resin composition that constitutes the encapsulation layer 20 is injected into the case 16 and heat-cured. The heat-curing process can be, for example, a two-stage curing. When an epoxy resin is used as the main agent of the thermosetting resin, it is heated at 90 to 120 °C for 1 to 2 hours to be in a semi-cured state. Then, further heating can be performed at 175 to 185 °C for 1 to 2 hours (final curing). However, it is not limited to specific temperatures and times, and there may be cases where two-stage curing is not necessary.

[0052] Next, a silicone rubber composition constituting the protective layer 21 is applied to contact the sealing layer 20 inside the case 16, and then cured. In the case of a room temperature curing type silicone rubber composition, it is cured by a condensation reaction due to moisture, so it may be held at room temperature (about 15°C to 25°C) and at a constant temperature and humidity of about 40%RH to 60%RH for a predetermined time (for example, about one day to one week). In the case of a heat curing type, it may be held at about 100°C to 200°C for about 0.5 hours to 5 hours, or may have multiple heating steps. However, the curing conditions are not limited to a specific temperature, humidity, or time. Depending on the embodiment of the protective layer 21, the protective layer 21 may be formed after the sealing layer 20 is completely cured, or the protective layer 21 may be formed in a state in which the sealing layer 20 is temporarily cured. In addition, the order of lamination and curing when the protective layer 21 has multiple layers may be such that multiple protective layers are laminated and then cured, or each protective layer is cured and then laminated.

[0053] As a modified form of the illustrated power semiconductor module, a primer layer may be provided at the interface between the sealing material and the sealing member including the laminated substrate, the semiconductor element, and the conductive connecting member. The primer layer may be preferably used from the viewpoint of ensuring adhesion at the interface between the sealing material and the sealing member. The primer layer may be a layer made of a resin containing polyamide, polyimide, or polyamideimide. The thickness of the primer layer is not particularly limited as long as it is thick enough to provide adhesion. The thickness of the primer layer may be, for example, about 1 to 20 μm, and is preferably 1 to 10 μm. In the above range, the primer layer has a stress relaxation effect, so that the adhesion can be improved, which is more preferable. The primer layer may be provided so as to cover the entire surfaces of the semiconductor element 11, the laminated substrate 12, the lead frame 18, and the aluminum wire 14 shown in FIG. 1.

[0054] In the method for manufacturing a power semiconductor module having a primer layer, a primer layer is formed after assembling the members to be sealed and before injecting the sealing material. The primer layer can be provided on the entire surface of the members to be sealed including the semiconductor element 11, the lead frame 18, the laminated substrate 12, the aluminum wire 14, and the case 16 shown in FIG. 1 by, for example, spray coating, dipping, or coating with a dispenser. After the primer layer is formed, it is preferable to heat the assembly stepwise at 70 to 100° C. for about 60 to 80 minutes in an inert oven into which nitrogen gas is introduced, and then heat the assembly stepwise at 200 to 220° C. for 60 to 80 minutes. This heating operation heats Cu constituting the lead frame 18, vaporizes the solvent, and solidifies the primer. After the primer layer is formed, insulation and sealing can be performed with a sealing material in the same manner as in the method for manufacturing a power semiconductor module shown in FIG. 1.

[0055] The illustrated configuration of the power semiconductor module is an example, and the present invention is not limited to this configuration. For example, any conductive connection member may be used, and an implant pin may also be used. The conductive connection member may be configured to be only a lead frame or only a wire. When a primer layer is provided in a module in which the conductive connection member includes an implant pin, the primer layer can be formed on the surface of the implant pin. When a primer layer is provided in a module in which the conductive connection member includes only a wire, the primer layer can be formed on the surface of the wire.

[0056] The power semiconductor module may be a caseless power semiconductor module that does not have a case. Although not shown, the caseless power semiconductor module may have a structure that includes an implant pin and a printed circuit board bonded to the implant pin instead of the lead frame and aluminum wire in FIG. 1, and the members including these are sealed with a sealing material. The printed circuit board may be a polyimide film board or an epoxy film board on which a conductive layer of Cu, Al, or the like is formed. The implant pin may be a copper pin using copper. The conductive layer of the printed circuit board and the implant pin may be Cu or Al that has been treated with Ni plating or the like for the purpose of rust prevention. The printed circuit board and the implant pin electrically connect the semiconductor elements to each other, or between the semiconductor element and the laminated substrate. The implant pin and the laminated substrate or the semiconductor element can be joined by a solder joint layer. The implant pin can be used as an external connection terminal by drawing the implant pin from the laminated substrate to the outside of the sealing material. In the manufacture of the power semiconductor module of this embodiment, the members to be sealed including the laminated substrate, the semiconductor element, the implant pin, and the printed circuit board are assembled, and a primer layer is optionally formed on the surfaces of the laminated substrate, the semiconductor element, the implant pin, and the printed circuit board by a method such as spray coating, and then the members to be sealed are placed on an appropriate mold, and the thermosetting resin composition constituting the sealing layer is filled into the mold and temporarily cured. Examples of molding methods for such a sealing body include vacuum casting, transfer molding, liquid transfer molding, potting, and the like, but are not limited to a specific molding method. Next, a protective layer is formed by applying a silicone rubber composition with a spray or dispenser, and the protective layer is fully cured. In the caseless power semiconductor module, it is preferable that the sealing layer is not in contact with the atmosphere and is covered with the protective layer. In the caseless power semiconductor module, by forming a protective layer that satisfies a specific physical property condition on the surface of the sealing layer, even if the sealing layer is cracked, the protective layer prevents moisture from entering the sealing layer, and a highly reliable semiconductor device can be provided.

[0057] According to the semiconductor device of this embodiment, even if a crack occurs in a part of the sealing material, , protection The protective layer prevents the intrusion of moisture, making it possible to provide a highly reliable semiconductor device. EXAMPLES

[0058] 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.

[0059] 1. Mechanical properties and reliability of protective layer (P / C tolerance) Power semiconductor modules having a two-layer sealing structure of a sealing layer and a protective layer shown in Figure 1 were manufactured by changing the material of the protective layer, and after performing moisture absorption treatment, their reliability was evaluated. In addition, the physical properties of the resin cured products constituting the sealing layer and protective layer used in each example and comparative example were evaluated, and their relationship with reliability was examined.

[0060] The sealing layer was made of a cured epoxy resin. The epoxy resin base was ME-276 (manufactured by Pernox Co., Ltd.), and 121 parts by mass of MV-138 (manufactured by Pernox Co., Ltd.) was added as an acid anhydride curing agent to 100 parts by mass of the base. The inorganic filler was spherical silica (manufactured by AGC Co., Ltd.) with an average particle size of 10 μm, and 270 parts by mass was added to 100 parts by mass of the total mass of the epoxy resin base and curing agent.

[0061] The protective layer was produced without adding an inorganic filler, using each of the materials shown in Tables 1 and 2. In Example 7, a 10 μm primer layer made of Himal HL1200F (Showa Denko Materials), whose main component is polyamide, was formed on the laminate substrate, the semiconductor element, the lead frame, the wire, and the case. [Table 1]

[0062] [Table 2]

[0063] In the manufacture of the power semiconductor modules of the examples and comparative examples, after assembling the members to be sealed, a primer layer was formed in Example 7. After the primer layer was formed, it was heated at 100°C for 60 minutes in an inert oven into which nitrogen gas was introduced, and then heated at 200°C for 60 minutes. This heating operation suppressed oxidation of the Cu surface, heated the Cu constituting the lead frame, etc., promoted the reaction between the primer layer and Cu, and improved the adhesion between the primer layer and the lead frame, etc. Next, the above-mentioned thermosetting resin composition constituting the sealing layer 20 was injected into the case 16 and heat-cured. The heat-curing process was performed by heating at 120°C for 1 hour to a semi-cured state, and then heating at 175°C for 1 hour. Next, the silicone rubber composition constituting the protective layer was applied with a dispenser and cured. The curing conditions were as shown in Table 3 below. [Table 3]

[0064] The manufactured power semiconductor module was subjected to moisture absorption treatment by leaving it at 85℃ and 85% RH for 300 hours. The moisture absorption treatment was performed not on the power semiconductor module immediately after manufacture, but in order to reproduce moisture absorption conditions similar to those of the saturated water absorption of the product after manufacture. Note that the sealing material and case material that make up the product have the property of absorbing water, and saturated water absorption refers to a state in which the water absorption rate has reached nearly saturation. Next, the reliability of the power semiconductor module after moisture absorption treatment was evaluated using T j Power cycle resistance (T j The power cycle test was performed at 40 to 175°C (ΔT j The number of cycles required for electrical characteristics to reach abnormal values ​​was investigated, with one cycle consisting of two seconds of current operation and nine seconds of rest at a temperature of 135°C. At least 50k cycles are required to obtain sufficient reliability. Insulation properties were evaluated by insulation tests. Specifically, when a specified voltage of AC or DC voltage 10 to 20 times the voltage normally handled is applied for a specified period of time, if no dielectric breakdown (a sudden increase in current that does not follow Ohm's law) occurs, the insulator is deemed to have sufficient dielectric strength.

[0065] Tables 1 and 2 show the protection of the examples and comparative examples. In layers The elastic modulus, tensile strength T2, elongation at break E2, strength x elongation at break A2, insulation and film thickness, and T j The evaluation results of P / C tolerance and reliability are shown. j The unit of P / C resistance is k cycles. The sealing layer in all of the examples and comparative examples was made of the same material as in Comparative Example 2, and had a tensile strength T1 of 100 MPa, an elongation at break E1 of 1%, and a strength × elongation at break A1 of 100 MPa.

[0066] (1) Elasticity and reliability of protective layer For Examples 1 to 7 and Comparative Examples 1 to 5, the elastic modulus of the protective layer was plotted on the horizontal axis and the reliability (P / C tolerance) was plotted on the vertical axis for evaluation. FIG. 2 shows Examples and Comparative Examples with an elastic modulus in the range of 0 to 10,000 MPa, and in FIG. 2, the white circle ◯ shows the result when the epoxy resin of Comparative Example 2 was used as the protective layer. FIG. 3 shows Examples and Comparative Examples with an elastic modulus in the range of 0 to 400 MPa, which is small in FIG. 2. Therefore, FIG. 3 corresponds to the part of FIG. 2 excluding the epoxy resin of Comparative Example 2, Example 6, and Comparative Example 4. FIGS. 2 and 3 show that there is no clear correlation between the elastic modulus and reliability (P / C tolerance) of various protective layers.

[0067] (2) Tensile strength and reliability of the protective layer For Examples 1 to 7 and Comparative Examples 2 and 5, the tensile strength of the protective layer was plotted on the horizontal axis and the reliability (P / C tolerance) on the vertical axis for evaluation. FIG. 4 shows Examples and Comparative Examples with tensile strength in the range of 0 to 150 MPa, and in FIG. 4, the white diamonds indicate the results when the epoxy resin of Comparative Example 2 was used as the protective layer. FIG. 5 shows Examples and Comparative Examples with tensile strength in the low range of 0 to 15 MPa in FIG. 4. Therefore, FIG. 5 corresponds to the portion of FIG. 4 excluding the epoxy resin of Comparative Example 2. FIGS. 4 and 5 show that there is no correlation between the tensile strength and reliability (P / C tolerance) of various protective layers.

[0068] (3) Elongation and reliability of protective layer at break For Examples 1 to 7 and Comparative Examples 2 and 5, the elongation at break of the protective layer was plotted on the horizontal axis and the reliability (P / C tolerance) was plotted on the vertical axis for evaluation. The results are shown in FIG. 6. From FIG. 6, it was shown that there was no clear correlation between the elongation at break and the reliability (P / C tolerance) of various protective layers.

[0069] (4) "Tensile strength × elongation at break A2" of the protective layer and reliability For Examples 1 to 7 and Comparative Examples 2 and 5, the "tensile strength × elongation at break" of the protective layer was plotted on the horizontal axis and the reliability (P / C tolerance) was plotted on the vertical axis for evaluation. The results are shown in FIG. 7. In FIG. 7, the white circles 〇 show the results when the epoxy resin of Comparative Example 2 was used as the protective layer. From FIG. 7, a correlation was observed between the "tensile strength × elongation at break A2" of the protective layer and the reliability (P / C tolerance). The "tensile strength × elongation at break A1" of the sealing layer was the same as that of Comparative Example 2. From FIG. 7, when the condition of A1 < A2 was satisfied, the P / C tolerance exceeded the preferable standard and sufficient reliability was obtained. In particular, when A2 was less than 15 times A1, it was found that the P / C tolerance exceeded 240 k cycles and high reliability was obtained. That is, it was found that as A2 increased, the reliability did not increase monotonically, and even if it was too large, the reliability did not improve, and there was a suitable range. Specifically, when A2 was from 200 to 1600 MPa, the P / C tolerance was improved by 5 times or more compared to the case without the protective film. Furthermore, when A2 was generally from 200 to 1000 MPa, it was found that the improvement was 10 times or more. Note that when A2 was generally from 200 to 1600 MPa, it corresponded to the case where A2 was less than 25 times A1. This result shows that the larger the product of the tensile strength and the elongation at break of the protective layer, the higher the reliability of the module. This is presumably because when thermal stress acts on the protective layer and bending stress is applied, the protective layer has both the tensile strength that does not crack immediately and the ductility that can withstand (tensile strength) and does not easily crack or elongate even when a certain stress is applied (elongation at break), so that the reliability can be improved. That is, according to the present invention, it is presumed that the protective layer itself can protect the sealing layer without cracking.

[0070] Conventional power semiconductor modules sealed with sealing materials consisting only of epoxy resin are subject to thermal stress over time. application When the lead frame is heated, it is likely to repeatedly deform, and cracks tend to occur, particularly from the end of the lead frame upwards or from the periphery of the semiconductor element upwards. Here, "upwards" refers to the direction from the semiconductor element toward the opposite side of the laminated substrate. Moisture penetrates through such cracks, often leading to dielectric breakdown in the lead frame or semiconductor element. According to this embodiment, by using a sealing layer and a protective layer that satisfy the specified physical property conditions, a sufficient P / C resistance can be obtained.

[0071] 2. Thickness and reliability of protective layer (P / C resistance) The protective layer material of Example 4 was used, and the thickness of the protective layer was changed to evaluate the P / C resistance after moisture absorption treatment. Peeling was evaluated using an ultrasonic flaw detector (SAT). The results are shown in Table 4. As can be seen from Table 4, when the thickness of the protective layer was 1.5 mm or more, the protective layer and Sealing layer Peeling due to thermal stress occurred near the interface. On the other hand, if the protective layer is too thin at 20μm, it may not be able to cover cracks in the epoxy resin, and there may be places where the protective layer is thin, resulting in poor P / C resistance. Note that P / C resistance requires 20k cycles or more, with 100k or more being preferable. Therefore, 100k cycles or more was judged as ◯, and 20k cycles or more but less than 100k cycles was judged as △. When the protective film thickness was 20μm and 1.5mm, the number of cycles was 50k, and it was judged as △. Peeling was judged mainly by observing and evaluating the vicinity of the interface between the sealing layer and the surface of the sealing member, such as a wiring member such as a lead frame, a semiconductor element, or a laminated substrate, and the sealing layer, and the vicinity of the interface between the sealing layer and the protective layer, using SAT (Scanning Acoustic Tomography) and cross-sectional SEM (Scanning Electron Microscope). A rating of ◯ was given for no peeling of 10 μm or more, and a rating of △ was given for peeling of 10 μm or more but less than three places but less than 30 μm in size. Table 4 shows that a thickness of 100 μm to 1 mm is more preferable. Note that even when peeling is judged as △, it is still considered acceptable as a semiconductor module, just as when peeling is judged as ◯. ofThe electrical properties were good.

[0072] [Table 4]

[0073] 3. Effect of adding inorganic filler to the protective layer Using the protective layer material of Example 4, different types of inorganic fillers were added in various amounts to evaluate parameter A2 and P / C resistance after moisture absorption treatment. Of the inorganic fillers used, SiO2 was spherical silica with an average particle size of 30 μm, mica (muscovite) was a plate-like body with a, b, and c defined above of 50, 200, and 2, respectively, and mica (phlogopite) was a scale-like body with A and C defined above of 210 and 2, respectively. The evaluation results are shown in Table 5. The amounts added are shown in parts by mass when the silicone rubber constituting the protective layer is taken as 100 parts by mass.

[0074] [Table 5]

[0075] From Table 5, it was confirmed that the parameter A2 value was larger and the P / C resistance was also larger for scale-like and plate-like inorganic fillers (mica-based) than for spherical inorganic fillers. This is presumably because when plate-like and scale-like inorganic fillers are added, cracks are less likely to occur in the protective layer, and the protective layer itself is less likely to break.

[0076] Next, the amount of mica (muscovite) added to the protective layer was changed to evaluate the tensile strength × elongation at break A2 of the protective layer and the P / C resistance after moisture absorption treatment. The results are shown in Figure 8. From Figure 8, it was confirmed that the amount of inorganic filler added is preferably 50 to 200 parts by mass, assuming that the silicone rubber constituting the protective layer is 100 parts by mass. If the amount is too small, the effect is low, and if the amount is too large, the "tensile strength × elongation at break" decreases. [Explanation of symbols]

[0077] 11 semiconductor element, 12 laminated substrate, 121 conductive plate, 122 insulating substrate 123a, b conductive plate, 13 heat sink, 14 aluminum wire, 15 external terminal 16 case, 17 bonding layer, 18 lead frame 20 sealing layer, 21 protective layer

Claims

1. A semiconductor device in which a semiconductor element and a conductive connection member mounted on a laminated substrate are sealed with a sealing material, the sealing material seals the laminated substrate, the semiconductor element, and the conductive connection member, and includes a sealing layer containing a thermosetting resin, and a protective layer covering the sealing layer and containing a silicone rubber; The tensile strength of the sealing layer × the value of elongation at break A １ , the tensile strength of the protective layer × the elongation at break A ２ But the following relationship A 1 <A 2 <A 1 *15 And A ２ is 1600 MPa or less, The semiconductor device, wherein the protective layer has a thickness of 20 μm to 1000 μm.

2. The semiconductor device according to claim 1 , wherein the protective layer comprises an inorganic filler.

3. The semiconductor device according to claim 2 , wherein the inorganic filler is a plate-like or flaky inorganic filler.

4. 4. The semiconductor device according to claim 1, wherein the thermosetting resin contained in the sealing layer is an epoxy resin, the sealing layer further contains a curing agent for the epoxy resin, and the curing agent is an acid anhydride-based curing agent.

5. 5. The semiconductor device according to claim 1, further comprising a primer layer at an interface between the sealing material and a member to be sealed, the member including the laminated substrate, the semiconductor element, and the conductive connecting member.

6. 6. The semiconductor device according to claim 5, wherein the primer layer is made of a resin selected from the group consisting of polyamide resin, polyimide resin, and polyamideimide resin.

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