Semiconductor device and method for manufacturing the same

Abstract

Semiconductor device (100) comprising the following: - an insulating substrate (5) with a top surface on which a semiconductor element (4) is mounted; - a base plate (1) connected to a lower surface of the insulating substrate (5); - a housing element (2) that surrounds the insulating substrate (5) and is in contact with a surface of the base plate (1) to which the insulating substrate (5) is connected; - a sealing resin (8) provided in an area surrounded by the base plate (1) and the housing element (2) so that the insulating substrate (5) is sealed; - a cover part (9) which faces a surface of the sealing resin (8) and is fixed to the housing element (2); and - a retaining plate (10), wherein a lower surface of the retaining plate is in close contact with the surface of the sealing resin (8), whereby a pressure load can be generated on the sealing resin (8) during a heat cycle, wherein an upper surface of the retaining plate is fixed to a surface of the cover part (9) facing the surface of the sealing resin (8), wherein the size of the retaining plate (10) is greater than or equal to 50% of the surface of the insulating substrate (5), and a contact area of ​​the retaining plate (10) with the surface of the sealing resin (8) is less than 80% of the surface of the sealing resin (8).

Description

Technical field

[0001] The present invention relates to a sealing structure for a semiconductor device, wherein a power semiconductor element is sealed in a resin, and to a method for manufacturing the sealing structure. State of the art

[0002] A type of semiconductor device in which a conductive path is provided in the longitudinal direction of the device to handle high voltage or a large amount of current is generally referred to as a "power semiconductor device" (for example, an IGBT (insulated-gate bipolar transistor), a MOSFET (metal-oxide-semiconductor field-effect transistor), a bipolar transistor, a diode, or the like). A semiconductor device incorporating a power semiconductor device mounted on a circuit board and packed using a sealing resin is used in a wide range of applications, such as industrial equipment, vehicles, and railway vehicles. Recently, as the power output of a device incorporating such a semiconductor device increases, it has become necessary for the semiconductor device to offer higher power output, such as...an increased rated voltage and current, an increased operating temperature range (higher and lower temperatures) and the like.

[0003] A structure referred to as a "package structure" is primarily used for the packing structure of the semiconductor device. A package-type semiconductor device has a structure in which a power semiconductor element is mounted on a base plate for heat dissipation, with an insulating substrate sandwiched between them and a package bonded to the base plate. A power semiconductor element mounted within the semiconductor device is connected to a main electrode. A bond wire is used to connect the power semiconductor element to the main electrode. Generally, an insulating gel filler, such as silicone gel, is used as a sealing resin for the semiconductor device to prevent insulation failure when a high voltage is applied.

[0004] With reference to a conventional semiconductor device, a semiconductor device is disclosed which has a structure with a retaining cover which is inserted in close contact with the upper surface of a silicone gel to prevent a bond wire from being separated by the movement of the silicone gel, wherein the retaining cover has a side surface which is provided with a projection which engages in the inner wall of an outer housing so that it is movable up and down (for example, patent document 1).

[0005] Furthermore, a semiconductor device is disclosed which has a structure comprising a covering area that covers the upper surface of the silicone gel and whose end area is attached to a housing, wherein at least 80% of the upper surface of the silicone gel is in contact with the covering area, within a temperature range in which its use is permissible (for example, patent document 2).

[0006] Patent document 3 discloses a semiconductor device in which the air within a gel resin can be effectively and thoroughly cleaned. The device comprises a housing, a semiconductor device electrically connected by bond wires, and a gel resin filled into the housing, serving as an insulating cover for the semiconductor device and the bond wire. The device further includes a plate-shaped vibration damper in contact with the gel resin, provided with a plurality of perforations, each having an air inlet and an air outlet for the purpose of air extraction during the filling of the gel resin. The cross-sectional area of ​​the perforations is tapered and larger at the inlet than at the outlet, so that the perforations as a whole have the shape of a substantially conical trapezoid. Bibliography Patent document PTD 1: Japanese Patent Disclosure JP 2000 - 311 970 A (page 3; Fig. 1) PTD 2: Japanese Patent Disclosure JP 2014 - 130 875 A (page 4, Fig. 1) PTD 3: US 2003 / 0 089 974 A1 Summary of the invention: Technical problem

[0007] Generally speaking, a lower temperature allows a smaller amount of gas to dissolve in the silicone gel. Therefore, if the operating temperature range of the semiconductor device is increased and the silicone gel is used at a higher temperature, excess gas that cannot be dissolved in the gel will form bubbles within it. In areas with such bubbles, the insulating seal provided by the silicone gel is compromised. Consequently, the insulating properties of the semiconductor device deteriorate.

[0008] To prevent the formation of blisters in the silicone gel and its detachment, the internal stresses on the silicone gel should be compressive. This is because tensile stresses increase and promote blisters and detachment.

[0009] However, in the semiconductor device described in patent document 1, the following applies: Although the retaining cover is inserted in close contact with the upper surface of the sealing resin, it is movable up and down relative to the inner wall of the outer casing. Consequently, when the power semiconductor element is operated at high temperature, the sealing resin can thermally expand and push the retaining cover upwards, resulting in no compression or pressure stress being generated to prevent the formation of bubbles. As a result, the insulating properties of the semiconductor device deteriorate.

[0010] In the semiconductor device described in patent document 2, the following applies: Since the end of the cover area is fixed to the housing, the retaining plate cannot be pushed upwards by the silicone gel, which has thermally expanded at high temperatures. As a result, the internal stresses of the silicone gel become compressive stresses, thus preventing the formation of bubbles. However, since the end of the cover area is fixed to the housing, the silicone gel is drawn towards the cover area at low temperatures as it thermally contracts. As a result, the internal stresses of the silicone gel become tensile stresses. When the internal stresses of the silicone gel are tensile, only a very small bubble, if any, will increase in size due to the tensile forces.

[0011] Furthermore, if there is an area of ​​weak attraction at the interface between the silicone gel and the insulating substrate, the interface between the silicone gel and the power semiconductor element, or the interface between the gel and the wire, the tensile stresses will cause or promote delamination at the interface. In areas with such blistering or delamination, the insulating seal provided by the silicone gel is not maintained. Consequently, the insulating performance of the semiconductor device deteriorates.

[0012] Furthermore, when a higher voltage is used in the semiconductor device, dielectric breakdown is more likely to occur if the bubble sizes or delamination are smaller. Consequently, the module's insulating properties deteriorate.

[0013] Therefore, the insulation capacity of the conventional semiconductor device deteriorates if the semiconductor device is used at a higher or lower temperature within the extended operating temperature range of the semiconductor device, or if, adversely, a higher voltage is used for the semiconductor device.

[0014] The present invention was made to solve the problem described above and to obtain a semiconductor device whose insulating capacity is not degraded even at high temperature, low temperature and high voltage used therein, by preventing the formation of bubbles and the detachment of the silicone gel from an insulating substrate. Solution to the problem

[0015] The problem underlying the invention is solved by a semiconductor device with the features of independent claim 1 and / or the method according to independent claim 5. Advantageous embodiments of the semiconductor device according to the invention are specified in dependent claims 2 to 4, and an advantageous embodiment of the method is specified in dependent claim 6. Advantageous effects of the invention

[0016] According to the present invention, the retaining plate is positioned in close contact with the sealing resin between the sealing resin and the cover in the semiconductor device, thereby generating pressure loads on the sealing resin in the direction of the insulating substrate during a thermal cycle. As a result, the reliability of the semiconductor device during the thermal cycle can be improved. Brief description of the drawings Fig.Figure 1 is a schematic cross-sectional structural view showing a semiconductor device in a first embodiment of the present invention. Fig. Figure 2 is a schematic cross-sectional structural view showing the semiconductor device in the first embodiment of the present invention at low temperature. Fig. Figure 3 is a schematic cross-sectional structural view showing the semiconductor device in the first embodiment of the present invention at high temperature. Fig. Figure 4 is another schematic cross-sectional structural view showing the semiconductor device in the first embodiment of the present invention at low temperature. Fig. Figure 5 is a schematic top-view structural diagram showing the semiconductor device in the first embodiment of the present invention. Fig.Figure 6 is a schematic cross-sectional structural view showing another semiconductor device in the first embodiment of the present invention. Fig. Figure 7 is a schematic top-view structural diagram showing another semiconductor device in the first embodiment of the present invention. Fig. Figure 8 is a schematic cross-sectional structural view showing one step in the fabrication of the semiconductor device in the first embodiment of the present invention. Fig. Figure 9 is a schematic cross-sectional structural view showing one step in the fabrication of the semiconductor device in the first embodiment of the present invention. Fig. Figure 10 is a schematic cross-sectional structural view showing one step in the fabrication of the semiconductor device in the first embodiment of the present invention. Fig.Figure 11 is a schematic cross-sectional structural view showing the step for manufacturing the semiconductor device in the first embodiment of the present invention. Fig. Figure 12 is a schematic cross-sectional structural view showing a cover and a retaining plate in the first embodiment of the present invention. Fig. Figure 13 is a schematic cross-sectional structural view showing a further cover and retaining plate in the first embodiment of the present invention. Fig. Figure 14 is a schematic cross-sectional structural view showing a further cover and retaining plate in the first embodiment of the present invention. Fig. Figure 15 is a schematic cross-sectional structural view of a conventional semiconductor device. Description of embodiments

[0017] The following describes in detail embodiments of a semiconductor device of the present invention with reference to the figures. First embodiment.

[0018] Fig. Figure 1 is a schematic cross-sectional structural view showing a semiconductor device in a first embodiment of the present invention. In the drawing, a semiconductor device 100 comprises: a base plate 1; a housing part 2; a connecting material 3; power semiconductor elements 4, each serving as a semiconductor element; an insulating substrate 5; bond wires 6; a terminal 7; a silicone gel 8, serving as a sealing resin; a cover 9, serving as a cover part; a retaining plate 10; electrode patterns 51, 53; and an insulating layer 52.

[0019] The insulating substrate 5 has a lower surface (back surface) that is joined to the base plate 1 using the bonding material 3. The insulating substrate 5 has the insulating layer 52 and the electrode patterns 51, 53. In the insulating substrate 5, the electrode pattern 51 is formed on the upper surface (front surface) of the insulating layer 52, and the electrode pattern 53 is formed on the lower surface (back surface) of the insulating substrate 5. The power semiconductor element 4 is fixed to the electrode pattern 51, which is formed on the upper surface of the insulating substrate 5, using the bonding material 3, such as solder. Examples of the power semiconductor element 4 used herein include: a power-controlling semiconductor element, such as a MOSFET or an IGBT, that controls a large amount of current; and a reverse-flow diode.

[0020] Furthermore, the electrode pattern 53 is fixed to the base plate 1 on the lower surface of the insulating substrate 5 using the bonding material 3, such as solder. A region (hereinafter referred to as the "housing") enclosed by the base plate 1 and the housing part 2 arranged around the base plate 1 is formed with the base plate 1, which serves as a bottom plate.

[0021] To ensure the insulating properties in the semiconductor device 100, the silicone gel 8, which serves as a sealing resin, is provided in the housing. In this case, the silicone gel 8 is provided up to a height at which the power semiconductor element 4 and the bond wire 6 are sealed within the silicone gel 8.

[0022] A connection, such as the bond wire 6, is connected to the power semiconductor element 4, thus electrically connecting one electrode of the power semiconductor element 4 to the outside. This bond wire 6 is also connected to the terminal 7, and is therefore electrically connected to the outside of the housing. The terminal 7 is formed in the housing part 2 by insert forming or outsert forming.

[0023] The cover 9 is located on the upper part of the housing 2 (opposite the area in contact with the base plate 1). The cover 9 separates the interior and exterior of the semiconductor device 100, thus preventing dust and the like from entering the semiconductor device 100. The cover 9 is attached to the housing part 2 by means of an adhesive (not shown) or a screw (not shown).

[0024] The retaining plate 10 is arranged so that it is connected to the lower surface of the cover 9, which in this case is the inside of the cover 9; that is, it is arranged so that it is connected to the surface of the cover 9 facing the silicone gel 8. The retaining plate 10 is in contact with the silicone gel 8. The retaining plate 10 is arranged so that it projects from the cover 9, thus bringing the retaining plate 10 and the silicone gel 8 into contact with each other. Consequently, pressure loads are generated in the silicone gel 8 by the retaining plate 10, in the direction from the retaining plate 10 towards the insulating substrate 5.

[0025] Details of each component are described below.

[0026] A significant improvement is achieved when a semiconductor element using a semiconductor material capable of operating at 150°C or higher is employed as the power semiconductor element 4. In particular, a significant improvement is achieved when a so-called "wide bandgap semiconductor" is used. The wide bandgap semiconductor is made of a material such as silicon carbide (SiC), gallium nitride (GaN), or diamond (C), and it has a band gap larger than that of silicon (Si).

[0027] Furthermore, it shows Fig.1 For example, two power semiconductor elements 4 are mounted in a single semiconductor device 100. However, the number of power semiconductor elements 4 is not limited to this, and the required number of power semiconductor elements 4 can be mounted depending on the application and circuit configuration.

[0028] Although solder is used as the joining material 3, the joining material 3 is not limited to this. Silver or a silver alloy can be used to join the power semiconductor element 4 and the electrode pattern 51, and it can be used to join the electrode pattern 53 and the base plate 1.

[0029] Each of the electrode patterns 51, 53, base plate 1, and terminal 7 is normally made of copper. However, their material is not limited to copper. Any material can be used as long as it has the necessary heat dissipation properties.

[0030] For example, aluminum or iron can be used, or a material in combination with these. Alternatively, a composite material such as copper / Invar / copper can be used, or an alloy such as AlSiC or CuMo can be used.

[0031] A surface of the material used for each of electrode patterns 51, 53, base plate 1, and terminal 7 is normally nickel-plated. However, the plating is not limited to nickel, and gold or tin plating can also be used. Any structure can be used as long as the necessary current and voltage can be supplied to the power semiconductor element 4. Furthermore, since at least a portion of terminal 7 and electrode pattern 51 is embedded in the sealing resin 8, slight irregularities can be provided on the surfaces of terminal 7 and electrode pattern 51, thus improving the adhesion between the sealing resin 8 and each of terminal 7 and electrode pattern 51.

[0032] In the insulating substrate 5, the electrode patterns 51 and 53, each made of copper or aluminum, are provided on the respective surfaces of the insulating layer 52, which uses a ceramic such as Al₂O₃, SiO₂, AlN, BN, or Si₃N₄. The material of the insulating substrate 5, which must have high thermal conductivity and insulating properties, is not limited to the material described above. In the insulating substrate 5, the electrode patterns 51 and 53 can be provided on the insulating layer 52, for example, as a cured resin with ceramic powder dispersed therein or a cured resin with a ceramic plate embedded therein.

[0033] Furthermore, the ceramic powder used for the insulating substrate 5 (the insulating layer 52) may be Al₂O₃, SiO₂, Al₂Ain, Bn, Si₃N₄, or the like. However, the ceramic powder is not limited to these, and diamond, SiC, B₂O₃, or the like may also be used. Additionally, a resin powder such as a silicone resin or an acrylic resin may be used.

[0034] Such a powder often has a spherical shape. However, the shape is not limited to this, and a granular, grain-like, flake, aggregate, or similar form can also be used. The amount of powder provided can be such that the necessary heat dissipation and insulating properties are achieved. Although an epoxy resin is normally used for the insulating substrate 5 (the insulating layer 52), the resin is not limited to this, and a polyimide resin, a silicone resin, an acrylic resin, or the like can also be used. Any material can be used as long as it possesses both insulating and adhesive properties.

[0035] For the bond wire 6, a wire material made of aluminum or gold with a circular cross-sectional shape is used, but the material is not limited to this. For example, a copper plate in the form of a strip (band) with a square cross-sectional shape can be used. As in Fig. As shown in Figure 1, in the first embodiment four bond wires 6 are used to connect the power semiconductor elements 4, the power semiconductor element 4 and the terminal 7, and the electrode pattern 51 and the terminal 7. However, the bond wires 6 are not limited to these connections. The required number of bond wires 6, each with a specific thickness (size), can be provided depending on the current density of the power semiconductor element 4 or the like.

[0036] Furthermore, the bond wire 6 can be connected to a target area by melting a piece of metal such as copper or tin, or by ultrasonic bonding or the like. However, the connection method is not particularly limited, and any method or structure can be used as long as the necessary current and voltage can be supplied to the power semiconductor element 4.

[0037] For housing part 2, it is preferred to use a resin material with a high softening point, such as PPS resin (polyphenylene sulfide resin). However, the material is not particularly limited as long as it is not thermally deformed within the operating temperature range of the semiconductor device 100 and possesses insulating properties.

[0038] The cover 9 is located at the top of the housing part 2, so that the inside and outside of the semiconductor device 100 are separated, preventing dust and the like from entering the semiconductor device 100.

[0039] The retaining plate 10 is arranged such that it is connected to the side of the lower surface (the surface facing the silicone gel 8) of the cover 9 for the purpose of contact with the sealing resin 8, and it is in contact with the silicone gel 8, which is the material of the sealing resin. The retaining plate 10 can be made of a material such as a thermoplastic resin or a thermosetting resin. For example, if the retaining plate 10 is made of the same material as the element of the cover 9, the retaining plate 10 and the cover 9 can be manufactured together in the same step as the production of the cover 9 of the semiconductor device 100. By manufacturing them together, operation can be simplified. The retaining plate 10 projects from the surface of the cover 9 facing the silicone gel 8 in the direction of the silicone gel 8.The retaining plate 10 is always in contact with the silicone gel 8 to prevent the occurrence of negative pressure (tensile loads) with respect to the silicone gel 8. Since the retaining plate 10 is positioned so that it projects from the cover 9, the lower surface of the retaining plate 10 and a portion of its side surface are in close contact with the silicone gel 8. The retaining plate 10 is in contact with the surface of the cured silicone gel 8, which serves as a sealing resin.

[0040] To ensure insulation in the semiconductor device 100, the silicone gel 8 is provided in the area surrounded by the base plate 1 and the housing part 2. The silicone gel 8 is provided up to a height at which the power semiconductor element 4 and the bond wire 6 are sealed within the silicone gel 8.

[0041] It should be noted that silicone resin, for example, is used as a sealing resin. However, the sealing resin is not limited to this. Any resin can be used as long as it possesses both the desired modulus of elasticity and heat resistance.

[0042] Fig. Figure 2 is a schematic cross-sectional structural view showing the semiconductor device in the first embodiment of the present invention at low temperature. Fig. Figure 3 is a schematic cross-sectional structural view showing the semiconductor device in the first embodiment of the present invention at high temperature. Fig. Figure 4 is another schematic cross-sectional structural view showing the semiconductor device in the first embodiment of the present invention at low temperature. Each of Fig. 2 and Fig.Figure 4 is a schematic cross-sectional structural view showing the interior of the semiconductor device when the temperature of the semiconductor device is reduced to less than or equal to normal temperature. Fig. Figure 3 is a schematic cross-sectional structural view showing the interior of the semiconductor device when the temperature of the semiconductor device is increased to the point where it is greater than or equal to the curing temperature of the silicone gel.

[0043] The curing temperature of the silicone gel 8, used for the insulating seal of the semiconductor device 100, is typically 60 to 150 °C. Furthermore, the coefficient of linear expansion of the silicone gel 8, used for the insulating seal of the semiconductor device 100, is typically 300 to 500 ppm / K. On the other hand, the coefficient of linear expansion of each of the other components used for the semiconductor device 100 is 3 to 25 ppm / K.

[0044] The linear expansion coefficient of silicone gel 8 is, in terms of value, several tens to several hundred times greater than the linear expansion coefficient of each of the other components used for the semiconductor device 100.

[0045] When the temperature of the semiconductor device 100 is reduced to normal temperature after the sealing step has been performed by curing the silicone gel 8 provided in the housing 2, the silicone gel 8 contracts thermally more than the other components. On this occasion, as a result of the thermal contraction of the silicone gel 8, the height of the surface area of ​​the silicone gel 8 becomes lower than its height during curing (see Figure 1). Fig. 1).

[0046] If the temperature of the semiconductor device 100 becomes lower than the normal temperature, the height of the area of ​​the silicone gel 8 becomes even lower, as shown in Fig. 2 shown.

[0047] As in Fig. As shown in Figure 4, the height of the area of ​​the silicone gel 8 can also correspond to the contact position with a peripheral area of ​​the retaining plate 10.

[0048] If, in turn, the temperature of the semiconductor device 100 is higher than the curing temperature, the silicone gel 8 expands thermally more than the other components, with the result that the height of the surface of the silicone gel 8 becomes greater than its position during curing, as in Fig. 3 shown.

[0049] Here, the ratio ΔL = V × β × ΔT × 1 / S is satisfied, where ΔL represents the change value of the silicone gel 8 as a result of the temperature change, S represents the surface area of ​​the silicone gel 8, V represents the volume of the silicone gel 8, β represents the volumetric expansion coefficient of the silicone gel 8, and ΔT represents a temperature change value.If the value with which the retaining plate 10, which is arranged on the cover 9, is pressed from the surface of the silicone gel 8 is greater than the change value ΔLmin of the silicone gel 8 at a temperature difference ΔTmin of the lowest temperature under an operating temperature environment of the semiconductor device 100 from a temperature when the retaining plate 10 is pressed from the surface of the silicone gel 8 in the direction of the insulating substrate 5, the retaining plate 10 is always in contact with the surface of the silicone gel 8 under the operating temperature environment of the semiconductor device 100, with the result that the internal stresses of the silicone gel 8 below the retaining plate 10 become pressure stresses.

[0050] Therefore, the pressure applied to the retaining plate 10, in the direction from the surface of the silicone gel 8 towards the insulating substrate 5, is preferably set to be greater than ΔLmin. For example, if the retaining plate 10 is located at room temperature (25°C) in the case where the lowest temperature environment in which the semiconductor device 100 is used is -40°C, then ΔTmin is 65°C, and the pressure value ΔLmin is set accordingly. For example, ΔLmin = 1.7 mm applies to the case of a semiconductor device where sealing is performed up to a height of 20 mm, using a resin that has a volumetric expansion coefficient β of 1300 ppm / K. By applying pressure greater than this ΔLmin, the retaining plate is always positioned in the gel at the low temperature, thus allowing pressure loads to be exerted.

[0051] Furthermore, if the mounting plate 10 is positioned (pressed) at a temperature of -40 °C, i.e., at the lowest temperature at which the semiconductor device 100 is used, ΔTmin is 0, and therefore the pressure value ΔLmin is also 0. This means that when the mounting plate 10 is merely in contact (close contact) with the surface of the silicone gel 8, the pressure loads are always exerted on the power semiconductor element 4 and the insulating substrate 5 below the mounting plate 10 under the operating environment of the semiconductor device 100. Consequently, bubble growth and detachment of the silicone gel 8 from the insulating substrate 5 can be prevented, thus preventing insulation degradation of the power module. Therefore, a reliable semiconductor device can be maintained under the operating ambient temperature.

[0052] It should be noted that even with a pressure value of less than or equal to ΔLmin, the effect is achieved that the bubbles and detachment caused by an interface between the silicone gel 8 and the power semiconductor element 4 or the insulating substrate 5 are prevented.

[0053] Fig. Figure 5 is a schematic top-view structural diagram showing the semiconductor device in the first embodiment of the present invention. Fig. Figure 6 is a schematic cross-sectional structural view showing another semiconductor device in the first embodiment of the present invention. Fig. Figure 7 is a schematic top-view structural diagram showing another semiconductor device in the first embodiment of the present invention. Fig. Figure 5 is a schematic top view of the structure, showing the case in which a retaining plate 10 is provided. Fig. 6 and Fig.Figures 7 are schematic cross-sectional structural views and a schematic structural top view, each showing the case in which two retaining plates 10 are provided.

[0054] In the semiconductor device 100, which has the silicone gel 8 for sealing, bubbles are generated at the following locations: a location to which the bond wire 6 is connected; an interface between the insulating substrate 5 and the bonding material 3; an interface between the housing and the adhesive; and the like. It is very important to ensure insulation in the power semiconductor element 4 and the insulating substrate 5. Therefore, it is preferred that the retaining plate 10 be arranged to cover the upper surface of the insulating substrate 5. The schematic top view of the structure, shown in Fig. Figure 5 illustrates such a structure in which the insulating substrate 5 is arranged below the retaining plate 10.

[0055] Furthermore, it shows Fig. 1 the case in which a single insulating substrate 5 is provided. However, it is also applicable to a semiconductor device with two or more insulating substrates 5 mounted therein. Furthermore, instead of a single mounting plate 10, a plurality of divided areas of the mounting plate 10 can also be provided on the cover 9. For example, the same effect can also be achieved if two divided areas of the mounting plate 10 are arranged, as in a semiconductor device 200 as described in Fig. 6 and Fig. 7 is shown.

[0056] Furthermore, according to the present embodiment, the retaining plate 10 has a flat shape at its contact area with the silicone gel 8. However, the retaining plate 10 can also have a shape that projects in the direction of the insulating substrate 5. The retaining plate 10 is pressed from the surface of the silicone gel 8 towards the insulating substrate 5 after the silicone gel 8 has hardened. If the tensile strength of the silicone gel 8 is low, cracks may therefore be caused in the silicone gel 8 from an end region of the retaining plate 10 when the retaining plate 10 is pressed into the silicone gel 8. Therefore, it is preferred to round off a corner of the end region of the retaining plate 10.

[0057] A manufacturing process according to the first embodiment is described below. In particular, a method for arranging the cover 9 including the retaining plate 10 is described below.

[0058] Each of Fig. 8 to Fig. Figure 11 is a schematic cross-sectional structural view showing a method for manufacturing the semiconductor device in the first embodiment of the present invention. Fig. Figure 12 is a schematic cross-sectional structural view showing the cover and the retaining plate in the first embodiment of the present invention. Fig. Figure 13 is a schematic cross-sectional structural view showing a further cover and retaining plate in the first embodiment of the present invention. Fig. Figure 14 is a schematic cross-sectional structural view showing a further cover and retaining plate in the first embodiment of the present invention. Fig. Figure 8 is a schematic cross-sectional structural view after mounting and connecting the power semiconductor element 4 and the like, and completing the sealing with the sealing resin. Fig.Figure 9 is a schematic cross-sectional structural view in which the retaining plate 10 is arranged on the cover 9. Fig. Figure 10 is a schematic cross-sectional structural view immediately before the cover 9 is attached to the housing part 2. Fig. Figure 11 is a schematic cross-sectional view of the semiconductor device 100 after the cover 9 has been fitted. Fig. Figure 12 shows a structure in which the retaining plate 10 is arranged on the cover 9. Fig. Figure 13 shows a structure in which a projection 101, which serves as the retaining plate, is provided in the cover 9. Fig. Figure 14 shows a structure in which a plate 103 is arranged on the cover 9 at a rod 102.

[0059] The semiconductor device 100 can be manufactured using a process (through steps) as described in Fig. 8 to Fig. 11 shown. Fig.Figure 8 shows a step (element arrangement step, resin provisioning step, and resin curing step) in which the semiconductor device 100 is prepared before the cover 9 is attached. In this step, the base plate 1, the housing part 2, the insulating substrate 5, the power semiconductor element 4, the bonding wire 6, and the silicone gel 8 are arranged appropriately, thus forming the semiconductor device 100 before the cover 9 is attached.

[0060] More precisely: The power semiconductor element 4 is fixed to the electrode pattern 51 on the front surface of the insulating substrate 5 using the bonding material 3, such as solder. The electrode pattern 53 is also fixed to the base plate 1 on the back surface of the insulating substrate 5 using the bonding material 3, such as solder (element assembly step). The area enclosed by the base plate 1 and the housing part 2 is formed by the base plate 1, which serves as a bottom plate. This area serves as the housing. The silicone gel 8 is applied to a height sufficient to seal the power semiconductor element 4 and the bond wire 6 within this housing (resin application step).After sealing with the silicone gel 8 in the housing, the semiconductor device 100 is placed under reduced pressure, which removes bubbles in the silicone gel 8 inside the semiconductor device 100 (resin curing step).

[0061] Next, a step is described in which the retaining plate 10 is positioned on the cover 9. Fig. Figure 9 shows the state after the retaining plate 10 has been attached to the cover 9. Furthermore, each of the Fig. 12 to Fig. Figure 14 shows a schematic cross-sectional structural view illustrating the shape of the retaining plate 10. Fig. 12 is a plate-shaped structure arranged on the cover 9 as a retaining plate 10 (see Fig. 9). In Fig. In 13, the projection 101 is shaped such that it protrudes in the direction of the insulating substrate 5, which is arranged on the cover 9. Fig.In section 14, the plate 103 extends along the rod 102 from the cover 9. Therefore, the shape of the retaining plate 10 is not particularly restricted, as long as the retaining plate 10 can function in such a way as to push downwards the sealing resin (silicone gel 8) that covers the power semiconductor element 4.

[0062] Regarding the step in which the retaining plate 10 is positioned on the cover 9, the following applies: If the element of the retaining plate 10 is made of the same material as that of the element of the cover 9, the retaining plate 10 can be formed together with the cover 9 in the same step. Furthermore, if the element of the cover 9 differs from that of the retaining plate 10, the retaining plate 10 can be formed by bonding, using an adhesive or the like, a projection onto the surface of the cover 9 that faces the insulating substrate 5. If, in addition, the height of the retaining plate 10 needs to be adjusted, it can be adjusted by threading a screw into the cover 9 and the retaining plate 10. In this case, a screw is first inserted into a threaded hole provided on the side of the cover 9 in an outward direction, i.e.,h. the side of the cover 9 inwards. Then a threaded hole of the retaining plate 10 is screwed into the protruding screw which is arranged on the cover 9, whereby the retaining plate 10 can be adjusted to a predetermined height.

[0063] The following describes a step (close contacting step) in which the silicone gel 8 is compressed (brought into close contact) using the cover 9, which forms the retaining plate 10 on it. As in Fig.As shown in Figure 10, the silicone gel 8 is provided in the housing. The silicone gel 8 is then cured at a predetermined curing temperature, and the temperature of the cured silicone gel 8 is then reduced to a temperature less than or equal to room temperature. The cover 9, with the retaining plate 10 attached to it, is then positioned so that the retaining plate 10 is in contact with the surface of the silicone gel 8, thus pressing the cover 9 with the retaining plate 10 in a direction that compresses the silicone gel 8 towards the insulating substrate 5. The cover 9 is then fixed at a predetermined height.

[0064] The value with which the retaining plate 10 is pressed away from the surface of the silicone gel 8 is preferably greater than or equal to ΔLmin in the temperature range from the temperature in the state in which no load is applied, i.e., the temperature when the retaining plate 10 is arranged in the semiconductor device 100, to the lowest temperature at which the semiconductor device 100 is used. This is because pressure loads are preferably always exerted on the insulating substrate 5 in the operating temperature range of the semiconductor device 100.

[0065] For example, if the mounting plate 10 is located at room temperature (25 °C) in the case where the lowest temperature environment in which the semiconductor device 100 is used is -40 °C, then ΔTmin is 65 °C, and the pressure value ΔLmin is set accordingly.

[0066] For example, ΔLmin = 1.7 mm applies to the case of a semiconductor device where sealing is performed up to a height of 20 mm, using a resin with a volumetric expansion coefficient β of 1300 ppm / K. By pressing the retaining plate more firmly than ΔLmin, the retaining plate remains embedded in the gel even at low temperatures, thus exerting pressure loads.

[0067] Furthermore, if the mounting plate 10 is positioned (pressed) at a temperature of -40 °C, i.e., at the lowest temperature at which the semiconductor device 100 is used, ΔTmin is 0 °C, and therefore the pressure value ΔLmin is 0 mm. This means that when the mounting plate 10 is merely in close contact with the surface of the silicone gel 8, the pressure loads are always exerted on the power semiconductor element 4 and the insulating substrate 5 below the mounting plate 10 under the operating environment of the semiconductor device 100, thus ensuring a reliable semiconductor device. Therefore, bubble growth and delamination under the operating ambient temperature of the semiconductor device 100 can be prevented, and the delamination of the silicone gel 8 from the insulating substrate 5 can be prevented, thereby preventing insulation degradation of the power module.

[0068] It should be noted that even with a pressure value of less than or equal to ΔLmin, the effect is achieved that the bubbles and detachment caused by an interface between the silicone gel 8 and the power semiconductor element 4 or the insulating substrate 5 are prevented.

[0069] Next, a step is described in which the cover 9 is fixed to the housing part 2. Fig. Figure 11 shows a state after the cover 9 has been fixed to the housing.

[0070] A method for fixing the cover 9 to the mounting plate 10 attached to it is not particularly restricted, as long as the mounting plate 10 is fixed at a predetermined height. However, the cover 9 can also be fixed using an adhesive or by means of fastening screws.

[0071] If the cover 9 is to be fixed to the housing part 2 using an adhesive, an uncured adhesive is inserted into a syringe and applied to the required areas of the cover 9 and the housing part 2 using a device such as a dispenser. After the cover 9 has been bonded to the housing part 2, it is pressed together using a clamping device so that the cover 9 and the retaining plate 10 are fixed at predetermined heights. After the adhesive has cured under a predetermined curing condition, the clamping device is removed. For example, if KE-1833, a silicone resin supplied by Shin-Etsu Chemical Co. Ltd., is used as the adhesive, the curing process is carried out for 1 hour at 120 °C.After the adhesive has cured, the clamping device is cooled to room temperature and removed, thereby producing the semiconductor device 100 in which the silicone gel 8 is compressed by means of the holding plate 10.

[0072] The adhesive for the cover 9 and the housing part 2 is not particularly restricted as long as the fixed cover 9 is not separated from the housing part 2 due to forces resulting from the thermal expansion of the silicone gel 8 during high-temperature operation of the semiconductor device 100. However, the adhesive strength with respect to the housing part is preferably greater than or equal to 1.5 MPa.

[0073] If the cover 9 is fixed to the housing part 2 by means of fastening screws, threaded holes are provided in the housing part 2, and screws are evenly inserted into the provided threaded holes so that the silicone gel 8 is at a predetermined height when the retaining plate 10 is pressed. The number of fastening screws is not particularly limited. However, preferably an even number of screws is provided so that the force for compressing the silicone gel 8 against the retaining plate 10 is applied evenly.

[0074] The semiconductor device 100 can be manufactured using such a manufacturing process.

[0075] The following describes features of the semiconductor device 100, which was manufactured using such a manufacturing process. In a semiconductor device manufactured by placing a conventional holding plate at a predetermined position within the device before the silicone gel is supplied, and by curing the silicone gel at a predetermined temperature, the silicone gel is thermally expanded under a high-temperature environment. Consequently, the silicone gel expanded below the holding plate is prevented from expanding further by the holding plate, and thus pressure is exerted below the holding plate, preventing the formation of bubbles and detachment below the holding plate.

[0076] However, since the silicone gel contracts thermally under a low-temperature environment that is less than or equal to its curing temperature, the contracted silicone gel beneath the mounting plate generates tensile stresses in all directions, including on the mounting plate itself, with which it is in close contact. Consequently, tensile stresses are also generated in the direction of the cover above, specifically on the base area of ​​the semiconductor device where the power semiconductor element and the insulating substrate beneath the mounting plate are located. This can promote blistering and delamination.

[0077] In the semiconductor device 100 manufactured using the manufacturing process of the present embodiment, however, the retaining plate 10 is pressed away from the surface of the silicone gel 8 after the silicone gel 8 has hardened, so that pressure loads are exerted on the power semiconductor element 4 and the insulating substrate 5. By exerting a pressure value greater than or equal to ΔLmin, pressure loads are exerted even when the silicone gel 8 contracts in the lowest temperature range under the operating environment of the semiconductor device 100.Therefore, not only during the expansion of the silicone gel 8 under the high-temperature environment, but also during its contraction under the low-temperature environment, bubble growth or detachment caused by the power semiconductor element 4 and the insulating substrate 5 can be prevented below the mounting plate 10, thereby improving the insulation reliability of the semiconductor device 100.

[0078] In the semiconductor device 100 configured as described above, compressive loads can be exerted on the power semiconductor element 4 and the insulating substrate 5 below the mounting plate 10 to cause the silicone gel 8 to expand under the high-temperature operating environment of the semiconductor device 100, and tensile loads are also exerted on the power semiconductor element 4 and the insulating substrate 5 below the mounting plate 10 to cause the silicone gel 8 to contract under the low-temperature operating environment, thereby improving the insulation reliability of the semiconductor device.

[0079] Furthermore, the silicone gel 8 is thermally expanded at a high temperature, and the expanded silicone gel 8 is pressed downwards from the retaining plate 10, thereby transforming the internal stresses of the silicone gel 8 into pressure stresses in the direction of the insulating substrate 5 below the retaining plate 10, thus preventing bubble growth or detachment. Consequently, the effect of preventing insulation deterioration of the semiconductor device is achieved.

[0080] Although the pressure loads in the direction of the insulating substrate 5 are reduced at low temperatures compared to high temperatures, due to the thermal contraction of the silicone gel 8 at low temperatures, the pressure loads are still exerted, thus preventing bubble growth and delamination. Consequently, a reliable semiconductor device can be obtained.

[0081] Furthermore, the invention can be made by appropriately combining a plurality of components disclosed in the embodiments described above. Examples

[0082] In the present example, the following describes the result of a thermal cycle test performed with the mounting plate 10 attached to a test semiconductor device 100, whereby the pressure value and size of the mounting plate 10 were varied. The thermal cycle test was performed by placing the entire semiconductor device 100 in a temperature-controlled chamber capable of regulating the temperature and by repeatedly varying the temperature of the temperature-controlled chamber between -40 °C and 150 °C.

[0083] In semiconductor device 100, the base plate 1 measured 90 × 140 mm for evaluation, and a substrate using Si3N4, measuring 50 × 60 mm, was used for the insulating substrate 5. Four IGBTs, each measuring 11 × 12 mm, were used as power semiconductor elements 4. Aluminum with a wire diameter of 0.4 mm was used as the bonding wire 6. WACKER SilGel612, supplied by Wacker Asahikasei Silicone Co. Ltd., was used as the silicone gel 8 for sealing. Each of the housing part 2, cover 9, and mounting plate 10 was manufactured using PPS resin Z240, supplied by DIC Corporation.

[0084] The semiconductor device 100, containing the elements described above, was not subjected to a reduced-pressure process to promote the formation of bubbles in the silicone gel 8 and its detachment. It was manufactured by introducing 160 g of silicone gel 8 under atmospheric pressure, leaving the silicone gel 8 at atmospheric pressure for 30 minutes, and curing the silicone gel 8 at 70 °C / lhr. The mounting plate 10 is manufactured by cutting 20 mm thick PPS to a predetermined size and bonding it to the back surface of the cover 9 using a silicone adhesive.

[0085] The thermal cycling test determined whether or not bubbles were generated in the silicone gel and whether or not delamination occurred between the silicone gel and each of the various components. In this determination, "o" represents the case where the number of bubbles generated by visual observation is 0, "Δ" represents the case where the number of bubbles generated by visual observation is 1 to 4, and "×" represents the case where the number of bubbles generated by visual observation is equal to or greater than 5. Regarding delamination, "o" represents the case where no delamination or cracking occurs at the interface between the silicone gel 8 and each of the various components, and "x" represents the case where delamination and cracking occur at the interface between the silicone gel 8 and each of the various components.

[0086] Fig.Figure 15 is a schematic cross-sectional structural view of a conventional semiconductor device. Fig. Figure 15 shows that in a conventional semiconductor device 300 according to comparative example 1, no retaining plate 10 such as the one provided on the cover 9 in the first embodiment was provided.

[0087] Table 1 shows the relationship between the pressure value of each fabricated and evaluated retaining plate and the thermal cycle test. The samples were fabricated by positioning the 50 × 60 mm retaining plate 10 just above the insulating substrate 5 and by varying the pressure value under a temperature environment of 25 °C. The thermal cycle test was performed under the following three conditions: the pressure value of the retaining plate 10 was 0 mm (Comparison Example 1); the pressure value of the retaining plate 10 was 1 mm (Example 2); and the pressure value of the retaining plate 10 was 3 mm (Example 1). Table 1 Reliability test (thermal cycle test: -40 °C / 150 °C) Number of test cycles / cycle 0 250 500 1000 With no mounting plate (pressed down by 0 mm) Blow ◯ × × × Replacement ◯ ◯ × × With mounting plate (pressed down by 1 mm) Blow ◯ △ △ △ Replacement ◯ ◯ ◯ ◯ With mounting plate (pressed down by 3 mm) Blow ◯ ◯ ◯ ◯ Replacement ◯ ◯ ◯ ◯

[0088] According to Table 1, in the sample without a retaining plate 10 in comparative example 1, some bubbles were generated, originating from a lower area of ​​the bonding material 3 of the insulating substrate 5 at 250 cycles in the thermal cycle test. On the other hand, in each of the samples with retaining plates 10 in examples 1 and 2, it was found that the formation of bubbles and delamination was prevented. However, some bubbles were confirmed in the sample in example 2, in which the pressure value of the retaining plate 10 was set to 1 mm. In the sample from example 1, where the pressure value of the retaining plate 10 was set to 3 mm, it was found that the formation of bubbles and delamination was not observed even after 1000 cycles of the thermal cycle test.

[0089] According to the above results, it was found that the formation of bubbles and detachment is prevented by positioning the retaining plate 10 above the power semiconductor element 4 and insulating substrate 5 in such a way that it constantly exerts pressure on the silicone gel 8. It was also found that a higher pressure value on the retaining plate 10 is more effective in preventing the formation of bubbles and detachment.

[0090] Table 2 shows the relationship between the size of each manufactured and evaluated mounting plate and the thermal cycle test. The samples were manufactured by varying the size of the mounting plate 10, positioning the mounting plate 10 just above the insulating substrate 5, and pressing the mounting plate 10 with a set pressure of 3 mm below an ambient temperature of 25 °C. The mounting plate size was specified as follows: 10 × 15 mm (Example 2), 25 × 30 mm (Example 3), 30 × 50 mm (Example 4), 50 × 60 mm (Example 1), and 84 × 120 mm (Example 5). The mounting plate was centered on the insulating substrate 5. Table 2 Reliability test (thermal cycle test: -40 °C / 150 °C) Number of test cycles / cycle 0 250 500 1000 Mounting plate size (10x15 mm) Blow ◯ × × × Replacement ◯ ◯ × × Mounting plate size (25x30 mm) Blow ◯ △ △ × Replacement ◯ ◯ ◯ × Mounting plate size (30x50 mm) Blow ◯ ◯ ◯ ◯ Replacement ◯ ◯ ◯ ◯ Mounting plate size (50x60 mm) Blow ◯ ◯ ◯ ◯ Replacement ◯ ◯ ◯ ◯ Mounting plate size (84 x 120) Blow ◯ ◯ ◯ ◯ Replacement ◯ × × ×

[0091] According to Table 2, the same result was achieved with regard to the occurrence of bubbles and detachment as without the retaining plate 10, as shown in Table 1, for the sample from Example 2, where the size of the retaining plate 10 was 15 mm. Therefore, when the size of the retaining plate 10 was 5% of the area of ​​the insulating substrate 5, the effect of compression on preventing bubbles and detachment was hardly observed with respect to the power semiconductor element 4 and the insulating substrate 5.

[0092] In the sample from Example 3, where the size of the retaining plate was 25 × 30 mm, it was found that the formation of bubbles and delamination could be prevented, in comparison with the sample without retaining plate 10, as shown in Table 1. Although the formation of bubbles from an area above which the retaining plate 10 was located was not confirmed, it was confirmed that bubbles are generated from the bonding material 3 at the lower area of ​​the insulating substrate 5 when the size of the retaining plate 10 was 25% of the area of ​​the insulating substrate 5 and the retaining plate 10 was not present above the outer periphery of the insulating substrate 5.

[0093] In the sample from Example 4, where the size of the holding plate was 30 × 50 mm, it was found that the occurrence of bubbles and detachment could be prevented, in comparison with the sample without a holding plate 10, as shown in Table 1. It was found that when the size of the holding plate 10 had a value of 50% of the area of ​​the insulating substrate 5, the occurrence of bubbles and detachment was not observed even after 1000 cycles of the thermal cycle test.

[0094] In the sample from Example 1, where the size of the retaining plate 10 was 50 × 60 mm, it was found that the formation of bubbles and detachment could be prevented, in comparison with the sample without retaining plate 10, as shown in Table 1. It was found that when the size of the retaining plate 10 was as large as the area of ​​the insulating substrate 5, the formation of bubbles and detachment was not observed even after 1000 cycles of the thermal cycling test.

[0095] In the sample from Example 5, where the size of the retaining plate 10 was 84 × 120 mm, it was found that the occurrence of bubbles and delamination could be prevented, compared to the sample without the retaining plate 10, as shown in Table 1. Although the occurrence of bubbles from an area above which the retaining plate 10 was positioned was not confirmed, the following is true: When the retaining plate was larger than or equal to 80% of the area of ​​the outermost surface of the silicone gel 8 of the semiconductor device 100 (when the contact area was larger than or equal to 80% of this), delamination from a side face of the housing part 2 and cracking of the silicone gel from a side face of the retaining plate 10 were confirmed at 250 cycles of the thermal cycle test. This is presumably due to the following reason.If the size of the retaining plate 10 was greater than or equal to 80% of the size of the base plate 1 of the semiconductor device 100, the silicone gel 8, which expanded at a high temperature, contracted intensely in the area not covered by the retaining plate 10, i.e., the area less than or equal to 20% of it, with the result that the value of the displacement of the silicone gel 8 became large, which resulted in the detachment of the silicone gel 8 from the housing part 2 and the cracking of the silicone gel 8.

[0096] To prevent detachment and cracking, it was found that the contact area of ​​the retaining plate 10 with the silicone gel 8 should therefore be less than 80%.

[0097] Based on the above result, the following applies: Since the insulating substrate 5 is covered by the retaining plate 10, the formation of bubbles and detachment can be prevented. Furthermore, detachment and cracking can be prevented if the area of ​​the retaining plate is greater than or equal to 50% of the area of ​​the insulating substrate 5 and its contact area with the area of ​​the silicone gel 8 is less than 80%. Reference symbol list 1 Base plate; 2 cases; 3 Connecting material; 4 Power semiconductor element; 5 Insulating substrate; 6 Bond wire; 7 electrode connection; 8 silicone gel; 9 Cover; 10 Mounting plate; 51, 53 Electrode patterns; 52 Insulating layer; 100, 200, 300 semiconductor device; 101 lead; 102 Staff; 103 plate.

Claims

[1] Semiconductor device (100) comprising the following: - an insulating substrate (5) with a top surface on which a semiconductor element (4) is mounted; - a base plate (1) connected to a lower surface of the insulating substrate (5); - a housing element (2) that surrounds the insulating substrate (5) and is in contact with a surface of the base plate (1) to which the insulating substrate (5) is connected; - a sealing resin (8) provided in an area surrounded by the base plate (1) and the housing element (2) so that the insulating substrate (5) is sealed; - a cover part (9) which faces a surface of the sealing resin (8) and is fixed to the housing element (2); and - a retaining plate (10), wherein a lower surface of the retaining plate is in close contact with the surface of the sealing resin (8), whereby a pressure load can be generated on the sealing resin (8) during a heat cycle, wherein an upper surface of the retaining plate is fixed to a surface of the cover part (9) facing the surface of the sealing resin (8), wherein the size of the retaining plate (10) is greater than or equal to 50% of the surface of the insulating substrate (5), and a contact area of ​​the retaining plate (10) with the surface of the sealing resin (8) is less than 80% of the surface of the sealing resin (8). [2] Semiconductor device (100) according to claim 1, wherein the retaining plate (10) is arranged above the insulating substrate (5). [3] Semiconductor device (100) according to one of claims 1 to 2, wherein a plurality of divided areas of the retaining plate (10) is formed. [4] Semiconductor device (100) according to any one of claims 1 to 3 wherein the retaining plate (10) is made of a material that is different from a material of the cover part (9). [5] Method for manufacturing a semiconductor device (100), wherein the method comprises: - Providing an insulating substrate (5) on a base plate (1); - Providing a sealing resin (8) in an area surrounded by the base plate (1) and a housing element (2); - Hardening of the provided sealing resin (8); - Arranging a retaining plate (10) in close contact with the cured sealing resin (8) at the lowest temperature in a temperature range in which the use of the semiconductor device (100) is permissible, wherein the size of the retaining plate (10) is greater than or equal to 50% of the area of ​​the insulating substrate (5), and the contact area of ​​the retaining plate (10) with the area of ​​the sealing resin (8) is less than 80% of the area of ​​the sealing resin (8); and - Fixing the retaining plate (10) at a predetermined height. [6] Method for manufacturing the semiconductor device (100) according to claim 5, wherein when the retaining plate (10) is brought into close contact with the sealing resin (8), the sealing resin (8) is pressed from the retaining plate (10) in a direction towards the base plate (1).

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