JP2016134540A - Power semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power semiconductor device in which wet-rising of an affluent solder is made better so as to suppress shorting failure due to extrusion of the solder.SOLUTION: A power semiconductor device is equipped with a power semiconductor element, and an electrode plate which is arranged to face a surface of a main electrode of the power semiconductor element and is jointed to the surface of the main electrode using a jointing material. An opening part is provided at a portion jointed to the surface of the main electrode of the electrode plate, and around the opening part, a projection is formed which is an inside surface of the opening part, with a surface nature being continuous from a front surface or a rear surface of the electrode plate.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power semiconductor device used in every scene from power generation / transmission to efficient use / regeneration of energy.

  Power modules (power semiconductor devices) are becoming widespread in all products from industrial equipment to home appliances and information terminals. Modules installed in home appliances are highly productive and highly reliable, capable of supporting a wide variety of products as well as being smaller and lighter. Is required. In addition, since the operating temperature is high and the efficiency is excellent, a package form that can be applied to a wide band gap semiconductor such as a SiC semiconductor that is likely to become a mainstream in the future is also required.

  Power semiconductor devices generate large amounts of heat in order to handle high voltages and large currents, and ceramic substrates with excellent thermal conductivity are often used as insulating substrates for the purpose of efficiently exhausting heat. Further, with the increase in the density of power semiconductor elements, a technique of directly soldering a copper electrode plate to a power semiconductor element is being used to form a circuit with a high current density. If the gap between the copper electrode plate and the power semiconductor element is constant, the shape of the joint is stabilized by keeping the supplied amount of solder constant, but in reality, the gap varies due to the tolerance of the member. In particular, when the gap is small, there is a possibility of short-circuiting due to excess solder protruding. Therefore, a method has been studied in which an opening is formed in the copper electrode plate and excess solder wets up to prevent the solder joint from protruding.

  In order to suppress the deterioration of solder wettability due to natural oxidation during transportation / storage after manufacture of copper electrode plates and oxidation due to heating in the assembly process prior to the joining process with power semiconductor elements, In many cases, a rust preventive material is applied to the front and back surfaces of the plate. When an opening is formed in the copper electrode plate, a cut surface without a rust preventive material is exposed on the side surface of the opening, so that there is a concern that the solder wettability deteriorates due to oxidation and the wetting of excess solder is hindered. .

  Patent Document 1 discloses a method of forming an opening in a heat spreader (electrode) disposed on a power semiconductor element, and joining by supplying solder. Patent Document 2 discloses a method of bonding by controlling the gap by providing protrusions on the back surface of the electrode other than the opening and injecting solder from the opening. Patent Document 3 describes that a stable connection strength can be obtained by providing a protrusion at the lower part of the opening of the through-hole of the electrode to ensure a gap.

JP 2004-303869 A JP 2004-134445 A Japanese Patent Laying-Open No. 2008-182074 (FIG. 5)

  According to the method described in the above-mentioned patent documents, there is a possibility that the solder wettability of the side surface of the opening portion becomes poor, and no solution is shown in any patent document.

  The present invention has been made to solve the above-described problems, and by improving the solder wettability of the side surface of the opening, the wettability of excess solder is improved, and short-circuit failure due to solder protrusion is prevented. The object is to obtain a suppressed power semiconductor device.

  The present invention relates to a power semiconductor device comprising a power semiconductor element and an electrode plate disposed opposite to the main electrode surface of the power semiconductor element and bonded to the main electrode surface by a bonding material. An opening is provided in the portion of the plate that is joined to the surface of the main electrode, and a protrusion is formed on the periphery of the opening that forms the inner surface of the opening that is continuous with the surface or back surface of the electrode plate. did.

  According to the present invention, it is possible to provide a power semiconductor device in which wetting of excess solder is improved and short-circuit defects due to solder protrusion are suppressed.

1 is a side sectional view showing a schematic configuration of a power semiconductor device according to a first embodiment of the present invention. It is a 1st figure which shows the manufacturing process of the power semiconductor device by Embodiment 1 of this invention. It is a 2nd figure which shows the manufacturing process of the power semiconductor device by Embodiment 1 of this invention. It is a 3rd figure which shows the manufacturing process of the semiconductor device for electric power by Embodiment 1 of this invention. It is a 4th figure which shows the manufacturing process of the power semiconductor device by Embodiment 1 of this invention. It is a top view which removes direct potting sealing resin and shows the structure of the power semiconductor device by Embodiment 1 of this invention. It is an expanded side sectional view which shows an example of the detailed structure of the opening part of the electrode plate of the power semiconductor device by Embodiment 1 of this invention. It is an expanded side sectional view which shows the detailed structure of the opening part of the electrode plate of the conventional semiconductor device for electric power. It is an expanded side sectional view which shows another example of the detailed structure of the opening part of the electrode plate of the power semiconductor device by Embodiment 1 of this invention. It is an expanded side sectional view which shows another example of the detailed structure of the opening part of the electrode plate of the power semiconductor device by Embodiment 1 of this invention. It is side surface sectional drawing which shows schematic structure of the semiconductor device for electric power by Embodiment 2 of this invention. It is a top view which removes direct potting sealing resin and shows the structure of the power semiconductor device by Embodiment 2 of this invention. It is an expanded side sectional view which shows the detailed structure of the opening part of the electrode plate of the semiconductor device for electric power by Embodiment 2 of this invention.

Embodiment 1 FIG.
1 is a side sectional view showing a schematic structure of a power semiconductor device according to a first embodiment of the present invention. 2 to 5 are conceptual diagrams showing manufacturing processes of the power semiconductor device according to the first embodiment. First, as shown in FIG. 2, a diode 21 (15 mm × 15 mm × thickness) is formed on a ceramic substrate 11 (AlN, 40 mm × 25 mm × thickness 0.635 mm, double-sided copper conductor layers 12 and 13 having a pattern thickness of 0.4 mm). And an IGBT (Insulated Gate Bipolar Transistor) 22 is mounted by a solder die bond 31. Next, as shown in FIG. 3, the case 5 (made of PPS resin, 48 mm × 28 mm × height 12 mm) is fixed with an adhesive 6 (made of silicone) and filled with a gap to be described later. The leakage of the resin 8 is prevented. An electrode plate 40 (made of copper, thickness 1 mm, width 13 mm, total length 35 mm) is insert-molded in the case 5, and a main electrode through which a large current flows, such as a source electrode and a drain electrode of a power semiconductor element such as the diode 21 and the IGBT 22 Connected. A screwing electrode portion 41 is formed at an end portion of the electrode plate 40 and is fixed to the outer peripheral portion of the case 5. Further, the signal terminal 42 is formed in another part of the outer periphery of the case 5. An opening 43 (opening diameter: 3 mm) is previously formed in the electrode plate 40 by burring (drawing) so that the periphery of the opening becomes a projection 44 (height 1 mm). Further, as shown in FIG. 4, the signal terminal 42 formed on the case is electrically connected to the gate electrode, the temperature sensor electrode, and the like of the IGBT 22 by bonding wires 7 (aluminum φ0.15 mm).
Finally, as shown in FIG. 5, the direct potting sealing resin 8 is poured in a state heated to 60 ° C., vacuum degassed, heated (100 ° C., 1.5 hours → 140 ° C., 1.5 hours), cured and sealed. The power semiconductor device is completed. It should be noted that the numerical values such as the above dimensions, temperature, and time are examples, and it goes without saying that other numerical values may be used. The same applies to the subsequent numerical values.

  FIG. 6 is a top view showing the configuration of the power semiconductor device according to the first embodiment, with the direct potting sealing resin removed. Two electrode plates (the width of the external terminal portion at the upper part of the case is 7 mm) are arranged, and the electrode plate 40 on which the opening 43 and the protrusion 44 are formed is fixed to the case 5 with a screw terminal portion 41s. The electrode plate 40 floats about 2 mm from the ceramic substrate 11 in the case, and is connected to the main electrode (source electrode) of the power semiconductor element such as the diode 21 and the IGBT 22 by the bonding material 32. Hereinafter, an example in which solder is used as the bonding material 32 will be described. The opening 43 of the electrode plate 40 is provided at a portion to be joined to the main electrode of the power semiconductor element. The other electrode plate 420 is fixed to the case 5 by a screw terminal portion 41d and is directly soldered to the circuit conductor layer 12 of the ceramic substrate 11 to be connected to the drain electrode of the IGBT 22. The signal terminal 42 (width 1.5 mm) is connected to the control electrode 222 (gate electrode, temperature sensor electrode, etc.) of the IGBT 22 by the bonding wire 7.

  FIG. 7 is an enlarged side sectional view showing details of the opening 43 and the protrusion 44 of the electrode plate 40. The front surface (the side opposite to the power semiconductor element) and the back surface (the power semiconductor element side) of the electrode plate 40 are subjected to a rust prevention treatment, and rust prevention material (for example, benzotriazole) layers 40a and 40b are formed. . On the other hand, an oxide film is formed on the cut surface 40c of the protrusion. Since the electrode plate 40 is formed with an opening 43 and a projection 44 around the opening in advance by burring (drawing), the inner surface of the opening is continuous with the back surface of the electrode plate. It is the surface where the antirust material layer 40b was formed like the back surface of a board. When the solder 32 as the bonding material is supplied, the solder wets the rust preventive material layer 40b, and the solder is sucked up to the inner surface of the opening 43, so that the main electrode 211 and the electrode plate 40 of the power semiconductor element 21 are absorbed. Is connected. On the other hand, FIG. 8 shows the structure of a conventional electrode plate. Since the oxide film of the cut surface 40c exists on the side surface of the opening 43, the solder cannot wet up and surplus solder spreads in the lateral direction. There is a concern that riding on the guard ring portion 212 may cause a decrease in insulation.

  FIG. 9 is an enlarged side sectional view showing another example of the detailed configuration of the opening of the electrode plate of the power semiconductor device according to the first embodiment of the present invention. In the example shown in FIG. 9, the protrusion 44 is protruded on the back surface side (power semiconductor element side) of the electrode plate. In this case, the rust preventive material layer 40 a formed on the surface of the electrode plate 40 continues to the inner surface of the opening 43. In this case, the protrusion can function to secure the gap, and the inner surface of the opening 43 is a surface on which a rust preventive material that is easily wetted by solder is formed. However, since an oxide film is formed on the copper electrode plate cross section 40c at the tip, solder may be difficult to wet, and it is necessary to devise a solder supply method.

  FIG. 10 is an enlarged side sectional view showing still another example of the detailed configuration of the opening of the electrode plate of the power semiconductor device according to the first embodiment of the present invention. In the example shown in FIG. 10, protrusions are provided around the opening 43 so that a part of the protrusion 441 protrudes on the side opposite to the power semiconductor element and a part of the protrusion 442 protrudes on the side of the power semiconductor element. ing. In this case, a part of the inner surface of the opening 43 is a surface in which the surface property is continuous with the rust preventive material layer 40 b on the back surface of the electrode plate 40, and a part is the surface property with the rust preventive material layer 40 a on the surface of the electrode plate 40. It is a continuous surface. Thus, by providing protrusions that project on both the front surface side and the back surface side of the electrode plate, it is possible to achieve both ensuring of the gap and improvement of solder wettability.

  For solder joining of the electrode plate 40 and the power semiconductor element, a method of reflowing with a necessary amount of plate-like solder sandwiched therebetween can be applied. Furthermore, a method of applying cream solder or injecting from the opening 43 using a dispenser is also applicable. Furthermore, the solder can be supplied by cutting and inserting a thread solder having a diameter smaller than that of the opening 43 into a desired length and reflowing.

  In the above, AlN is used as the material of the ceramic substrate 11, but the same effect can be obtained with a ceramic material such as alumina or SiN. Furthermore, when there is not much need for heat dissipation, a glass epoxy substrate or the like can be used. It is also possible to use a metal substrate using a resin insulating sheet. In the above description, PPS is used as the material for the case 5, but the same effect can be obtained by using LCP (liquid crystal polymer) having higher heat resistance.

  In the above description, the diode 21 and the IGBT 22 have a pair of 1 in 1 module configurations, but the same effect can be obtained even with two pairs of 2 in 1 and six pairs of 6 in 1. In the above description, the aluminum wire is used as the bonding wire. However, the same effect can be obtained by using a copper wire, an aluminum coated copper wire, or a gold wire. The same effect can be obtained by using a ribbon bond or a bus bar that ultrasonically bonds a metal plate. In addition, the direct potting sealing resin 8 can be obtained in the same kind by being poured and cured at room temperature.

  In addition, solder was used as a bonding material for the connection between the power semiconductor elements 21 and 22 and the ceramic substrate 11 and the connection between the electrode plate 40 and the power semiconductor elements 21 and 22, but Ag filler was dispersed in the epoxy resin. The same effect can be obtained even when a conductive adhesive, Ag nanopowder or Cu nanopowder for firing the nanoparticles at low temperature is used as the bonding material. The same effect can be obtained in a transfer mold package that is sealed with a transfer mold sealing resin using a mold without using a case.

  In the above description, an electrode plate to which a rust preventive agent has been applied in advance has been used. However, the same effect can be obtained by applying shape processing using an electrode plate that has not been applied and then applying a rust preventive agent.

Embodiment 2. FIG.
FIG. 11 is a conceptual diagram showing the structure of the power semiconductor device according to the second embodiment. As shown in FIG. 11, a diode 21 (15 mm × 15 mm × 0.3 mm thick) is formed on a ceramic substrate 11 (AIN, 40 mm × 25 mm × thickness 0.635 mm, double-sided copper conductor layers 12 and 13 having a pattern thickness of 0.4 mm). mm) and an IGBT (Insulated Gate Bipolar Transistor) 22 are mounted by a solder die bond 31. Next, the case 5 (made of PPS resin, 48 mm × 28 mm × height 12 mm) is fixed using the adhesive 6 (made of silicone), and the leakage of the direct potting sealing resin 8 is prevented by filling the gap. An electrode plate 400 (CIC clad material: made of copper / invar / copper clad material, thickness 1 mm, width 13 mm, total length 35 mm) is insert-molded in the case 5, and the source electrode and drain of a power element such as the diode 21 or IGBT 22 It is connected to a main electrode through which a large current flows, such as an electrode. A screwed electrode portion is formed at the end of the electrode plate 400 and is fixed to the outer peripheral portion of the case 5. Further, the signal terminal 42 is formed in another part of the outer periphery of the case 5. An opening 43 (opening diameter: 3 mm) and a protrusion 44 (height: 1 mm) are previously formed on the electrode plate 400 by burring (drawing). The protrusions 44 are processed so that a part is formed on the front surface side of the electrode plate 400 and a part is formed on the back surface side. Further, the signal terminals 42 formed on the case are electrically connected to the gate electrode and temperature sensor electrode of the IGBT 22 by bonding wires 7 (aluminum φ0.15 mm), respectively. Finally, the direct potting sealing resin 8 is poured in a state heated to 60 ° C., vacuum degassed and heated (100 ° C., 1.5 hours → 140 ° C., 1.5 hours) to cure and complete the sealing. Semiconductor device is completed.

  The CIC clad material used for the electrode plate 400 has a structure in which an invar 401 having a thickness of 0.5 mm is sandwiched with copper 402 and copper 403 having a thickness of 0.25 mm. The total thermal expansion coefficient of the electrode plate 400 is reduced by sandwiching invar having a small expansion coefficient with copper (approximately 0 ppm / K up to 400 ° C.) to be close to the thermal expansion coefficient of the ceramic substrate 11 and the power semiconductor elements 21 and 22. As a result, the thermal stress at the joint can be reduced. However, invar has the disadvantage that solder wettability is very poor and easily oxidizes. Therefore, if the invar is exposed on the cut surface, the solder may not wet.

FIG. 12 is a top view of the power semiconductor device according to the second embodiment, with the direct potting sealing resin 8 removed. Two electrode plates (the width of the external terminal portion at the top of the case is 7 mm) are arranged, and the electrode plate 400 on which the opening 43 and the protrusion 44 are formed is fixed to the case 5 with a screw terminal portion 410s. The electrode plate 400 floats about 2 mm from the ceramic substrate 11 in the case, and is connected to the diode 21 and the main circuit electrode (source electrode) of the IGBT 22 by the solder 32. The other electrode plate 420 is fixed to the case 5 by a screw terminal portion 420d and is directly soldered to the circuit conductor layer 12 of the ceramic substrate 11 to be connected to the drain electrode of the power semiconductor element. Signal terminal 42 (width 1.5mm) is IGBT2
Two control electrodes 222 (gate electrode, temperature sensor electrode, etc.) are connected by a wire 7.

  FIG. 13 is an enlarged side sectional view showing details of the opening 43 and the protrusion 44 of the electrode plate 400. Protrusions 44 are formed around the opening 43, partly upward and partly downward, and the inner surface of the opening is a surface that is continuous with the surface or back surface of the electrode plate 400. For this reason, when the solder 32 is supplied, the solder gets wet with respect to the copper 402 and 403, and the solder is also sucked up to the inner surface of the opening 43.

  For solder joining of the electrode plate 400 of the CIC clad material and the power semiconductor element, a method of reflowing with a necessary amount of plate-like solder sandwiched therebetween can be applied. Furthermore, a method of applying cream solder or injecting from the opening 43 using a dispenser is also applicable. Furthermore, the solder can be supplied by cutting and inserting a thread solder having a diameter smaller than that of the opening 43 into a desired length and reflowing.

  By forming the protrusions 44 on both the front surface side (the side opposite to the power semiconductor element) and the back surface side (the power semiconductor element side) of the electrode plate 400, the copper on both sides of the electrode plate 400 of the CIC clad material Solder connection can be surely made to 402 and 403, and copper having low electrical resistance and thermal resistance can be utilized to the maximum. Of course, it goes without saying that the protrusion may be a protrusion protruding from the front surface side or the back surface side of the electrode plate 400, as in FIGS. Note that the invar and copper may have a structure in which a large number of layers such as copper, invar, copper, invar, and copper are stacked. In the above description, the electrode plate 400 has a structure in which invar is sandwiched between copper, but other materials, for example, a structure in which stainless steel is sandwiched between copper and a structure in which invar is sandwiched between aluminum are the same. It is. In other words, the electrode plate 400 has a structure in which a plurality of plates having different expansion coefficients are stacked, thereby reducing the total thermal expansion coefficient of the electrode plate 400 and increasing the thermal expansion coefficient of the ceramic substrate 11 and the power semiconductor elements 21 and 22. You can get closer.

  In the above, AlN is used as the material of the ceramic substrate 11, but the same effect can be obtained by using a ceramic material such as alumina or SiN. Furthermore, when there is not much need for heat dissipation, a glass epoxy substrate or the like can be used. It is also possible to use a metal substrate using a resin insulating sheet. In the above description, PPS is used as the material for the case 5, but the same effect can be obtained by using LCP (liquid crystal polymer) having higher heat resistance.

  In the above description, the diode 21 and the IGBT 22 have a pair of 1 in 1 module configurations, but the same effect can be obtained even with two pairs of 2 in 1 and six pairs of 6 in 1. In the above description, the aluminum wire is used as the bonding wire. However, the same effect can be obtained by using a copper wire, an aluminum coated copper wire, or a gold wire. The same effect can be obtained by using a ribbon bond or a bus bar that ultrasonically bonds a metal plate. In addition, the direct potting sealing resin 8 can be obtained in the same kind by being poured and cured at room temperature.

  Moreover, although the solder was used as a joining material for connecting the power semiconductor elements 21 and 22 and the ceramic substrate 11 and connecting the electrode plate and the power semiconductor element, a conductive adhesive in which an Ag filler is dispersed in an epoxy resin, The same effect can be obtained by using Ag nanopowder, Cu nanopowder, or the like for firing the nanoparticles at a low temperature as a bonding material. The same effect can be obtained in a transfer mold package that is sealed with a transfer mold sealing resin using a mold without using a case.

  The present invention is high when applied to a power semiconductor device in which a power semiconductor element using, for example, silicon carbide (SiC), which is a wide band gap semiconductor material capable of high-temperature operation, is mounted as a power semiconductor element. This is particularly effective because a circuit having a current density can be formed. Other wide band gap semiconductor materials include gallium nitride-based materials and diamond.

  21 diode (power semiconductor element), 22 IGBT (power semiconductor element), 32 solder joint (joint material), 40, 400 electrode plate, 40a, 40b anticorrosive layer, 43 opening, 44, 441, 442 Protrusion, 211 Main electrode of power semiconductor element

Claims (7)

In a power semiconductor device comprising: a power semiconductor element; and an electrode plate disposed opposite to the surface of the main electrode of the power semiconductor element and bonded to the surface of the main electrode of the power semiconductor element by a bonding material ,
An opening is provided in a portion of the electrode plate that is joined to the surface of the main electrode of the power semiconductor element. The power semiconductor device is characterized in that a protrusion is formed.   2. The power semiconductor device according to claim 1, wherein at least a part of the protrusion protrudes on a side opposite to the power semiconductor element.   The power semiconductor device according to claim 1, wherein the opening and the protrusion are formed by drawing.   4. The power semiconductor device according to claim 1, wherein the electrode plate is a copper plate having a front surface and a back surface subjected to a rust prevention treatment. 5.   4. The power semiconductor device according to claim 1, wherein the electrode plate has a structure in which a plurality of plates having different thermal expansion coefficients are stacked. 5.   The power semiconductor device according to claim 1, wherein the power semiconductor element is formed of a wide band gap semiconductor.   The power semiconductor device according to claim 6, wherein the wide band gap semiconductor is a semiconductor of silicon carbide, a gallium nitride material, or a diamond.

Images