Press-packed semiconductor device

Abstract: A common insulation plate (32) is provided on a heat-­ discharging support member (31), and a plurality of press­ packed semiconductor elements (35, 35) is provided on the common insulation plate (32). These semiconductor ele­ ments (35, 35) are coupled to common electrodes (33a, 40b) by a plurality of spring mechanisms (47a, 47b). An internal connection terminal (42a, 42b) is slidably provided at each of the common electrodes (33a, 40b) and is bent perpen­ dicular to a pressing surface. Each of the internal connec­ tion terminals (42a, 42b) faces the adjacent one. After the common electrodes (33a, 40b) are pressed against the re­ spective semiconductor elements (35, 35) with adjustment, the internal connection terminals (42a, 42b) are electrically coupled together.

Description: This invention relates to a press-packed semiconductor device assembly comprising semiconductor devices such as transistors and thyristors. The invention is applicable to such assemblies where the semiconductor devices are high-power modules. An example of a conventional high-power semiconductor module is a transistor module as shown in Fig. 1. In Fig. 1, numeral 1 denotes a first transistor composite comprising a power transistor 11 and a diode 12, and numeral 2 represents a second transistor composite comprising a power transistor 13 and a diode 14. These first and second transistor composites 1,2 are commonly connected to a metal substrate 17 through insulation substrates 15 and 16, respectively. The first and second transistor composites 1,2 are housed in a package 18. A collector electrode terminal 19 of the first transistor composite 1, a collector electrode terminal 21 of the second transistor composite 2, which is coupled to an emitter electrode terminal 20 of the first transistor composite 1, and an emitter electrode terminal 22 of the second transistor composite 2 are arranged to extend outside of the package 18 on the top side thereof. This arrangement provides easy assembling of the transistor module into an electric device and reduces the space necessary for installation, thus lightening the electric device. The conventional transistor module, however, has the following drawbacks. Connection lines are bonded or soldered to the emitter electrodes and the collector electrodes of the first and second transistor composites 1 and 2. With a transistor module of a large current, e.g. above 100A, such a connection causes current concentrate on the bonded or soldered sections. This results in thermal distortion or thermal fatigue, making it difficult to provide a desirable high-power transistor module. Further, if the bonded or soldered sections are damaged by over-current, a sort of explosion may occur, namely, melted silicon may spout out from the package 18. Furthermore because the metal substrate 17, package 18 and electrode terminals extending outside the package are simultaneously sealed by adhesive resin, a crack may easily occur due to the difference in the thermal expansion coefficients of the individual materials, impeding a proper sealing. Further known press-packed semiconductor device assemblies are illustrated by DE-A-29 42 409 and EP-A-0 035 135. An object of this invention is to provide a reliable press-packed semiconductor device assembly which may prevent current concentration on connecting sections between a plurality of circuit elements provided in the same semiconductor device assembly or between a plurality of semiconductor elements. According to the invention, there is provided a press-packed semiconductor device assembly comprising a heat discharging support member, and at least one semiconductor device including a semiconductor element having first, second and third electrodes, the first electrode positioned on one side of the semiconductor device and the second and the third electrodes positioned on the other side of the semiconductor device, the assembly including for each semiconductor device: a parallel pair of connection plates, embracing the semiconductor element; an electrode plate provided between one connection plate and the second electrode of the semiconductor element, the electrode plate having a through hole; a plurality of circuit elements mutually insulated and connected by said other connection plate; an insulating plate provided between the support member and the other connection plate; first pressing means for elastically pressing said one connection plate onto the electrode plate to electrically connect said one connection plate to the second electrode through the electrode plate and to connect the first electrode electrically to the other connection plate; a first connection member extending through the through hole in the electrode plate and contacting the third electrode; second pressing means mounted in the through hole in the electrode plate for elastically pressing one end portion of the connection member onto the third electrode of the semiconductor element to make an electrical connection; and a second connection member extending from each pair of connection plates and passing outside a cover for the semiconductor devices provided on said support member. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a cross-sectional view showing a conventional transistor module; Fig. 2 is a plan view partially showing the interior of a press-packed transistor module embodying this invention; Fig. 3 is a view partially showing a cross section of the transistor module illustrated in Fig. 2; Fig. 4 is an oblique view showing the electrodes used in the module of Fig. 2; and Fig. 5 is a cross-sectional view showing an emitter plate. An embodiment of this invention will now be explained with reference to the accompanying drawings. In Figs. 2 and 3, numeral 31 denotes a heat-discharging substrate which is made of a high thermal conductive metal, such as cast aluminum. On the heat-discharging substrate 31 is provided a ceramic substrate 32 which is electrically insulated and is common to semiconductor elements 35 (to be described later). Two collector electrodes 33a and 33b made of, for example, copper are arranged on the ceramic substrate 32 at predetermined positions, respectively (see Fig. 4). The collector electrode 33a has an external connection terminal 34a bent perpendicular to the pressing surface A of the collector electrode 33a. The collector electrode 33b also has an external connection terminal 34b bent perpendicular to the pressing surface A of the collector electrode 33b. These external connection terminals 34a, 34b extend outside a lid 52 (to be described later) on the top thereof. A semiconductor element 33 is provided on each of the collector electrodes 33a, 33b. The semiconductor element 35 has two circuit elements, a main transistor and a free wheeling diode, provided on the same semiconductor substrate. Emitter plates 36a and 36b made of, for example, copper, are provided on the respective semiconductor elements 35, 35. These emitter plates 36a, 36b have the configuration as illustrated in Fig. 5 (the emitter plate 36a is exemplified in this Figure). A base lead 37, an insulation guide member 38 and a spring 39 are attached to the emitter plate 36a. The resilient force of the spring 39 presses the base electrode of the semiconductor element 35 against the base lead 37. Emitter electrodes 40a and 40b are respectively provided on the emitter plates 36a, 36b. Like the collector electrodes 33a, 33b, the emitter electrode 40a has an external connection terminal 41a, which is bent perpendicular to the pressing surface A (see Fig. 4) and extends outside the lid 52 on the top thereof. The other emitter electrode 40b has an internal connection terminal 42b bent perpendicular to the pressing surface A. The collector electrode 33a has an internal connection terminal 42a, which is shaped similar to the internal connection terminal 42b, and which faces it. These internal connection terminals 42a, 42b have a groove 43 of, for example, a U-shape at the distal end. The collector electrode 33a and the emitter electrode 40b are electrically connected by a bolt 44 and a nut 45 fastened at the grooves 43, 43, thus forming a common electrode for the two semiconductor elements 35, 35. On the emitter electrode 40a is mounted an insulation member 46a resistant to spring force and a spring mechanism, which comprises a cup spring 47a assembled in the insulation member 46a and a metal fixing plate 48a. Similarly, on the emitter electrode 40b is mounted an insulation member 46b resistant to the force of a spring and a spring mechanism, which comprises a cup spring 47b assembled in the insulation member 46b, and a metal fixing plate 48b. The metal fixing plates 48a, 48b are fixed to the heat-discharging substrate 31 by bolts 49a and 49b, respectively. This arrangement permits the resilient force of the cup springs 47a, 47b to press the individual electrodes, semiconductor elements 35, ceramic substrate 32 and heat-discharging substrate 31 against each other. Each of the collector electrodes 33a, 33b is coupled to a driving circuit element 50, such as a driving transistor and a speed-up diode, which is provided separately from the corresponding semiconductor. Unlike the semiconductor elements 35 forced to contact the collector electrodes 33a, 33b by means of the spring mechanisms, the driving circuit elements 50 are bonded or soldered to these collector electrodes. Numerals 51a and 51b denote external connection terminals each coupled to a base terminal and an emitter terminal. The device thus arranged is protected by a gel material to prevent damage to the individual electrodes which may result from poor insulation. The heat-discharging substrate 31 is covered with a lid 52 made of, for example, epoxy resin. The space between the heat-discharging substrate 31 and the lid 52 is filled with an adhesive 53a, which is epoxy-resin-based, for example. After the designated holes in the lid 52 have received the external connection terminals 34a, 34b, 41a, they are sealed with another epoxy-resin-based adhesive 53b. Similarly, any remaining holes in the lid 52, after receiving the external connection terminals 51a, 51b, are sealed with an epoxy-resin-based adhesive 53c. The adhesive 53a has a thermal expansion coefficient close to that of aluminum (Al) which is the material for the heat-discharging substrate 31. In contrast, the adhesives 53b, 53c have a thermal expansion coefficient close to that of copper (Cu) which is the material for the external connection terminals 34a, 34b, 41a, 51a, 51b. The difference in the thermal expansion coefficient between the adhesive 53a and the adhesives 53b, 53c thermally increases the sealing effect. The lid 52 is also provided with a tube 54 for mixing nitrogen in the gel inside the lid 52 to form spaces. These spaces suppress the expansion of the gel due to the increase in temperature. In the aforementioned press-packed transistor module, first, the spring mechanisms comprising the cup springs 47a, 47b are mounted on the emitter electrodes 40a, 40b, respectively. The bolts 49a and 49b are separately fastened so that the two semiconductor elements 35, 35 can be evenly pressed by the spring mechanisms. Then, the bolts 44 and nut 45 are fastened together at the grooves 43, 43 so as to electrically connect the internal connection terminal 42a of the collector electrode 33a and the internal connection terminal 42b of the emitter electrode 40b, thus forming the common electrode. When the electrode surfaces of two or more circuit elements are to be evenly pressed by a single common electrode, it is extremely difficult to evenly press the electrode surfaces due to the difference in precision of the sizes of the parts or semiconductor elements. Accordingly, there may arise an imbalence in pressure between the semiconductor elements or electrodes. This results in mechanical distortion, deteriorating the semiconductor elements, or an increase in temperature when heat-discharging partially occurs, also deteriorating the semiconductor elements. According to the transistor module of the embodiment, two circuit elements, a main transistor and a feedback diode, are assembled in a single semiconductor element 35 and the electrodes of the two elements are evenly pressed, thus applying pressure evenly. Further, the transitor module has the common electrode of two semiconductor elements 35, 35 separated into the collector electrode 33a and the emitter electrode 40b. These electrodes respectively have internal connection terminals 42a and 42b arranged so as to face each other. This enables the emitter electrode 40b to slide in a direction perpendicular to the surface A. As a result, after the collector electrode 33a and the emitter electrode 40b are separately pressed, the internal connection terminals 42a, 42b are fastened with the bolt 44 and nut 45 to make those electrodes a common electrode. Therefore, the individual electrodes of the two semiconductor elements 35, 35 can be pressed evenly and coupled together. The elements of the semiconductor device are classified into two groups: one from which current can be obtained by a spring-pressured connection and the other from which it is difficult to obtain the current by that connection. The application of spring pressure even to the second section reduces area efficiency and is therefore uneconomical. In the aforementioned transistor module, the semiconductor elements 35, 35 such as the main transistors, which are the current-obtainable elements, are subjected to pressure-coupling by the spring mechanisms. On the other hand, the driving circuit elements 50, such as driving transistors and which are difficult to provide current, are soldered to the collector electrodes 33a, 33b at the locations other than the press-coupled portions. This arrangement improves the area efficiency and makes it possible to miniaturize the semiconductor device. In the above-described embodiment, the collector electrode 33a of one of the semiconductor elements 35, 35 is coupled to the emitter electrode 40b of the other semiconductor element 35 to form a common electrode, providing a series circuit arrangement. However, a parallel circuit arrangement merely requires that the emitter electrodes 40a and 40b should be coupled together to form the common electrode and should have internal connection terminals, respectively. Also, in the embodiment, a plurality of circuit elements such as a main transistor and a free wheeling diode is assembled in a single semiconductor element 35, and these elements are pressed by a single spring mechanism. But, this invention is not limited to such a configuration. The circuit elements may be assembled in different semiconductor elements, which are even pressed by a plurality of spring mechanisms. The preferred embodiment described above is directed to a transistor module. However, this invention is not limited to such a case; it may, of course, be applied to other modules such as a thyristor module. As described above, a plurality of circuit elements assembled in the same semiconductor element are coupled to one another through a common electrode pressed against the circuit elements, and a plurality of semiconductor elements is connected to one another by the same manner. Unlike the conventional arrangements employing the bonding or soldering technique, the present arrangement eliminates the possibility of a large current concentrating on a certain area and permits a current to evenly flow through connecting sections, thus preventing any damage due to a large current concentrating on a specific area.

Claims: A press-packed semiconductor device assembly comprising a heat discharging support member (31), and at least one semiconductor device including a semiconductor element (35) having first, second and third electrodes, the first electrode positioned on one side of the semiconductor device and the second and the third electrodes positioned on the other side of the semiconductor device, the assembly including for each semiconductor device: a parallel pair of connection plates, (33a,40a,33b,40b) embracing the semiconductor element; an electrode plate (36a,36b) provided between one connection plate (40a,40b) and the second electrode of the semiconductor element, the electrode plate having a through hole; a plurality of circuit elements mutually insulated and connected by said other connection plate (33a,33b); an insulating plate (32) provided between the support member (31) and the other connection plate; first pressing means (47a,47b) for elastically pressing said one connection plate (40a,40b) onto the electrode plate (36a,36b) to electrically connect said one connection plate to the second electrode through the electrode plate and to connect the first electrode electrically to the other connection plate; a first connection member (37) extending through the through hole in the electrode plate (36a,36b) and contacting the third electrode; second pressing means (39) mounted in the through hole in the electrode plate (36a,36b) for elastically pressing one end portion of the connection member (37) onto the third electrode of the semiconductor element to make an electrical connection; and a second connection member (34a,34b,41a) extending from each pair of connection plates and passing outside a cover (52) for the semiconductor devices provided on said support member (31). The press-packed semiconductor device assembly according to claim 1, wherein each of said circuit elements comprises a main transistor and a free wheeling diode, and driving circuit elements are coupled to part of said other connection plate by means different from said first pressing means. A press-packed semiconductor device assembly according to claim 1, wherein at least two semiconductor devices are provided and said insulating plate (32) is provided between the support member (31) and the other connection plate (33a,33b) of each semiconductor device to locate the respective other connection plate in the same plane. A press-packed semiconductor device assembly according to claim 1 or 3, further including means (44,45) for electrically and mechanically connecting the other connection plate (33a) for one semiconductor device to the one connection plate (40b) for the other semiconductor device in a slidable manner in a direction perpendicular to the pressing surface of the first pressing means (47a,47b). A press-packed semiconductor device assembly according to claim 4, wherein said connecting means includes slits (43) formed in respective extensions of the connected plates and a bolt and nut assembly (44,45) for connecting the plates. A press-packed semiconductor device assembly according to claim 5, wherein said extensions extend perpendicular to the pressing surfaces of said first pressing means. A press-packed semiconductor device assembly according to claim 2, wherein said support member (31) is made of metal; said cover (52) is made of resin; and that the space between said support member (31) and said cover (52) is sealed by resin with a thermal expansion coefficient different from that of resin for sealing the spaces between said cover (52) and said second connection member (34a,34b,41a).

Inventors: IWASAKI MASAMI C O PATENT DIVI, SAKURAI HIROSHI C O PATENT DIV, IWASAKI, MASAMI C/O PATENT DIVISION, SAKURAI, HIROSHI C/O PATENT DIVISION
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1984
Main classification: H01L25
IPC codes: H01L23, H01L25