Patent Publication Number: US-8981542-B2

Title: Semiconductor power module and method of manufacturing the same

Description:
This is a Continuation of U.S. application Ser. No. 13/247,105, filed on Sep. 28, 2011, and allowed on May 14, 2013 as U.S. Pat. No. 8,525,315, the subject matter of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor power module and a method of manufacturing the same. 
     2. Description of Related Art 
     A semiconductor power module is an apparatus loaded with a plurality of semiconductor power devices for obtaining an output from the semiconductor power devices electrically connected with one another. Such a semiconductor power module is employed for an inverter circuit constituting a driver circuit for driving an electric motor, for example. The electric motor is employed as a power source for an electric car (including a hybrid car), an electric train or an industrial robot, for example. The semiconductor power module is also applied to an inverter circuit converting power generated by a power generator (particularly a private power generator) such as a solar cell or a wind power generator to match with the power of a commercial power source. 
     The semiconductor power devices loaded on the semiconductor power module are connected to an external terminal of the semiconductor power module through wires. 
     For example, a semiconductor power module disclosed in FIG. 1 of Patent Document 1 (Japanese Unexamined Patent Publication No 2007-305962) includes a circuit board having a structure obtained by integrating a metal substrate electrode, an insulated substrate and a heat sink with one another, a plurality of SiC semiconductor power devices connected. onto the metal substrate electrode of the circuit board, a case fixed to the heat sink for storing the SiC semiconductor power devices, and an external electrode mounted on the case. The SiC semiconductor power devices and the external electrode are connected with one another through Al wires. 
     SUMMARY OF THE INVENTION 
     The Al wires connected to the semiconductor power devices must feed high current operated by the semiconductor power devices. In general, therefore, a plurality of Al wires are bonded to each semiconductor power device. 
     Even if a plurality of Al wires are bonded to each semiconductor power device, however, the bonding area between each Al wire and the semiconductor power device is so small that current concentrates on the junction between the Al wire and the semiconductor power device. The waveform of the current is disturbed due to the current concentration, to disadvantageously result in local heat generation in the semiconductor power device. While the heat generated in the semiconductor power device is partially released through the Al wire, the heat releasing effect is insufficient if the diameter of the Al wire is small. 
     When the number of the Al wires connected to each semiconductor power device is increased thereby ensuring large bonding areas, a sufficient heat releasing effect may be attained. However, the pitch of the Al wires connected to the semiconductor power device is limited, and hence the heat releasing effect is desirably improved by another technique. 
     Accordingly, a principal object of the present invention is to provide a semiconductor power module capable of leveling current flowing from a semiconductor power device and capable of efficiently releasing heat generated in the semiconductor power device and a method of manufacturing the same. 
     Another object of the present invention is to provide a method of manufacturing a semiconductor power module, capable of simply manufacturing a semiconductor power module capable of leveling current flowing from a semiconductor power device and capable of efficiently releasing heat generated in the semiconductor power device with high quality. 
     The foregoing and other objects, features and effects of the present invention will become more apparent from the following detailed description of the embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates the overall structure of a semiconductor power module according to a first embodiment of the present invention. 
         FIG. 2  illustrates the internal structure of the semiconductor power module shown in  FIG. 1 . 
         FIG. 3  is a sectional view of the semiconductor power module shown in  FIG. 1 , taken along a cutting plane line A-A in  FIG. 1 . 
         FIGS. 4A to 4E  are sectional views, taken along the cutting plane line A-A in  FIG. 1  similarly to  FIG. 3 , successively showing partial manufacturing steps for the semiconductor power module shown in  FIG. 1 . 
         FIG. 5  is a sectional view of the semiconductor power module shown in  FIG. 1 , taken along a cutting plane line A′-A′ in  FIG. 1 . 
         FIG. 6  illustrates the overall structure of a semiconductor power module according to a second embodiment of the present invention. 
         FIG. 7  illustrates the internal structure of the semiconductor power module shown in  FIG. 7 . 
         FIG. 8  is a sectional view of the semiconductor power module shown in  FIG. 6 , taken along a cutting plane line B-B in  FIG. 6 . 
         FIG. 9  is a sectional view of the semiconductor power module shown in  FIG. 6 , taken along a cutting plane line C-C in  FIG. 6 . 
         FIGS. 10A to 10E  are sectional views, taken along the cutting plane line B-B in  FIG. 6  similarly to  FIG. 8 , successively showing partial manufacturing steps for the semiconductor power module shown in  FIG. 6 . 
         FIG. 11  illustrates the internal structure of a semiconductor power module according to a modification of a metal block shown in  FIG. 2 . 
         FIG. 12  is a sectional view of the semiconductor power module according to the modification of the metal block shown in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A semiconductor power module according to an aspect of the present invention includes a base member, a semiconductor power device having a surface and a rear surface with the rear surface bonded to the base member, a metal block, having a surface and a rear surface with the rear surface bonded to the surface of the semiconductor power device, uprighted from the surface of the semiconductor power device in a direction separating from the base member and employed as a wiring member for the semiconductor power device, and an external terminal bonded to the surface of the metal block for supplying power to the semiconductor power device through the metal block. 
     According to this structure, the metal block having a larger diameter than a wire is employed as the wiring member connecting the semiconductor power device and the external terminal of the semiconductor power module with each other. Thus, a wire can be bonded to the semiconductor power device with a large area. Therefore, the junction between the wire (the metal block) and the semiconductor power device can be prevented from current concentration. Consequently, current can be leveled. Further, heat generated in the semiconductor power device can be efficiently released, whereby a heat releasing effect can also be improved. 
     Preferably, the semiconductor power module according to the present invention further includes a case having a base portion provided with a device region where the semiconductor power device is arranged and a frame portion fixed to the base portion for surrounding the device region, and a top plate, made of resin, fixed to the frame portion of the case and opposed to the device region, while the external terminal includes a plate terminal provided along the top plate, and the top plate has a support portion overlapping with the plate terminal in plan view for supporting the plate terminal from the side of a rear surface thereof. 
     When the external terminal is the plate terminal provided along the top plate blocking the case and the plate terminal is subjected to an external shock or the like, the shock may be transmitted to the semiconductor power device through the metal block, to break the semiconductor power device as a result. 
     According to this structure, therefore, the top plate has the support portion supporting the plate terminal from the side of the rear surface thereof. Even if the plate terminal is subjected to a shock or the like, therefore, the support portion can absorb the shock. Consequently, the semiconductor power device can be absolutely protected against transmission of the shock, or the shock transmitted to the semiconductor power device can be reduced. Therefore, the semiconductor power device can be prevented from breakage caused by the shock. 
     Preferably in the semiconductor power module according to the present invention, an opening smaller than the plane area of the plate terminal is formed in a region of the top plate opposed to the plate terminal, the metal block is bonded to the plate terminal through the opening, and the support portion of the top plate includes a peripheral edge portion of the opening surrounding the metal block in the top plate. 
     According to this structure, the support portion constituted of the peripheral edge portion of the opening surrounding the metal block can effectively absorb a shock transmitted from the plate terminal to the metal block. 
     Preferably in the semiconductor power module according to the present invention, the top plate is a member provided to be separable from the frame portion. 
     According to this structure, the top plate is separable from the frame portion. In order to manufacture the semiconductor power module, therefore, the semiconductor power device is first arranged on the device region so that the metal block can be bonded to the semiconductor power device while e the top plate is separated from the frame portion. Therefore, the semiconductor power module can be manufactured with excellent workability. 
     Preferably in the semiconductor power module according to the present invention, the top plate is formed in a U shape in plan view having an open end on a position on one side with respect to the plate terminal and having a blocked end on a position on a side opposite to the open end with respect to the plate terminal, and supported by the frame portion to be slidable in a sliding direction along a direction where the blocked end separates from the plate terminal, the metal block is bonded to the plate terminal in a region surrounded by the top plate between the open end and the blocked end, and the support portion of the top plate includes an edge portion of the region in the top plate. 
     According to this structure, the top plate is slidably supported by the frame portion, and separable from the frame portion. In order to manufacture the semiconductor power module, therefore, the semiconductor power device is first arranged on the device region so that the metal block can be bonded to the semiconductor power device while the top plate is separated from the frame portion. Therefore, the semiconductor power module can be manufactured with excellent workability. Further, an end portion of the top plate opposite to the direction where the same is extracted by sliding forms the open end. Also after the top plate is fixed to the frame portion, therefore, the device region can be exposed by extracting the top plate without detaching the metal on from the plate terminal. Consequently, maintenance in the case can be easily performed. 
     Further, the support portion constituted of the edge portion surrounding the region where the metal block is arranged can effectively absorb a shock transmitted from the plate terminal to the metal block. 
     Preferably in the semiconductor power module according to the present invention, the plate terminal is in the form of a quadrangle in plan view having a pair of first opposite sides extending along the sliding direction and a pair of second opposite sides orthogonal to the first opposite sides, the top plate has a pair of arm portions along the first opposite sides and a coupling portion coupling sides of the pair of arm portions in the sliding direction with each other, and is provided to surround three sides in the periphery of the plate terminal with the arm portions and the coupling portion, the pair of arm portions have first portions coming into contact with the peripheral edge portion of the plate terminal from outside in a transverse direction orthogonal to the sliding direction and second portions projecting from lower ends of the first portions along the rear surface of the plate terminal respectively, and the peripheral edge portion of the plate terminal along the first opposite sides fits into a recess portion partitioned by the first portions of the arm portions and the second portions of the arm portions. 
     According to this structure, the peripheral edge portion of the plate terminal along the first opposite sides fits into the recess portion partitioned by the first portions of the arm portions and the second portions of the arm portions. When the top plate is slid along the frame portion, therefore, the plate terminal can he utilized as a guide member for guiding the top plate. Thus, the top plate can be easily positioned. 
     Preferably in the semiconductor power module according to the present invention, the coupling portion has a first portion coming into contact with the peripheral edge portion of the plate terminal from outside in the sliding direction and a second portion projecting from a lower end of the first portion along the rear surface of the plate terminal, and the peripheral edge portion of the plate terminal along the second opposite sides fits into a recess portion partitioned by the first portion of the coupling portion and the second portion of the coupling portion. 
     According to this structure, the peripheral edge portion of the plate terminal along the second opposite sides (the opposite sides orthogonal to the sliding direction) fits into the recess portion partitioned by the first portion of the coupling portion and the second portion of the coupling portion. When the top plate is slid along the frame portion, therefore, the sliding of the top plate can be stopped by bringing the peripheral edge portion of the plate terminal into contact with the first portion of the coupling portion of the top plate. In other words, the plate terminal can also be utilized as a stopper member for stopping the sliding of the top plate. Therefore, the top plate can be more easily positioned. 
     Preferably in the semiconductor power module according to the present invention, both of the base portion and the frame portion are made of a metal, the base portion serves also as the base member supporting the semiconductor power device, and the frame portion serves also as a second external terminal for supplying power to the semiconductor power device through the base portion. 
     According to this structure, the frame portion uprighted from the base portion serves al so as the second external terminal, whereby electrical contact with the rear surface of the semiconductor power device can be attained from the side of the surface of the semiconductor power module. 
     In the semiconductor power module according to the present invention, the semiconductor power device may be a device employing an SiC semiconductor. 
     In this case, the metal block is preferably made of Cu or an alloy material containing Cu. 
     According to this structure, the difference between the linear expansion coefficients of SiC and the wiring member can be reduced as compared with a case of employing an Al wire as the wiring member for the semiconductor power device. Therefore, thermal stress caused between the semiconductor power device and the wiring member can be reduced. Consequently, thermal fatigue of the semiconductor power device can be reduced, whereby a semiconductor power module having a long life and high reliability can be attained. The alloy material containing Cu can be prepared from a CuMo alloy or a CuW alloy, for example. 
     For example, the linear expansion coefficient of SiC is about 4.5 ppm/K, and that of a CuMo alloy is about 9.0 ppm/K (about twice the linear expansion coefficient of Sic). On the other hand, the linear expansion coefficient of Al is about 23 ppm/K (about five times the linear expansion coefficient of Sic). 
     The metal block may be in the form of a rectangular parallelepiped, or may have a tapered shape whose sectional area spreads from the rear surface toward the surface thereof. 
     If the metal block has a tapered shape, heat generated in the semiconductor power device can be released with the optimum heat releasing efficiency when designing the area of the rear surface of the metal block in response to the surface area of the semiconductor power device and designing the area of the surface of the metal block in response to the size of the external terminal. 
     The semiconductor power module according to the present invention may be provided with a plurality of semiconductor power devices, and the external terminal may be collectively bonded to the metal block bonded to each of the semiconductor power devices. 
     Preferably in the semiconductor power module according to the present invention, the top plate is provided with a through-hole passing through the top plate in the thickness direction in a region other than a region overlapping with the plate terminal in plan view. 
     According to this structure, an insulated state in the case can be simply maintained by pouring resin into the case from the through-hole formed in the top plate. 
     A method of manufacturing a semiconductor power module according to another aspect of the present invention includes the steps of bonding a rear surface of a semiconductor power device having a surface and the rear surface to a base member, bonding a rear surface of a metal block, having a surface and the rear surface, employed as a wiring member for the semiconductor power device to the surface of the semiconductor power device after bonding the base member and the semiconductor power device to each other, performing preliminary soldering on an external terminal, for supplying power to the semiconductor power device, and bonding the external terminal and the metal block to each other by bringing the metal block into contact with a portion of the external terminal subjected to the preliminary soldering and heating the external terminal. 
     When the metal block having a high heat releasing effect is utilized as the wiring material for the semiconductor power device as in the present invention, heat may be released through the metal block having a high heat releasing effect if the side of the external terminal is merely heated while a solder material is held between the metal block and the external terminal. Consequently, the previously held solder material may not be excellently melted, but the metal block and the external terminal may be defectively bonded to each other. 
     According to the inventive manufacturing method, therefore, the preliminary soldering is previously performed on the external terminal, and the metal block is brought into contact with and bonded to the portion subjected to the preliminary soldering. Thus, the metal block and the external terminal can be excellently bonded to each other. In other words, a semiconductor power device such as that according to the present invention can be simply manufactured with high quality. 
     Preferably in the method of manufacturing a semiconductor power module according to the present invention, the external terminal is a plate terminal in the form of a flat plate, and the step of performing the preliminary soldering includes a step of piling not less than a prescribed volume of solder on the plate terminal. 
     According to this structure, the solder of not less than the prescribed volume can compensate for a vertical difference caused between a plurality of metal blocks. 
     Embodiments of the present invention are now described in detail with reference to the attached drawings. 
     &lt;First Embodiment&gt; 
       FIG. 1  illustrates the overall structure of a semiconductor power module according to a first embodiment of the present invention. 
     A semiconductor power module  1  includes a case  2  having an open surface, a top plate  3  blocking the open surface of the case  2 , a source terminal  4  as an external terminal, a source sensing terminal  5 , and a gate terminal  6 . 
     For the convenience of illustration, directions X, Y and Z shown in  FIG. 1  may hereinafter be employed. The direction X is a direction along the long sides of the case  2  rectangular in plan view. The direction Y is a direction along the short sides of the case  2  rectangular in plan view. The direction Z is a direction along the height direction of the case  2 . When the case  2  is placed on a horizontal plane, the directions X and Y form two horizontal directions (first and second horizontal directions) along two horizontal straight lines (X- and Y-axes) orthogonal to each other, and the direction Z forms a vertical direction (a height direction) along a vertical straight line (a Z-axis). 
     The case  2  integrally has a base portion  8 , rectangular in plan view, having a uniform thickness and a frame portion  9 , rectangular in plan view, uprighted from a peripheral edge portion of the base portion  8 . In the semiconductor power module  1 , semiconductor power devices  18 , described later, are arranged on a region (a device region  16  described later) of the base portion  8  surrounded by the frame portion  9 . 
     The base portion  8  and the frame portion  9  are made of a metallic material in the first embodiment. In particular, the base portion  8  and the frame portion  9  are preferably made of a metal such as aluminum or copper having high heat releasing characteristics. 
     A base  12  made of a resin material is mounted on the frame portion  9 . The source sensing terminal  5  and the gate terminal  6  in the form of narrow columns are provided to extend inside and outside the case  2  through the base  12 . The source sensing terminal  5  and the gate terminal  6  are so provided through the base  12  made of resin that the source sensing terminal  5  and the gate terminal  6  can be insulated from each other and from the frame portion  9  made of a metal. 
     The top plate  3  is a platelike body, in the form of a rectangle having a uniform thickness in plan view, separable from the case  2 . The top plate  3  is made of a resin material in the first embodiment. The top plate  3 , particularly preferably made of heat-resistant resin such as PPS (polyphenylene sulfide), may alternatively be made of a liquid crystal polymer or a ceramic material. The top plate  3  is fixed to the frame portion  9  with an adhesive or the like, for example. 
     The source terminal  4  is a platelike body (a plate terminal), in the form of a rectangle having a uniform thickness in plan view, elongated along the direction Y, and placed on the upper surface of the top plate  3 . 
     In the top plate  3 , a plurality of openings  14  (shown by two-dot chain lines in  FIG. 1 ) smaller than the plane area of the source terminal  4  are formed in a region opposed to the source terminal  4 . The plurality of openings  14  are formed in the same number as the semiconductor power devices  18  described later. According to the first embodiment, three openings  14  are arrayed in a triangular shape in plan view. 
     In the top plate  3 , a through-hole  15  passing through the top plate  3  in the thickness direction is formed on a position between the source terminal  4  and the base  12 . The through-hole  15  is in the form of an ellipse elongated along the direction Y in plan view in the first embodiment. 
       FIG. 2  illustrates the internal structure of the semiconductor power module  1  shown in  FIG. 1 .  FIG. 3  is a sectional view of the semiconductor power module  1  shown in  FIG. 1 , taken along a cutting plane line A-A in  FIG. 1 . 
     In the case  2 , an insulated substrate  17  and the plurality of semiconductor power devices  18  are arranged on the device region.  16  surrounded by the frame port on  9  in this order from the side closer to the base  12  along the direction Y. 
     The insulated substrate  17  is constituted of a ceramic substrate, for example. The insulated substrate  17  is a platelike body, in the form of a rectangle having a uniform thickness in plan view, elongated along the direction Y, and a platelike source sensing wire  19  and a platelike gate wire  20  are formed thereon at an interval from each other. An end of the source sensing terminal  5  is connected to the source sensing wire  19 . An end of the gate terminal  6  is connected to the gate wire  20 . 
     The plurality of semiconductor power devices  18  include a plurality of switching elements Tr and a plurality of diode elements Di. According to the first embodiment, the semiconductor power devices  18  include two switching elements Tr and one diode element Di. The semiconductor power devices  18  are devices employing an SiC semiconductor in the first embodiment. The plurality of semiconductor power devices  18  are arranged to be in one-to-one correspondence to the openings  14  of the top plate  3  respectively. More specifically, one diode element Di and the two switching elements Tr are arrayed in a triangular shape in plan view. Rear surfaces  182  of the plurality of semiconductor power devices  18  are bonded to the base portion  8  of the case  2 , so that the semiconductor power devices  18  are electrically connected to the case  2 . 
     Among the semiconductor power devices  18 , the switching elements Tr are electrically connected to the gate wire  20  and the source sensing wire  19  through different Al wires  22  and  23  respectively. 
     Rear surfaces  242  of metal blocks  24  employed as wiring materials supplying power to the semiconductor power devices  18  are bonded one by one to surfaces  181  (opposite to the rear surfaces  182  bonded to the base portion  8 ) of the semiconductor power devices  18 . The metal blocks  24  are in the form of rectangular parallelepipeds uprighted from the surfaces  181  of the semiconductor power devices  18  in a direction (approaching the source terminal  4 ) separating from the base portion  8  in the first embodiment. 
     The metal blocks  24  are preferably made of Cu or an alloy material (such as a CuMo alloy or a CuW alloy, for example) containing Cu. Thus, the difference between the linear expansion coefficients of SiC and the metal blocks  24  can be reduced as compared with a case of employing Al wires as wiring members for the SiC power devices  18 . Therefore, thermal stress caused between the semiconductor power devices  18  and the metal blocks  24  can be reduced. Consequently, thermal fatigue of the semiconductor power devices  18  can be reduced, whereby a semiconductor power module  1  having a long life and high reliability can be attained. For example, the linear expansion coefficient of SiC is about 4.5 ppm/K, and that of a CuMo alloy is about 9.0 ppm/K (about twice the linear expansion coefficient of SiC). On the other hand, the linear expansion coefficient of Al is about 23 ppm/K (about five time the linear expansion coefficient of SiC). Surfaces  241  of the plurality of metal blocks  24  are bonded to the source terminal  4  through the openings  14  of the top plate  3 . 
     In the top plate  3 , a recess portion  25  having a contour along the shape of the source terminal  4  in plan view (overlapping with the source terminal  4  in plan view) is formed on the region opposed to the source terminal  4 , and the source terminal  4  is fitted into the recess portion  25 . The openings  14  for connecting the metal blocks  24  and the source terminal  4  with one another are formed to pass through a bottom. wall  26  of the recess portion  25 . A portion, surrounding the openings  14 , of the bottom wall  26  of the recess portion  25  as a support portion is in contact with the source terminal  4  from the side of the rear surface. Thus, a part of the source terminal  4  is supported by the metal blocks  24  due to the bonding, and most of the remaining parts are supported by the top plate  3  (the bottom wall  26  of the recess portion  25 ) entering the side of the rear surface thereof. 
       FIGS. 4A to 4E  are sectional views successively illustrating manufacturing steps for the semiconductor power module  1  shown in  FIG. 1 . 
     First, the insulated substrate  17  provided with the platelike wires  19  and  20  is mounted on the device region  16  in the case  2 , as shown in  FIG. 4A . Then, the base  12  having the source sensing terminal  5  and the gate terminal  6  inserted thereinto is mounted on the frame portion  9  of the case  2 . Then, the source sensing terminal  5  and the gate terminal  6  and the platelike wires  19  and  20  are bonded to one another. Then, the semiconductor power devices  18  are set on the base portion  8  through plate solder members  27 , for example. Then, the case  2  is set on a heater  28 , and heated to 250 to 400° C., for example. Due to the heating, heat conducted to the case  2  made of a metal is transmitted to the plate solder members  27 , to melt the plate solder members  27 . Thus, the semiconductor power devices  18  are bonded to the base portion  8  of the case  2 .  FIGS. 4B to 4E  omit illustration of the plate solder members  27  employed for the bonding. 
     Then, while the case  2  is set on the heater  28 , the metal blocks  24  are set on the surfaces  181  of the semiconductor power devices  18  through plate solder members  29 , for example, as shown in  FIG. 4B . Then, the case  2  is heated to 250 to 400° C., for example. Due to the heating, heat conducted to the case  2  made of a metal is transmitted to the plate solder members  29  through the semiconductor power devices  18 , to melt the plate solder members  29 . Thus, the metal blocks  24  are bonded to the semiconductor power devices  18 .  FIGS. 4C to 4E  omit illustration of the plate solder members  29  employed for the bonding. 
     Then, the top plate  3  is positioned to align the openings  14  thereof with the metal blocks  24  respectively, and fixed to the frame portion  9 , as shown in  FIG. 4C . 
     Then, the source terminal  4  is singly placed on the heater  28 , and preliminary solder members  30  are applied onto the source terminal  4 , as shown in  FIG. 4D . Then, the case  2  is inverted (so that the top plate  3  is directed downward) to position the metal blocks  24  on the preliminary solder members  30 , thereby bringing the metal blocks  24  into contact with the preliminary solder members  30 . 
     Then, the metal blocks  24  and the source terminal  4  are heated by the heater  28  to be bonded to one another, as shown in  FIG. 4E . 
     According to the semiconductor power module  1 , as hereinabove described, the metal blocks  24  larger in diameter than wires are employed as the wiring members for connecting the semiconductor power devices  18  and the source terminal with one another. Thus, the wires (the metal blocks  24 ) can be bonded to the semiconductor power devices  18  with large areas. Therefore, current concentration on the junctions between the wires (the metal blocks  24 ) and the semiconductor power devices  18  can be suppressed. Consequently, current can be leveled. Further, the metal blocks  24  and the platelike source terminal  4  can efficiently release heat generated in the semiconductor power devices  18 , whereby the heat releasing effect can also be improved. 
     When the external terminal is the platelike source terminal  4  provided along the upper surface of the top plate  3  as in the first embodiment and the source terminal  4  is subjected to an external shock or the like, the shock may be transmitted to the semiconductor power devices  18  through the metal blocks  24 , to break the semiconductor power devices  18  as a result. 
     According to the first embodiment, therefore, the bottom wall.  26  of the recess portion  25  of the top plate  3  supports the source terminal  4  from the side of the rear surface thereof. Even if the source terminal  4  is subjected to a shock or the like, therefore, the bottom wall  26  of the recess portion  25  can absorb the shock. Consequently, the semiconductor power devices  18  can be absolutely protected against transmission of the shock, or the shock transmitted to the semiconductor power devices  18  can be reduced. Thus, the semiconductor power devices  18  can be prevented from breakage caused by the shock. According to the first embodiment, further, the support portion supporting the source terminal  4  is constituted of peripheral edge portions (the bottom wall  26  of the recess portion  25 ) of the openings  14  surrounding the metal blocks  24  in one-to-one correspondence along the plane contours of the metal blocks  24 , whereby the shock transmitted from the source terminal  4  to the metal blocks  24  can be effectively absorbed. 
     The top plate  3  is separable from the frame portion  9 . In order to manufacture the semiconductor power module  1 , therefore, the semiconductor power devices  18  are first arranged on the device region  16  so that the metal blocks  24  can be bonded to the semiconductor power devices  18  while the top plate  3  is separated from the frame portion  9 . Therefore, the semiconductor power module  1  can be manufactured with excellent workability. 
     The rear surfaces  182  of the semiconductor power devices  18  are directly bonded to the base portion  8  made of a metal, whereby electrical contact with the rear surfaces  182  (drain sides) of the semiconductor power devices  18  can be attained through the case  2  of the semiconductor power module  1 . 
     The top plate  3  is provided with the through-hole  15 , whereby an insulated state in the case  2  can be simply maintained by pouring resin into the case  2  from the through-hole  15 . 
     When the metal blocks  24  having a high heat releasing effect are utilized as the wire materials for the semiconductor power devices  18  as in the first embodiment, heat may be released through the metal blocks  24  having a high heat releasing effect if the source terminal  4  is heated with the heater  28  while the plate solder members  27  or  29  are held between the metal blocks  24  and the source terminal  4  as in the step shown in  FIG. 4A  or  4 B, for example. Consequently, the previously held plate solder members  27  or  29  may not be excellently melted, but the metal blocks  24  and the source terminal  4  may be defectively bonded to one another. 
     According to the first embodiment, therefore, the preliminary solder members  30  are previously applied to the source terminal  4  so that the metal blocks  24  are brought into contact with and bonded to the portions provided with the preliminary solder members  30 , as shown in  FIG. 4D . Thus, the metal blocks  24  and the source terminal  4  can be excellently bonded to one another. In other words, the semiconductor power module  1  can be simply manufactured in high quality. 
     Even if a vertical difference  h  is caused between the plurality of metal blocks  24  as shown in  FIG. 5 , for example, a prescribed volume of preliminary solder members  30  can compensate for the vertical difference  h  according to the method. Consequently, the platelike source terminal  4  can be collectively reliably bonded to the plurality of metal blocks  24 . 
     &lt;Second Embodiment&gt; 
       FIG. 6  illustrates the overall structure of a semiconductor power module according to a second embodiment of The present invention.  FIG. 7  illustrates the internal structure of the semiconductor power module shown in  FIG. 6 .  FIG. 8  is a sectional view of the semiconductor power module shown in  FIG. 6 , taken along a cutting plane line B-B in  FIG. 6 .  FIG. 9  is a sectional view of the semiconductor power module shown in  FIG. 6 , taken along a cutting plane line C-C in  FIG. 6 . 
     A power module  51  includes a case  52  having an open surface, a top plate  53  blocking the open surface of the case  52 , a source terminal  54  as an external terminal, a source sensing terminal  55 , and a gate terminal  56 . 
     For the convenience of illustration, directions X, Y and Z shown in  FIG. 6  may hereinafter be employed. The direction X is a direction along the long sides of the case  52  rectangular in plan view. The direction Y is a direction along the short sides of the case  52  rectangular in plan view. The direction Z is a direction along the height direction of the case  52 . When the case  52  is placed on a horizontal plane, the directions X and Y form two horizontal directions (first and second horizontal directions) along two horizontal straight lines (X- and Y-axes) orthogonal to each other, and the direction Z forms a vertical direction (a height direction) along a vertical straight line (a Z-axis). 
     The case  52  has a base portion  58 , rectangular in plan view, having a uniform thickness and a frame portion  59 , rectangular in plan view, uprighted from a peripheral edge portion of the base portion  58 . In the semiconductor power module  51 , semiconductor power devices  74 , described later, are arranged on a region (a device region  61 ) of the base portion  58  surrounded by the frame portion  59 . 
     The base portion  58  is made of a metallic material in the second embodiment. In particular, the base portion  58  is preferably made of a metal such as aluminum or copper having high heat releasing characteristics. 
     On the other hand, the frame portion  59  is made of a resin material in the second embodiment. The frame portion  59 , particularly preferably made of heat-resistant resin such as PPS (polyphenylene sulfide), may alternatively be made of a liquid crystal polymer or a ceramic material. 
     The frame portion  59  is provided with a low-stage portion  63 , having a constant depth, lower by one stage than a top portion thereof. The low-stage portion  63 , U-shaped in plan view, is a portion for sliding the top plate  53  also U-shaped in plan view. The depth of the low-stage portion  63  is preferably generally identical to the thickness of the top plate  53 , or example. Thus, the frame portion  59  and the top plate  53  can form a rectangular parallelepiped having a planar surface when the top plate  53  is fixed. 
     A base  64  made of a resin material is mounted on the frame portion  59 . The source sensing terminal  55  and the gate terminal  56  in the form of narrow columns are provided to extend inside and outside the case  52  through the base  64 . The source sensing terminal  55  and the gate terminal  56  are so provided through the base  64  made of resin that the source sensing terminal  55  and the gate terminal  56  can be insulated from each other and from the frame portion  59  made of a metal. 
     The top plate  53  is a platelike body, in the form of a rectangle having a uniform thickness in plan view, separable from the case  52 . The top plate  53  is made of a resin material in the second embodiment. The top plate  53 , particularly preferably made of heat-resistant resin such as PPS (polyphenylene sulfide), may alternatively be made of a liquid crystal polymer or a ceramic material. 
     The source terminal  54  is a platelike body (a plate terminal), in the form of a rectangle having a uniform thickness in plan view, elongated along the direction Y, and provided to be opposed to the device region  61  of the base portion  58 . 
     The top plate  53  has a pair of arm portions  65  along the long sides of the source terminal  54  as first opposite sides and a coupling portion  66  coupling portions of the pair of arm portions  65  on a side of the source terminal  51  closer to the source sensing terminal  55  with each other. The top plate  53  is provided to surround three sides in the periphery of the source terminal  54  with the arm portions  65  and the coupling portion  66 , and has a blocked end blocked with the coupling portion  66  on the side closer to the source sensing terminal  55  in the direction X and an open end opposite thereto. Thus, the top plate  53  is supported by the frame portion  59 , to be slidable in a sliding direction (the direction X) along a direction where a coupling end separates from the source terminal  54 . 
     As shown in  FIG. 9 , the pair of arm portions  54  have first portions  67  coming into contact with a peripheral edge portion of the source terminal  54  from outside in a transverse direction (the direction Y) orthogonal to the sliding direction and second portions  68  projecting from lower ends of the first portions  67  along the rear surface of the source terminal  54  respectively. Thus, the peripheral edge portion of the source terminal  54  along the log sides fits into a recess portion  69  partitioned by the first portions  67  of the arm portions  65  and the second portions  68  of the arm portions  65 . 
     As shown in  FIG. 8 , the coupling portion  66  has a first portion  70  coming into contact with the peripheral edge portion of the source terminal  54  from outside in the sliding direction (the direction X) and a second portion  71  projecting from a lower end of the first portion  70  along the rear surface of the source terminal  54 . Thus, the peripheral edge portion of the source terminal  54  along the short sides as second opposite sides fits into a recess portion  72  partitioned by the first portion  70  of the coupling portion  66  and the second portion  71  of the coupling portion  66 . 
     In other words, the source terminal  51  is supported by the arm portions  65  and the coupling portion  66  on a position U-shaped in plan view. 
     In the case  52 , an insulated substrate  73  and the plurality of semiconductor power devices  74  are arranged on the device region  61  surrounded by the frame portion  59  in this order from the side of the base  64  along the direction Y. 
     The insulated substrate  73  is constituted of a ceramic substrate, for example. The insulated substrate  73  is a platelike body, in the form of a rectangle having a uniform thickness in plan view, elongated along the direction Y, and a platelike source sensing wire  75  and a platelike gate wire  76  are formed thereon at an interval from each other. An end of the source sensing terminal  55  is connected to the source sensing wire  75 . An end of the gate terminal  56  is connected to the gate wire  76 . 
     The plurality of semiconductor power devices  74  include a plurality of switching elements Tr and a plurality of diode elements Di. According to the second embodiment, the semiconductor power devices  74  include two switching elements Tr and one diode element Di. The semiconductor power devices  74  are devices employing an SiC semiconductor in the second embodiment. In the plurality of semiconductor power devices  74 , two switching elements Tr are arranged at an interval from each other along the direction Y, and one diode element Di is arranged on a side of the switching elements Tr opposite to the insulated substrate  73  in the direction X. More specifically, one diode element Di and the two switching elements Tr are arrayed in a triangular shape in plan view. Rear surfaces  742  of the plurality of semiconductor power devices  74  are bonded to the base portion  58  of the case  52 , so that the semiconductor power devices  74  are electrically connected to the case  52 . 
     Among the semiconductor power devices  74 , the switching elements Tr are electrically connected to the gate wire  76  and the source sensing wire  75  through different Al wires  81  and  82  respectively. 
     Rear surfaces  832  of metal blocks  83  employed as wiring materials supplying power to the semiconductor power devices  74  are bonded one by one to surfaces  741  (opposite to the rear surfaces  742  bonded to the base portion  58 ) of the semiconductor power devices  74 . The metal blocks  83  are in the form of rectangular parallelepipeds uprighted from the surfaces  741  of the semiconductor power devices  74  in a direction (approaching the source terminal  54 ) separating from the base portion  58  in the second embodiment. 
     The metal blocks  83  are preferably made of Cu or an alloy material (such as a CuMo alloy or a CuW alloy, for example) containing Cu. Thus, the difference between the linear expansion coefficients of SiC and the metal blocks  83  can be reduced as compared with a case of employing Al wires as wiring members for the SiC power devices  71 . Therefore, thermal stress caused between the semiconductor power devices  74  and the metal blocks  83  can be reduced. Consequently, thermal fatigue of the semiconductor power devices  74  can be reduced, whereby a semiconductor power module  51  having a long life and high reliability can be attained. For example, the linear expansion coefficient of SiC is about 4.5 ppm/K, and that of a CuMo alloy is about 9.0 ppm/K (about twice the linear expansion coefficient of SiC). On the other hand, the linear expansion coefficient of Al is about 23 ppm/K (about five times the linear expansion coefficient of SiC). Surfaces  831  of the plurality of metal blocks  83  are bonded to the source terminal  54  in a region of the top plate  53  surrounded by the arm portions  65  and the coupling portion  66 . 
       FIGS. 10A to 10E  are sectional views successively illustrating manufacturing steps for the semiconductor power module  51  show in  FIG. 6 . 
     First, the insulated substrate  73  provided with the platelike wires  75  and  76  is mounted on the device region  61  in the case  52 , as shown in  FIG. 10A  Then, the base  64  having the source sensing terminal  55  and the gate terminal  56  inserted thereinto is mounted on the frame portion  59  of the case  52 . Then, the source sensing terminal  55  and the gate terminal  56  and the platelike wires  75  and  76  are bonded to one another. Then, the semiconductor power devices  74  are set on the base portion  58  through plate solder members  84 , for example. Then, the case  52  is set on a heater  85 , and heated to 250 to 400° C., for example. Due to the heating, heat conducted to the base portion  58  made of a metal is transmitted to the plate solder members  84 , so melt the plate solder members  84 . Thus, the semiconductor power devices  74  are bonded to the base portion  58  of the case  52 .  FIGS. 10B to 10E  omit illustration of the plate solder members  84  employed for the bonding. 
     Then, while the case  52  is set on the heater  85 , the metal blocks  83  are set on the surfaces  741  of the semiconductor power devices  74  through plate solder members  36 , for example, as shown in  FIG. 10B . Then, the case  52  is heated to 250 to 400° C., for example. Due to the heating, heat conducted to the base portion  58  made of a metal is transmitted to the plate solder members  86  through the semiconductor power devices  74 , to melt the plate solder members  86 . Thus, the metal blocks  83  are bonded to the semiconductor power devices  74 ,  FIGS. 10C to 10E  omit illustration of the plate solder members  86  employed for the bonding. 
     Then, the source terminal  54  is singly placed on the heater  85 , and preliminary solder members  87  are applied onto the source terminal  54 , as shown in  FIG. 10C , Then, the case  52  is inverted to position the metal blocks  83  on the preliminary solder members  67 , thereby bringing the metal blocks  83  and the preliminary solder members  87  into contact with one another. 
     Then, the metal blocks  83  and the source terminal  54  are heated by the heater  85  to be bonded to one another, as shown in  FIG. 10D . 
     Then, the sop plate  53  is positioned to align the recess portion  72  thereof with the peripheral edge portion of the source terminal  54 , and the top plate  53  is slid with respect to the frame portion  59  until she coupling portion  66  thereof comes into contact with the source terminal  54 , as shown in  FIG. 10E . Thus, the device region  61  is blocked. 
     According so the semiconductor power module  51 , as hereinabove described, the metal blocks  83  larger in diameter than wires are employed as the wiring members for connecting the semiconductor power devices  74  and the source terminal  54  with one another. Thus, the wires (the metal blocks  83 ) can be bonded to the semiconductor power devices  74  with large areas. Therefore, current concentration on the junctions between the wires (the metal blocks  83 ) and the semiconductor power devices  74  can be suppressed. Consequently, current can be leveled. Further, the metal blocks  83  and the platelike source terminal  54  can efficiently release heat generated in the semiconductor power devices  74 , whereby a heat releasing effect can also be improved. 
     When the external terminal is the platelike source terminal  54  provided along the upper surface of the top plate  53  as in the second embodiment and the source terminal  54  is subjected to an external shock or the like, the shock may be transmitted to the semiconductor power devices  74  through the metal blocks  83 , to break the semiconductor power devices  74  as a result. 
     According to the second embodiment, therefore, the second portions  68  and  71  of the arm portions  65  and the coupling portion  66  of the top plate  53  support the source terminal  54  from the side of the rear surface thereof. Even if the source terminal  54  is subjected to a shock or the like, therefore, the arm portions  65  and the coupling portion  66  can absorb the shock. Consequently, the semiconductor power devices  74  can be absolutely protected against transmission of the shock, or the shock transmitted to the semiconductor power devices  74  can be reduced. Thus, the semiconductor power devices  74  can be prevented from breakage caused by the shock. 
     The top plate  53  is slidably supported by the frame portion  59 , and separable from the frame portion  59 . In order to manufacture the semiconductor power module  51 , therefore, the semiconductor power devices  74  are first arranged. on the device region  61  so that the metal blocks  83  can be bonded to the semiconductor power devices  74  while the top plate  53  is separated from the frame portion  59 . Therefore, the semiconductor power module  51  can be manufactured with excellent workability. Further, an end portion of the top plate  53  opposite to the direction where the same is extracted by sliding is open. Also after the top plate  53  is fixed to the frame portion  59 , therefore, the device region  61  can be exposed by extracting the top plate  53  without detaching the metal blocks  83  from the source terminal  54 . Consequently, maintenance in the case  52  can be easily performed. 
     The peripheral edge portion along the long sides of the source terminal  54  fits into the recess portion  69  partitioned by the first potions  67  of the arm portions  65  and the second portions  68  of the arm portions  65 . When the top plate  53  is slid along the frame portion  59 , therefore, the source terminal  54  can be utilized as a guide member for guiding the top plate  53 . Therefore, the top plate  53  can be easily positioned. 
     The peripheral edge portion along the short sides (opposite sides orthogonal to the sliding direction) of the source terminal  54  fits into the recess portion  72  partitioned by the first portion  70  of the coupling portion  66  and the second portion  71  of the coupling portion  66 . When the top plate  53  is slid along the frame portion  59 , therefore, the sliding of the top plate  53  can be stopped by bringing the peripheral edge portion of the source terminal  54  into contact with the first portion  70  of the coupling portion  66  of the top plate  53 . in other words, the source terminal  54  can also be utilized as a stopper member for stopping the sliding of the top plate  53 . Therefore, the top plate  53  can be more easily positioned. 
     The rear surfaces  742  of the semiconductor power devices  74  are directly bonded to the base portion  58  made of a metal, whereby electrical contact with the rear surfaces  742  (drain sides) of the semiconductor power devices  74  can be attained through the case  52  of the semiconductor power module  51 . 
     When the metal blocks  83  having a high heat releasing effect are utilized, as the wire materials for the semiconductor power devices  74  as in the second embodiment, heat may be released through the metal blocks  83  having a high heat releasing effect if the source terminal  54  is heated with the heater  85  while the plate solder members  84  or  86  are held between the metal blocks  83  and the source terminal  54  as in the step shown in  FIG. 10A  or  10 B, for example. Consequently, the previously held plate solder members  84  or  86  may not be excellently melted, but the metal blocks  83  and the source terminal  54  may be defectively bonded to one another. 
     According to the second embodiment, therefore, the preliminary solder members  87  are previously applied to the source terminal  54  so that the metal blocks  83  are brought into contact with and bonded so the portions provided with the preliminary solder members  87 , as shown in  FIG. 10C . Thus, the metal blocks  83  and the source terminal  54  can be excellently bonded to one another. In other words, the semiconductor power module  51  can be simply manufactured in high quality. 
     Even if the vertical difference  h  shown in  FIG. 5  is caused between the plurality of metal blocks  83  as described in the aforementioned first embodiment, for example, a prescribed volume of preliminary solder members  87  can compensate for the vertical difference  h  according to the method. Consequently, the platelike source terminal  54  can be collectively reliably bonded to the plurality of metal blocks  83 . 
     While the embodiments of the present invention have been described, the present invention may be embodied in other ways. 
     For example, the metal blocks  24  may alternatively have tapered shapes whose sectional areas spread from the rear surfaces  242  toward the surfaces  241  thereof, as in a power module  101  shown in  FIGS. 11 and 12 . 
     Further, the material for the metal blocks  24  or  83  may alternatively be prepared from a metallic material such as Cu, Al or Fe. 
     While the present invention has been described in detail by way of the embodiments thereof, it should be understood that these embodiments are merely illustrative of the technical principles of the present invention but not limitative of the invention. The spirit and scope of the present invention are to be limited only by the appended claims. 
     This application corresponds to Japanese Patent Application No. 2010-219030 filed with the Japan Patent Office on Sep. 29, 2010, the disclosure of which is incorporated herein by reference.