Abstract:
An electronic circuit device comprises: a semiconductor element having a first surface and a second surface, with the first and second surfaces being on first and second sides of the semiconductor element, respectively, and facing in opposite directions; a first electrode on the first surface; a second electrode on the second surface; a first circuit board electrically connected to the first electrode via a metallic plate such that the metallic plate and the semiconductor element are on the first circuit board; a second circuit board on the second side of the semiconductor element, the second circuit board having a control circuit for the semiconductor element; and a metallic wire for directly electrically interconnecting the second electrode and the second circuit board.

Description:
[0001]     This is a divisional application of Ser. No. 10/221,853, filed Sep. 17, 2002, which is a National Stage application of PCT /JP02/00167 filed Jan. 15, 2002. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to an electronic circuit device of a power control system using semiconductor elements such as IGBTs (Insulated Gate Bipolar Transistors), diodes and the like, for driving motors, and a method for manufacturing the electronic circuit device.  
       BACKGROUND ART  
       [0003]     Lately, a working current in a motor driving device has increased in accordance with an enhancement in performance and function of electronic devices used in the motor driving device, thereby requiring semiconductors to be used to meet a high current. A motor driving device used conventionally is shown in  FIG. 16 . An example of this conventional motor driving device will be described below with reference to  FIG. 16 .  
         [0004]     In  FIG. 16 , reference numerals respectively indicate:  1   a  an IGBT;  1   b  a diode;  3  a high temperature solder;  4  a metallic element;  5  a sealing resin;  6  a solder;  7  a circuit board;  10  a heat radiation plate;  10   a  a projecting screw bed;  11  a screw;  12  a surface mounting electronic component (passive element);  13  a surface mounting electronic component (semiconductor element);  14  a metallic base circuit board;  15  a silicone grease;  18  a metallic wire;  19  a metallic lead;  22  a projecting connector;  23  a dented connector; and  24  an insulation resin.  
         [0005]     A method for manufacturing this thus-constituted conventional motor driving device will be discussed hereinbelow.  
         [0006]     Semiconductor components such as the IGBT  1   a,  the diode  1   b  and the like are connected by the high temperature solder  3  to metallic elements  4 . The IGBT  1   a  and the diode  1   b,  and these semiconductor components and metallic lead  19 , are electrically joined together with use of the metallic wire  18 . An aluminum wire or a gold wire is normally used as the metallic wire  18 . In using a metallic wire  18  formed of, e.g., aluminum, the metallic wire  18  is connected to a second electrode of one of these semiconductor components by performing wedge bonding of the aluminum wire. The second electrode is present opposite to a first electrode of this semiconductor component, which is joined to the metallic element  4 . The second electrode of the semiconductor component is formed of aluminum. Oxide films of aluminum on surfaces of both the second electrode and the metallic wire  18  are removed when the second electrode and the metallic wire are pressed into contact with each other with an ultrasonic energy being applied thereto in an ordinary temperature state. The second electrode and the metallic wire  18  are thus joined. The metallic wire  18  joined to the second electrode of the one semiconductor component is routed to the metallic lead  19  obtained by plating copper with tin, and is joined to the metallic lead  19  by performing a wedge bonding method.  
         [0007]     Thereafter, for a purpose of physically protecting the one semiconductor component and the metallic wire  18 , and improving reliability, the semiconductor component  1  and the metallic wire  18  are coated and sealed with the sealing resin  5  by performing a transfer molding technique or injection molding technique. The metallic lead  19  is bent and cut by molds to be even with the metallic element  4 . During this sequence of procedures, an electronic component named “TO-220” comprising the one semiconductor component, the high temperature solder  3 , the metallic element  4 , the metallic wire  18 , the metallic lead  19  and the sealing resin  5  is completed.  
         [0008]     After a solder paste is printed onto the metallic base circuit board  14 , various components such as the above electronic component “TO-220”, the projecting connector  22 , and the like are placed on the metallic base circuit board. The metallic base circuit board  14  in its entirety is put into a heating furnace, whereby the solder paste is melted. The solder paste is then set by being returned to an ordinary temperature. This set solder  6  electrically and physically joins the metallic base circuit board  14  to various electronic components such as the electronic component “TO-220”, the projecting connector  22 , and the like.  
         [0009]     For providing electrical insulation, the sealing resin  24  is applied to the metallic base circuit board  14  in its entirety. The metallic base circuit board  14 , with the various electronic components, is put into a reduced pressure furnace to remove bubbles mixing inside the sealing resin  24 , and then put into a heating furnace to set the sealing resin  24 .  
         [0010]     Next, the silicone grease  15  is applied to the heat radiation plate  10 . The metallic base circuit board  14  is brought into intimate contact with the heat radiation plate  10  and fixed by screws. Then, by inserting the projecting connector  22  into the dented connector  23  after registering the projecting connector  22  mounted on the metallic base circuit board  14  with the dented connector  23  mounted on the circuit board  7 , the circuit board  7  is brought into intimate contact with the projecting screw bed  10   a  and fixed by screws  11 .  
         [0011]     In the manner as above, the process of mounting to the metallic base circuit board  14  electronic components which include electronic components “TO-220” for switching a motor driving current and requiring heat radiation, and the process of combining the circuit board  7  including the circuit for controlling the electronic components “TO-220” and requiring no heat radiation, are completed.  
         [0012]     The above-described arrangement generates a loss caused by a resistance of metallic wires  18  and metallic leads  19  and also a stray inductance because of a length of the wires  18  and leads  19 . In addition, for example, since the electronic component “TO-220” is equipped with a metallic lead  19 , a larger area than an area of the electronic component “TO-220” is required for the metallic base circuit board  14 , thereby impeding miniaturization and high-density mounting.  
         [0013]     Meanwhile, a motor driving device for electric products alike has been required to be made compact and highly efficient in terms of heat radiation to meet a recent trend towards lighter, thinner, shorter and smaller construction of electric products. However, when bubbles are present inside the high temperature solder  3 , the bubbles obstruct heat transfer generated by a semiconductor component, thereby increasing a resistance from the semiconductor component to the metallic element  4 . As a result, only a bubble part becomes high in temperature, which leads to breakage of the semiconductor component  1  in a worst case.  
         [0014]     As described hereinabove, the metallic wire  18  is joined to the second electrodes of semiconductor components by performing a wedge bonding method with the aluminum wire. In the conventional art, the metallic wire  18  is limited in thickness due to this joining method, and at the same time the metallic wire  18  is limited in length due to an arrangement of substrate electrodes, thereby making it impossible to reduce a wiring resistance. Coping with an on-state resistance decrease in consequence of recent progress of semiconductor components is thus hindered, with an imposing problem of noise increase resulting from electrical signals&#39; requirement of a high frequency and a large current.  
       SUMMARY OF THE INVENTION  
       [0015]     The present invention is devised to solve the above problems and has for its essential object to provide an electronic circuit device which is compact, has good heat radiation efficiency and can reduce resistance and stray inductance, and provide a method for manufacturing the electronic circuit device.  
         [0016]     In order to accomplish this objective, an electronic circuit device is provided according to a first aspect of the present invention, which comprises: 
        a semiconductor element requiring heat radiation and having electrodes formed on opposite faces thereof;     a first circuit board electrically connected via a metallic plate to a first electrode of the electrodes formed on one of the opposite faces of the semiconductor element, on which circuit board the metallic plate and the semiconductor element are placed;     a second circuit board arranged on a side of the other of the opposite faces of the semiconductor element so as to be opposite to the first circuit board, and having a control circuit for the semiconductor element; and     a metallic wire for directly electrically connecting to each other a second electrode, of the electrodes present on the other of the opposite faces, and the second circuit board.        
 
         [0021]     The above metallic wire may be formed to include a first bend portion for absorbing expansion and contraction of the first circuit board and the second circuit board resulting from heat radiation of the semiconductor element.  
         [0022]     The metallic wire joined to the second electrode may be extended in a thickness direction of the semiconductor element.  
         [0023]     The electronic circuit device may be constituted to further include a heat radiation member with supporting members for receiving the first circuit board thereon and supporting the second circuit board. The metallic wire may be provided with a second bend portion for absorbing, in a state with the second circuit board being supported by the supporting members, expansion and contraction of the first circuit board and the second circuit board resulting from heat radiation, and for pressing the first circuit board against the heat radiation member.  
         [0024]     An electronic circuit device of a power control system according to a second aspect of the present invention comprises: 
        a semiconductor element requiring heat radiation and having first electrodes and second electrodes respectively formed on opposite faces thereof;     bumps formed on the second electrodes; and     a metallic member having a first face arranged opposite to the first electrodes so as to be electrically connected to the first electrodes, and including installation members formed of a metal erected on the first face, along a thickness direction of the semiconductor element, to a height which exceeds a height of the bumps in the thickness direction when the semiconductor element with the bumps is placed on the first face.        
 
         [0028]     Three or more installation members may be provided for one metallic member in the above electronic circuit device of the second aspect.  
         [0029]     The electronic circuit device of the second aspect may further include a second circuit board which is arranged on a side opposite to that of the first electrodes so as to be electrically connected to the bumps and leading ends of the installation members, and is provided with a control circuit for the semiconductor element.  
         [0030]     Also, the above electronic circuit device of the second aspect may further include a heat radiation member with supporting members for receiving the metallic member thereon via an electric insulating member, and dissipating heat conducted from the semiconductor element to the metallic member.  
         [0031]     According to a third aspect of the present invention is provided a method for manufacturing an electronic circuit device having: 
        a semiconductor element requiring heat radiation and having first electrodes and second electrodes respectively formed on opposite faces thereof;     bumps formed on the second electrodes; and     a metallic member having a first face arranged opposite to the first electrodes so as to be electrically connected to the first electrodes, and including installation members formed of a metal erected on the first face, along a thickness direction of the semiconductor element, to a height which exceeds a height of the bumps in the thickness direction when the semiconductor element with the bumps is placed on the first face,     wherein the method comprises:     bringing the first face of the metallic member and the first electrodes into contact with each other, placing the semiconductor element on the first face, and heating the semiconductor element;     supplying a molten solder to the first face;     relatively pressing the semiconductor element and the metallic member to remove bubbles from inside the molten solder present between the first face and the first electrodes; and     decreasing a temperature of the molten solder while maintaining a pressing state, thereby solidifying the molten solder and joining the semiconductor element and the metallic member to each other.        
 
         [0040]     In the manufacturing method of the third aspect, after joining of the semiconductor element and the metallic member, the method further includes a step of electrically connecting the bumps and leading ends of the installation members to a second circuit board which is arranged on a side of the other face and is provided with a control circuit for the semiconductor element, 
        wherein, when a plurality of the metallic members are attached to the second circuit board, heights of the installation members of the metallic members may be adjusted to unify all the metallic members in terms of height with respect to the second circuit board.        
 
         [0042]     As described hereinabove, the electronic circuit device according to the first aspect of the present invention is provided with the metallic wire for directly electrically connecting the second electrode formed on the other of the opposite faces of the semiconductor element and the second circuit board arranged on the side of the other opposite face. Since the conventional dented connector and projecting connector can be eliminated, the electronic circuit device can be made compact.  
         [0043]     Moreover, when the metallic wire is provided with the bend portion, the bend portion can absorb expansion and contraction between the first circuit board and the second circuit board resulting from heat of the semiconductor element.  
         [0044]     Since the metallic wire is extended in the thickness direction of the semiconductor element, the electronic circuit device can furthermore be miniaturized.  
         [0045]     When the metallic wire is extended in the thickness direction of the semiconductor element and is further provided with the second bend portion, not only miniaturizing the electronic circuit device and absorbing expansion and contraction can both be achieved, but the first circuit board can be pressed against the heat radiation plate, so that heat can be stably removed.  
         [0046]     In the electronic circuit device according to the second aspect of the present invention, the semiconductor element is provided with the bumps on the second electrodes and with the metallic member having installation members, so that wiring lines are eliminated. Consequently, stray inductance and conduction resistance resulting from wiring lines can be reduced.  
         [0047]     In the case where a plurality of the metallic members are provided, the height of the metallic members can be made uniform by being adjusted by the installation members.  
         [0048]     Since the semiconductor element and the second circuit board can be directly electrically connected to each other by providing the metallic member, the conventional dented connector and projecting connector are eliminated, thus making the electronic circuit device small in size. When the heat radiation member is provided to support the second circuit board, heat from the metallic member can be stably dissipated by the one heat radiation member.  
         [0049]     According to the manufacturing method for the electronic circuit device in the third aspect of the present invention, the solder between the semiconductor element and the metallic member is solidified after the semiconductor element and the metallic member are relatively pressed against each other so as to remove bubbles from inside the solder. Therefore, thermal conduction from the semiconductor element to the metallic member will not be obstructed by bubbles, thus being able to prevent an abnormal temperature rise of the semiconductor element. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0050]     These and other objects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings in which:  
         [0051]      FIG. 1  is a sectional view of a second circuit device as an electronic circuit device of a power control system according to a first embodiment of the present invention;  
         [0052]      FIG. 2  is a diagram of semiconductor elements constituting a first circuit unit in  FIG. 1 ;  
         [0053]      FIG. 3  is a diagram showing a state with bumps formed on the semiconductor elements of  FIG. 2 ;  
         [0054]      FIG. 4  is a diagram showing a state in which the semiconductor elements with bumps shown in  FIG. 3  are mounted to a metallic member;  
         [0055]      FIG. 5  is a diagram of a state having a sealing resin further provided to the state of  FIG. 4 ;  
         [0056]      FIG. 6  is a sectional view of a state in which the first circuit unit of  FIG. 5  is mounted to a second circuit board;  
         [0057]      FIG. 7  is a sectional view of a state in which a plurality of the first circuit units are mounted to the second circuit board;  
         [0058]      FIG. 8  is a sectional view of a second circuit device as an electronic circuit device of a power control system according to a second embodiment of the present invention;  
         [0059]      FIG. 9  is a sectional view of a modified example of the second circuit device of  FIG. 8 ;  
         [0060]      FIG. 10  is a sectional view of a second circuit device as an electronic circuit device of a power control system according to a third embodiment of the present invention;  
         [0061]      FIG. 11  is a sectional view of a modified example of the second circuit device of  FIG. 10 ;  
         [0062]      FIG. 12  is a sectional view of a second circuit device as an electronic circuit device of a power control system according to a fourth embodiment of the present invention;  
         [0063]      FIG. 13  is a sectional view of a modified example of the second circuit device of  FIG. 12 ;  
         [0064]      FIG. 14  is a sectional view of a second circuit device as an electronic circuit device of a power control system according to a fifth embodiment of the present invention;  
         [0065]      FIG. 15  is a sectional view of a modified example of the second circuit device of  FIG. 14 ; and  
         [0066]      FIG. 16  is a sectional view of a conventional electronic circuit device of a power control system. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0067]     Before description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings.  
         [0068]     Electronic circuit devices according to the preferred embodiments of the present invention and a method for manufacturing the electronic circuit devices will be described below with reference to the drawings.  
       First Embodiment  
       [0069]      FIG. 5  shows a first electronic circuit device of a power control system (referred to as “a first circuit unit” hereinbelow)  100  which is one example of an electronic circuit device of this embodiment.  FIG. 1  shows a second electronic device of a power control system (referred to as “a second circuit device” below)  101  including first circuit units  100 , which corresponds to another example of an electronic circuit device.  
         [0070]     The second circuit device  101  of  FIG. 1  is constituted as follows.  111  is a drive semiconductor element which is used in a control system for controlling a driving current to a driving device, e.g., a motor or the like and which requires a heat radiation treatment. The drive semiconductor element includes an IGBT (Insulated Gate Bipolar Transistor)  111 - 1  and a diode  111 - 2 . As shown in  FIG. 3 , the drive semiconductor element  111  has a first electrode  111   c  and second electrodes  111   d  formed on opposite faces  111   a  and  111   b,  respectively.  112  are bumps (projecting electrodes) formed on the second electrodes  111   d  of the drive semiconductor element  111 .  114  is a metallic member which radiates and diffuses heat generated from the drive semiconductor element  111  as shown in  FIG. 4 . An entire surface of the metallic member  114  is plated with tin after projecting parts corresponding to installation members  114   b,  to be described later, are formed from copper as a base material with use of molds. The metallic member  114  has a first face  114   a,  arranged opposite to the first electrode  111   c,  to be electrically connected to the first electrode  111   c.   113  is a high temperature solder for joining the first electrode  111   c  of the drive semiconductor element  111  and the first face  114   a  of the metallic member  114  to each other. The aforementioned installation members  114   b  are projected from the first face  114   a  parallel to a thickness direction  111   e  of the drive semiconductor element  111 , and have a height to exceed the bumps  112  in the thickness direction  111   e  when the drive semiconductor element  111 , with the bumps  112  thereon, is placed onto the first face  114   a.  Although the installation members  114   b  of a pair are formed in the embodiment, three or more installation members can be formed for one first circuit unit  100 . If three or more installation members are formed, a flatness of the first circuit unit  100 , when mounted to a second circuit board  116 , can be further improved as will be described later.  
         [0071]     As indicated in  FIG. 5, 115  is a sealing resin for protecting the drive semiconductor element  111  and the bumps  112 , which is applied to the drive semiconductor element  111 , mounted together with the bumps  112 , to the first face  114   a  to such a level that nearly half a height of the bump  112  is exposed in the thickness direction  111   e.  The first circuit unit  100  is constituted in the above-described manner.  
         [0072]     As is shown in  FIG. 6 , the first circuit unit  100  is electrically connected, with the bumps  112  and leading ends  114   c  of the installation members  114   b,  through a solder  117  applied thereto to the second circuit board  116  arranged at a side of the face  111   b  of the drive semiconductor element  111 .  
         [0073]     As shown in  FIG. 1 , the second circuit board  116  includes a control circuit for the drive semiconductor element  111 , with passive electronic components  122 , such as a capacitor, a resistor and the like, and active electronic components  123 , such as a transistor, a memory, and the like, constituting the control circuit mounted to one face or to both faces of the second circuit board. Internal wirings  124  are provided in the second circuit board  116  to electrically connect the electronic components  122  and  123  to the drive semiconductor element  111 .  
         [0074]     A heat radiation member  120 , on which the metallic member  114  is placed, dissipates heat transferred from the drive semiconductor element  111  to the metallic member  114  into surrounding air. The heat radiation member  120  also has, for instance, a recessed part  120   b  as shown in  FIG. 1  formed by supporting members  120   a  which support the second circuit board  116 . The first circuit unit  100  is stored in the recessed part  120   b,  and both end parts of the second circuit board  116  are fixed by screws  121  to the pair of the supporting members  120   a.  An insulating resin  119  of a high heat dissipation efficiency is applied, by performing a heat press method, to a bottom face  120   c  of the recessed part  120   b  so as to conduct heat from the metallic member  114  to the heat radiation member  120 , and at the same time electrically insulate the metallic member  114  and the heat radiation member  120  from each other. Moreover, a silicone grease  118  is filled between the insulating resin  119  and the metallic member  114  to decrease heat resistance at a contact portion between the metallic member  114  and the insulating resin  119 . Since a height of the metallic member  114  is specified as will be discussed later, the silicone grease  118  works as a buffer to press the metallic member  114  towards the insulating resin  119 , thereby bringing the metallic member  114  and the insulating resin  119  into intimate contact with each other at all times. A soft sheet may be used in place of the silicon grease  118 .  
         [0075]     The second circuit device  101  is constituted as above.  
         [0076]     A process of forming the above first circuit unit  100  will be described with reference to  FIGS. 2-6 .  
         [0077]     Referring to  FIG. 3 , gold plating bumps  112  are formed on second aluminum electrodes  111   d  of the drive semiconductor element  111  of  FIG. 2  with use of a projecting electrode forming machine which is an improved wire bonding apparatus, or with use of plating. Then as shown in  FIG. 4 , in a state in which the drive semiconductor element  111  is placed at a predetermined position on the first face  114   a  of the metallic member  114 , the drive semiconductor element  111  and the metallic member  114  are put into a high temperature furnace heated to 350° C., in which a reducing atmospheric state in a mixed atmosphere of nitrogen and hydrogen is maintained. Molten high temperature solder  113  is supplied, specifically by being dropped according to the embodiment, onto the first face  114   a  of the metallic member  114  in the high temperature furnace. As a consequence, the first face  114   a  of the metallic member  114  and the first electrode  111   c  of the drive semiconductor element  111  are joined by the high temperature solder  113 .  
         [0078]     After the high temperature solder  113  is supplied, the drive semiconductor element  111  and the metallic member  114  are relatively pressed against each other to remove bubbles from inside the molten solder present between the first face  114   a  and the first electrode  111   c.  The metallic member  114  is pressed parallel to the drive semiconductor element  111  so as to bring the metallic member  114  into intimate contact with the drive semiconductor element  111 . With an absolute contact state maintained, the metallic member  114  and the drive semiconductor element  111  are cooled to solidify the solder  113 . The metallic member  114  and the drive semiconductor element  111  are returned to air after this solidification.  
         [0079]     Next in  FIG. 5 , the sealing resin  115  is formed to mechanically protect the drive semiconductor element  111  itself and joining portions between the drive semiconductor element  111  and the bumps  112 . The sealing resin  115  is applied in a liquid state and set by heating, or formed by a transfer molding or an injection molding technique. The first circuit unit  100  is formed during this process.  
         [0080]     Subsequently, for protecting the drive semiconductor element  111  and enabling the drive semiconductor element  111  to be handled as an electronic component, the first circuit unit  100  is joined simultaneously to the electronic components  122  and  123  on the second circuit board  116  with use of the solder  117  as shown in  FIG. 6 . A normally used surface mounting technique (SMT) is employed for this joining.  
         [0081]     In the present embodiment as discussed hereinabove, the metallic member  114  is provided with installation members  114   b  of metal which project from the first face  114   a  of the metallic member  114  in the thickness direction  111   e  of the drive semiconductor element  111 . Accordingly, an electric connection between the first electrodes  111   c  of the drive semiconductor element  111  and the second circuit board  116  can be achieved through the installation members  114   b,  and moreover, the metallic member  114  with the drive semiconductor element  111  can be fixed to the second circuit board  116  through the installation members  114   b.  Since a conventionally required dented connector  23  and projecting connector  22  are hence eliminated, the first circuit unit  100  and the second circuit device  101  can be made compact in size. At the same time, since the second electrodes  111   d  of the drive semiconductor element  111  are electrically connected to the second circuit board  116  via the bumps  112 , a stray capacity can be reduced in comparison with conventional art which uses metallic wires  18  and metallic leads  19 , and a resistance can be decreased.  
         [0082]     Since wiring resistance is reduced by this joining via the bumps  112  as compared with the conventional art, reduction of on-state resistance and noise is enabled.  
         [0083]     As above, bubbles are removed from inside the solder  113  by relatively pressing the first electrode  111   c  of the drive semiconductor element  111  and the metallic member  114  against each other to join the same. Thus, the drive semiconductor element  111  is prevented from abnormally overheating because of voids.  
         [0084]      FIG. 7  shows a state in which a plurality of first circuit units  100  are joined to the second circuit board  116  upon completion of procedures in  FIGS. 2-5 . Although two first circuit units  100  are installed in  FIG. 7 , needless to say, there may be installed three or more units, or in contrast one unit may be installed. In a case where the plurality of the first circuit units  100  are installed, an error range of heights H 1  and H 2  of the first circuit units  100 , as measured from the second circuit board  116 , should be maintained within a specified value. While the metallic member  114  has the installation members  114   b,  a height of the installation members  114   b  of each of the metallic members  114  can be adjusted by, e.g., cutting the installation members  114   b,  whereby a positional accuracy with an error range of within ±50 μm can be realized for the heights H 1  and H 2 .  
         [0085]     The second circuit device  101  shown in  FIG. 1  is a combination of the second circuit board  116 , in a state of  FIG. 7 , and the heat radiation member  120 . The second circuit device  101  naturally exerts the same effects as those of the first circuit unit  100 .  
       Second Embodiment  
       [0086]     A fourth circuit device  103  as a modified example of the second circuit device  101  will be described with reference to  FIG. 8 .  
         [0087]     The fourth circuit device  103  includes a third circuit unit  102  which is a modified example of the above first circuit unit  100 . Reference numeral  133  of  FIG. 8  indicates a first circuit board formed of a metal. Single-sided surface mounting is performed for the second circuit board  116  in  FIG. 8 .  
         [0088]     The third circuit unit  102  has spring wires  136  of a metal and a second metallic member  134  respectively attached in place of the bumps  112  and the metallic member  114  of the first circuit unit  100 . Each spring wire  136  is a conductor for electrically connecting the drive semiconductor element  111  and the second circuit board  116  to each other, and has a second bend portion  136   a  as indicated in  FIG. 8 . In the fourth circuit device  103  of  FIG. 8 , one end of each spring wire  136  penetrating the second circuit board  116  is soldered to the second circuit board  116 . The second metallic member  134  has no installation member  114   b.  The second bend portion  136   a  of each spring wire  136  is not resin sealed by sealing resin  115 .  
         [0089]     The third circuit unit  102  is constituted the same in other points as the above-described first circuit unit  100 .  
         [0090]     The third circuit unit  102  of the above constitution has the second metallic member  134  joined to the first circuit board  133  by solder  117 . The first circuit board  133  is placed on heat radiation member  120  via silicone grease  118 .  
         [0091]     In the fourth circuit device  103  constituted as above, the first circuit board  133  can be pressed by the second bend portions  136   a  of the spring wires  136  to the heat radiation member  120 , and moreover, a thermal stress can be absorbed by the spring wires  136 , so that a high reliability is realized.  
         [0092]     Since each of the spring wires  136  is arranged parallel to thickness direction  111   e  and is not directed orthogonally to the thickness direction  111   e  as illustrated, the fourth circuit device  103  is made compact. Furthermore, since bubbles present in solder  113  between drive semiconductor element  111  and the second metallic member  134  are eliminated, the drive semiconductor element  111  can be prevented from abnormally overheating because of voids.  
         [0093]     A fourth circuit device  103 - 1  shown in  FIG. 9  is a modification of the fourth circuit device  103  of  FIG. 8 , in which spring wires  136 - 1  are soldered to one face of second circuit board  116  without penetrating the second circuit board  116  as shown in  FIG. 9 . Double-sided mounting is provided for the second circuit board  116 . This modified fourth circuit device  103 - 1  is of the same constitution in other points as the above-described fourth circuit device  103  indicated in  FIG. 8 .  
         [0094]     The same effects as in the fourth circuit device  103  in  FIG. 8  can also be obtained in the fourth circuit device  103 - 1  of  FIG. 9 .  
       Third Embodiment  
       [0095]     A fifth circuit device  104  as a modified example of the second circuit device  101  will be depicted with reference to  FIG. 10 .  
         [0096]     The fifth circuit device  104  has a constitution such that the projecting connector  22  and the dented connector  23  are removed from the driving device described with reference to  FIG. 16 , and a fresh metallic lead  139  is connected to metallic wire  18 . Operation of removing bubbles described above is performed during soldering to join drive semiconductor element  111  and second metallic member  134  to one another. Single-sided surface mounting is provided for the second circuit board  116  in  FIG. 8 .  
         [0097]     The metallic lead  139  is a metal wire having tin plating on copper, which is joined to aluminum metallic wire  18  subjected to wedge bonding of aluminum. A first bend portion  139   a  is formed in a halfway portion of the metallic lead  139 . One end of the metallic lead  139  is soldered after passing through the second circuit board  116 . Double-sided mounting is performed for the second circuit board  116 .  
         [0098]     Since the projecting connector  22  and the dented connector  23  are eliminated and the metallic lead  139  is directly connected to the second circuit board  116 , the fifth circuit device  104  can be made compact. The first bend portion  139   a  formed in the metallic lead  139  can absorb thermal stress, thereby realizing a high reliability. Further, since bubbles are removed from inside solder  113  present between the drive semiconductor element  111  and the second metallic member  134 , the drive semiconductor element  111  can be prevented from abnormally overheating due to voids.  
         [0099]     A fifth circuit device  104 - 1  in  FIG. 11  is a modification of the fifth circuit device  104  of  FIG. 10 . A metallic lead  139 - 1  is, as shown in  FIG. 11 , soldered to one face of second circuit board  116  without penetrating the second circuit board  116 . The constitution of the fifth circuit device  104 - 1  in other points is the same as that of the above-described fifth circuit device  104  shown in  FIG. 10 .  
         [0100]     The fifth circuit device  104 - 1  can obtain the same effects as in the fifth circuit device  104  shown in  FIG. 10 .  
       Fourth Embodiment  
       [0101]     A sixth circuit device  105  as a modified example of the above fourth circuit device  103  will be described below with reference to  FIG. 12 .  
         [0102]     The sixth circuit device  105  is provided with metallic wires  141  in place of the spring wires  136  in the fourth circuit device  103 . Each metallic wire  141  has a gold ball  140  formed by melting a gold wire by using an electric spark. Each gold ball  140  is joined to drive semiconductor element  111  or the like. Joining of the gold balls  140  is executed by performing a wire bonding technique through heating and ultrasonically vibrating the gold wires. After this joining, each metallic wire  141  is pulled up in a thickness direction  111   e,  cut to a predetermined length and sealed by the sealing resin  115  to be prevented from deformation. One end of each metallic wire  141  passing through the second circuit board  116  is soldered. The constitution of other points of the sixth circuit device is the same as that of the fourth circuit device  103  described earlier and shown in  FIG. 8 .  
         [0103]     According to the sixth circuit device  105 , similar to the fourth circuit device  103 , since the metallic wires  141  extend in the thickness direction  111   e,  the sixth circuit device  105  can be made compact. Moreover, since bubbles are removed from inside solder  113  present between the drive semiconductor element  111  and second metallic member  134 , the drive semiconductor element  111  can be prevented from abnormal overheating because of voids.  
         [0104]     A sixth circuit device  105 - 1  in  FIG. 13  is a modification of the sixth circuit device  105  in  FIG. 12 , wherein metallic wires  141  - 1  are soldered to one face of second circuit board  116  without being passed through the second circuit board  116 , as is clear from  FIG. 13 . The sixth circuit device  105 - 1  is constituted the same in other points as is the sixth circuit device  105  described above.  
         [0105]     The sixth circuit device  105 - 1  of  FIG. 13  can obtain the same effects as the effects of the sixth circuit device of  FIG. 12 .  
       Fifth Embodiment  
       [0106]     Referring to  FIG. 14 , a seventh circuit device  106  as a modified example of the fourth circuit device  103  will be depicted herein.  
         [0107]     The seventh circuit device  106  uses metallic wires  142  of, e.g., aluminum or copper. The metallic wires  142  are joined to drive semiconductor element  111  or the like by performing a wedge bonding technique with ultrasonic vibration applied. Each metallic wire  142  after being so joined is pulled up in a thickness direction  111   e,  cut to a predetermined length and sealed by sealing resin  115  to be prevented from deformation. One end of each metallic wire  142 , penetrating through second circuit board  116 , is soldered. The seventh circuit device  106  is constructed the same in other points as the above-described fourth circuit device  103  shown in  FIG. 8 .  
         [0108]     According to the seventh circuit device  106 , similar to the fourth circuit device  103 , since the metallic wires  142  extend in the thickness direction  111   e,  the seventh circuit device  106  can be formed compact in size. Also, since aluminum or copper is used for the metallic wires  142 , the seventh circuit device  106  can be constructed inexpensively as compared with the case of using gold wires. Additionally, a process of removing bubbles prevents the drive semiconductor element  111  from being abnormally overheated.  
         [0109]     The seventh circuit device  106  in  FIG. 14  is modified by way of example to a seventh circuit device  106 - 1  shown in  FIG. 15 . As indicated in  FIG. 15 , metallic wires  142 - 1  are soldered to one face of second circuit board  116  without penetrating the second circuit board. The modified seventh circuit device  106 - 1  is of the same constitution in other points as the aforementioned seventh circuit device  106 .  
         [0110]     The seventh circuit device  106 - 1  of  FIG. 14  can obtain the same effects as the seventh circuit device  106  shown in  FIG. 13 .  
         [0111]     Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.