Patent Publication Number: US-2009237890-A1

Title: Semiconductor device and method for manufacturing the same

Description:
TECHNICAL FIELD  
     The present invention relates to a semiconductor device and a method for manufacturing the same, or more specifically, to a technique of cooling a power semiconductor device such as a power transistor, a thyristor, a power module or a power IC to be used in an inverter. 
     BACKGROUND ART  
     Power semiconductor devices including power ICs and power modules, which are collectively referred to as power devices, are used in, for example, home electric appliances, energy saving direct drives or intelligent actuators, and inverter controlled power appliances for driving vehicle motors and the like. 
       FIG. 1  is a cross-sectional view showing a structure of a conventional typical semiconductor device. Generally, a resin case  101  made of resin such as polyphenylene sulfide or polybutylene terephthalate is combined with a heat sink plate  102  made of metal such as copper, a copper alloy or a metal-matrix composite, to form a container on this semiconductor device. Inside the container, components including a semiconductor element are housed. The heat sink plate  102  is further attached to a cooler  103  with a heat conductive grease  112  in between. Adhesion to the heat conductive grease  112  is maintained by screwing the heat sink plate  102  and the cooler  103  together. 
     An insulation substrate  104  is soldered onto the heat sink plate  102 . Then, semiconductor elements  106  and bonding wires  107  serving as circuit components are disposed through conductive foils  105  on the insulation substrate  104 . An external connection terminal  108  is further provided. One end of the external connection terminal  108  is connected to the semiconductor element  106  through the bonding wire  107  while the other end is drawn out. Moreover, sealing resin  109  made of silicone gel, epoxy resin or other resin materials is filled inside the resin case  101 . The sealing resin  109  is further sealed with solid resin  110  such as epoxy resin, and a terminal holder  111  made of either the same material as or a different material from the resin case is fixed onto this solid resin  110 . In some cases, alternatively, the solid resin  110  is omitted, and the terminal holder  111  is disposed on the entire surface of the resin case  101  as a lid. With this structure, a semiconductor device having relatively excellent electric characteristics and reliability is achieved. 
     Incidentally, if a power semiconductor device has the semiconductor element  106  operating at a high temperature in excess of 100° C., and is used at a high voltage (kV class), a material used as the insulation substrate  104 , which is provided between the semiconductor element  106  and the heat sink plate  102 , needs to be able to release heat generated by the semiconductor element  106  promptly to the heat sink plate  102  and needs to have a high insulation property. For this reason, in the conventional semiconductor device shown in  FIG. 1 , a material made of a ceramic such as aluminum nitride having excellent heat conductivity and insulation property is used as the insulation substrate  104 . Then, it is configured so that the heat is efficiently released from the heat sink plate  102  to the cooler  103  by interposing the heat conductive grease  112  between the heat sink plate  102  and the cooler  103 . 
     In the conventional semiconductor device configured as described above, the heat conductive grease  112  is interposed between the heat sink plate  102  and the cooler  103 , and the heat sink plate  102  is pressurized and attached onto the cooler  103  by means of fitting screws provided around the semiconductor device. However, there has been a problem that a pressurizing force becomes uneven and contact thermal resistance thereby becomes uneven when forces to tighten the screws come to differ from one another and when any of or both of the heat sink plate  102  and the cooler  103  become deformed, for example. 
     Meanwhile, having a small thickness and a small heat capacity, the insulation substrate  104  cannot be expected to produce an effect of diffusing the heat generated by the semiconductor element  106 . In this context, there has been a problem as follows. The temperature of the semiconductor element  106  rises particularly when the semiconductor device is initiated. At this time, the thermal resistance becomes large during a transitional period, thereby raising a transitional temperature. Moreover, another problem is that, when the contact thermal resistance is temporarily increased between the heat sink plate  102  and the cooler  103  as described previously, the temperature rises significantly, which leads to degradation in cooling efficiency. 
     In addition, there is a large difference between a linear expansion coefficient of the insulation substrate  104  made of the ceramic and a linear expansion coefficient of the heat sink plate  102  made of the metal. For this reason, the heat sink plate  102  becomes deformed because of the difference in the thermal expansion associated with the heat generation at the time of operating the semiconductor device. Accordingly, a distance between the heat sink plate  102  and the cooler  103  is expanded to have a thickness more than a coating thickness of the heat conductive grease at the time of assembly. Then, the deformation returns to the initial distance when the operation is stopped or less heat is generated. These actions occur repeatedly. By this repetition of expansion and contraction, there is observed a phenomenon that the heat conductive grease  112  is gradually squeezed out from a contact surface. As a consequence, the amount of the heat conductive grease  112  between the heat sink plate  102  and the cooler  103  becomes insufficient. This causes a problem that the contact thermal resistance is significantly increased, thereby leading to thermal runaway of the semiconductor element  106 . 
     To avoid these various problems, JP-A 2005-348529 discloses an inverter device which is capable of improving a current-carrying capacity and downsizing of an inverter device by improving cooling efficiency of a power semiconductor device, and which also has excellent productivity.  FIG. 2  is a cross-sectional view showing a structure of a portion where semiconductor element is mounted on the semiconductor device disclosed in JP-A 2005-348529. In this semiconductor device, multiple semiconductor elements  106  are soldered to multiple conductors  13  to  15 , and the conductors  13  to  15  are bonded to a heat sink plate  11  through an insulator  12 . 
     In this semiconductor device disclosed in JP-A 2008-348529, the conductors  13  to  15  are bonded directly to the heat sink plate  11  through the sheet-like insulator  12 . Accordingly, unlike the above-described conventional semiconductor device, an increase in the contact thermal resistance does not occur, while the thermal resistance is reduced by half. Moreover, since the semiconductor element is cooled down from both surfaces, it is possible to achieve a cooling effect twice as large as that achieved in the above-described conventional semiconductor device. Further, since a thermal time constant becomes greater due to a heat capacity effect owing to thicknesses of the conductors  13  to  15 , the transitional thermal resistance is reduced, and an effect to suppress the temperature rise at the time of initiation is also obtained. Thus, a total cooling performance is significantly improved. 
     DISCLOSURE OF THE INVENTION  
     However, the semiconductor device disclosed in JP-A 2005-348529 has the following problem. Specifically, the temperatures of the conductors  13  to  15  rise due to the heat generation by the semiconductor element  106  at the time of initiating the semiconductor device. However, there is a problem that the expansions and deformations of the conductors  13  to  15  due to this temperature rise act, as repetitive heat stresses, on the solder for bonding the semiconductor element  106  to the conductors  13  to  15  and on the insulator  12  provided between the conductors  13  to  15  and the heat sink plate  11 , leading to reduction in the life of junctions between the conductors  13  to  15  and the semiconductor element  106 , and between the conductors  13  to  15  and the insulator  12 . 
     An object of the present invention is to provide a semiconductor device having excellent reliability and a method for manufacturing method the semiconductor device by improving a cooling performance to enhance durability. 
     A first invention is a semiconductor device including: a semiconductor element having a surface on a positive electrode side and a surface on a negative electrode side; a plurality of conductors bonded respectively to the surface on the positive electrode side and to the surface on the negative electrode side of the semiconductor element; a heat sink plate disposed as intersecting a junction interface between the semiconductor element and each of the plurality of conductors and configured to discharge heat of the semiconductor element; and an insulator bonding the heat sink plate to the plurality of conductors. In the semiconductor element, the insulator includes a heat conductive insulator disposed inside a portion facing all of the plurality of conductors and a flexible insulator disposed at a portion other than the heat conductive insulator. 
     A second invention is according to the first invention, in which the heat conductive insulator is made of resin containing a heat conductive inorganic filler, and the flexible insulator is made of rubber-like elastic resin. 
     A third invention is according to the first invention, which includes an adhesive resin layer between the insulator and the plurality of conductors. 
     A fourth invention is according to the first invention, which includes insulating resin located around the plurality of conductors and configured to cover and fix the insulator. 
     A fifth invention is a semiconductor device including: a semiconductor element having a surface on a positive electrode side and a surface on a negative electrode side; a plurality of conductors bonded respectively to the surface on the positive electrode side and to the surface on the negative electrode side of the semiconductor element; a first heat sink plate disposed as intersecting a junction interface between the semiconductor element and each of the plurality of conductors and configured to discharge heat of the semiconductor element; a first insulator bonding the first heat sink plate to the plurality of conductors; a second heat sink plate located opposite to the first heat sink plate with the plurality of conductors sandwiched therebetween, and configured to discharge heat of the semiconductor element; and a second insulator bonding the second heat sink plate to the plurality of conductors. 
     A sixth invention is according to the fifth invention, which further includes a metal body connecting the first heat sink plate and the second heat sink plate so as to surround the plurality of conductors bonded to the semiconductor element. 
     A seventh invention of a method for manufacturing a semiconductor device according to the present invention includes a conductor bonding step of bonding a plurality of conductors respectively to a surface on a positive electrode side and a surface on a negative electrode side of a semiconductor element including the surface on the positive electrode side and the surface on the negative electrode side; and an insulation bonding step of bonding a heat sink plate to the plurality of conductors by use of an insulator, the heat sink plate disposed as intersecting a junction interface between the semiconductor element and the plurality of conductors and configured to discharge heat of the semiconductor element, and the insulator including an adhesive sheet which constitutes a heat conductive insulator, and a flexible insulator. In the method, in the insulation bonding step, after the plurality of conductors are attached, by use of the adhesive sheet, to the heat sink plate inside a portion in which all of the plurality of conductors face the heat sink plate, the flexible insulator is formed by injecting liquid resin to an outer peripheral portion of the adhesive sheet and by solidifying or hardening the liquid resin. 
     According to the present invention, it is possible to provide a semiconductor device having excellent reliability and a method for manufacturing the semiconductor device by improving a cooling performance and enhancing durability. 
     To be more precise, according to the first invention, since the heat conductive insulator is formed inside the portion facing all of the multiple conductors, the cooling performance can be improved. Since the flexible insulator is formed at the portion other than the heat conductive insulator where a stress applied to the insulator is particularly high, the durability can be improved by easing the stress. As a result, the reliability as a whole can be enhanced. 
     According to the second invention, since the resin containing the heat conductive inorganic filler is formed inside the portions respectively facing the multiple conductors, it is possible to improve the cooling performance. Since the rubber-like elastic resin is formed at the portion other than the heat conductive insulator where the stresses of the multiple conductors respectively acting on the insulator are particularly high, the stress is eased to thereby improve the durability. As a result, the reliability as a whole can be improved even more than that in the invention disclosed in claim 1. 
     According to the third invention, since the adhesive resin layer is provided between the insulator and the multiple conductors, it is possible to ease a difference in the state of stress on a junction interface between the insulator and the multiple conductors and thereby to establish uniformity as a whole. For this reason, it is possible to improve the durability against a temperature cycle attributable to heat generation of the semiconductor element, an external environment, and the like as well as the reliability. 
     According to the fourth invention, since the insulating resin for covering and fixing the insulator is provided around the multiple insulators, the insulating resin can ease a heat stress generated by the heat generation of the semiconductor element, and it is possible to improve the durability against the temperature cycle attributable to heat generation of the semiconductor element, the external environment, and the like as well as the reliability. Moreover, by insulating and sealing the insulator and the multiple conductors by using the insulating resin, penetration of moisture or impurities from outside can be prevented. Accordingly, it is possible to improve moisture resistance and the reliability of the semiconductor device. 
     According to the fifth invention, since the first heat sink plate and the second heat sink plate are disposed to face each other while sandwiching the multiple conductors, it is possible to establish stress balance by a symmetric structure in which the multiple conductors are located in the center. For this reason, it is possible to suppress thermal deformations of the heat sink plates in a manufacturing process or at the time of operating the semiconductor device, for example, and thereby to improve the durability against the temperature cycle attributable to heat generation of the semiconductor element, the external environment, and the like as well as the reliability. 
     According to the sixth invention, the metal body metal body connects the first heat sink plate and the second heat sink plate so as to surround the multiple conductors bonded to the semiconductor element, and this metal body functions as a radiator. Hence, the radiation effect can be enhanced even further. As a result, it is possible to suppress the thermal deformations of the heat sink plates and to improve the durability against the temperature cycle attributable to heat generation of the semiconductor element, the external environment, and the like as well as the reliability. 
     According to the seventh invention, after the multiple conductors are attached, by use of the adhesive sheet, to the heat sink plate inside a portion in which all of the plurality of conductors face the heat sink plate, the flexible insulator is formed by injecting liquid resin to an outer peripheral portion of the adhesive sheet and by solidifying or hardening the liquid resin. For this reason, it is possible to improve the reliability of the semiconductor device. Moreover, the manufacturing process is simplified and manufacturing time can be reduced. Accordingly, it is possible to improve mass productivity of the semiconductor device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [ FIG. 1 ]  FIG. 1  is a cross-sectional view showing a structure of a conventional typical semiconductor device. 
       [ FIG. 2 ]  FIG. 2  is a cross-sectional view showing a structure of a conventional semiconductor device disclosed in JP-A 2005-348529. 
       [ FIG. 3 ]  FIG. 3  is a cross-sectional view partially showing a structure of a semiconductor device according to Embodiment 1 of the present invention. 
       [ FIG. 4 ]  FIG. 4  is an external perspective view partially showing the structure of the semiconductor device according to Embodiment 1 of the present invention. 
       [ FIG. 5 ]  FIG. 5  is a graph showing comparison of thermal resistance characteristics among the semiconductor device according to Embodiment 1 of the present invention and other semiconductor devices. 
       [ FIG. 6 ]  FIG. 6  is a cross-sectional view partially showing a structure of a semiconductor device according to Embodiment 2 of the present invention. 
       [ FIG. 7 ]  FIG. 7  is a graph showing an elastic modulus characteristic of an insulator used in the semiconductor device according to Embodiment 2 of the present invention. 
       [ FIG. 8 ]  FIGS. 8(   a ) to  8 ( d ) are views for explaining a method, according to Embodiment 3 of the present invention, for manufacturing a semiconductor device. 
       [ FIG. 9 ]  FIG. 9  is a cross-sectional view partially showing a structure of a semiconductor device according to Embodiment 4 of the present invention. 
       [ FIG. 10 ]  FIG. 10  is a cross-sectional view partially showing a structure of a semiconductor device according to Embodiment 5 of the present invention. 
       [ FIG. 11 ]  FIG. 11  is a cross-sectional view partially showing a structure of a semiconductor device according to Embodiment 6 of the present invention. 
     
    
    
     BEST MODES FOR CARRYING OUT THE INVENTION  
     Now, embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the following, components having the same function are described while being designated by the same reference numerals. Moreover, it is to be noted that the drawings are schematic and therefore relations between thicknesses and flat dimensions, proportions, and the like are different from the actuality. Therefore, the concrete thicknesses and dimensions should be determined in consideration of the following description. Further, the drawings may include aspects having different dimensional relations and proportions. 
     EMBODIMENT 1 
       FIG. 3  is a cross-sectional view partially showing a structure of a semiconductor device according to Embodiment 1 of the present invention, and  FIG. 4  is an external perspective view partially showing the structure of the semiconductor device. This semiconductor device includes semiconductor elements  106  each having a positive electrode side surface and a negative electrode side surface, a conductor  13  bonded to the positive electrode side of the semiconductor element  106 , a conductor  14  bonded to the negative electrode side, and a conductor  15  provided in the middle of the conductor  13  and the conductor  14 . Counting these semiconductor elements  106  and the conductors  13  to  15  as one phase, the semiconductor device is configured with three phases. Here, the conductor  15  in the middle may be omitted. The semiconductor elements  106  are disposed respectively between the conductors  13  and  15  while being bonded thereto. 
     A space between a heat sink plate  11  and the conductors  13  to  15  is connected by use of an insulator  12 . The insulator  12  includes a heat conductive insulator  16  disposed inside a portion facing all of the conductors  13  to  15  and a flexible insulator  17  disposed at an outer peripheral portion of the conductors  13  to  15 . 
     Metal such as copper is suitable for the material of the conductors  13  to  15 , and a plating process using nickel or the like may be provided on a surface of this metal. Here, each of the conductors  13  to  15  may also be configure of three or more conductors by being divided. 
     Various power devices such as an IGBT, a power MOSFET, a power BJT, a thyristor, a GTO thyristor, a SI thyristor and a diode can be used as the semiconductor element  106 . The semiconductor element  106  may be bonded to the conductors  13  to  15  either directly or by further interposing a terminal plate, a buffer plate, or the like between the semiconductor element  106  and the conductors  13  to  15 . 
     The bonding between the semiconductor element  106  and the conductors  13  to  15  may be established by use of a variety of solders, conductive paste, and the like. 
     In addition to the semiconductor element  106 , various electronic components such as resistors, capacitors or coils, and circuits such as a power source may be mounted on this semiconductor device. Alternatively, the semiconductor device may be formed as a simple module that mounts only the power semiconductor element. 
     Meanwhile, this semiconductor device may include a control circuit such as an nMOS control circuit, a pMOS control circuit, a CMOS control circuit, a bipolar control circuit, a BiCMOS control circuit or a SIT control circuit. These control circuits may be configured to contain an overvoltage protection circuit, an overcurrent protection circuit, an overheat protection circuit, and the like. 
     Metal such as copper or a copper alloy, or a metallic material having excellent heat conductivity such as a metal-matrix composite is used as the heat sink plate  11 . 
     Resin can be used as the insulator  12 . For example, epoxy resin, phenol resin, urethane resin, silicone resin, and the like are suitable for the resin to be used as the insulator  12 . 
     The heat conductive insulator  16  constituting the insulator  12  is formed by adding at least one of a hardening accelerator, a stress reducer, a filler, a solvent, a coupling agent to improve blending between the filler and the resin, a mold releasing agent to facilitate peeling a sheet, and a pigment, to resin such as epoxy resin, phenol resin, urethane resin or silicone resin. In this way, the heat conductivity of the heat conductive insulator  16  is made adjustable. 
     Meanwhile, the flexible insulator  17  constituting the insulator  12  is formed by adding at least one of a flame retardant, a solvent, a mold releasing agent, and a pigment, to flexible resin such as urethane resin or silicone resin. In this way, the elastic modulus, the hardening temperature, and the like of the flexible insulator  17  is made adjustable. 
     As the filler, it is possible to use any one of or a combination of inorganic fillers including silica, calcium carbonate, alumina, boron nitride, aluminum nitride, and the like, for example. 
     According to the semiconductor device of Embodiment 1, the heat generated by the semiconductor element  106  is transmitted from both surfaces of the semiconductor element  106  to the heat sink plate  11  through the conductors  13  to  15  that are bonded on both sides of the semiconductor element  106 , as similar to the semiconductor device disclosed in JP-A 2005-348529. For this reason, it is possible to obtain thermal efficiency twice as large as that of the conventional typical semiconductor device shown in  FIG. 1 . Moreover, since a wire bonding process is not necessary, it is possible to reduce manufacturing time and to improve production yields. Further, it is possible to eliminate internal inductance attributable to wiring which is generated at wire bonding portions. 
     Moreover, according to the semiconductor device of Embodiment 1, out of the insulator  12  for bonding the conductors  13  to  15  to the heat sink plate  11 , the outer peripheral portion of the conductors  13  to  15  where the stress becomes largest, i.e. the outside of the heat conductive insulator  16  is formed of the flexible insulator  17 . For this reason, the stress acting on the insulator  12  is eased, and a radiation property is maintained at the remaining portion by the heat conductive insulator  16 . As a result, the cooling performance equivalent to that achieved by the conventional semiconductor device disclosed in JP-A 2005-348529 is achieved while improving the durability against the stress at the time of operating the semiconductor device. 
       FIG. 5  is a graph showing comparison in terms of an energization cycle lives of the thermal resistance characteristics of the semiconductor devices among the conventional semiconductor device, the semiconductor device disclosed in JP-A 2005-348529, and the semiconductor device according to Embodiment 1. As apparent from  FIG. 5 , the semiconductor device according to Embodiment 1 of the present invention has drastically reduced thermal resistance and excellent reliability, as compared to the conventional typical semiconductor device and the semiconductor device disclosed in JP-A 2005-348529. 
     As described above, according to the semiconductor device of Embodiment 1 of the present invention, the cooling performance is improved, and the durability is improved. As a result, it is possible to enhance the reliability and thereby to achieve a higher performance and size reduction. 
     EMBODIMENT 2 
       FIG. 6  is a cross-sectional view partially showing a structure of a semiconductor device according to Embodiment 2 of the present invention. The semiconductor device according to Embodiment 2 is different from that according to Embodiment 1 in the structure of the insulator  12 . Specifically, in the insulator  12 , multiple heat conductive insulators  16  are formed inside the portions respectively facing the conductors  13  to  15 , and the flexible insulator  17  is formed at outer peripheral portions of the respective conductors  13  to  15 , that is, at the portions excluding the heat conductive insulators  16 . 
     Resin containing a heat conductive inorganic filler is used as the heat conductive insulators  16  constituting the insulator  12 . For example, silica, calcium carbonate, alumina, boron nitride, aluminum nitride, and the like, are suitable for the heat conductive inorganic filler. The heat conductive inorganic filler may also be formed by combining these substances. Here, if importance is put on the heat conductivity, alumina, boron nitride, aluminum nitride, and the like are suitable. 
     Rubber-like elastic resin is used as the flexible insulator  17  constituting the insulator  12 . For example, synthetic rubber, silicone resin, urethane resin, and the like are suitable for the elastic resin. Other configurations are similar to those in Embodiment 1, and description will therefore be omitted. 
       FIG. 7  is a graph showing comparison of elastic modulus characteristics between high heat conductive resin and the rubber-like elastic resin which are used as the insulator  12  in the semiconductor device according to Embodiment 2. As apparent from  FIG. 7 , the rubber-like elastic resin has a low elastic modulus as compared to the resin containing the heat conductive inorganic filler. Accordingly, the rubber-like elastic resin can reduce the stress generated by a deformative strain more. 
     As described above, according to the semiconductor device of Embodiment 2 of the present invention, it is possible to enhance the effect to ease the stress with the flexible insulator  17  as compared to the semiconductor device according to Embodiment 1. 
     EMBODIMENT 3 
     Embodiment 3 of the present invention is a method for manufacturing a semiconductor device. Here, an example of manufacturing the semiconductor device according to Embodiment 1 will be explained. 
     First, the heat sink plate  11  is prepared as shown in  FIG. 8(   a ). Subsequently, as shown in  FIG. 8(   b ), a heat conductive adhesive sheet serving as the heat conductive insulator  16  is placed on the heat sink plate  11 . As for the heat conductive adhesive sheet, it is possible to use a prepreg sheet prepared by combining and semi-curing the resin such as epoxy resin and silicone resin with the heat conductive inorganic filler, for example. Here, the heat conductive adhesive sheet may also be formed by applying a combination of the resin such as epoxy resin and silicone resin with the heat conductive inorganic filler on the heat sink plate, for example. 
     Subsequently, as shown in  FIG. 8(   c ), the component formed by bonding the conductors  13  to  15  to the semiconductor elements  106  is placed on the heat conductive adhesive sheet, and any one of or both of heating and pressurizing processes are performed. In this way, the heat sink plate  11  is attached to the multiple conductors  13  to  15  through the heat conductive insulator  16 . 
     Subsequently, as shown in  FIG. 8(   d ), liquid resin is injected to the outer peripheral portions of the multiple conductors  13  to  15  and is subjected to solidification or hardening to form the flexible insulator  17 . Injection of the liquid resin can be performed by potting or other methods such as transfer molding or injection molding. Other configurations are similar to those in the semiconductor device according to Embodiment 1 or Embodiment 2, and description will therefore be omitted. 
     As described above, according to the method for manufacturing a semiconductor device of Embodiment 3, the heat sink plate  11  is attached to the multiple conductors  13  to  15  through the heat conductive insulator  16  by use of the adhesive sheet. Hence, the manufacturing process is simplified, and manufacturing time can be reduced. Accordingly, it is possible to improve mass productivity of the semiconductor device. 
     EMBODIMENT 4 
       FIG. 9  is a cross-sectional view partially showing a structure of a semiconductor device according to Embodiment 4 of the present invention. This semiconductor device is formed by adding an adhesive resin layer  18  to a space between the insulator  12  and the conductors  13  to  15  of the semiconductor device according to Embodiment 1. As for the adhesive resin layer  18 , it is possible to use the resin having the same composition as the insulator  12 , for example. Alternatively, resin such an ethylene-methacrylate copolymer and phenoxy resin may also be used. The thickness of the adhesive resin layer  18  may be set in a range from 10 μm to 50 μm, for example. Other configurations are similar to those in the semiconductor device according to Embodiment 1, and description will therefore be omitted. 
     According to the semiconductor device of Embodiment 4, the provision of the adhesive resin layer  18  makes it possible to ease a difference in the state of stress on a junction interface between the multiple conductors  13  to  15  and the heat conductive insulator  16  and the flexible insulator  17 , and thereby to establish uniformity as a whole. As a result, it is possible to improve the durability against a temperature cycle attributable to heat generation of the semiconductor element  106 , an external environment, and the like, as well as the reliability. 
     EMBODIMENT 5 
       FIG. 10  is a cross-sectional view partially showing a structure of a semiconductor device according to Embodiment 5 of the present invention. This semiconductor device is formed by adding insulating resin  19  for covering and fixing the insulator  12  around the conductors  13  to  15  of the semiconductor device according to Embodiment 1. 
     The insulating resin  19  may be filled in a thickness sufficient to cover the surface of the insulator  12 , or may be filled to cover the semiconductor element  106  and the conductors  13  to  15 . A material suitable for the insulating resin  19  is resin (hard resin generally used as a sealing member) prepared by combining insulating resin such as epoxy resin as a base material, with a filler such as fused silica powder, quartz powder, glass powder or glass short fiber. The insulating resin  19  is filled by use of a dispenser or the like. Other configurations are similar to those in the semiconductor device according to Embodiment 1, and description will therefore be omitted. 
     According to the semiconductor device of Embodiment 5, it is possible to ease a heat stress generated by the heat generation of the semiconductor element  106  at the time of operation and to improve the durability against the temperature cycle attributable to the heat generation of the semiconductor element, the external environment, and the like as well as the reliability. Moreover, by insulating and sealing the insulator  12  and the conductors  13  to  15  by using the insulating resin  19 , penetration of moisture or impurities from outside can be prevented. Accordingly, it is possible to improve moisture resistance and the reliability of the semiconductor device. 
     EMBODIMENT 6 
       FIG. 11  is a cross-sectional view partially showing a structure of a semiconductor device according to Embodiment 6 of the present invention. In this semiconductor device, a first heat sink plate  11  is bonded to the first insulator  12  by use of the conductor  13  to  15 , and a second heat sink plate  21  and a second insulator  22  are disposed on an opposite surface while interposing the conductors  13  to  15 . Further, the semiconductor device according to Embodiment 6 may also be configured so as to bond between the first heat sink plate  11  and the second heat sink plate  21  by use of a metal body  20 . In this case, the metal body  20  serves as a radiator. 
     According to the semiconductor device of Embodiment 6, it is possible to further enhance cooling efficiency by radiating the heat generated by the semiconductor element  106  from both surfaces of the conductors  13  to  15 . Moreover, it is possible to establish stress balance by a symmetric structure in which the conductors  13  to  15  are located in the center, and to suppress thermal deformations of the heat sink plates in the manufacturing process, at the time of operating the semiconductor device, and so forth. Moreover, it is possible to improve the durability against the temperature cycle attributable to heat generation of the semiconductor element at the time of operation, the external environment, and the like as well as the reliability. 
     INDUSTRIAL APPLICABILITY  
     The present invention is applicable to a small and lightweight semiconductor which is expected to achieve high conversion efficiency.