Abstract:
An insulating substrate board for a semiconductor of the present invention comprises a ceramic substrate board ( 2 ) and a metal alloy layer ( 3 ) consisting of aluminum formed on one surface portion of the ceramic substrate board ( 2 ), wherein the Vickers hardness of the metal alloy layer ( 3 ) is not less than 25 and not more than 40. The metal alloy layer ( 3 ) includes silicone of not less than 0.2% by weight and not more than 5% by weight. The ceramic substrate board ( 2 ) is made of a material selected from a group consisting of alumina, aluminum nitride, and silicone nitride. A power module of the present invention comprises a metal base plate ( 7 ), a ceramic substrate board ( 2 ), one surface of which is bonded to the metal base plate ( 7 ), and the other surface of which is bonded on a semiconductor tip ( 1 ), at least one surface portion of the ceramic substrate board ( 2 ) having a metal alloy layer ( 3 ) consisting of aluminum, wherein the Vickers hardness of the metal alloy layer ( 3 ) is not less than 25 and not more than 40.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an insulating substrate board for a semiconductor and a power module and, more particularly, relates to a metal-ceramic circuit substrate board having a high heat-cycle resistance, which is suitable for the installation of high power electronic parts, such as power modules, and a power module having the insulating substrate board.  
           [0003]    2. Description of the Prior Art  
           [0004]    Recently, high power modules have been used to control a heavy electric current of electric automobiles, electric cars, tooling machines or the like. The power modules have mainly a plurality of semiconductor tips. A high electric insulation performance is required for a substrate board to which the semiconductor tips are fixed, in order to obtain a large current from a front surface and a back surface of each semiconductor tip. Further, a temperature of the semiconductor tip is elevated by heat generated when a heavy current is passed through the semiconductor tip. Accordingly, a good heat transferability has been required for the substrate board on which the semiconductor tips are fixed, and parts surrounding the board. Furthermore, a high reliability and a durability have been required for the substrate board which is installed on the automobiles, electric cars or the like.  
           [0005]    So-called thermal cycle test is normally carried out in order to know the reliability and durability of the substrate board. In such thermal cycle test, a thermal shock is applied on the substrate board by changing the temperature of the substrate board between the possible highest temperature and the possible lowest temperature within a short time, and any damage of the substrate board is investigated. In general, the substrate board for use in the automobiles or the electric cars is required to withstand the thermal cycle test of 1000 times.  
           [0006]    [0006]FIG. 1 shows a conventional power module in section. The power module has semiconductor tips  1 , brazing material layers  4 , a metal layer  3 , a ceramic substrate board  2  as an insulating substrate board, a metal layer  5 , a brazing material layer  6 , and a metal base plate  7  piled in this order. Reference numeral  8  denotes plating layers formed on the metal layers  3  and  5 , and the metal base plate  7 . Wirings between the semiconductor tips  1  are omitted in FIG. 1.  
           [0007]    It is considered that an insulating substrate board consisting of a ceramic substrate board bonded to an aluminum plate may be suitable for a power module having a high reliability for use in the automobiles or the electric cars. In general, if the insulating substrate board consisting of a metal and ceramics is subjected to the thermal cycle test as mentioned above, a stress is generated on the boundary surface between the metal and the ceramics, because the metal is different in thermal expansion coefficient from the ceramics, so that the ceramic substrate board is broken finally. However, if the metal is aluminum, the evaluation of the thermal cycle may be enhanced remarkably compared with copper, because the aluminum is deformable so as to reduce the stress applied to the ceramics.  
           [0008]    Heretofore, various methods have been proposed to bond an aluminum plate and a ceramic substrate board using a brazing material as shown in Japanese Unexamined Utility Model Publication No. 57945/1991 and Japanese Unexamined Utility Model Publication No. 68448/1990. Among these methods, an aluminum plate is bonded to an aluminum nitride board or an alumina board by using a brazing material of Al—Si series or Al—Ge series. U.S. Pat. No. 3,994,430, published on 1976, shows the use of silicone as an aluminum binding assistant. Further, Japanese Unexamined Patent Publications No. 193358/1995 and No. 276035/1955 disclose such a method that aluminum in molten state is contacted with a substrate board of aluminum nitride or an alumina substrate board, and the aluminum is solidified, so that the aluminum is bonded directly to the substrate board.  
           [0009]    The insulating substrate board consisting of aluminum and ceramics is used for a power module by bonding semiconductor tips to the aluminum by using brazing materials. In such a case, the aluminum is held between the ceramics and the brazing materials with the semiconductor tips, and accordingly, the aluminum must have a role for protecting the ceramics and have a function to arrange the brazing materials and the semiconductor tips. Thus, an insulating substrate board which is not so affected by the thermal shock is required. Specifically, the heat transferability of the power module is reduced remarkably by the cracks formed due to the thermal shock in the aluminum or the brazing material of the lead solder or in the boundary surface between the brazing material and the aluminum, so that the semiconductor is elevated in temperature and broken finally.  
         SUMMARY OF THE INVENTION  
         [0010]    Therefore, an object of the present invention is to solve the above problems.  
           [0011]    The present inventors have made various studies and found that the above task could be solved by setting a hardness of aluminum of an aluminum-ceramics insulating substrate board within a predetermined range.  
           [0012]    Specifically, the inventors found a range of the hardness of aluminum of the insulating substrate board, within which the ceramics was protected from the thermal shock and no crack was formed in the brazing material. The above range was not less than 25 and not more than 40 in Vickers hardness. If the Vickers hardness is not more than 25, the ceramics is protected from the thermal shock, however, the aluminum is deformed largely and cracks are formed easily in the brazing material when the thermal shock is applied repeatedly. If the Vickers hardness is not less than 40, the cracks are formed easily in the ceramics when the thermal shock is applied repeatedly, because the aluminum is hardly deformed and the thermal stress is hardly absorbed.  
           [0013]    It is sufficient to add an another metal element such as silicone to the aluminum in order to realize the above hardness of the predetermined range. Silicone is suitable, because it is diffused easily in the aluminum and it makes a eutectic at a low temperature. In order to realize the Vickers hardness of not less than 25 and not more than 40, silicone of not less than 0.2 weight % and not more than 5 weight % is required. It is possible to add further Mn, Mg or the like.  
           [0014]    An insulating substrate board for a semiconductor according to the present invention is characterized by comprising a ceramic substrate board and a metal alloy layer consisting mainly of aluminum formed on at least one surface portion of the ceramic substrate board, wherein the Vickers hardness of the metal alloy layer is not less than 25 and not more than 40.  
           [0015]    A power module according to the present invention is characterized by comprising a metal base plate, a ceramic substrate board, one surface of which is bonded to the metal base plate, and the other surface of which is bonded to a semiconductor tip, at least one surface portion of the ceramic substrate board having a metal alloy layer consisting mainly of aluminum, wherein the Vickers hardness of the metal alloy layer is not less than 25 and not more than 40.  
           [0016]    The metal alloy layer includes silicone of not less than 0.2% by weight and not more than 5% by weight. The metal alloy layer includes Mn of not more than 1.5% by weight.  
           [0017]    The metal alloy layer includes Mg of not more than 1% by weight.  
           [0018]    The ceramic substrate board is made of a material selected from a group consisting of alumina, aluminum nitride, and silicone nitride.  
           [0019]    The metal alloy layer includes Cu, Zn or Ni of not less than 0.2% by weight and not more than 3% by weight.  
           [0020]    These and other aspects and objects of the present invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the present invention, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is a vertically sectioned front view of a conventional power module; and  
         [0022]    [0022]FIG. 2 is a vertically sectioned front view of a manufacturing device for making a substrate board in accordance with the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     EXAMPLE 1  
       [0023]    In a first example of the present invention, as shown in FIG. 2, a raw material  11  including aluminum of 99.8% by weight and silicone of 0.2% by weight were set in a concave portion  10  formed at an upper portion of a crucible  9  of graphite. The concave portion  10  was closed by a piston  12  of graphite. A ceramic substrate board  14  of aluminum nitride of 0.635 mm in thickness was set in a cavity  13  formed at a lower portion of the crucible  9 . Then, the crucible  9  was inserted into a furnace heated at 800° C. As a result, the raw material  11  was molten and pushed out by the weight of the piston  12  into the cavity  13  including therein the ceramic substrate board  14 . The crucible  9  was taken out of the furnace and cooled at a room temperature. In this example 1, the heating and cooling of the crucible  9  were performed in an atmosphere of nitrogen gas in order to prevent the crucible  9  from being oxidized. Thus obtained ceramic substrate having at each of side surfaces thereof an aluminum alloy layer of 0.5 mm in thickness was subjected to the mechanical and electrolytic polishing.  
         [0024]    The Vickers hardness of the aluminum alloy layer of the ceramic substrate board was  25 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al-SiC composite material by using a brazing material of eutectic composition.  
         [0025]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 2  
       [0026]    A metal-ceramic substrate board was formed under the same condition as in the example 1 except that the composition of the raw material  11  was formed of aluminum of 99.5% by weight and silicone of 0.5% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  30 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al-SiC composite material by using a brazing material of eutectic composition.  
         [0027]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 3  
       [0028]    A metal-ceramic substrate board was formed under the same condition as in the example 1 except that the composition of the raw material  11  was formed of aluminum of 98% by weight and silicone of 2% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  35 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al-SiC composite material by using a brazing material of eutectic composition.  
         [0029]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 4  
       [0030]    A metal-ceramic substrate board was formed under the same condition as in the example 2 except that alumina was used as the ceramics. The Vickers hardness of the aluminum alloy layer of the substrate board was  30 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al-SiC composite material by using a brazing material of eutectic composition.  
         [0031]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 5  
       [0032]    A metal-ceramic substrate board was formed under the same condition as in the example 2 except that silicone nitride was used as the ceramics. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  30 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0033]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 6  
       [0034]    A plate of 0.4 mm in thickness consisting of aluminum of 99.5% by weight and silicone of 0.5% by weight was laminated on each of both side surfaces of aluminum nitride substrate board of 0.635 mm in thickness through a brazing material layer of 50 μm in thickness consisting of aluminum of 87.5% by weight and silicone of 12.5% by weight. Then, the plate was inserted into a furnace heated at 640° C. As a result, a metal-ceramic substrate board was formed of an aluminum alloy plate and aluminum nitride. The Vickers hardness of the aluminum alloy layer of the substrate board was  31 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0035]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 7  
       [0036]    A metal-ceramic substrate board was formed under the same condition as in the example 1 except that the composition of the raw material  11  was formed of aluminum of 97.9% by weight, silicone of 0.6% by weight, and Mn of 1.5% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  32 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition. Here, Mn was used to increase the hardness.  
         [0037]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 8  
       [0038]    A metal-ceramic substrate board was formed under the same condition as in the example 6 except that the laminated plate was formed of aluminum of 98.6% by weight, silicone of 0.4% by weight, and Mg of 1% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  30 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition. Here, Mg was used to increase the hardness.  
         [0039]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 9  
       [0040]    A metal-ceramic substrate board was formed under the same condition as in the example 1 except that the composition of the raw material  11  was formed of aluminum of 98% by weight and Mn of 2% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  30 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0041]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 10  
       [0042]    A metal-ceramic substrate board was formed under the same condition as in the example 1 except that the composition of the raw material 11 was formed of aluminum of 99.8 by weight and Mn of 0.2% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  25 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0043]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 11  
       [0044]    A metal-ceramic substrate board was formed under the same condition as in the example 1 except that the composition of the raw material  11  was formed of aluminum of 99.5% by weight, and Mn of 0.5% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  27 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0045]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 12  
       [0046]    A metal-ceramic substrate board was formed under the same condition as in the example 11 except that alumina was used as the ceramics. The Vickers hardness of the aluminum alloy layer of the substrate board was  27 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0047]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 13  
       [0048]    A metal-ceramic substrate board was formed under the same condition as in the example 11 except that silicone nitride was used as the ceramics. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  27 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0049]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 14  
       [0050]    A metal-ceramic substrate board was formed under the same condition as in the example 1 except that the composition of the raw material  11  was formed of aluminum of 99.0% by weight, and Cu of 1% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  30 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
       EXAMPLE 15  
       [0051]    A metal-ceramic substrate board was formed under the same condition as in the example 1 except that the composition of the raw material  11  was formed of aluminum of 98% by weight, and Cu of 2% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  32 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
       EXAMPLE 16  
       [0052]    A metal-ceramic substrate board was formed under the same condition as in the example 15 except that alumina was used as the ceramics. The Vickers hardness of the aluminum alloy layer of the substrate board was  32 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0053]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 17  
       [0054]    A metal-ceramic substrate board was formed under the same condition as in the example 15 except that silicone nitride was used as the ceramics. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  32 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0055]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 18  
       [0056]    A metal-ceramic substrate board was formed under the same condition as in the example 1 except that the composition of the raw material  11  was formed of aluminum of 98% by weight and Zn of 2% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  34 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0057]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 19  
       [0058]    A metal-ceramic substrate board was formed under the same condition as in the example 1 except that the composition of the raw material  11  was formed of aluminum of 99.5% by weight and Ni of 0.5% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  33 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0059]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 20  
       [0060]    A plate of 0.4 mm in thickness consisting of aluminum of 98% by weight and Mn of 2% by weight was laminated on each of both side surfaces of aluminum nitride substrate board of 0.635 mm in thickness through a brazing material layer of 50 μm in thickness consisting of aluminum of 87.5% by weight and silicone of 12.5% by weight. Then, the plate was inserted into a furnace heated at 640° C. As a result, a metal-ceramic substrate board was formed of an aluminum alloy plate and aluminum nitride. The Vickers hardness of the aluminum alloy layer of the substrate board was  25 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0061]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 21  
       [0062]    A metal-ceramic substrate board was formed under the same condition as in the example 20 except that the laminated plate was formed of aluminum of 99.8% by weight, and Mg of 0.2% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  25 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition. Here, Mg was used to increase the hardness.  
         [0063]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 22  
       [0064]    A metal-ceramic substrate board was formed under the same condition as in the example 20 except that the laminated plate was formed of aluminum of 99.5% by weight, and Mg of 0.5% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  27 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition. Here, Mg was used to increase the hardness.  
         [0065]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 23  
       [0066]    A metal-ceramic substrate board was formed under the same condition as in the example 22 except that alumina was used as the ceramics. The Vickers hardness of the aluminum alloy layer of the substrate board was  27 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0067]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 24  
       [0068]    A metal-ceramic substrate board was formed under the same condition as in the example 22 except that silicone nitride was used as the ceramics. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  27 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0069]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 25  
       [0070]    A metal-ceramic substrate board was formed under the same condition as in the example 20 except that the composition of the raw material  11  was formed of aluminum of 99.0% by weight, and Cu of 1% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  31 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0071]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 26  
       [0072]    A metal-ceramic substrate board was formed under the same condition as in the example 20except that the composition of the raw material  11  was formed of aluminum of 98% by weight, and Cu of 2% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  33 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0073]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 27  
       [0074]    A metal-ceramic substrate board was formed under the same condition as in the example 26 except that alumina was used as the ceramics. The Vickers hardness of the aluminum alloy layer of the substrate board was  33 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0075]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 28  
       [0076]    A metal-ceramic substrate board was formed under the same condition as in the example 26 except that silicone nitride was used as the ceramics. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  33 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0077]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 29  
       [0078]    A metal-ceramic substrate board was formed under the same condition as in the example 20 except that the composition of the raw material  11  was formed of aluminum of 98% by weight, and Zn of 2% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  35 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0079]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 30  
       [0080]    A metal-ceramic substrate board was formed under the same condition as in the example 20 except that the composition of the raw material  11  was formed of aluminum of 99.5% by weight, and Ni of 1% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  33 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0081]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 3  
       [0082]    A metal-ceramic substrate board was formed under the same condition as in the example 1 except that the composition of the raw material  11  was formed of aluminum of 99.4% by weight, silicone of 0.1% by weight, and Mg of 0.5% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  28 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0083]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 32  
       [0084]    A plate of 0.4 mm in thickness consisting of aluminum of 99.4% by weight, Mg of 0.5% by weight and silicone of 0.1% by weight was laminated on each of both side surfaces of aluminum nitride substrate board of 0.635 mm in thickness through a brazing material layer of 50 μm in thickness consisting of aluminum of 87.5% by weight and silicone of 12.5% by weight. Then, the plate was inserted into a furnace heated at 640° C. As a result, a metal-ceramic substrate board was formed of an aluminum alloy plate and aluminum nitride. The Vickers hardness of the aluminum alloy layer of the substrate board was 28. Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0085]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 33  
       [0086]    A metal-ceramic substrate board was formed under the same condition as in the example 31 except that the laminated plate was formed of aluminum of 98.9% by weight, silicone of 0.1% by weight, and Cu of 1% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  32 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0087]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 34  
       [0088]    A metal-ceramic substrate board was formed under the same condition as in the example 32 except that the laminated plate was formed of aluminum of 98.9% by weight, silicone of 0.1% by weight, and Cu of 1% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  32 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0089]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 35  
       [0090]    A metal-ceramic substrate board was formed under the same condition as in the example 31 except that the laminated plate was formed of aluminum of 98.8% by weight, silicone of 0.1% by weight, Cu of 1% by weight, and Mg of 0.1% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  33 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition. Here, Mg was used to increase the hardness.  
         [0091]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       EXAMPLE 36  
       [0092]    A metal-ceramic substrate board was formed under the same condition as in the example 32 except that the laminated plate was formed of aluminum of 98.8% by weight, silicone of 0.1% by weight, Cu of 1% by weight, and Mg of 0.1% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  33 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition. Here, Mg was used to increase the hardness.  
         [0093]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 3000 times, no change was recognized in the ceramics and the brazing material layer between the ceramics and the base plate.  
       COMPARATIVE EXAMPLE 1  
       [0094]    A following sample was prepared for comparison. As shown in FIG. 2, a raw material  11  of aluminum of 100% by weight and a piston  12  of graphite were set in a concave portion  10  formed at an upper portion of a crucible  9  of graphite. A ceramic substrate board  14  of aluminum nitride of 0.635 mm in thickness was set in a cavity  13  formed at a lower portion of the crucible  9  of graphite. Then, crucible  9  was inserted into a furnace heated at 800° C. As a result, the raw material was molten and pushed out by the weight of the piston  12  into the cavity  13  including therein the ceramic substrate board  14 . The crucible  9  was taken out of the furnace and cooled at a room temperature. In this comparative example 1, the heating and cooling of the crucible  9  were performed in an atmosphere of nitrogen gas in order to prevent the crucible  9  from being oxidized. Thus obtained ceramic substrate board  14  having at each of side surfaces thereof an aluminum alloy layer of 0.5 mm in thickness was subjected to the mechanical and electrolytic polishing.  
         [0095]    The Vickers hardness of the aluminum alloy layer of the substrate board was  20 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0096]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 2000 times, small cracks were recognized in the brazing material layer between the ceramics and the base plate. However, the function of the module was not reduced.  
       COMPARATIVE EXAMPLE 2  
       [0097]    A metal-ceramic substrate board was formed under the same condition as in the comparative example 1 except that the composition of the raw material  11  was formed of aluminum of 95% by weight and silicone of 5% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  40 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al- SiC composite material by using a brazing material of eutectic composition.  
         [0098]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 1000 times, cracks were recognized in the ceramics.  
       COMPARATIVE EXAMPLE 3  
       [0099]    A plate of 0.4 mm in thickness consisting of aluminum of 95% by weight and silicone of 5% by weight was laminated on each of both side surfaces of aluminum nitride substrate board of 0.635 mm in thickness through a brazing material layer of 50 μm in thickness consisting of aluminum of 87.5% by weight and silicone of 12.5% by weight. Then, the plate was inserted into a furnace heated at 640° C. As a result, a metal-ceramic substrate board was formed of an aluminum alloy plate and aluminum nitride. The Vickers hardness of the aluminum alloy layer of the substrate board was  40 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0100]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 1000 times, cracks were recognized in the ceramics.  
       COMPARATIVE EXAMPLE 4  
       [0101]    A metal-ceramic substrate board was formed under the same condition as in the comparative example 1 except that the composition of the raw material  11  was formed of aluminum of 95% by weight and Ni of 5% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was 42. Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0102]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 1000 times, cracks were recognized in the ceramics. However, after the thermal cycle of 1000 times, no crack was recognized in the brazing material layer between the ceramics and the base plate.  
       COMPARATIVE EXAMPLE 5  
       [0103]    A metal-ceramic substrate board was formed under the same condition as in the comparative example 1 except that the composition of the raw material  11  was formed of aluminum of 95% by weight and Cu of 5% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  68 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0104]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 100 times, cracks were recognized in the ceramics. However, after the thermal cycle of 100 times, no crack was recognized in the brazing material layer between the ceramics and the base plate.  
       COMPARATIVE EXAMPLE 6  
       [0105]    A metal-ceramic substrate board was formed under the same condition as in the comparative example 1 except that the composition of the raw material  11  was formed of aluminum of 98% by weight and Mg of 2% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  67 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0106]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 100 times, cracks were recognized in the ceramics. However, after the thermal cycle of 100 times, no crack was recognized in the brazing material layer between the ceramics and the base plate.  
       COMPARATIVE EXAMPLE 7  
       [0107]    A metal-ceramic substrate board was formed under the same condition as in the comparative example 1 except that the composition of the raw material  11  was formed of aluminum of 95% by weight and Zn of 5% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was 40. Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0108]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 1000 times, cracks were recognized in the ceramics. However, after the thermal cycle of 1000 times, no crack was recognized in the brazing material layer between the ceramics and the base plate.  
       COMPARATIVE EXAMPLE 8  
       [0109]    A metal-ceramic substrate board was formed under the same condition as in the comparative example 3 except that the composition of the raw material  11  was formed of aluminum of 95% by weight and Cu of 5% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  68 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition. A thermal cycle test was performed to evaluate the power  
         [0110]    module. After the thermal cycle of 100 times, cracks were recognized in the ceramics. However, after the thermal cycle of 100 times, no crack was recognized in the brazing material layer between the ceramics and the base plate.  
       COMPARATIVE EXAMPLE 9  
       [0111]    A metal-ceramic substrate board was formed under the same condition as in the comparative example 3 except that the composition of the raw material  11  was formed of aluminum of 98% by weight and Mg of 2% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  67 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0112]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 100 times, cracks were recognized in the ceramics. However, after the thermal cycle of 100 times, no crack was recognized in the brazing material layer between the ceramics and the base plate.  
       COMPARATIVE EXAMPLE 10  
       [0113]    A metal-ceramic substrate board was formed under the same condition as in the comparative example 1 except that the composition of the raw material  11  was formed of aluminum of 99.9% by weight and Cu of 0.1% by weight. The Vickers hardness of the aluminum alloy layer of the aluminum substrate board was  22 . Then, a power module was formed by combining the metal-ceramic substrate board with a base plate of Al—SiC composite material by using a brazing material of eutectic composition.  
         [0114]    A thermal cycle test was performed to evaluate the power module. After the thermal cycle of 2000 times, cracks were recognized in the ceramics. However, after the thermal cycle of 2000 times, no crack was recognized in the brazing material layer between the ceramics and the base plate.  
                                                                                                                         TABLE 1                                       Example 1   Example 2   Example 3   Example 4   Example 5   Example 6                        Vickers hardness   25   30   35   30   30   31       composition of   Al 99.8%   Al 99.5%   Al 98%   Al 99.5%   Al 99.5%   Al 99.5%       aluminum   Si 0.2%   Si 0.5%   Si 2%   Si 0.5%   Si 0.5%   Si 0.5%       ceramics   aluminum   aluminum   aluminum   almina   silicone   aluminum           nitride   nitride   nitride       nitride   nitride       manner of bond   direct   direct   direct   direct   direct   bonding by           bonding   bonding   bonding   bonding   bonding   brazing       thermal cycle   more than   more than   more than   more than   more than   more than       resistance   3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle       crack in ceramics   no crack at   no crack at   no crack at   no crack at   no crack at   no crack at           3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle       crack in brazing   no crack at   no crack at   no crack at   no crack at   no crack at   no crack at       material   3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle                        Example 7   Example 8   Example 9   Example 10                            Vickers hardness   32   30   30   25           composition of   Al 97.9%   Al 98.6%   Al 98%   Al 99.8%           aluminum   Si 0.6%   Si 0.4%   Mn 2%   Mg 0.2%               Mn 1.5%   Mg 1%               ceramics   aluminum   aluminum   aluminum   aluminum               nitride   nitride   nitride   nitride           manner of bond   direct   bonding by   direct   direct               bonding   brazing   bonding   bonding           thermal cycle   more than   more than   more than   more than           resistance   3000 cycle   3000 cycle   3000 cycle   3000 cycle           crack in ceramics   no crack at   no crack at   no crack at   no crack at               3000 cycle   3000 cycle   3000 cycle   3000 cycle           crack in brazing   no crack at   no crack at   no crack at   no crack at           material   3000 cycle   3000 cycle   3000 cycle   3000 cycle                      
 
         [0115]    [0115]                                                                                                                         TABLE 2                                       Example 11   Example 12   Example 13   Example 14   Example 15   Example 16                        Vickers hardness   27   27   27   30   32   32       composition of   Al 99.5%   Al 99.5%   Al 99.5%   Al 99%   Al 98%   Al 98%       aluminum   Mg 0.5%   Mg 0.5%   Mg 0.5%   Cu 1%   Cu 2%   Cu 2%       ceramics   aluminum   almina   silicone   aluminum   aluminum   almina           nitride       nitride   nitride   nitride           manner of bond   direct   direct   direct   direct   direct   direct           bonding   bonding   bonding   bonding   bonding   bonding       thermal cycle   more than   more than   more than   more than   more than   more than       resistance   3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle       crack in ceramics   no crack at   no crack at   no crack at   no crack at   no crack at   no crack at           3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle       crack in brazing   no crack at   no crack at   no crack at   no crack at   no crack at   no crack at       material   3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle                        Example 17   Example 18   Example 19   Example 20                            Vickers hardness   32   34   33   31           composition of   Al 98%   Al 98%   Al 99.5%   Al 98%           aluminum   Cu 2%   Zn 2%   Ni 0.5%   Mn 2%           ceramics   silicone   aluminum   aluminum   aluminum               nitride   nitride   nitride   nitride           manner of bond   direct   direct   direct   bonding by               bonding   bonding   bonding   brazing           thermal cycle   more than   more than   more than   more than           resistance   3000 cycle   3000 cycle   3000 cycle   3000 cycle           crack in ceramics   no crack at   no crack at   no crack at   no crack at               3000 cycle   3000 cycle   3000 cycle   3000 cycle           crack in brazing   no crack at   no crack at   no crack at   no crack at           material   3000 cycle   3000 cycle   3000 cycle   3000 cycle                        
         [0116]    [0116]                                                                                                                         TABLE 3                                       Example21   Example22   Example 23   Example 24   Example 25   Example 26                        Vickers hardness   25   27   27   27   31   33       composition of   Al 99.8%   Al 99.5%   Al 99.5%   Al 99.5%   Al 99%   Al 98%       aluminum   Mn 0.2%   Mn 0.5%   Mn 0.5%   Mn 0.5%   Cu 1%   Cu 2%       ceramics   aluminum   aluminum   almina   silicone   aluminum   aluminum           nitride   nitride       nitride   nitride   nitride       manner of bond   bonding by   bonding by   bonding by   bonding by   bonding by   bonding by           brazing   brazing   brazing   brazing   brazing   brazing       thermal cycle   more than   more than   more than   more than   more than   more than       resistance   3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle       crack in ceramics   no crack at   no crack at   no crack at   no crack at   no crack at   no crack at           3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle       crack in brazing   no crack at   no crack at   no crack at   no crack at   no crack at   no crack at           3000 cycle   3000 cycle   3000 cycle   3000 cycle   3000 cycle   300 cycle                        Example 27   Example 28   Example 29   Example 30                            Vickers hardness   33   33   35   33           composition of   Al 98%   Al 98%   Al 98%   Al 99.5%           aluminum   Cu 2%   Cu 2%   Zn 2%   Ni 0.5%           ceramics   almina   silicone   aluminum   aluminum                   nitride   nitride   nitride           manner of bond   bonding by   bonding by   bonding by   bonding by               brazing   brazing   brazing   brazing           thermal cycle   more than   more than   more than   more than           resistance   3000 cycle   3000 cycle   3000 cycle   3000 cycle           crack in ceramics   no crack at   no crack at   no crack at   no crack at               3000 cycle   3000 cycle   3000 cycle   3000 cycle           crack in brazing   no crack at   no crack at   no crack at   no crack at           material   3000 cycle   3000 cycle   3000 cycle   3000 cycle                        
         [0117]    [0117]                           TABLE 4                               Example 31   Example 32   Example 33               Vickers hardness   28   28   32       composition   Al 99.4%   Al 99.4%   Al 98.9%       of   Si 0.1%   Si 0.1%   Si 0.1%       aluminum   Mg 0.5%   Mg 0.5%   Cu 1%       ceramics   aluminum   aluminum   aluminum           nitride   nitride   nitride       manner of bond   direct   bonding by   direct           bonding   brazing   bonding       thermal cycle   more than   more than   more than       resistance   3000 cycle   3000 cycle   3000 cycle       crack in   no crack at   no crack at   no crack at       ceramics   3000 cycle   3000 cycle   3000 cycle       crack in brazing   no crack at   no crack at   no crack at       material   3000 cycle   3000 cycle   3000 cycle                   Example 34   Example 35   Example 36               Vickers hardness   32   33   33       composition   Al 98.8%   Al 98.8%   Al 98.8%       of   Si 0.1%   Si 0.1%   Si 0.1%       aluminum   Cu 1%   Mg 0.1%   Mg 0.1%               Cu 1%   Cu 1%       ceramics   aluminum   aluminum   aluminum           nitride   nitride   nitride       manner of bond   bonding by   direct   bonding by           brazing   bonding   brazing       thermal cycle   more than   more than   more than       resistance   3000 cycle   3000 cycle   3000 cycle       crack in   no crack at   no crack at   no crack at       ceramics   3000 cycle   3000 cycle   3000 cycle       crack in brazing   no crack at   no crack at   no crack at       material   3000 cycle   3000 cycle   3000 cycle                    
         [0118]    [0118]                                                                                                                         TABLE 5                                       Comparative   Comparative   Comparative   Comparative   Comparative   Comparative           Example 1   Example 2   Example 3   Example 4   Example 5   Example 6                        Vickers   20   40   40   42   68   67       hardness       composition   Al 100%   Al 95%   Al 95%   Al 95%   Al 95%   Al 98%       of aluminum       Si 5%   Si 5%   Ni 5%   Cu 5%   Mg 2%       ceramics   aluminum   aluminum   aluminum   aluminum   aluminum   aluminum           nitride   nitride   nitride   nitride   nitride   nitride       manner of   direct   direct   bonding by   direct   direct   direct       bond   bonding   bonding   brazing   bonding   bonding   bonding       thermal cycle   2000 cycle   1000 cycle   1000 cycle   1000 cycle   100 cycle   100 cycle       resistance       crack in   no crack at   crack at 1000   crack at 1000   crack at 1000   crack at 100   crack at 100       ceramics   2000 cycle   cycle   cycle   cycle   cycle   cycle       crack in   crack a little   no crack at   no crack at   no crack at   no crack at   no crack at       brazing   at 2000 cycle   1000 cycle   1000 cycle   1000 cycle   100 cycle   100 cycle       material                        Comparative   Comparative   Comparative   Comparative           Example 7   Example 8   Example 9   Example 10                            Vickers   40   68   67   22           hardness           composition   Al 95%   Al 95%   Al 98%   Al 99.9%           of aluminum   Zn 5%   Cu 5%   Mg 2%   Cu 0.1%           ceramics   aluminum   aluminum   aluminum   aluminum               nitride   nitride   nitride   nitride           manner of   direct   bonding by   bonding by   direct           bond   bonding   brazing   brazing   bonding           thermal cycle   1000 cycle   100 cycle   100 cycle   2000 cycle           resistance           crack in   crack at 1000   crack at 100   crack at 100   crack at 2000           ceramics   cycle   cycle   cycle   cycle           crack in   no crack at   no crack at   no crack at   no crack at           brazing   1000 cycle   100 cycle   100 cycle   2000 cycle           material                        
         [0119]    According to the power module of the present invention, as stated above, a high reliability and a high thermal-cycle resistance can be obtained, and the ceramics can be protected from the thermal shock and cracks are prevented from being formed in the brazing material, by setting the hardness of the aluminum of the aluminum-ceramics insulating substrate board in a predetermined range.  
         [0120]    Au plating or Ni plating may be carried out on the ceramic substrate board in order to increase the corrosion resistance and the affinity for the brazing material.  
         [0121]    Aluminum among the ceramics has a high heat insulating ability and is cheap. The aluminum nitride has a high heat conductivity and a high heat radiation, so that it is preferable to hold heavy current control tip. The silicone nitride has a high strength and a high thermal cycle resistance, so that it can be used in the hard circumstances, such as in the engine room.  
         [0122]    Further, the Vickers hardness of the aluminum surface was measured with respect to the ceramics bonded with a weight of 50 g for 15 seconds to aluminum by using a micro-Vickers hardness meter (MVK-G1 made of Kabushiki Kaisya Mei Seki Sha). The values of the Vickers hardness in the Table 1 are average values obtained at twenty portions. The thermal cycle test was carried out in the gaseous phase and one cycle thereof was that the temperature of −40° C. was maintained for 30 minutes, 25° C. was maintained for 10 minutes, 125° C. was maintained for 30 minutes, 25° C. was maintained for 10 minutes and then −40° C. was maintained for 30 minutes.  
         [0123]    While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.