| 摘要 |
PCT No. PCT/JP93/00918 Sec. 371 Date Nov. 8, 1993 Sec. 102(e) Date Nov. 8, 1993 PCT Filed Jul. 2, 1993A composite substrate 30 is constituted by an alumina substrate 16, a metallic layer 34, and a copper sheet 26 bonded to the alumina substrate 16 via the metallic layer 34. The metallic layer 34 is constituted by a tungsten sub-layer 34a having a low coefficient of thermal expansion, a tungsten/silver-copper alloy mixture sub-layer 34b, and a silver-copper alloy sub-layer 34c having a high coefficient of thermal expansion. In the mixture sub-layer 34b, the ratio of the percentage content of the silver-copper alloy to that of the tungsten increases with distances from the alumina substrate 16.
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