| 摘要 |
<p>PROBLEM TO BE SOLVED: To relieve concentration of a thermal stress on a corner part by a method wherein a thermal transmission layer contains ceramics of specific wt.% and curvature at the corner part of the transmission layer is specified. SOLUTION: A recess rectangular in a plan shape having specific curvature 5 at a corner part 4 is formed in a specific area of a second layer from a surface layer of an insulating layer 2 of a three-layer structure. The curvature 5 has an option value within a range of 1/10 to 1/2 times the length of a rectangular short side. A mixture excellent in thermal conduction property and composed of high melting point metal and ceramics is filled in this recess part and integrally sintered to form a thermal transmission layer 3. The thermal transmission layer 3 contains ceramics of 5 to 20wt.% (10 to 15wt.%, preferably). When the curvature 5 is 1/10 times or less the length of a short side of the thermal transmission layer, cracks are developed and resistivity is changed. When exceeding 1/2, cracks generate in a wire board. It is possible to relieve concentration of a thermal stress developed due to a difference of a coefficient of thermal expansion in both the thermal transmission and wire board on the vicinity of the corner part of the thermal transmission layer.</p> |
