Circuit board, process for producing the same and a power module employing the same

摘要

Composite member 2 consisting of ceramic insulator substrate 3 and two metal layers 4A and 4B such as aluminum sheets is subjected to milling in order to remove the unwanted areas of metal layer 4A (where inter-element spacings are to be formed). In order to suppress cracking due to substrate warpage, a small bottom portion of 4A is left intact as residual metal layer 4Aa which is preferably removed by etching. Milling is performed after thin-film layer of etching resist 5 is applied to the surface of metal layer 4A. By milling in two stages, a step is formed at the bottom of lateral sides of a pattern element to make a skirt which contributes to reducing external stresses.