Abstract
Since a metal-base printed wiring board (PWB) with superior thermal conductivity has been widely used in power electronics products, high reliability is required at high electric field. Many reports have already covered surface' copper ionic migrations on PWBs which occur short-circuits on the board. The migration growing into the depth direction of a insulation layer has been clearly observed recently, and it is revealed that the growth depends on the ionic impurities of the resin.
We measured space charge behaviour in the insulation layer to know the relationship between the internal space charge and the ionic migration. The results suggest that internal negative charges are generated at high temperature with high humidity, and that a conductive region is formed near a copper electrode under dc electric field.
