Internal space charge and ionic migration in a printed wiring board

Internal space charge and its influence on electrical insulation are being widely discussed, but these discussions have been limited to materials used in high-voltage apparatus, such as the insulation for high-voltage dc cables. We used the space charge observation to investigate copper ion migration occurring in an insulation layer of a metal-base printed wiring board for inverter circuits, and compared the space charge behaviour with ion impurities detected by ion chromatography and copper distribution observed by an electron probe X-ray microanalyser. The space charge profiles measured during an ageing test suggested that internal negative charges were generated, and that a high conductive region was formed near the copper electrode under dc electric field. The high conductive region was the same as that with the copper ion migration. Thus we found that space charge observation is useful for investigating the ageing phenomena of a printed wiring board.