抄録
More and more electronics are to be used under various adverse environments at high temperatures with high humidity. Spatial distributions of internal charge carriers mainly due to ionic impurities that appear in hot and humid environments are considered to affect the reliability of bulk insulation. Therefore, the authors examined space charge behavior inside paper/phenol-resin composites for printed circuit boards under dc voltages, focusing on the effect of water absorption temperature. Both the sample weight and thickness are increased monotonically by the immersion in water with an increase in water temperature from 24°C to 85°C, indicating that the water absorption by the sample is temperature dependent. In early periods of water absorption up to 10 hours, the electric field decreases near the two electrodes and increases in the other regions. Furthermore, heterocharge formation is observed near the cathode as the water absorption progresses, which becomes more significant at higher water temperatures. Ion chromatography analyses detected a lot of ions such as Na+, NH4+ and Cl- from the water, in which the sample had been immersed for 100 hours at various temperatures. It is highly possible that these ions are responsible for the heterocharge formation.
