The properties of bulk insulation in printed circuit boards (PCBs) have become even more important, especially for those with a multilayered or embedded structure. In particular, the spatial distribution of internal charge carriers, mainly due to ionic impurities, is thought to affect the reliability of bulk insulation. Therefore, the effects of humidity and temperature on space charge distribution profiles in a five-layered composite of aramid paper and epoxy resin are studied in this paper. More charge carriers are induced at higher temperatures with humidity. A relative humidity of 55 00 is high enough to induce a saturated amount of charge carriers in the present samples at 40°C.

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More and more electronics are intended for use in adverse environments at high temperatures with high humidity. The 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 the water absorption temperature. Both the sample weight and thickness were increased monotonically by immersion in water with an increase in the water temperature from 24 to 85 , indicating that the water absorption by the sample was temperature dependent. In the early periods of water absorption (up to 10 hours), the electric field decreased near the two electrodes and increased in the other regions. Furthermore, heterocharge formation was observed near the cathode as the water absorption progressed, becoming more significant at higher water temperatures. Ion chromatography analyses detected numerous ions such as Na+, $NH_{4}^{+}$ 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. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(2): 1–7, 2010; Published online in Wiley InterScience (http://www.interscience.wiley.com). DOI 10.1002/eej.20992

SUMMARYMore and more electronics are intended for use in adverse environments at high temperatures with high humidity. The 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 the water absorption temperature. Both the sample weight and thickness were increased monotonically by immersion in water with an increase in the water temperature from 24°C to 85 °C, indicating that the water absorption by the sample was temperature dependent. In the early periods of water absorption (up to 10 hours), the electric field decreased near the two electrodes and increased in the other regions. Furthermore, heterocharge formation was observed near the cathode as the water absorption progressed, becoming more significant at higher water temperatures. Ion chromatography analyses detected numerous ions such as Na + , NH 4 + , 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.

No abstract