Effect of water treatment temperature on space charge profiles in printed circuit board insulations

The reliability of bulk insulation is particularly important in multilayered or embedded printed circuit boards (PCBs). Moreover, PCBs are mounted in quite a lot of devices, which are often used at high temperatures and in high humidity. We observed internal space charge behavior in two typical types of epoxy composites for PCBs, namely those with aramid and with glass, under dc voltage to investigate the effect of water temperature. It was observed that the space charge profiles showed spatial oscillation with 3 or 5 iterative units in agreement with the number of composite layers in samples. In the case of the aramid/epoxy composite, homocharge is formed near the two electrodes in the sample at 40 °C, while hetrocharge is accumulated at 85 °C. The ion chromatography analysis showed that the contents of several kinds of cations were much higher especially in the aramid/epoxy composite treated in water at 85 °C than in the one treated at 40 °C. This indicates that the water treatment enhances dissociation of ions. In the case of the glass/epoxy composite, homocharge is formed near the electrodes in the sample under dc voltage if it was treated in water at 85 °C. Water seems to enhance the charge accumulation in both samples.