Experiments were carried out using space charge distribution measurements as a major measurement method in order to find effective measures to suppress electrochemical migration (ECM) along the thickness direction of a printed wiring board (PWB). As a result, the following valuable knowledge was obtained. First, in a PWB consisting of paper/ phenol-resin composite and a copper electrode, the electrical resistivity of epoxy resin used as an adhesive layer to connect the composite and the electrode is usually higher than that of the composite. In such a case, ECM is easily grown in the PWB. The resistance against ECM was found to increase significantly if we use an adhesive layer with a similar electrical resistivity to the insulating material in a PWB. Another important fact is that the growth of ECM can be suppressed if silica nanofillers were added to epoxy resin in the case of an epoxy-based PWB.
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