Electrochemical migration growth along the thickness direction in a two-layered dielectric, consisting of an Al cathode, paper/phenol-resin composite, epoxy resin, and a Cu anode that simulates a laminated structure of a printed wiring board, was detected by the pulsed electroacoustic (PEA) method. The PEA signals obtained were analyzed using a numerical model on the generation and propagation of acoustic waves. Accumulation of positive charge appears in front of the Cu anode of the sample, in which the growth of electrochemical migration was observed by SEM-EDS. At the same time, the signal due to negative charge at the interface between the resin and the composite decreases significantly. This is ascribable to the progress of electrochemical migration in the thickness direction. The numerical analysis done by assuming that the conductivity of the epoxy resin layer near the anode was increased gives a good agreement with the PEA spectra. As for the charge on the anode, the PEA signal appears at the correct position when the anode material is semi-conductive polymer, while it appears as if the anode were inside the real anode when the material is Cu. In order to solve this puzzle, numerical calculations were carried out by the finite difference method. As a result, it has become clear that the discontinuity in the acoustic impedance between the epoxy resin and Cu electrode is responsible.
ASJC Scopus subject areas
- Electrical and Electronic Engineering