電食による銅金属化合物の増殖現象と絶縁物の劣化

抄録

Paper phenolic laminates are widely used as insulation boards for printed and integrated circuits and for battery switches. The insulation is sometimes affected by electrolytic corrosion under polluted conditions. The tracking in organic insulators under wet polluted conditions has been studied by many investigators. However, no satisfactory analysis regarding the behavior of metals which are dissolved and deposited from copper electrodes on an insulation surface under low dc or ac voltage has been reported.
This paper describes the correlation between deterioration of insulating material and the behavior of dissolved and deposited metals from copper electrodes at the interface between an electrolyte and paper phenolic laminate using a test method similar to the IEC (International Electrotechnical Commission) tracking test under application of dc or ac voltage. The paper also describes the results of an analysis of the dissolved and deposited metals obtained by scanning electron microscopy (SEM) and X-ray diffraction.
In the case of dc voltage application, the metal was dissolved from the positive electrode in the first stage of applying drops of electrolytic solution. In successive stages metals were deposited from the negative electrode. When the deposited metals bridged both electrodes, the test solution was evaporated by Joule heating caused by the leakage current flowing through the deposited metals produced at the insulation surface. Then, scintillation appeared at the edge of the positive electrode. From the results of the analysis of dissolved and deposited metals obtained by SEM and X-ray diffraction, it was found that the dissolved metallic compounds from the copper electrode were Cu(OH)Cl and Cu₂(OH)₃Cl. On the other hand, the deposited metal originating from negative electrode was Cu. Furthermore, the deposited metals after scintillation appeared were Cu(OH)Cl, CuCl, Cu₂O and Cu.
In the case of ac voltage application, the test solution was evaporated by Joule heating caused by the leakage current in the test solution in the first stage of applying the drops, and then the metal was dissolved from both electrodes. It was observed that the dissolved metallic compounds were Cu(OH)Cl and Cu₂(OH)₃Cl. In successive stages scintillation appeared at the center between electrodes, and Cu(OH)Cl, Cu₂O, CuCl and Cu were produced. After scintillation disappeared, these deposited metals diffused to both electrodes. In spite of repeat of these processes, tracking was not formed.
From these experimental results, the relation between the processes and mechanism of production and diffusion of copper metallic compounds and the deterioration of insulating material were discussed.