Metal-base printed circuit boards (PCBs), multilayer PCBs and embedded PCBs are constructed with a thin insulation layer. In these PCBs, particularly those used for Power Electronics, the insulation layer is stressed under a high-strength electric field. Metal-base PCBs are applied to 100-400 V power circuits for power transistor modules, general purpose inverters and so on. Since the insulation layer is stressed under a high-strength electric field of approximately 1-3 kV/mm, the reliability of the insulation layer is important. In order to investigate the migration process, we have studied the behaviour of ionic impurities in the insulation layer of various PCBs by measuring space charge profiles using the pulsed electroacoustic (PEA) method. Since space charge behaviour affects the internal field profile, the experimental results should contribute to the insulation design of PCBs. Consequently, hetero charge accumulated in the vicinity of the electrode in the insulation layer of two types of metal-base PCBs and two types of Aramid/Epoxy PCBs, and the electric field strength near each electrode are enhanced two-three times more than the average field strength of 5 kV/mm and 10kV/mm. Two types of PCBs (Glass/Epoxy, PTFE/Epoxy) do not exhibit significant electric field distortion under 5 kV/mm and 10 kV/mm. After thermal humidity bias (THB) testing for 20 and 59 hours (DC 1250 V at 85°C and 70% RH), the space charge measurement detected a conductive region that was formed in the insulation layer near the anode of the metal-base PCB A. Element distribution analysis verifies that the conductive region is formed due to copper ionic migration. These results reveal that space charge measurement can carry out a non-destructive observation of the growth of copper migration.
展开▼
