Three-dimensional space charge observation of ion migration in a metal-base printed circuit board

Internal space charge measurement has been mainly applied to investigate insulating materials used in RV apparatus, such as HVDC cables. We have observed the space charge profiles to monitor copper ion migration occurring in an insulation layer of a metal-base printed circuit board and found that the space charge distribution along the thickness direction corresponds to the progress of ion migration in insulation. The migration, however, can proceed in any direction in the specimen simultaneously; therefore, it should be measured in three dimensions. We measured metal-base epoxy resin insulated printed circuit boards by a newly developed threedimensional pulsed electroacoustic method. The results show that the space charge density varies in the lateral direction when ion migration occurs in the specimen.