Automatic inspection of visible or hidden solder joints-a new concept

An automatic solder joint inspection technique based on the use of a microplasma between the solder joint, which constitutes the cathode, and a mobile local anode is described. The principle of the approach is described, and experimental results are presented and discussed. In particular, measurements of buildup voltage versus various experimental parameters and of the relationship between the current and the size of the cathode surface are reported. The electronic current emitted by the solder joint surface serves as a measure of the size (area) of this surface. The promising initial test results confirm the importance of this concept