03

Poor Wetting
Poor solderability on tin/lead boards is uncommon if the correct thickness of tin/lead is applied to the pad surface. As a guide a minimum thickness of 0.005um should provide a solderable coating which will exceed a twelve month shelf life. It will most probably protect the surface in normal conditions for a couple of years and still be highly solderable. In the case of the sample shown the tin/lead was less than 0.002um on the surface of the board. It was also a plated finish which had not been reflowed during board manufacture, hence the shorter shelf life of the product. Only part of the through hole pad surface has wetted with solder; the outer and inner edge of the pad has failed to wet.