Residues on Soldered Printed Circuit Assemblies

Visible surface residues, commonly referred to as white residues, on soldered printed circuit assemblies are a very common but intermittent and unpredictable problem. Such residues, which are insoluble in normal solvents, are generally a rejectable condition. The chemistry of the deposition of white residues is complex; the deposits themselves are of a number of types and origins, and their incidence is associated with both materials and process parameters. This paper attempts to identify the different causes of the problem and suggest ways in which avoidance or removal is possible.