The role of intermetallic compounds in lead-free soldering

The role of intermetallics in soldered joints is ambivalent. They are an es sential part of joints to common basis materials and at low levels they hav e a strengthening effect on solder alloys. At higher levels, however, it is well known that they can cause joint embrittlement, In this paper three as pects of their role have been studied: the microstructure of intermetallic containing solder alloys, the effects of soldering parameters on the quanti ty of intermetallic formed and, finally, the rates of growth of intermetall ic compounds in the solid state. The results suggest that alloys which are pre-doped with copper tend to form slightly more interfacial intermetallic during soldering than those which are not. In the solid state the rates of growth appear to be a function of the melting point of the alloy, with the higher melting point lead-free alloys exhibiting lower rates than lower mel ting point alloys such as 63Sn37Pb (183 degrees C) or 42Sn58Bi (138 degrees C).