Effect of processing parameters on the morphology of the interfacial intermetallics between Cu and SnPb solders

The wetting reaction between Cu substrate and the molten Sn-Pb solder alloys of four different compositions had been studied to characterise the morphology of the intermetallic compound (IMC) at the interface between Cu and solder. The morphological changes of the IMC layer is analysed with respect to the Pb-content of the solder alloy, molten solder temperature (10°C, 20°C, 40°C and 60°C above the liquidus temperature of each alloy) and immersion time of Cu. The morphology of the IMC is classified into three broad groups namely, cellular, scallop and planar. These morphologies are found to vary gradually from one type to the other with the Pb-content, temperature and time. Fractal Dimension (FD), a measure of roughness, is estimated from the digitized SEM micrographs of the IMC layer at each reaction condition and it is correlated with reaction conditions.