Fractal analysis of intermetallic compounds in Sn–Ag, Sn–Ag–Bi, and Sn–Ag–Cu diffusion couples

The Sn–Ag/Au/Ni–P/Cu, Sn–Ag–Bi/Au/Ni–P/Cu, and Sn–Ag–Cu/Au/Ni–P/Cu diffusion couples were prepared by reflowing the Pb free solders on the top surface metallization of the substrate at 250 °C. They were annealed at 150 and 170 °C for 4, 8, 16, 36, 45 days. The surface morphological features of intermetallic compounds (IMC) formed among the different elements in the solder alloys were characterized by Fractal Dimension using FE-SEM micrographs. The influence of processing parameters on morphological features was studied in the present work. The Box counting technique has been used to measure the fractal dimension of the IMC. It was observed that the morphology of the IMC varies from scallop to planar with increasing annealing time.