Fractal analysis of Sn-Ag, Sn-Ag-Cu, Sn-Ag-Bi interfacial morphology in flipchip packaging applications

Abstract

In the present study Sn-Ag/Au/Ni-P/Cu, Sn-Ag-Cu/Au/Ni-P/Cu, and Sn-Ag-Bi/Au/Ni-P/Cu diffusion couples were prepared by reflowing the Pb free solders on the top surface metallization of the substrate at 250degC. The diffusion couples were annealed at 150degC up to 4, 8, 16, 36, 45 days. The growth of IMCs formed among the different elements in the solder alloys was studied and their morphology were characterised by fractal dimension using SEM micrographs. The role of processing parameters on different morphological features was studied in detail. The box counting technique has been used to measure the fractal dimension of the IMCs. It has been observed that the morphology of the IMC varies from scallop to planar with increasing annealing time