Interfacial reaction between Sn-Ag-based solder alloys and substrates

Abstract

The interfacial reaction at the interface between solders and substrates was studied both in the liquid and the solid states, especially with a focus on the intermetallic compound thereafter, IMC) phase formed. The solder systems of Sn-3.5Ag and Sn-3.5Ag-8.5In (in wt%) were selected from the phase equilibria calculations. The calculated phase diagram agreed well with measurements by differential scanning calorimetry and X-ray diffractometry. Four types of substrates were used: Cu, Cu/Sn, Cu/Ni, and Cu/Ni/Pd. The interface was observed by the use of scanning electron microscopy, and the compositions of the IMC at the interface were measured by energy-dispersive X-ray analyses. The growth kinetics of the IMC followed a parabolic-type behavior and palladium was very effective as a diffusion barrier element.