Effect of Sn Component Surface Finish on 92.5Pb-5Sn-2.5Ag

This work investigates the effect of Sn component surface finish on the melting temperature, microstructure, and mechanical behavior of 92.5Pb-5Sn-2.5Ag. 92.5Pb-5Sn-2.5Ag was doped with up to 7% Sn to simulate the final composition of a joint after reflow with a component having Sn surface finish. Differential Scanning Calorimetry (DSC) was used to measure the change in matrix liquidus temperature with increasing Sn concentration. Microstructure evaluation and mechanical tests were carried out on 20 mil solder spheres reflowed on high temperature polyimide test coupons. Solder joints of each composition were cross-sectioned to examine the microstructure. The area fraction of β-Sn and Ag3Sn was quantified for each composition using image analysis software. Shear and isothermal fatigue tests of individual solder joints with varying Sn concentrations were conducted at room temperature. Joints were also sheared at 200°C after aging for 1024hrs at 200°C to simulate a downhole environment. The failed interfaces were examined to determine the mode of failure. Beyond providing guidance for surface finish selection, this work examines the microstructure and mechanical behavior of 92.5Pb-5Sn-2.5Ag as a function of Sn concentration and temperature. An understanding of the microstructure-mechanical performance relationship will aid in the development of new alloys for high temperature applications.