Effect of Alloying Element on Microstructure and Mechanical Properties of Sn-0.7cu Solder

Abstract

Due to environment concern of lead Sn-0.7Cu eutectic solder has been successfully applied to practical production of consumer products. However, Sn-Cu has been reported to exhibit somewhat inferior mechanical properties compared to Ag containing lead free solder alloys. In this work, 1.0wt.% In and 0.1wt.% Fe had been added into Sn-0.7Cu eutectic solder. Three different solders have been fabricated by adding In and Fe into the solder, i.e., Sn.0.7Cu, Sn.0.7Cu.1.0In and Sn.0.7Cu.1.0In.0.1Fe. DSC result showed that adding indium decreases the melting point of Sn-Cu solder. The addition of In and Fe is expected to refine the β-Sn grains with fine Cu6Sn5 distributed within the eutectic colony of the bulk solder and contribute to higher solder strength. Characterization of the solder alloys focused on the bulk solder microstructure, IMC evaluation and wettability of solder alloys in reflowed and aged conditions. Reflow temperature was 270°C. Aging was done for 100, 250 and 500 hours at 150 °C and 180°C. The IMC observed for reflowed samples seem to decrease in thickness with addition of In and Fe. Isothermally aged samples on the other hand, did grow at higher rate when In and Fe was added. The IMC formed at the interface between solder and the copper substrate was identified as Cu6Sn5in reflowed samples, and both Cu6Sn5and Cu3Sn when aged. The shear strength of samples improved as In and Fe were added.