Growth orientations and mechanical properties of Cu6Sn5 and (Cu,Ni)6Sn5 on poly-crystalline Cu

Abstract

Lead-free solders are important materials in current generation electrical packages, due to the increasingly stringent legislative requirement aimed at reducing the use of lead. The lead-free solders based on the Sn–Cu system with Ni addition have become popular because of their superior soldering properties, as well as their comparatively low cost. This research investigates the effect of Ni addition on the growth morphologies, crystal orientations and mechanical properties of Cu6Sn5 at the interface between hyper-eutectic Sn–Cu high-temperature lead-free solder alloys and Cu substrates, prior to and after aging, by the use of X-ray diffraction (XRD), scanning electron microscopy (SEM) and nanoindentation. The (Cu,Ni)6Sn5 in Sn–Cu–Ni/Cu solder joints showed a more strongly oriented (101) texture, compared to the Cu6Sn5 in Sn–Cu/Cu solder joints. The Ni-induced (101) texture contributes to higher and more scattered average values with larger standard deviations in both elastic modulus and hardness for (Cu,Ni)6Sn5.