Substrate Patterning Effect on the Wetting Behaviour and Intermetallic Formation of SnCu Alloy

Abstract

This paper explains the effect of a micro-patterned substrate fabricated via photolithography on soldering applications. The dimple micro-pattern was fabricated on the copper substrate with a 100–500 μm diameter with a fixed depth of 25±2 μm. The dimple micro-pattern substrate was metallurgically joined with Sn-0.7Cu lead-free solder in the reflow process. The dimple micro-pattern was examined using an optical microscope (OM) to observe all the critical parameters of the photolithography. The depth of the dimple(s) was observed and measured using a 3D surface profiler. The solder joints of the dimple micro-patterned substrate and the Sn-0.7Cu solder alloy were analysed in terms of their solderability, wettability, formation of intermetallic compounds (IMCs), and microstructures to determine the influence of dimple micro-patterning on the performance of the Sn-0.7Cu solder alloy. It was observed that a fixed depth of 25±2 μm was achieved for all dimple diameters at an etching time of 45 minutes. In terms of the performance of Sn-0.7Cu solder alloy on a micro-patterned substrate, it can be seen that as the diameter of the dimples increases, the flow rate and spreading area increase. At the same time, the IMC thickness decreased as the dimple’s diameter increased. The dimple micro-pattern substrate enhances copper diffusion, which reduces the β-Sn area and promotes Cu-Sn intermetallic formation, resulting in a rich, fine eutectic area of solder compared to its non-patterned counterpart.