Influence of Copper Substrate Roughness on the Growth of Intermetallic Compounds Layer in SAC305 Solder Joints

Abstract

This study aimed to evaluate the effect of surface morphology of copper (Cu) substrate on the intermetallic compound (IMC) growth and interfacial reactions when soldered with SAC305 lead-free solder during a thermal aging process. The surface morphology conditions of the Cu substrate influence the growth activity of the IMC layer. This study used different grits of silicon carbide (SiC) abrasive paper (400, 800 and 1200) to grind the Cu substrate to produce different surface roughness. The resulting Cu surface morphologies were examined using an infinite focus microscope (IFM), and the parameters used in this stereometric analysis were profile roughness. Hand soldering was used to melt the SAC305 solder on the Cu substrates with different surface roughness. Subsequently, the samples were subjected to an aging temperature of 150 °C for 800 hours to grow the IMC layers. Thermal aging increased the IMC thickness at the Cu-SAC305 interfaces. After thermal aging, the IMC layer thickness and related parameters were measured and analyzed with the IFM. The growth of the IMC layer thickness depended on the different surface morphology of the substrate when the aging temperatures and Cu materials were maintained in this study. In general, the IMC morphology for the rougher Cu substrate had a scallop-shaped and uniformed layer compared to those IMC from the smooth Cu substrate. The Cu substrate ground surface roughness with 400 grit SiC abrasive paper produced an average roughness, Ra of 505.02 nm; this roughness produced the thinnest IMC layers compared to the different Cu substrates ground by SiC abrasive paper of different grits.