Controlling the distribution of porosity during transient liquid phase bonding of Sn-based solder joint

Abstract

The rapid growth of (Cu,Ni)6Sn5 intermetallic compounds (IMCs) when Sn reacts with Cu containing 6 wt%Ni (Cu-6Ni) offers huge potential for resolving the lengthy transient liquid phase (TLP) processing time. However, the uncontrolled formation of voids at the centre of the joint remains a serious issue. Therefore, we have studied the influence of different Ni concentrations (0, 2 and 6 wt%) in the Cu substrate and the relative location of the porosity when reacting with Sn-0.7Cu solder in the sandwich structure of the joint. Through in-situ X-ray microradiography, the changes in the void positions and the reaction time required to form the IMC joints was interpreted with reference to growth kinetics equations. The results indicate that the different growth rates of (Cu,Ni)6Sn5 and Cu6Sn5 IMCs due to the different Ni concentrations of the Cu-Ni substrates can control the location of the porosity and influence the shear strength of the TLP lap joint. This discovery is a potential gateway to developing reliable electronic interconnects for the power device industry.