The effect of reflow temperature on IMC growth in Sn/Cu and Sn0.7Cu/Cu solder bumps during multiple reflows

The interfacial intermetallic compound (IMC) is a crucial factor for solder jointing reliability assessment and a suitable IMC layer size guarantees the quality of solder joints. On one hand, the interfacial grains keep growing with reaction time during soldering; On the other hand, with the coming universal application of 3D electronic packaging in modern electron industry, multiple reflows become a common soldering technology at the same time, which result in the much longer effective reaction time for solder materials. In this case, the size of interfacial IMCs at solder/substrate interface should arouse close attention of material scientists and engineering designers. In this article, the effect of welding temperature on IMC growth kinetics in Sn/Cu and Sn0.7Cu/Cu solder bumps was investigated respectively during multiple reflow process, by high pressure blowing (HP) experimental method and scanning electron microscope observing technology. It was found that the IMC thickness as well as the grain width increases with soldering temperature and reflow cycle for both pure Sn and Sn0.7Cu alloys; furthermore, the length of prism crystal is larger in higher temperature; besides, the value of time exponent n also grows with welding temperature, especially for Sn0.7Cu solder; finally, the reason for the kinetic difference between Sn and Sn0.7Cu alloys may be attributed to the fine grains at solder/substrate interface in Sn0.7Cu/Cu joint.