Effects of soldering temperature and cooling rate on the as-soldered microstructures of intermetallic compounds in Sn-0.7Cu/Cu joint

In this study, Sn-0.7Cu solder alloy, being selected as the research object, was allowed to react with polycrystalline Cu substrate at 250°C, 275°C and 300°C. After soldering reaction of 10 minutes, it underwent cooling in the three types of cooling medium: water, air and heating furnace, along with the simultaneous application of high pressure air for blowing away the liquid solder on the top of the intermetallic compounds (IMCs) of the specimens. Scalloped, faceted, prismatic and hexagonal shape Cu6Sn5 grains were observed at the solder/Cu interface, respectively. Scalloped shape grains were found at 250°C. At higher soldering temperatures such as 275°C and 300°C, faceted grains were dominant and the other two were mainly discovered under smaller cooling rates. With these observations, in-depth analyses of the morphology and size of Cu6Sn5 IMC as well as effect of brazing temperature and cooling rate on the microstructure of the joint were made. Moreover, synchrotron radiation real-time imaging technology, was utilized in observing the dynamic growth behavior of IMC during brazing process, thereby, providing direct evidence to the hypothesis regarding the IMC evolution pattern.