Study on interfacial reactions in Cu/Sn-9Zn/Ni micro solder joints under temperature gradient

摘要

The interfacial reactions in Cu/Sn-9Zn/Ni micro solder joints during reflow under temperature gradient was investigated in this study. And corresponding isothermal reflow of the micro solder joints as a reference experiment was also conducted. The results indicate that the Cu atoms can migrate to the opposite Ni side even against the temperature gradient while the Ni atoms can only migrate to the opposite Cu side along the temperature gradient during reflow. With the Cu substrate as the hot-end, the Cu atomic flux towards the Ni side is strongly enhanced and the Ni atomic flux is totally inhibited by the combination of the chemical potential gradient and temperature gradient. As a result, significantly asymmetric growth of the interfacial IMCs is observed and Cu-Ni cross-interaction occurs only at the Ni side. With the Ni substrate as the hot-end, both Cu and Ni atoms can reach the opposite interfaces after a long time reflow, resulting in the Cu-Ni cross-interaction at both Cu and Ni sides. Temperature gradient plays an important role in the interfacial reactions as well as the Cu-Ni cross-interaction in the Cu/Sn-9Zn/Ni micro solder joints.