Investigation of soldering process and interfacial microstructure evolution for the formation of full Cu3Sn joints in electronic packaging

With the purpose of ensuring that solder joints can service under high temperature, full Cu3Sn solder joints with the interfacial structure of Cu/Cu3Sn/Cu can be a substitute due to the high melting point of Cu3Sn (676 °C). In this investigation, soldering process parameters were optimized systematically in order to obtain such joints. Further, interfacial microstructure evolution during soldering was analyzed. The soldering temperature of 260 °C, the soldering pressure of 1 N and the soldering time of 5 h were found to be the optimal parameter combination. During soldering of 260 °C and 1 N, the Cu6Sn5 precipitated first in a planar shape at Cu-Sn interfaces, which was followed by the appearance of planar Cu3Sn between Cu and Cu6Sn5. Then, the Cu6Sn5 at opposite sides continued to grow with a transition from a planar shape to a scallop-like shape until residual Sn was consumed totally. Meanwhile, the Cu3Sn grew with a round-trip shift from a planar shape to a wave-like shape until the full Cu3Sn solder joint was eventually formed at 5 h. The detailed reasons for the shape transformation in both Cu6Sn5 and Cu3Sn during soldering were given. Afterwards, a microstructure evolution model for Cu-Sn-Cu sandwich structure during soldering was proposed. Besides, it was found that no void appeared in the interfacial region during the entire soldering process, and a discuss about what led to the formation of void-free joints was conducted.