Formation of plate-like channels in Cu6Sn5 and Cu3Sn intermetallic compounds during transient liquid reaction of Cu/Sn/Cu structures

• Formation of Sn channels in Cu6Sn5 IMCs were observed after Cu-Sn reactions.
• Cu6Sn5 channels formed in Cu3Sn IMCs in later stages of the reactions.
• These channels provide fast diffusion paths for Cu to react with the remaining Sn.

Transient liquid reactions in Cu/Sn/Cu sandwich structures during various stages were conducted at 340 °C. In the early stages of the reaction, Cu atoms dissolved into the molten Sn through the valleys between the scallop-like Cu6Sn5 intermetallic compounds (IMCs). When the Sn layer was almost consumed, formation of plate-like Sn channels in Cu6Sn5 IMCs was observed at later stages of the reaction. In addition, plate-like Cu6Sn5 channels formed in Cu3Sn IMCs because Cu atoms diffused faster in Cu6Sn5 than in Cu3Sn IMCs. These channels serve as fast diffusion paths for Cu to react with the remaining Sn. Hence, the growth kinetics at later stages are quite different from those at the beginning stages.