Extremely rapid grain growth in scallop-type Cu₆Sn₅ during solid–liquid interdiffusion reactions in micro-bump solder joints

In 3D IC technology, when the size of the micro-bump solder joint is reduced to 10 µm, the scallop-type Cu₆Sn₅ grains on opposite sides of the joint can interact directly by contacting each other during the solid–liquid interdiffusion reaction. Upon contact, an extremely rapid grain growth of the scallops occurs. We propose that the liquid solder wets the grain boundary between scallops and provides an extremely fast kinetic path of liquid channel for grain growth. The width of the liquid channel has been estimated to be about 1.5 nm. This is a unique phenomenon observed in micro-bump solid joints.