Eliminate Kirkendall voids in solder reactions on nanotwinned copper

Electroplating was used to fabricate a high density of nanotwins that exhibited the preferred (1 1 1) orientation in Cu. We found no formation of Kirkendall voids in solder reactions on the nanotwinned Cu. This was due to the high density of steps and kinks on the nanotwin boundaries, which serve as vacancy sinks. Thus the vacancy concentration cannot reach supersaturation and nucleate voids. The finding is a significant advance in the problem of solder joint reliability in microelectronic three-dimensional integrated circuit devices.