Suppression of Kirkendall Voids at the Interface of Sn/nc-Cu Solder Joint

Electroplated Cu film plays an important role in electronics, communications, aerospace and other fields. With DC plating, nanocrystalline Cu (nc-Cu) film was prepared by a new plating solution and commercial nanocrystalline Cu (cnc-Cu) film was prepared by a commercial plating solution in this paper. Sn/Cu solder joints formed by reflowing pure tin on the Cu films at 250 °C for 1 min were aged at 150 °C for 50 h, 200 h and 500 h. It was found that no Kirkendall voids formed at the Sn/nc-Cu interface, while a large number of Kirkendall voids formed at the Sn/cnc-Cu interface. More impurities in the cnc-Cu could reduce the vacancy formation energy and then promote the aggregation of vacancies to form voids. Impurities could also hinder the growth of Cu grains, which could produce more grain boundaries and promote the generation of Kirkendall voids at the boundaries. Therefore, the Sn/Cu solder joints prepared by nc-Cu showed significant suppression of Kirkendall voids, which should be benefit to improve the reliability of electronic products in service.