Effects of additive formula and plating current density on the interfacial reactions between Sn and Cu electroplated layer

Electroplating Cu technique becomes more and more important in advanced three-dimensional integrated circuit (3D-IC) packaging because of its advantages in the electrical/thermal conductivity, low cost, and hole-filling performance. Formula of the Cu electroplating solution, especially the additive like suppressor, accelerator, and leveler, plays a crucial role in the electroplating process. Previous studies have indicated that some organic impurities originated from the additives were incorporated in the Cu plated layer during the electroplating process. Moreover, the incorporated organic impurities segregated to the interface between the Cu plated layer and solder in a solder joint and led to formation of voids at the Cu/solder interface. In this study, effects of additive formula and plating current density on the Cu/solder interfacial reactions thermally aged at 150 and 200 degrees C. were further investigated. If the additive formula contained only suppressor, the grain size in the Cu electroplated layer became bigger and the void quantity reduced as the current density reduced. However, when accelerator was added in the plating solution, an opposite trend was observed. The grain became smaller and a larger number of voids formed at the Cu/solder interface as the current density reduced.