Observed correlation of Sn oxide film to Sn whisker growth in Sn-Cu electrodeposit for Pb-free solders

Localized cracking of surface oxide has been proposed as a necessary step in the nucleation of Sn whiskers in Sn electrodeposited films. To evaluate the effects of the oxide film on Sn whisker growth, a bright Sn-Cu electrodeposited film was inserted into an ultrahigh vacuum Auger system, cleaned using an Ar+ ion beam to remove the oxide film, and aged in the 2 X 10(-9) Pa Auger system chamber. Whiskers and other features present during Ar+ ion cleaning left visible "shadows" on the surface. During aging in the ultrahigh vacuum system, new whiskers, identified by the absence of the telltale shadows, nucleated and grew. Based on these observations, the presence or absence of an oxide film has. a minimal effect on Sn whisker nucleation and growth.