Surface wettability analysis of nichrome alloy based on the measurements of sessile droplet contact angles

Abstract

Nichrome (Ni/Cr) alloys are widely used in electrical devices due to their favorable electrical properties. However, these alloys are known to have a protective oxide layer on their surfaces. The presence of this oxide layer leads to a significant reduction of wettability of common solder materials on the nichrome surfaces. Poor solderability will cause loose connections and electrical resistance fluctuations. This paper discusses an attempt made to address this issue through electroplating. Instead of the conventional industrial approach, this study has adopted a contact angle based method to monitor the solder wettability changes. A new piece of equipment, together with analytical software, was developed to do the task. Electrodeposition significantly improved solderability on the nichrome surface. The contact angle reduction due to electrodeposition was over 60%. It was concluded that the passivation oxide layer was removed at the strike bath because of the reactions that occurred between the passive oxide layer and chloride ions. The formation of Ni-rich surface has favorably altered the surface energies to achieve better solderability.