Effects of current density on the solder wettability of nickel electrodeposited ni20cr alloy

Abstract

Nickel-chromium alloys are in high demand in the electrical industry, as they have some favorable electrical properties. The formation of a thin chromium oxide layer on the alloy surface protects the alloy from further oxidation. The passivation layer formation is almost instantaneous when exposed to the ambient atmosphere. It prevents the strong bonding between the solder and the substrate due to the alteration of the substrate's surface energy by the passivation layer. Poor solderability could cause short-circuiting and resistance variations in electrical devices. This paper reviews the effect on solderability due to the passive layer formation and proposes solutions to overcome the problems caused by this layer. The introduction of solder-compatible metal layers such as Ni onto the substrate surface is a way to overcome this. However, solder-compatible metals such as Ni cannot be introduced with conventional electroplating baths due to the alloy's passive behavior. Therefore, a breakdown of the passivity is required before the nickel coating. A three-bath electrodeposition strategy comprising; pre-cleaning, activation, and electroplating, were used to achieve the task. The study examines the dependency of solder wettability on the current density, using an in-house fabricated contact-angle measuring device and analytical software.