Lead free solder compatibility improvement on nichrome alloy through contact angle modification

Abstract

Nichrome (Ni/Cr) alloys which are used in many industrial applications are known to have a surface passivation layer of chromium oxide (𝐂𝐫𝟐𝐎𝟑 ). This layer alters the surface tension and thereby decreases the surface wettability in the case of soldering. This phenomenon is critically addressing in electronic applications such as electronic industry because, if the wettability inhabitance of nichrome thin films tends to reduce the solderability. In this study, liquid salt solution used in an acidic environment (ZnCl2/HCl) to remove the oxide layer and enhance the wettability. Lead free industrial solder alloy SN100C (Sn / Cu 0.70% / Ni 0.06% / Ge 0.005%.) was used as soldering material for this experiment. Solder drops were formed in 325-350°C temperature range, on the ZnCl2/HCl treated nichrome thin films. In order to evaluate the wettability changes, an experimental setup was developed to measure the contact angles of solder droplets on the nichrome thin films. A computer software was developed to process the image and letting the user to measure the contact angles by polynomial and ellipse fitting methods. The results of the study revealed that contact angle values were reduced by more than 50% after the ZnCl2/HCl treatment. Limitations of this study were stated and future improvements to enhance the wettability on nichrome thin films were suggested.