Solderability testing in nitrogen atmosphere of plasma treated HASL finish PCBs for fluxless soldering

The global restrictions on the use of chemicals that emit volatile organic compounds (VOC), such as fluxes, has prompted the electronics industry to evaluate alternative methods to flux application. In this paper, the soldering performance of plasma treated hot air solder level (HASL) finish PCBs in nitrogen and air atmospheres have been evaluated using the wetting balance technique. The results were compared with the performance of conventionally flux treated samples soldered in air and nitrogen atmospheres and nonflux treated samples soldered in air. An oxygen level of 200 ppm (parts per million) was used for all tests conducted under nitrogen atmosphere. The gas mixture used for the plasma cleaning was two noble gases, xenon/neon (Xe/Ne), and a molecular gas, oxygen (O₂) to obtain the combined effect of both physical sputtering and chemical etching respectively for increased etch rate. The results of Auger chemical analysis show a significant drop in organic (carbon) levels for the plasma treated samples. The significant drop in the level of carbon (C) leads to a decrease in contact angle and an increase in both surface energy and solder wettability. The results indicate that plasma cleaning using the Xe-O₂-Ne combination is a viable alternative to the use of flux in nitrogen soldering atmosphere