EVALUATION OF PLASMA TREATED HASL FINISH PCBs USING DCA MEASUREMENTS

Abstract

The use of plasma as a method of preparing PCBs and components prior to soldering is being investigated by the electronics industry as an alternative method to the conventional flux application. High surface energy is a requirement for improved wettability and good solderability. The surface energy of a solid is an important quantity which cannot be obtained directly by measurement. It can be obtained by contact angle measurements using probe liquids. In this paper, the methodology of dynamic contact angle (DCA) analysis is described and demonstrated for the assessment of the removal of organic contaminants from hot air solder levelled (HASL) finish PCBs by plasma cleaning. The DCA data was compared with Auger surface analysis results and SEM micrographs in order to obtain a complete profile of the surface in terms of the level of cleanliness. In the study, PCB samples were plasma treated under different plasma conditions using Xe/O2/Ne and Xe/O2/Ar gas combinations. The DCA results show a substantial decrease in advancing contact angles between the control and plasma treated samples. This indicates an increase in both surface energy and wettability which is confirmed by the lower carbon (organic contamination) levels in the Auger results. SEM micrographs of as-received plasma treated and untreated samples show a cleaner (wettable) surface in the case of the plasma treated sample and a poor (non-wettable) surface for the untreated sample. The results indicate that plasma treated HASL finish PCBs using Xe/O2/Ne gas mixtures can reduce organic contaminants to levels that will promote fluxless soldering.