Study of the effects of PCB surface finish on plasma process time for lead-free wave soldering

Purpose - The purpose of this paper is to investigate the end point of the plasma cleaning process, in order to save valuable production time and also to prevent the destruction of expensive devices through overheating. Design/methodology/approach - Post plasma cleaning analysis using dynamic contact angle (DCA) analysis and video microscope observations have been conducted on plasma treated Entec coated copper, hot air solder levelled (HASL) and electroless nickel immersion gold (ENIG) surfaces in order to determine the effect of surface finish on plasma process times. Post plasma cleaning and lead-free wave soldering analysis of the three surface finishes have been evaluated. Findings - The DCA results indicate that the end-point for plasma cleaning of Entec coated copper is achieved within one to three minutes (indicated by a low contact angle hysteresis). Further cleaning after three minutes may lead to surface degradation and poor solder wettability. This is consistent with the results of the video microscope observations which show well soldered component leads and pads with good solder coverage for copper surface finish treated at a short plasma process time (one minute) and poorly soldered component leads and pads for a surface treated at a long process time (ten minutes). Similar work conducted on HASL and ENIG finishes show better results (well soldered component leads and solder pads) for longer plasma process times of five to ten minutes. Originality/value - This paper indicates that plasma process time determines the wettability and solderability of the treated samples. It shows that the plasma conditions including the process time must be optimised and characterised for every application in order to avoid damage to expensive devices. The findings also give the confidence to implement plasma cleaning of lead-free (99.35n/0.7Cu) solder PCBs for fluxless soldering.