Assessment of Lead-Free Inert Gas Soldering Using a Novel Reflow Technology

A lead-free surface mounting process was assessed using an inert gas soldering with a novel reflow technology and compared a conventional reflow oven with a conventional lead. Three different soldering processes were performed based on reflow atmospheres, which were considered on a Sn-37Pb board finish. These conditions were with an ERSA Hotflow-7 (100% air), T-TRACK (100% air) and T-TRACK (nitrogen). The ternary lead free solder paste Sn-3.0Ag-0.5Cu solder paste was compared to Sn-36Pb-2Ag as reference with both no-clean and water soluble fluxes. The experimental investigation commenced with temperature profile optimization of both the T-TRACK and ERSA Hotflow 7 reflow oven. The boards were aged in a temperature/humidity chamber under the influence of 85degC/85%RH for a period of 30days. The solderability results were also analysed, where factors such as wetting, solder balls, bridges and solder joint shape with conformal coating integrity were considered. Board cleanliness and flux residues of the different fluxes were examined. The visual inspection result shows better wetting when reflowed in inert nitrogen gas. The void content was slightly lower in T-TRACK (nitrogen) than ERSA Hotflow-7. The result shows that T-TRACK (nitrogen) is the preferred process with respect to shear strength. The shear strength result shows that unaged-samples attained a higher shear strength value compared to the aged ones. The shear strength value of the T-TRACK oven attained a highest shear strength value when reflowed with inert nitrogen gas. In addition board cleanliness and flux residues were minimal and better with nitrogen when compared to 100% air