Investigating the effect of nitrogen atmosphere on lead-free solder wetting angle

In this paper the effect of nitrogen atmosphere on the quality of reflowed solder joints is presented. During the experiment, solder joints were formed in nitrogen and in air atmosphere. For comparing the nitrogen and air atmosphere, several test methods were applied using a FR4 class printed wiring board with immersion tin finish. The applied solder was a lead-free, tin-silver-copper (SAC) alloy, which was deposited by stencil printing onto the pads. The spreading of the solder after reflow soldering was inspected by optical microscopy and the wetting angle was measured by analyzing cross-sectional samples. For mechanical characterization, the shear strength of 0603 size chip resistors' solder joints were measured as well. The detailed results of the measurements are presented in the paper.