Study of fluxless soldering using formic acid vapor

This paper presents a systematic study of the use of formic acid vapor fluxless soldering with eutectic Pb/Sn solder. The study focused on the solder joint self-aligning process and the final alignment accuracy. The main effect considered was the formic acid vapor concentration. In addition, other effects of solder joint height and background vibration were studied. The self-alignment characteristics of the fluxless soldering process was as good as those using liquid flux at 220°C. 2 μm alignment accuracy could be achieved within 10 s. The most important parameter was the formic acid vapor concentration in the reflow chamber. The effective concentration window was found to be greater than 0.7% in volume