Abstract
A quantitative evaluation method of solder bridging in micro-soldering has been established using a printed wiring board with copper comb pattern conductors. Bridge tests were conducted by immersing the comb pattern board into molten solder bath. The total length of solder bridging between conductors against the total length between conductors was measured as a measure of the occurrence of solder bridging. The occurrence of bridging depended on the number of immersion, flux activity including solid content, conductor spacing, solder bath temperature and solder composition. The increase in number of immersion enhanced bridging. The rosin flux without activators showed higher bridging than the activated flux. Sn-37Pb solder showed lower bridging than Sn-3.5Ag-5Bi solder. Solder bridging was found to be closely correlated with wettability, therefore, the improvement of wettability could be effective to suppress solder bridging. The proposed method is believed to be suitable for the evaluation of solder bridging.
