A study for a typical leakage failure of PCBA with no-cleaning process

Low solids flux/paste (Users like to refer as “no-cleaning”) had been widely used driven by pressure of cost reduction, environmental protection and worker safety. The advent of low solids flux/paste put electronics manufactures into a common misconception that cleaning had become a concern of the past and cleaning process could be removed. In fact, no-cleaning approach is often not a viable option. It was found use of no-cleaning flux had caused many current leakage problems from statistic analysis of failure cases analyzed by our center (RAC, CEPREI) every year. In this paper, a typical leakage failure on PCBA with no-cleaning process was detected in humidity & heat environment. Test methods including visual examination, insulation resistance test, PTI, water absorption, FTIR and ion chromatography analysis were applied to investigate the root cause of this failure. It was concluded that leakage was attributed to ionic bromide residues which came from the pyrolytic dissociation of covalent bromides in flux under high soldering temperature. It is suggested to use ion chromatography measure ionic halides on critical locations with residues of board after reflow before removing the cleaning process.