Abstract: Glycolic acid and phthalic acid were used as weak organic acid activators of halogen-free rosin-based flux that was utilized to solder low silver content SAC105 solder on Cu substrate. The influence of activators content and the corresponding proportional ratio of glycolic acid and phthalic acid on the solderability,spreading rate and electronic stability was studied. It is found that,the adequate solderability and spreading rate of SAC105/Cu can be achieved by using the designed flux with 4 wt. % of weak organic acids consisted of glycolic acid and phthalic acid with a proportional ratio of 1∶ 1. In addition,by using aforesaid flux,very few residues are left with strong electronic stability via the evaluation of surface insulation resistance,which indicates the failure due to ionic migration under hygrothermal condition can be avoided. Therefore,glycolic acid and phthalic acid have the potential for commercial use in soldering flux.