| This work started from choosing the optimum component of fluxes through orthogonal experiment and some performance tests of the fluxes were proceeded accordingly. Then the chosen fluxes were mixed with Sn-Ag-Cu alloy solder to synthesize lead-free solder pastes. The following results are obtained from comparing the performances of resultant solder pastes with the purchased solder paste according to the standard.The major results are as follows:The main components of flux are rosin,activator,filmogen and solvent. In this work, the rosin was prepared by mixing refined hydrogenated rosin and water-white rosin with the ratio of 1:1;the activator was prepared by mixing citric acid and stearic acid with the ratio of 2:1; meanwhile, triethanolamine was added as a secondary activator and acidity regulator; the filmogen was decided to be polyethylene glycol 2000;the solvent of no-clean flux and rosin-based flux were both composed by ethanol,glycerol and diethylene glycol monobutyl ether while they differed in proportion(the former is 3:5:2,the latter is 3:4:3).The results indicate that the degree of influence on spreading areas varies with different components.In no-clean flux, the order is activator>temperature> rosin> solvent while in rosin-based flux it is temperature>rosin>solvent>activator. Examination of the two fluxes was carried out according to the standard:no-clean flux is milky white translucent liquid with PH value of 5.1 and 17.57% non-volatile matter. Rosin-based flux is light yellow transparent liquid with PH value of 5.4 and 26.56% non-volatile matter. The stability test of the two fluxes shows there isn't obvious appearance of delamination or crystals which means they can meet the request of utilization.The optimized fluxes were mixed with Sn-Ag-Cu alloy solder with different ratios to make different solder pastes. The ratio of flux to alloy solder in no-clean solder paste was 8.8:1.2,and in rosin-based solder paste it was 9:1.Then the performance of the prepared solder paste as well as the purchased solder paste was tested according to the standard. In the solder ball test, all the solder pastes are evaluated as 1 class in 15minutes (with the fluctuation of 5 minutes).After 4 hours (with the fluctuation of 15 minutes), the rosin-based solder paste and the purchased solder paste stays 1 class.The spreading area of no-clean solder paste, rosin-based solder paste and purchased solder paste is 36.72 mm2,39.84 mm2 and 35.94 mm2 respectively;the spread rate is 84.52%,87.35% and 85.48% respectively. After reflow soldering, the three solder pastes all have obvious IMC layer with different thickness:the no-clean solder paste is 1-3μm,the rosin-based flux is 1-5μm.They are both better than the purchased solder paste (4～6μm).
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