| In this paper, the organic acid was chosen as the activator of the flux. Chosen the contact angle, spreading property and TG thermal decomposition property as the scale index to filter the activator and then optimize it. High and low boiling point solvent compound treatment was adopted to confect flux, then all kinds of the component of the flux was optimize utilized the analytical method of variance in the orthogonal design. The properties were tested according to the industry standard and then contrasted with homemade choiceness flux. Every kind of made flux was mixed with Sn37Pb soldering tin micro-powder or Sn3Ag2.8Cu lead-free micro-powder separately to make solder paste, then comparative studied the jointing capabilities. The results showed that:(1) The contact angle of citric acid and malic acid spreading in the not oxidated copperplate was small. The acid whose solder-assist was better and the corruption in low temperature was feebleness could be chosen as the activator in the flux. No only did the triethanalamine has good soldering-assist but also could regulate the pH value of the flux, could be chosen as the regulator. Polymethacrylates was a good kind of film former material which could be used in making active substance—the capsule wall of micro encapsulation. The decomposing characteristic of citric acid and malic acid satisfied the compound demand and early compound proportion is 5:2. The best compound proportion of organic acid, organic amine, film former was equal to 7:3:20±1. After micro encapsulation treatment, the compound activator was the best one to make flux.(2) The colophony based flux was milk white ropy liquid, the pH value was 6.45.The growth rate of lead-free solder paste was 81%. And could never find corrupt tract after causticity test, and only a little colophony leftover could be find. The content of activator in No-clean flux was 3%, and the pH value of the flux could approach to 6 after joining some triethanalamine. The growth rate of lead-free solder paste was 84%, zero causticity after weld and the leftover was infinitesimal. The preparation techniques of water-solubility fluxwas more complex,the flux was salmon pink ropy liquid, the pH value was 6.2.The activator after micro encapsulation treatment could be reduced to the lowest one, but never effected the activation. The growth rate of lead-free solder paste was 81%.The leftover was mainly water-solubility sheltered rosin after weld, and was easy to wipe off by bath.(3) The proportion of No-clean solder paste between solder powder and flux was 8.5:1.5,the water-solubility solder paste was 9:1 and the colophony solder paste was 8:2. All of the three solder pastes could form plump and splendid solder point, and the appearance of Sn-Pb solder point was more regular and sleek. The solder ball assess grade was 3 stage upwards,others were all 1 stage.(4) The growth rate of Sn-Pb based solder paste approached to 90%,and the growth rate of lead-free solder paste was hopeful to 85%.The contact angle of Sn-Pb based solder paste could be controlled to below 10°,and lead-free solder paste was not preponderate over 20°.The thickness of IMC in Sn-Pb based solder paste was about 2～4um,and the lead-free solder was 4～6um.The grain of solder in Sn-Pb based solder paste was thin and the property of the solder paste was fine. The grain of lead-free solder paste was thick and microstructure was complex.
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