| Since the environmental problem has become a topic of common concern to the international community, the classic tin-lead solder paste within lead, gradually being left out of the mainstream market, SAC305 as the replacement product of tin-lead solder paste,has been well received,but because of the high price,it was difficult to be promoted in large area.lt is meaningful to study lead-free and halogen-free, low silver content solder paste for the promotion of lead-free solder paste.Raw materials of soldering flux is the main study object of this paper, the optimum proportion of soldering flux were screened out by the uniform experimental design and the performance of soldering flux were tested. Then collocated this soldering flux with Sn0.3Ag0.7Cu alloy solder powder to form the unleaded soldering paste, which had a performance comparison with the homebred soldering paste under the test standard. The research results are as follows:(1)Rosin were selected as film forming agent, its content in the system is 25wt%, hydrogenated rosin and polymerized rosin were compounding, and its compounding ratio is 2:3. Through unifom recipe design, solvent system were studied. Tetrahydrofurfuryl alcohol,diethylene glycol diethyl ether and glycerin were screened as solvent with ratio 11.8:2.6:1,which showed good volatilization performance and solubility property.(2)Acid a, b, c were selected as activators to compound, through the uniform experimental design, its optimum compounding ratio is acid a:acid b:acid c=26:1:23. Triethanolamine were used as Acidity regulator and its content is 0.4wt%. Two kinds of nonionic surfactants, OP-10 and TX-10 were compounded, with spreading areas as index,its optimum compounding ratio is OP-10:TX-10=5.3:1,and its content is 0.95wt%.(3)Based on the principle of soldering flux, combined influence on spreading areas of activators, film forming agent and surfactants were studied, the final optimized formula of soldering flux is with rosin system 25wt%, activator 5wt%, thixotropic agent lwt%, both antioxidant and corrosion inhibitor were 0.5wt%, Triethanolamine 0.4wt% and the rest were solvent.(4)The developed halogen-free flux was a thick milk white pasty fluid, with stable physical properties, good wettability, low corrosiveness,nonvolatile matter content 23.18% and fine combination property.(5)The alloy solder powder that used in this experiment is No.3 solder powder of Sn0.3Ag0.7Cu which with low silver content, its powder form was sphere, biggest aspect ratio was 1.16. The mass ratio of soldering flux and solder powder was 88.5:11.5, tested viscosity was 178.0 (Pa-s,25℃),coefficient of thixotropy (Ti) was 0.54, with favourable stripping results and printing effect.(6)Compare to the homebred soldering paste, the own-made solder paste tin beads appeared a little solder ball after been placed for 4h which reached the level 2 evaluation standard of the solder ball test and the homebred soldering paste reached level 1 evaluation standard, both were conform to commercial standard. The own-made solder paste has favorable wettability, not showed anti wetting phenomenon or non wetting phenomenon. With no splash around the welding spot, assessed it as level 1. Rate of spread test were carried out on both the own-made solder paste and the homebred soldering paste, their spread rate were 92.5% and 89.8% respectively, both spread rate were reached level H.(7)Hot and cold collapse test were carried out on both the developed solder paste and the homebred soldering paste,0.2 mm thick screen printing template were used to print bonding pad A (0.6mm×2.03mm) and bonding pad B (0.33mm×2.03mm),0.1 mm thick screen printing template were used to print bonding pad C (0.33mm×2.03mm) and bonding pad D (0.20mm×2.03mm), both the developed solder paste and the homebred soldering paste could meet technical requirements, and the bridged space of the two were very close, which means good hot and cold collapse performance. Shear strength test were carried out on both the own-made solder paste and the homebred soldering paste, and their Shear strength were 33.33Mpa and35.62MPa respectively. |
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