The Preparation Of Lead-free Solder Paste Containing Zinc And Its Performance Study

Sn-3.0Ag-0.5Cu Pb-free solder(SAC305) has been widely used to replace toxic Sn-37 Pb solder in electronic industry due to its better wettability, solderability, physical and mechanical properties than other Pb-free solders, but the properties and development on domestic Pb-free solder paste is now unacceptable to use. On the other hand, with the minimize size on electronic products, the size on solder joint is also smaller, which makes a more important reliability on the drop and vibration performances of SAC305. In this thesis, we developed a new solder paste for SAC305 by mixing the soldering flux with optimized compositions and SAC305 solder alloy powder without or with minor Zn addition. The viscosity and thixotropic properties of solder paste was tested with rotary thermometer. The reflow soldering of solder paste was finished in ATV eutectic reflowing oven under air or vacuum condition. The shear strength on solder joints was tested with PTR-1103 shear tester. The microstructure and fracture surface were observed with optical microscope and JSM6480 scanning electronic microscope(SEM). The main collusions are listed as flowing:(1)An optimized composition on soldering flux was finished. It includes the film former comprising 30 wt.% ARAKAWA KE-604 rosin and 15 wt.% dimerized rosin DMER-145, the thixotropic agent comprising 5wt.% Hydrogenated castor oil(HCO) and 5wt.% Ethylene bis(EBS), the solvent decided with TGA results comprising of 18 wt.% Hexyl ether, 10 wt.% buthyl ether and 10 wt.% pentanediol, the activators decided from their solubility, wettability and corrosion resistance comprising organic acids mixed with 1.6wt.% adipic acid, 1.4wt.% succinic acid and 2wt.% glutaric acid, and further comprising an amine selected as 1wt.% diethanolamine, the corrosion resistor comprising 0.4wt.% 1,2,3- Benzotriazole and 0.4wt.% 8-Hydroxyquinoline, the anti-oxidation agent with 0.1wt.% Hydroquinone and finally the deodorant with 0.1wt.% menthol.(2)The above no-clean soldering flux shows very good dispensability, solderability and wetting characteristic, also it showed very good paste stability. The PH is about 5.5 to 6.0. The content of un-evaporated substances in the flux is about 34.79%. Compared with international famous products, it provides an acceptable viscosity, thixotropic characteristic, slump testing results and solder ball testing.(3)To improve the drop reliability of solder paste, minor Zn was added into SAC to get the Zn-contained solder paste. Compared with the above vehicle and international famous product, their spreadability is 88.2%, 86.3% and 89.8%, respectively. The wettability of Zn-contained solder paste was not affected with the Zn addition. Optical and SEM microstructure showed that the thickness of intermetallic compound(IMC) at the interface in the solder joint was decreased, and the shear strength was increased with the Zn addition. The fracture mode was ductile crack.