Development Of A Soldering Flux For Lead-free Solder Wires In Soldering Process Of Electronic Packaging

The use of cleaning-free and zero-halogen rosin-based flux is gradually increasing in the lead-free electronics packaging field, owing to its advantages of safety, eco-friendly and good reliability. However, there is very little research about the flux which is not well-studied enough to replace the traditional flux. In this thesis study, the effect of carriers, activators, surfactants, high boiling point solvents and membranous plasticizer on the performance of the flux was investigated and then the compositions were optimized.The test of spreading, surface resistivity, maximum decomposition pressure, smoke, pungent odor and the methods of orthogonal experimental design and thermal gravimetric experiment are performed to study the influence of different components on the flux. The main conclusions are as following:(1)When rosin 125 and colorless hydrogenated rosin mix as carriers with the proportion of 2:3, the flux showed high expansion rate and surface resistivity, less smoke and maximum decomposition pressure.(2) The optimized content of activators is 4.0 wt%-6.0 wt%, with which the flux exhibits high activity and SIR value is higher than 1×108 Ω, meeting well the requirement of the standard. The optimized mixing ratio of succinic acid amine, sebacic acid and glutaric acid is 1:2:6 when the total amount is 6.0 wt %. Combined activators with reasonable activity gradient enables flux to keep effective in a large temperature range,while wettability having been improved significantly..(3) Adding FSN-100 in the flux with an amount of 1.5wt% can obviously improve the wettability of the flux.(4)The amount of high boiling point solvent which is based on 2-Butoxy ethanol and supplemented with DBE is optimized to 3 wt % and the proper proportion of the two solvents is 4:1.Practical effects of flux were examined by simulating actual usage, applying the solder wire with rosin-core flux to the heated soldering iron tip. The result shows that welding speed was slow, and spitting problem was found. A highly active iodate D2 is added to the original formulation with the proportion of 0.7 wt% to improve the welding speed with other properties unchanging. The plasticizer staybelite ester is helpful to reduce spattering rate and improve electrical performance after soldering. And the optimal amounts content of staybelite ester is 7.0wt%. After making rosin-based flux according to the new adjusted formulation, the overall comparison in processing performance between our soldering flux and other two commercial soldering fluxes shows that the flux developed by this thesis study has superior processing properties over the commercial flux of cooperative corporation, but not as good as the other one.