Development Of Halogen-free Flux For Sn-0.7Cu Lead-free Flux-cored Solder Wire

Lead-free solder is an inevitable trend.Among lead-free solders,Sn-0.7Cu lead-free solder has good physical and mechanical properties,and it is one of the lowest-priced lead-free solders,so it is widely used in electronic packaging to replace traditional Sn-Pb solder.However,the wettability of Sn-0.7Cu lead-free solder is insufficient,leading to the higher requirements on flux activity.At the same time,because of the limitation of halogen content,etc.,the flux faces more restrictions.Under the restrictions such as halogen-free and VOC-free,it is necessary to develop a flux for Sn-0.7Cu lead-free flux-cored solder wire with good activity,less spatter and low smoke.This study takes Sn-0.7Cu solder as the research object to test the influence of each component on the performance of the flux,so as to select and optimize each component,and analyze and improve the general deficiencies of the flux.Finally,a halogen-free rosin-based flux was prepared.Research indicates:(1)Using spreading rate,smog size as indicators,it was found that water-white hydrogenated rosin has small smog,but slightly low activity,full hydrogenated rosin has slightly high activity,but heavy smog.When the both are used as a carrier,the overall activity of the flux can be guaranteed,and the smog can also be reduced.On this basis,compounding rosin is carried out.When the mass ratio of water-white hydrogenated rosin and full hydrogenated rosin is 6:13,it has higher activity and the smog of the flux have been significantly reduced.(2)Using the spreading rate,residual after welding,and decomposition pressure etc.as indicators.Comparing the effects of different organic acids and anhydrides on these properties,it was found that the activities of diglycolic acid,glutaric acid,and adipic acid were high with low residual after welding,and hopefully obtaining the high comprehensive performance.The Uniform formula design experiments on them was conducted,and the results showed that when the mass ratio of diglycolic acid,glutaric acid and adipic acid is 0.158:0.456:0.386,the activity is high and the smog is less.The three activators are mixed in this ratio as the compound activator,and the effect of the addition amount on the flux performance is explored.The research results show that the effect is best when the compounded activator content is 11wt%,the activity is high and there is no obvious residue.(3)The effect of the solvents and surfactants on the performance of the flux is studied.The results showed that the content of the solvent is positively correlated with the decomposition pressure of the flux.The addition of rosin surfactant can not only increase the flux spreading rate,but also increase the wetting speed.The spreading rate increases with the content of rosin surfactant first and then decreases.(4)In the orthogonal experiment of the activity enhancer,it was found that a small amount of iodized salt had a significant effect on the expansion rate of the flux,and as the addition amount increased,the expansion rate increased.A small amount of p-toluenesulfonic acid monohydrate had insignificant effect on the expansion rate.(5)The the addition of polyamide can reduce the decomposition pressure,and the bubble release inhibitor A containing long-chain siloxane can significantly change the gas release mode.