Halogen-free Flux With Low Content Of Modified Rosin For The Lead-Free Solder Wire

With Pb and Pb compounds, there is an increasing impact of environmental pollution and human health, the lead-free electronic products become the inevitable trend of the development of electronic industries, However there is a considerable gap between the lead-free solder alloy and the SnPb solder alloy for weld-ability because the lead-free solder alloy has the higher melting point, easily oxidized and poor wettability. Adding Cu to the SnAg alloy can not only reduce the melting point of the lead-free solder, reduce the corrosion of the substrate material, but also does not need a significant adjustment to the existing welding technology and equipment, Although there is a big gap compared with the SnPb lead solder, the SnAgCu alloy has been recognized as the best alternatives for the SnPb solder alloy.When the component of the lead-free solder alloy is determined, the solder alloy weld-ability primarily depends on flux, due to the poor physical and welding properties of the lead-free solder, so developing a suitable lead-free solder flux is very important. In this study, based on the using principle of the solder wire flux and its physical and chemical properties, the flux components have initially been chose, then by experimental results, the kind and the content of the flux components has been determined, finally, a flux good for the SnAgCu solder wire has been developed according to the process requirements of the lead-free solder wire.In this study, we choose the different boiling points and decomposition temperatures of the organic acids as the composite activators based on a certain amount of the water white modified rosin and a certain amount of the ethanol. Through the spreading rate experiments, we determine the DL-malic acid, the succinic acid and the adipic acid as the component of the composite activators. Through the optimization test, we determine the best effect of DL-malic acid: succinic acid: adipic acid is2:6:5; Then we choose the different boiling points of the organic solvents when a certain quality of the water white rosin and the certain quality of the activators which has been determined by the optimization test. Through the orthogonal and optimization test, the optimum percentage of ethanol: tetrahydrofurfuryl alcohol:diethylene glycol ether:diethylene glycol butyl ether is1:2:3:0; through the orthogonal and optimization test, the best content of the polymerized rosin is1%, the lead-free rosin is5%, the rosin is2%and the water white rosin is0%; through the spreading rate experiments and orthogonal test, the best surfactant content of the AEO-7is0.6%, the span60is1.8%and the span80is1.8%; through the similar method, the optimum percentage content of other components has also been determined.Subsequently, we analyze the properties of the lead-free solder flux, and according to the requirement of the national standard, we analyze the performance test of the flux, the results show that the flux has the good solderability, and reaches the electronic industry standards.