| In this paper, The essential ingredient of flux for microelectronics soldering-organic acid activator's fluxing capacity was studied by measuring the spreading property of Sn37Pb eutectic alloy on copper substrate. The microstructure and intermetallic compounds on the interfacial layer of Sn3.0Ag2.8Cu/Cu solder jonts were investigated at different aging time.The effects of electroplated Ni layer and electroless plated Ni(P) layer on the diffusion behavior in Sn3.8Ag0.7Cu/Cu solder joint were also studied.(l)The content of activator in flux has an optimum value. Comparing with single activators, fluxes contening multiplex activators indicate excellent fluxing capacity. On base of which a flux with good properties was synthesized and a series of experiments according to different standards were performed to evaluate the reliability of the flux and test results showed the flux has characteristic of low residue, no corrosion and no cleaning after soldering.(2)After different times of aging,the growth rate coefficient of intermetallic compounds in Sn3.0Ag2.8Cu/Cu soldering joint is 5.65×10-1μm/h1/2, while Sn37Pb/Cu is 4.76×10-1μm/h1/2, the result showed the reaction rate between Sn3.0Ag2.8Cu solder and copper is fast than Sn37Pb solder and copper.(3)The results by EDX analysis show there was a IMC layer of IMC ((Cu,Ni)6Sn5) at interface of Sn3.8Ag0.7Cu/Ni / Cu and Sn3.8Ag0.7Cu/Ni(P) / Cu soldering joint. The electroless plated Ni(P) layer acted as a good diffusion barrier between Sn3.8Ag0.7Cusolder and Cu substrate. However, the electroplated Ni layer can not substantial hinder the interdiffusion and reaction between Sn3.8Ag0.7Cu solder and Cu substrate, indicating electroless plated Ni(P) layer can obviously decrease the generation of Sn-Cu IMC at the interface of SnAgCu / Cu, which is beneficial to improve the reliability of solder joint.
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