Evolution Of The Interface Organizational And Mechanical Properties Of SnAgCu/Cu Solder After Aging Process

In this study,the formation,morphology,size and performance of interface intermetallic compound(IMC)in SnAgCu/Cu solder joint had been researched after isothermal aging,thermal cycling and thermal-mechanical coupling.The growth law and diffusion activation energy of the IMC layer also had been calculated.The evolution of microstructure and morphology of SnAgCu/Cu solder joint interface were observed by metallographic microscopy and scanning electron microscopy.The composition of interface IMC was tested by X-ray diffraction and energy dispersive spectroscopy.The mechanical property of SnAgCu/Cu solder joint were tested by INSTRON5948 micro tensile machine,use scanning electron microscopy to observed the morphology of tensile fracture.Control the solder thickness respectively at 0.1,0.3,0.5,0.8 mm and the welding time respectively at 80,100,120,140 s to make a series of SnAgCu/Cu solder joints.Through observed the solder joint interface morphology and the tensile test experiment,it was found that with the increase of solder thickness the tensile strength of the solder joint were decreased.The tensile strength was stabled when the solder thickness control at 0.5 mm.Along with the welding time increased,the IMC serrate became bigger and the thickness of the whole IMC layer gradually increased,tensile strength of the solder joint were first increased then decreased.When the welding time control at 120 s the property of the solder joint best.The isothermal aging experiments showed,after welding the interface IMC present as a small serrate.Along the aging temperature increased and aging time prolonged,the interface IMC layer constantly grow up,the grow speed became slowly.The number,radius,height and distance of IMC serrate respectively became reduced,bigger,higher and larger.Analysis the two dimensional area of a certain three dimensional volume IMC,based on diffusion theory,the relationship between IMC equivalent thickness and aging time is x-x0 = A0 exp(-?H/RT)t,found that the IMC's activation energy is 88kJ/mol.Along the aging time prolonged,the tensile strength of solder joint was first increased then reduced.Also the solder joint dimple became more and more big.The section of the IMC serrate was smooth.The thermal cycling experiments showed,with the cycle increased the IMC equivalent thickness gradually increased.It could be found that when the cumulative time of the high-temperature was same the size of the interfacial IMC also basically the same.In low temperature condition,the thickness of the IMC almost didn't change.The IMC grow speed at 0 ??125 ? thermal cycle was slower than that at-20 ??125? thermal cycle,the tensile strength of the solder joint were first increased and then reduced with the cycle increased.The solder joint dimple became bigger because the growth of IMC serrate.Contrast the thermal cycle and the isothermal aging,it can be found that when the high-temperature time was same the IMC growth faster under isothermal aging,the reason was that solder joint didn't experienced low-temperature process the interface diffusion keeps high speed under isothermal aging.In thermal-mechanical coupling experiment the solder joint would be influenced by external stress,which made the IMC growth rate slower than in thermal cycling.The component test of actual solder showed that in domestic market the electronic products sold in the nearly two years were still used the traditional Sn-Pb solder.Even so the content of the Pb are decreasing year by year,the lead-free solder also had a long way to go.The most serious problem faced in the use of lead-free solder is the welding reliability.The interface IMC is the key factor of the wilding reliability,so it is significance to research the evolution of interface IMC.