Reserach On The Preparation Of The Au-20Sn Eutectic Solder And The Microstructure Of The Interface Of The Joints

With the development of the information industry and the advance in electronic packaging technology,the research and application of high-performance lead-free solders have received increasing attention.The Au-20Sn eutectic solder is widely used in the packaging of optoelectronics and high power electronic devices due to its high thermal conductivity and strength,as well as oxidation,thermal fatigue,and creep resistance properties.The Au-20Sn solder is very brittle,so it is difficult in further fabricating solder sheets and rings required for by packaging traditional produced method.Therefore it is of great significance to prepare Au-20Sn solder by a rapid solidification process?RSP?,and systematically study the solderability.The Au-20Sn eutectic solder was investigated in this paper.The rapidly solidified solder ribbons were produced by a single roll device,and the microstructure and property after annealing were studied using OM,XRD,EPMA and MTS ceramics test systems.At the same time,the effects of soldering process and aging on the microstructure,shear strength and interfacial intermetallic compound?IMC?layer evolution of Au-20Sn/Ni?Cu?solder joints were investigated.The microstructure of annealing ribbons was eutectic,and with the extension of annealing time,the?-AuSn phase gradually grew up,resulting in the increase of its volume fraction.When the annealing temperature increased,the?-AuSn phase was obviously coarsened and increased.All things considered,the optimal annealing process was at 200°C for 8h with the fracture strain 3.07%.After soldering,the eutectic structure and?Ni,Au?₃Sn₂IMC layer formed in the solder and Au-20Sn/Ni interface,respectively.With the prolonging of soldering time,the eutectic structure became coarse,and the IMC layer thickness increased.When the soldering temperature rised,IMC layer formed and grew faster.After aging,the compound layer of?Ni,Au?₃Sn₂and?Au,Ni?Sn layers formed at the interface.With the increase of aging time,the IMC layer thickness increased and was controlled by the volume diffusion.As the soldering temperature increased,the growth rate constant k of IMC layer became larger and the kinetic exponent n decreased,resulting in the IMC layer thickness increased,and the reduce of shear strength.After soldering the fan-like?-?Au,Cu?₅ Sn and?Ni,Au,C u?₃ Sn₂IMC formed at the Cu/Au-20Sn interface and Au-20Sn/Ni interface,respectively.With the prolonging of soldering time,the eutectic structure was gradually consumed,yielding the growth of IMC layer.With the prolonging of aging time,?Au,Cu?₅ Sn IMC layer and?Ni,Au,C u?₃ Sn₂IMC layer formed at the two interface,respectively.At the same time,their growth was mainly controlled by the volume diffusion.When the aging temperature rised,the k and n increased and reduced,respectively.The copper on the substrate could diffuse to the lower interface,generated coupling reaction and restrained the growth of IMC layer.