Study On Antiaging Performance Of Two Kinds Of Hot Press Soldering Joints For Microwave Power Device

With the development of microwave power devices towards high efficiency,high breakdown field strength and low power consumption,higher requirements are also placed on the welded joints which play the role of thermal,electrical and mechanical connections in the package.The Au80Sn20 solder with the melting point of 280 ℃,has the advantages of both excellent corrosion resistance and good thermal conductivity,is widely used in microwave power devices.However,due to the high soldering temperature of Au80Sn20 solder,it will affect other materials in the package.Meanwhile,the material cost is higher,which affects the application of the solder in the electronics industry.Therefore,in order to reduce costs,while ensuring the reliability of interconnected micro solder joint,This paper investigated the Au80Sn20 solder and Sn-0.7Ag-0.5Cu-3.5Bi-0.05Ni（hereinafter referred to as SAC0705-Bi-Ni,the melting point of 225 ℃）solder that is developed independently by our laboratory.By means of accelerated high temperature aging method,the interface microstructure evolution and mechanical properties of the two kinds of hot press soldered joints were studied.The antiaging behaviors of the two kinds of hot press soldered joints were comparatively analyzed.The influence of hot press process parameters on the interfacial evolution of micro-solder joints（Chip / Au / Au80Sn20 / Au / Ni / Cu）was analyzed.The high temperature dwell time and the peak temperature of the hot press soldering on the chip side of the Au layer consumption and the growth of interfacial compound（IMC）were revealed.The consumption rate of the Au layer on the chip side and the growth rate constant of the IMC layer at the interface were obtained under the six hot press process parameters.The results show that the peak temperature of hot press soldering and hot dwell time have a significant effect on the consumption of Au coating and the growth rate of IMC during the high temperature aging process.When the peak temperature is kept as a constant,the change rate of the consumption rate of Au coating layer and the change rate of the growth rate of interface IMC layer both show increase trend with the increase of holding time at liquid temperature.Comparing with the samples that soldered at hot press soldering temperature of 300 ℃ for 90 s,the change rate of consumption rate of Au coating of samples soldered at 320 ℃ decreased by 24.50% and the change rate of the growth rate of interface IMC layer increased by 56.09%.The IMC on the chip is（Au,Ni）₅Sn,and the eutectic structure（Au5Sn + Au Sn）in the bulk solder gradually becomes coarse with the increase of aging time,and a layer of（Ni,Au）3Sn2 appears below the IMC layer on the heat sink side.With the precipitating of（Ni,Au）3Sn2 phase,the Au Sn phase in the bulk solder will be consumed and the eutectic structure in the bulk solder will be destroyed,resulting in a large amount of dispersed（Au,Ni）₅Sn in the bulk solder.The influence of hot press process parameters on the performance of microsolder joints（Chip/Ni/Au/SAC0705-Bi-Ni/Ni/Cu）was analyzed.The interface evolution of micro-solder joints was revealed under this brazing process（hot press soldering peak temperature of 260 ℃,high temperature holding time of 60 s）.The results show that with the increase of aging time,the IMC layers on both sides of the interface are continuously thickening,but the increase rates are different.The thickness of interface IMC layer shows a linear relationship with the square root of aging time,which indicates that the increase of IMC layer thickness is controlled by element diffusion.The IMC at the interface between SAC0705-Bi-Ni and Ni substrate was found to be of（Ni,Au,Cu）3Sn₄.The IMC at the interface of SAC0705-Bi-Ni and ENIG layer was（Ni,Cu）3Sn₄.The needlelike（Au,Ni）Sn₄ dispersed inside the bulk solder.With the increase of aging time,the（Au,Ni）Sn₄ gradually moves to the interface of the two sides and adheres to the top of the generated interface IMC layer.The anti-aging properties of the two kinds of hot press soldered joints were analyzed.It was found that the growth rates of the interfacial IMC layers of the Au80Sn20 and SAC0705-Bi-Ni joints at the same aging temperature were 3.29×10-7 μm2·s-1 and 1.48×10-5μm2·s-1 respectively.The shear strength of the SAC0705-Bi-Ni hot press soldered joint is 9.71% lower than the Au80Sn20 joint.This is because the main constituent of SAC0705-Bi-Ni bulk solder is needle-like dispersed（Au,Ni）Sn₄ and Bi particles,but the main constituent of Au80Sn20 bulk solder is a homogeneous eutectic structured（Au5Sn+Au Sn）and thus improve the strength of the solder.