Study On Ultrasonic-Assisted Soldering Copper Plate With Tin-Based Lead-Free Solder

Electronic components applying in the aerospace,automotive manufacturing and other fields often work in harsh conditions,such as the high frequency,high power and extreme different temperature.So the reliability of the package solder joints need more demanding.In traditional soldering package solder joints,the introduction of flux in the connection process and residual after soldering often lead to solder joint porosity defects and pad second corrosion or other issues,which is not allowed absolutely in the aerospace field.Therefore,it is proposed that the introduction of ultrasonic-assisted soldering process,due to its unique "cavitation effect",can be used in soldering instead of flux to achieve the removal of the base oxide film.However,there are few studies on the application of ultrasonic in soldering at present in China.Particularly,the mechanism of anti-filming on the surface of base metal during ultrasonic assisted soldering is not very clear and it is necessary to conduct a further research.In this paper,ultrasound-assisted soldering with Sn-3.0Ag-0.5Cu soldering filler metal was carried out under the condition of no flux in atmospheric environment,using an ultrasonic soldering machine with an inherent ultrasonic power of 500 W and an ultrasonic frequency of 30 KHz,heated by an auxiliary heating device at a constant temperature of 240?process.Controlling ultrasonic amplitude and ultrasonic action time,under continuous ultrasonic application,the wetting and spreading behaviors of tin-based solder on the copper substrate under ultrasound were studied.The microstructure evolution and interface morphologies of soldering were observed.Analyzing the evolution of morphology,revealing the surface of the copper film to the membrane mechanism.The study found that:1.Ultrasonic wave propagate along the copper substrate with thickness of0.5mm in the distance from the center of the soldering location 0¹2mm around the scope of the effect with the distance increased first appeared and then weakened.Determining the distance from the center soldering position 8mm is the best soldering position.2.Under the action of small amplitude?20%?,the microstructure of?-Sn primary phase under the effect of ultrasonic cavitation appears obvious grain refinement with the extension of ultrasonic action time.While Ag₃Sn in the solder eutectic region is coarsened,which changes from granular-shape at 2s to a length of3?m plate-shape at 10 s,and Cu₆Sn₅ evolves from short rod-shape at 2s to a whisker shape at 10 s.The number increased obviously,whisker-like eutectic structure accounted for 50%of the solder ratio under the action of ultrasonic wave for 15 s.3.The extension of the time of ultrasound can cause the solder to wet and spread on the surface of the mother material.The effect of ultrasonic amplitude on the spreading coefficient is most obvious.Under the effect of vibration amplitude,the solder can be used to spread the wet parent substrate in a short time.Ultrasonic assisted soldering SAC305 solder/Cu process,and get good copper parent metal membrane and solder wetting under the condition of wetting Angle is greater than90°on the edge of the screen,and form a continuous at the interface between the intermetallic layer connection.With the extension of the time of ultrasound,the wetting Angle is decreasing gradually.4.SAC305/Cu solder joint interface goes to the film because of the plastic deformation of parent metal and oxide film in the ultrasonic time within 1-10 s,and come into being arc pit.Pit extents horizontally with increasing of time,the indentation depth generally remain at around 5-10 um without significantly increased;However,during the following 10-15 s ultrasound,the solder/parent material boundary was obviously transferred to the copper interior,and the pit depth was close to 20 um.5.By observing the evolution of the solder joint interface with the time of ultrasonic action,it is concluded that the breaking mechanism of the oxide film mainly includes four stages:the first stage:under the action of ultrasonic cavitation,the oxide film in the surface of the copper substrate undergoes deformation Cracks occur between the base material and the oxide film in the pit and the pit,and a fracture occurs at the bottom of the pit to generate a notch.In the second stage,the molten solder can enter into the notch and contact with Cu,and penetrate transversely along the crack on the Cu surface,So that the oxide film on the surface of the pit floats;The third stage:the spreading process continues to increase the lateral dimension of the arc pit,the oxide film floating in the molten solder breaks down under the action of the continuous ultrasonic wave;The fourth stage:the broken oxide The film melts into the soldering material with the flow of the liquid solder,the interface tends to be smooth,and the film removal process is completed.