Research On The Interfacial Reactions And Reliability Between In-3Ag Low Temperature Solder And Copper Or Nickel Substrates

In-3Ag solder is widely used in thermal-sensitive and low-temperature components packaging with a series advantages such as low melting point, long fatigue life and good wettability. The research about microstructure at the interface between solder matrix and substrate has a decisive effect to improve the reliability of solder joint and acts as a necessary step to develop new lead-free solder. In this paper, the evolution of microstructure at the interface between In-3Ag solder and copper or nickel substrates during brazing, multiple reflows and isothermal aging was systematically studied and the internal mechanism was deeply discussed.The melting characteristic of the solder was measured by Differential Scanning Calorimetry (DSC). The microstructure of solder joint and shear fracture were observed by Scanning Electricity Microscope (SEM). The phase composition of solder alloy and solder joint was analyzed by Energy Dispersive Spectrometer (EDS). The shear strength was tested by mechanical testing machine. The results were summarized as follows:(1) When soldered at160℃, the interfacial structure between the In-3Ag solder and Cu substrate remains as (Ag,Cu)In2intermetallic compounds (IMCs) during the extending soldering time. When soldered at170℃,180℃and190℃, the evolution of interfacial structure can be divided into three stages:(Ag,Cu)In2IMCs firstly forms, then (Cu,Ag)11In9IMCs separates out from the bottom, finally,(Ag,Cu)In2IMCs were replaced completely by (Cu,Ag)11In9IMCs. The growth indexes of (Cu,Ag)11In9IMCs were0.56,0.50and0.42respectively and the growth rates of it were0.51μm/s1/2,0.56μm/s1/2and0.58μm/s1/2respectively. The activation energy of the growth is23.69kJ/mol, controlled by component diffusion rate.(2) When soldered at250℃,275℃and300℃, the interfacial structure between the In-3Ag solder and Ni substrate remains as In27Ni10IMCs during the extending soldering time. The growth indexes of In27Ni10IMCs were0.53,0.55and0.46respectively and the growth rates of it were0.19μm/s1/2,0.33μm/s1/2and0.45μm/s1/2respectively. The activation energy of the growth is85.52kJ/mol, controlled by component diffusion rate.(3) With the increasing of the reflow soldering cycles or isothermal aging time, the thickness of (Ag,Cu)In2IMCs layer increases gradually, which is controlled by interfacial reaction rate and component diffusion rate respectively. The shear strength of solder joints decreases with the reflow soldering cycles and isothermal aging time increasing. The fracture type is ductile fracture in solder matrix after1cycles,2cycles and3cycles or aging for250h,500h and750h. After5cycles or aging for1000h, the fracture type belongs to the mixed fracture of toughness and brittleness.