Research Of Microstructure And Nanoindentation Performance Of Sn-3.0Ag-0.5Cu/Ni Micro-joint

Because the traditional Sn-Pb is toxic, the environmentally friendly lead-freesolder instead of traditional Sn-Pb solder is the trend of electronic manufacturing.Sn-Ag-Cu alloy has been widely regarded as the most potential leaded solderalternatives because of its fine wettability and mechanical properties. In the field ofmodern microelectronics packaging, multi-reflow soldering and isothermal aging testare important for the performance analysis of the solder joints.This paper uses Sn-3.0Ag-0.5Cu solder balls （diameter:200μ m,300μ m,400μ m,500μ m）, Ni pad, research the relationship between the interfacial IMCthickness, the microstructure of the solder joint and the size of the solder ball inmulti-reflow soldering and isothermal aging test, and use the nanoindentation test toanalyze the mechanical properties of solder joints.In the condition of multi-reflow soldering, interfacial IMC thickness of the samesize ball increases with the times of multi-reflow soldering increase, its morphologynear the body solder side transforms gradually to be uneven; when the times ofmulti-reflow soldering is same, the size of solder ball is smaller, the IMC thickness isthicker, and the relative morphology has no significant difference. IMC componentare multiphase mixture which base on (Cu_x,Ni_6-x)₆Sn₅phase, due to the increase ofthe times of multi-reflow soldering, Ni spread to body solder direction constantly, theproportion of Ni element will increase gradually.In the condition of isothermal aging test, interfacial IMC thickness of the samesize ball increases with the aging time increase, its morphology near the body solderside transforms gradually to be flat. When the aging time is same, the size of solderball is smaller, the IMC thickness is thicker, and the microstructure has no largedifference. IMC component are also multiphase mixture which bases on （Cux,Ni6-x）6Sn5phase, and there will be a part of the Ag₃Sn locally; but the difference is that,along with the aging time increase, Ni element continuous spread, it make area of alloy mixture which bases on Ni, Sn alloy increase, and we can see the differenttypes of compounds.Nanoindentation test is carried out on the solder balls after multi-reflowsoldering and isothermal aging test. In the condition of multi-reflow soldering, whenthe times of multi-reflow soldering is same, the body solder hardness increases withthe size decreases, elastic modulus is general waving in the range of12¹6Gpa. Inthe condition of isothermal aging test, when the aging time is same, the body solderhardness increases with the size decreases; and when the size of the ball is same, thehardness decreases with the aging time increases, elastic modulus is general wavingin the range of12¹8Gpa.