Shear and Pull Testing of Sn-3.0Ag-0.5Cu Solder with Ti/Ni(V)/Cu Underbump Metallization During Aging

Ti/Ni(V)/Cu underbump metallization (UBM) is widely used in flip-chip technology today. The advantages of Ti/Ni(V)/Cu UBM are a low reaction rate with solder and the lack of a magnetic effect during sputtering. Sn atoms diffuse into the Ni(V) layer to form a Sn-rich phase, the so-called Sn-patch, during reflow and aging. In this study, the relationship between interfacial reaction and mechanical properties of the solder joints with Ti/Ni(V)/Cu UBM was evaluated. Sn-3.0Ag-0.5Cu solder was reflowed on sputtered Ti/Ni(V)/Cu UBM, and then the reflowed samples were aged at 125°C and 200°C, respectively. (Cu,Ni)₆Sn₅ was formed and grew gradually at the interface of the solder joints during aging at 125°C. The Sn-patch replaced the Ni(V) layer, and (Ni,Cu)₃Sn₄ was thus formed between (Cu,Ni)₆Sn₅ and the Sn-patch at 200°C. The Sn-patch, composed of Ni and V₂Sn₃ after reflow, was transformed to V₂Sn₃ and amorphous Sn during aging. Shear and pull tests were applied to evaluate the solder joints under various heat treatments. The shear force of the solder joints remained at 421 mN, yet the pull force decreased after aging at 125°C. Both the shear and pull forces of the solder joints decreased during aging at 200°C. The effects of aging temperature on the mechanical properties of solder joint were investigated and discussed.