The decrease of electronic package size is required for high-performance silicon devices and more integrated circuit. This requirement leads to the development of new electronic packaging technology - BGA, CSP, etc - and the increase in the number of I/O (input/output) per unit area of semiconductor chip. The increase in the number of I/O (input/output) per unit area of semiconductor chip accompanies the decrease of the solder ball size in electronic package, so the variation of solder ball size is expected as the factor which influences the solder joints.
In this study the growth behavior of intermetallic compound in interface is investigated with the variation of solder ball size. Ni is used as the substrate because Ni is used as the barrier layer of UBM (under bump metallurgy), and only Sn is used as the solder for the simplicity of system considered. Sn solder balls having variable sizes are soldered on the Ni substrate by a hot-plate with the variation of soldering time, and the cross section of the joint is observed using SEM and EDS. The Ni-Sn binary system is assessed using the reported experimental data and Thermo-Calc program for thermodynamic understanding of interfacial phenomena.
The growth behavior divided into 3 stage is observed, and the precipitated IMC in Sn solder matrix can be found. The growth behavior is changed with the variation of solder ball size. The assessment results agree well with the experimental data.
