Interfacial Reaction Between Eutectic Sn-Pb Solder and Electroplated-Ni as well as Electroless-Ni Metallization During Reflow

Electroplated-Ni (EP-Ni) has been adopted gradually as an underbump metallization layer due to its comparatively lower resistivity and higher deposition rate. In this study, the metallurgical reaction between eutectic Sn-Pb solder and EP-Ni as well as electroless-Ni (EL-Ni) was investigated at 200°C, 210°C, 220°C, and 240°C. It is found that the growth rate of Ni₃Sn₄ intermetallic compound (IMC) on EP-Ni was slower than that on EL-Ni. The consumption rate is measured to be 0.97 × 10⁻³ μm/s and 1.48 × 10⁻³ μm/s for EP-Ni and EL-Ni, respectively. The activation energy is determined to be 51 kJ/mol and 48 kJ/mol for EP-Ni and EL-Ni, respectively. The dense structure of EP-Ni may be responsible for the lower IMC formation rate.