Preparation and temperature cycling reliability of electroless Ni(P) under bump metallization

The reliability of electroless Ni(P) under-bump metallization (UBM) was evaluated via temperature cycling and solder bump shear strength tests. Commercial diodes and dummy dies fabricated in-house were used as substrates for the electroless Ni(P) UBM deposition. Solder bumps were formed after reflowing eutectic 63Sn37Pb solder foils over the Ni(P) UBM. The solder bump shear strength was measured before and after different temperature cycling. The results from this study showed that the UBM thickness and dimension had important effects on the solder bump shear strength and reliability. Both the larger UBM dimension and larger UBM thickness tended to induce higher stress in the UBM, which resulted in the lower solder bump shear strength and lower temperature cycling reliability. A better UBM structure solution for high current electronic packaging application is indicated in this paper