Stresses in electroless Ni-P films for electronic packaging applications

Electroless-plated nickel films for electronic packaging applications such as under bump metallurgy (UBM) and flip chip bumps are investigated in this study. Quantitative stress of an electroless-plated Ni-P film on an Al coated Si wafer has been measured using a laser scanning profiler and the Stoney equation. A tensile intrinsic stress was developed due to plating defects, and also a tensile extrinsic thermo-mechanical stress due to temperature change and the CTE mismatch of Ni film and Si substrate was observed. It was found that the extrinsic stress became more tensile as the phosphorus content of the electroless Ni film decreased. Therefore, it is necessary to reduce the amount of stresses developed at the electroless Ni film by controlling phosphorous content of the electroless Ni film for reliable electronic packaging applications.