Methodology for studying the impact of intrinsic stress on the reliability of the electroless Ni UBM structure

Abstract

A methodology for evaluating the reliability and the impact of intrinsic stresses on the electroless Ni under bump metallurgy (UBM) structure is presented. The first part of this work will address the testing methodology, which uses a pressure sensing device to determine the intrinsic stress in Ni due to the plating process. An optical method is used to capture deformation in the sensing device due to the Ni plating process. A finite element model is then used to calculate the intrinsic stress in the Ni film using the deformation output from the optical measurements. The second part of this work will address a predictive model used to determine the reliability of applying intrinsic stress values to a low cost electroless Ni UBM structure during the bump formation and solder reflow process. The combined work of the testing and predictive methodology provides a more effective and accurate method of predicting the Ni UBM reliability.