Creep Parameters for Solder Interconnects by Nanoindentation Inverse-FEA Method

The creep property of solder materials determines their ability to resist deformation and the stresses being imparted to the interfaces they adhere, which in turn impacts the structural integrity over time. Therefore, accurate determination of solder properties is critical in selecting solder alloy and advancing the solder interconnects development.An inverse-FEA process methodology was developed to determine Norton’s creep parameters (n, A, and Q) for a solder material. To begin with, nanoindentation creep tests were performed at room temperature on assembled components with a Berkovitch indenter using a control-load -hold method. The solders’ stress exponent, n, can be determined, and a lumped parameter was defined to bound the pre-exponential coefficient, A and activation energy, Q. Afterwards, a 2D axis-symmetric FEA model was developed to estimate the range for A. Additionally, data matching technology is adopted to establish the material constitutive model. Through iterative adjustment of the above factors, with the objective of maximizing the similarity of the simulated warpage data to the lab determined reference, a set of parameters can be achieved. The material constitutive model was further validated through correlation with a full-size chip/laminate stress relaxation FEA model.