Validating Flip Chip Package Models Through Experimental Deflection Measurements

Abstract

Tektronix Component Solutions is advancing its simulation capabilities to improve product reliability, reduce development costs, and speed up time-to-market. Developing a model that accurately predicts performance requires that it be validated through correlation to real-world results. In this work, a high-fidelity, multi-step, nonlinear finite element model was built including processing steps and thermal cycling to mirror the real environment of a flip chip package. Extensive materials characterization was performed to capture accurate time-and-temperature dependent (viscoelastic) properties of the underfill adhesive, stiffener ring adhesive, and substrate components. Model accuracy was established through three measurement techniques to characterize package deflections. The Thermo-Moiré technique was used to measure package warpages as a function of processing step and thermal loading. Optical Interferometry was used as a secondary approach to measure package warpage as a function of processing step. Lastly, Digital Image Correlation was performed on a cross-section of the package to characterize shear and through-thickness strains of critical solder bumps. The simulation produced excellent correlation with the various measurement techniques, and it was found that component pre-warpage (inherent to the substrate and stiffener ring) was a necessary variable to account for during simulation and measurement. With the excellent correlation provided by the models, Tektronix Component Solutions is now using these methods in combination with material strength testing to advance critical stress and survivability predictions in advanced packages.