The Effect of Visco-elasticity on the Result Accuracy of FEM Panel Warpage Simulations Supporting Industrial Microelectronics Packaging

Based on measurement results of BGA substrate panel warpage, the accuracy of two FEM simulation approaches has been assessed. Relying on elastic/plastic material models, the first approach has only been capable of following the most fundamental trend qualitatively. In terms of magnitude, these simulations already exaggerated the dependency of the warpage on the die thickness by a factor of two. Even worse, this approach wrongly estimated the second basic trend. Reducing the area of the dies without changing their arrangement, the real substrate panel warpage changes towards negative magnitudes while the simulation results directly pointed in the opposite direction. In the alternative FEM approach, visco- elastic behavior of the organic materials and chemical shrinkage of the mold compound have been added to the models. Afterwards, the experimental results could all be matched in a wide range of die sizes. The residual root mean square error was as small as the measurement inaccuracy. Sensitivity analyses clearly showed the root cause for why the first approach must have failed. They also optimized the simulation effectiveness by minimizing the effort in simulation and material characterization for the accuracy required. The paper details the developed scheme for trustworthy FEM substrate panel war- page estimations.