Unit warpage control with universal die thickness

Abstract

The package warpage induced by residual stresses during molding process is one of the major thermo-mechanical reliability concerns in IC packaging. This paper proposes a method to find solution to unit warpage control with universal die thickness that ranges from 40 um to 250 um for the large FPBGA package. Firstly, the effect of each factor (mold cap thickness, substrate thickness, mold compound and die attach material) on warpage with these various die thickness was simulated and discussed. Then both tests and FEM simulations were conducted for few legs. The FEM simulation results were correlated with actual tests to determine the crying and smiling warpage boundary for satisfying warpage requirement in simulation. Based on actual tests and simulation results, three mold compounds (high CTE, middle CTE, low CTE), three mold cap thickness and two substrate thickness were selected to make full DoE simulation. Final simulation results showed that several combinations of mold cap thickness, substrate thickness and mold compound could be the solution to the warpage requirements with universal die thickness. Only a few more actual tests are needed to verify the final solution based on the simulation results.