An Integrated Warpage Prediction Model Based on Chemical Shrinkage and Viscoelasticity for Molded Underfill

Abstract

The molded underfill (MUF) offers many unique advantages, including lower material costs, higher throughput, and excellent reliability for flip-chip chip scale packages (fcCSP) and fan-out packages. The assembly process yield and reliability of these packages are significantly influenced by the warpage behaviors of MUF. We develop an integrated process modeling approach incorporated with real-time chemical shrinkage and cure-dependent viscoelastic constitutive model for warpage prediction. The cure-dependent chemical shrinkage, kinetics and viscoelasticity are measured using pressure-volume-temperature (PVT) method, differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The integrated model is applied to fcCSP and fan-out packages with different designs, and the simulation results are in good agreement with the experimental data. A simplified model is also constructed for MUF with a fast corss-linking rate. In addition to warpage prediction, we successfully demonstrate that the model is useful to select suitable MUF baseline materials.