THERMO-MECHANICAL SIMULATION AND OPTIMIZATION ANALYSIS FOR WARPAGE-INDUCED PBGA SOLDER JOINT FAILURES

摘要

In SMT assembly process, the thermal warpage becomes one of the root causes of solder joint reliability failures for PBGA. The accurate prediction for warpage of PBGA and PCB is an important and challenging task of numerical simulation of PBGA solder joint defect. In this paper, the numerical analysis of warpage in PBGA and PCBA is carried out in consideration of the residual stresses produced during SMT reflow process. The analysis methodology using a viscoelastic based material model is adopted to account the time and temperature dependent behavior of an epoxy molding compound. In order to get a series of material constant for Generalized Maxwell Viscoelastic Model, DMA (Dynamic Mechanical Analyzer) tests for mold compound material sample is performed to generate viscoelastic material relaxation function through curve fitting. The experimental research on thermo warpage at different temperature for both PBGA and assembled PCBA is carried out by using the Shadow Morie method. The experimental data is compared with the simulation results as verification for FEA modeling. It is found that the predictions are in agreement with experimental data, especially in qualitative analysis. Optimization analysis is also performed to study the effect of PBGA material properties, molding curing temperature and SMT process parameters on warpage and solder joint failures.