Combined experimental and numerical investigation on flip chipsolder fatigue with cure-dependent underfill properties

摘要

A cure-dependent viscoelastic constitutive relation is applied todescribe the curing process of epoxy underfill in Flip Chip on Board(FCOB). The chemical shrinkage of the epoxy underfill during the curingprocess is applied via incremental initial strains. Thus, the stress andstrain build-up, caused by the simultaneous increase in stiffness andshrinkage during the curing process, are simulated. Accelerated fatigueexperiments with thermal cycles from 55° C to 80° C are carriedout for a specially designed Flip Chip configuration. Based on theobtained curing induced initial stress and strain fields,thermo-mechanical predictions are presented for the test carriers. Thesolder bumps are modeled as temperature dependent visco-plasticproperties. A combination of a Coffin-Manson based fatigue relation anda creep fatigue model is used as fatigue failure criterion. The resultsshow that the FEM-based fatigue life predictions match better with theexperimental results, if the curing induced initial stress state istaken into account