A study of normal, restoring, and fillet forces and solder bumpgeometry during reflow in concurrent underfill/reflow flip chip assembly

摘要

Simulation of flip chip solder joints in an underfill environmentwas performed to evaluate the effect of underfill volume and materialproperties on concurrent underfill and solder reflow manufacturingtechnique. Forces during solder reflow, fillet shape and collapsedsolder ball geometry after reflow are reported. A multiple ball modelwas created based on single ball model and underfill fillet studies, topredict die stand-off in the presence of a pre-dispensed, fluxingunderfill. The predictions agree with experimental results within 1.5percent. Modeling allows the prediction of self-centering forces, gapheight, and die floating as a function of underfill volume andproperties in a no-flow, fluxing underfill assembly process