Study and modeling of the curing behavior of no-flow underfill

No-flow underfill is an original invention that has greatly improved the production efficiency of flip-chip process. Due to its unique characteristics including reaction latency, curing under solder reflow condition and the desire of no post-cure, there is need for fundamental understanding about the curing process of no-flow underfill. Starting with a promising no-flow underfill formulation, this paper seeks to develop a systematic methodology to study and model the curing behavior of this underfill. Differential Scanning Calorimeter (DSC) is used to characterize the heat flow during curing under isothermal and temperature ramp conditions. A modified autocatalytic model is developed with temperature dependent parameters. The Degree of Cure (DOC) is calculated; compared with DSC experiments, the model gives good prediction of DOC under different curing conditions. The temperature of the printed wiring board (PWB) during solder reflow is measured using thermo-couples and the evolution of DOC of the no-flow underfill during a reflow process is calculated and compared with experimental results.