Room temperature stable underfill with novel latent catalyst for wafer level flip-chip packaging applications

Imidazolium salts were explored as novel catalysts for underfill application. The catalytic properties of a series of imidazolium salts with different coordinating anions were studied by a dynamic differential scanning calorimeter (DSC). By changing the counter anions in these catalysts, the curing kinetics of the underfill can be adjusted. To understanding the curing mechanism of imidazolium salt, the thermal properties of these compounds were studied in terms of melting and decomposition temperatures. A possible reaction mechanism with these novel catalysts was proposed. One imidazolium salt was chosen as the catalyst for the underfill and shelf-life experiments were conducted at room temperature (R.T.), as well as using common imidazole catalyst in a control sample. During the test, the viscosity of underfill was measured by rheometer and the residue reaction heat of the underfill curing was monitored by a DSC. The B-stage stability of this underfill was also studied. With this novel catalyst, we have developed the RT stable epoxy resin based underfills which also process good thermal stability after B-stage