Effect of moisture on the curing behaviour of underfills

This paper describes the curing, processing and thermomechanical behaviours of an anhydride-cured liquid epoxy based underfill polymer that was contaminated with water. Water was added to the uncured underfill system using two different routes, simulating two possible ways in which the underfill resin can be contaminated. In the first case, known amounts of water were added directly to a fully-formulated underfill, whilst in the second case, water was added to the epoxy resin prior to formulating the underfill system. The effects of the added water were studied using Fourier transform infrared (FTIR) spectra, differential scanning calorimetry (DSC), dynamic mechanical analyser (DMA) and light microscopy. This study shows that the presence of water resulted in rapid hydrolysis of the anhydride hardener to form solid crystalline carboxylic acid. It was found that the major cause of the flow disturbances during underfilling and deterioration in the final properties of the underfill was closely related to the occurrence of the carboxylic acid. Direct contamination of the formulated underfill was found to have the greatest impact on the material processing and thermomechanical properties.