Published online by Cambridge University Press: 21 March 2011
The influence of aging in an environment with a high temperature and a high humidity on the adhesion performance of underfill material (epoxy cured with acid anhydride) to the passivation layer in flip chip packaging is discussed. Adhesion of underfill to different passivation materials degrades after aging in a high temperature and high humidity environment. The extent of this degradation is dependent on the hydrophilicity of the passivation material. Hydrophilic passivation such as silicon oxide (SiO2) and silicon nitride (Si3N4) shows much more severe adhesion degradation than hydrophobic passivation such as benzocyclobutene (BCB) and polyimide (PI). The mobility of absorbed water and of polymer chains is studied with solid state nuclear magnetic resonance (NMR) spectroscopy. Higher mobility of absorbed water and of polymer chains in rubbery state polymers contributes to faster adhesion degradation during high temperature and high humidity aging. The adhesion stability of hydrophilic passivation can be successfully improved by use of a silane coupling agent that introduces stable chemical bond at interface. A flow micro-calorimeter was used to study the absorption of silane coupling agent onto glass surface. The difference in adhesion retention improvement between aminosilane and epoxysilane is discussed.