On the Use of Nanoscale Materials to Toughen Model Epoxies

A typical underfill resin consists of an epoxy matrix filled with micron-size silica particles to reduce thermal expansion. The fracture toughness of such resins plays an important role in the reliability of flip-chip packages. In this work, we will investigate the use of nanoscale materials to improve the fracture toughness of a model epoxy resin. A lightly crosslinked model epoxy system was chosen due to its “toughenability.” The toughening mechanisms are elucidated using a combination of electron and optical microscopy techniques. For epoxies toughened with soft, nanosize rubber particles, the toughening mechanism is rubber particle cavitation and matrix shear banding. The toughening mechanism when hard, nanosize silica particles are used involves particle matrix debonding and matrix shear banding.