Application of flow microcalorimetry to develop underfill resins

A series of model underfill resins with different chemical structures have been characterized using flow microcalorimetry (FMC). FMC allows the direct observation of the strength of adsorption of molecules on to a surface. In this case, epoxy monomers, curing agents, and adhesion promoters, were adsorbed on to a borosilicate glass powder in an effort to predict adhesive strength. Adhesive strengths were measured mechanically using an asymmetric double cantilever beam test. Adhesive strengths of filled and unfilled epoxy resins were measured and often correlated to FMC results. Scanning electron and optical microscopy were used to identify mechanisms of plasticity/damage at interfacial crack tips. Greater adhesion strength can be attributed to increased damage near the crack tips. Such damage is enabled by strong molecular interactions at the interface.