Phenolic Resin Surface Restructuring upon Exposure to Humid Air: A Sum Frequency Generation Vibrational Spectroscopic Study

Epoxy and phenolic resins are extensively used for modern microelectronics, for example, as packaging materials. Humidity may greatly alter or degrade their function and application, leading to failure of the device. A nonlinear optical laser technique, sum frequency generation (SFG) vibrational spectroscopy, was used to investigate the molecular surface structures of the epoxy and phenolic resins after exposure to humid air. It was found that the adsorbed water molecules at the phenolic resin surface can induce substantial surface restructuring. The surface phenyl groups were reoriented closer to a perpendicular position to the surface after exposure to humid air from a more parallel position in air. Epoxide group surface restructuring was not observed.