The adhesion of epoxy treated by microwave oxygen plasma

Abstract Strong adhesion between epoxy and silicone is essential for optoelectronic packaging. The adhesion of epoxy can be enhanced by microwave plasma treatment in oxygen flow. However, the plasma effect is time dependent. The shear strength of un-aged and aged epoxy for up to two months was systematically investigated as a function of plasma power (200–600 W) with different surface analysis tools. The shear strength between epoxy and silicone assembly was correlated with surface wettability, chemical, and structural properties. 300-W plasma-treated epoxy revealed the highest shear strength and the factors contributing to the improved strength were identified. The phenomenon of hydrophobic recovery was recorded after ageing, which had minimal effect on the reduction of shear strength. By keeping the plasma-treated surface for up to two months, a significant increment of shear strength was demonstrated below one week of ageing. Beyond that, a slight deterioration of the strength was observed but the reduction was still higher than the un-aged surface. The reasons behind of these observations have been elucidated and justified.