A low-temperature parylene-C-to-silicon bonding using photo-patternable adhesives and its applications

Parylene-C has become a more and more popular material for BioMEMS implant applications due to its good biomedical properties [1, 2]. It was also used as an intermediate layer for silicon wafer bonding [3, 4]. However, the bonding between parylene-C and silicon is still problematic. In this paper, a low-temperature bonding between parylene-C and silicon using photo-patternable adhesives is presented. This method can not only determine the bonding pads but also reduce the residual stress in the packaging. Its application on high-density multi-channel chip integration is also demonstrated. Two commercially available photo-patternable materials, i.e., SU-8 and AZ-4620, with stable characteristics are chosen to demonstrate this method. The processing conditions are optimized in terms of bonding temperature, pressure, time, and surface treatment. The peeling force is measured by ASTM peeling tests under various bonding conditions. The results show that the epoxy-based SU-8 is better than AZ-4620 as an adhesive material with a peeling force up to 8.4 N/cm². This low-temperature bonding technique allows selectively local area bonding. Besides, bonding without applying a high electric field is especially suitable for the integration with microelectronics in MEMS packaging.