Laser patterned PDMS gasket as voids-free underfill material for implantable biomedical microsystems

A pre-cured homogeneous film of silicone rubber (Polydimethyl Siloxane, PDMS) is investigated for application as a gasket-underfill material between flexible polymeric electrodes array and electronics package or interposer for biomedical implants. The gasket is fabricated by structuring a thin sheet of the medical grade MED-1000 silicone with picosecond laser to adapt to the design of interconnections between the electrodes array and the package of implant electronics. The adhesion of the gasket-underfill with the overglazed ceramics (used as test vehicle for package) is evaluated. The application of pre-structured underfill applied prior to electrical bonding ensures voids & bubble-free underfilling and allows for contamination-free interfaces of the mating surfaces. It also eliminates the risk of air or entrapment during underfilling providing which poses a risk for water condensation and short circuiting between contacts. The results of the study show that the gasket with opening size as small as 35 μm with a center-to-center pitch size of 55 μm can be fabricated with the picosecond laser. The gasket-underfill showed sustained adhesion with overglazed ceramics during shear and short term aging tests.