Characterization of PDMS as Encapsulation for Implantable MEMS Systems

Modifications to a novel multi-layered polydimethylsiloxane (PDMS) encapsulation process that include improvements to the substrate cleaning procedure and roller casting application method were developed to produce a robust non-hermetic micropackage technology for chronic micro implant systems. Packaged interdigitated electrodes subjected to accelerated lifetime tests at 85 degree C in a saline environment had an average lifetime of 156.6 days, which exceeded the previous average lifetime by 22.3 days and suggests a packaging lifetime in the human body greater than 2 years and perhaps as long as 5 years. In order to understand the unexpectedly long lifetime, material characterization experiments were performed on PDMS films deposited by dip, spin and roller-casting. The results show that roller casting increases the mass density, decreases the vapor permeability, and increases bonding strength on FR4 PCB substrates by +2%, - 14%, +19%, respectively relative to the other deposition methods.