Development of a Packaging System for Clinical Evaluation of a Nanocomposite-Based Neural Electrode Array Fabricated from a Chemoresponsive Polymer Substrate
Authors: Andrew Barnes, Allison Hess, Christian Zorman, and Mondhita Diewvilai Company: Case Western Reserve University and Chulalongkorn Date Published: 4/30/2011
Abstract: This paper reports the results of an effort to develop a packaging system designed specifically for chronic, in vivo testing of microfabricated neural electrode arrays made from a novel, biologically-inspired, variable-stiffness nano-composite material (PVAc-NC). The package was designed to function as a head cap for a probe-based neural interface for use in long-term, in vivo testing and consists of a connector assembly to enable direct electrical interfacing with standard measurement equipment. The neural probe electrodes are electrically-linked to the connector assembly by wire bonds embedded into the package such that the wire bonds and connector remain protected from the high moisture environment surrounding the brain. Optimal wire bonding parameters were determined using a design of experiments methodology, then tested using a standard pull test protocol. Finite element modeling was performed to determine how varying materials and film thicknesses affect the mechanical deformation of the contact pad. It was found that optimal bonds were made to samples with 200 nm Au/50 nm Ti/1000 nm parylene/PVAc-NC with bonds coated with 11 µm parylene. These optimal conditions allowed for wire bonds that meet military standards on the nanocomposite both in the dry state and after soaking in deionized water. To the best of our knowledge, this effort is the first to explore wire bonding of any kind on a PVAc substrate. Moreover, since the PVAc-based neural probes soften significantly when deployed, our effort may be the first to develop a wire bonding process for a substrate that undergoes such a dramatic change in its mechanical properties.