Assembly and Packaging Developments for an Ab–Externo Retinal Prosthesis

Abstract

Abstract: : Purpose: To develop assembly and packaging schemes for long–term ab–externo implantation of a retinal prosthesis and potentially other neural prostheses having multiple components, scalable feedthroughs and/or a high–density of input/output interconnects. Methods: The retinal prosthesis design included discrete components, custom–wound power and data coils, a micro–fabricated flexible circuit substrate (FC) and stimulating electrode array (EA) and a custom integrated circuit (IC) stimulator chip (see related posters: Shire/Rizzo). Commercially available assembly techniques were pursued. The components were assembled on a flexible parylene or polyimide substrate, using a gold stud bump/conductive epoxy, flip–chip bonding process for the IC and EA. The discrete components and the power and data coils were electrically connected using conductive epoxy. The packaging technology development initially involved an investigation of current and emerging technologies/materials for implantable devices. Soak testing was performed in saline solution at 37°C while monitoring electrical current leakage. Initial soak tests were performed on micro–fabricated test structures coated with multi–layered test materials. A base layer of room temperature, chemical vapor deposited, 5µm thick parylene–C was typically used. Several biocompatible over–layers, including sapphire and carbon–based diamond–like films, were evaluated and biocompatibility enhancements were investigated, e.g. surface treatments such as poly(ethylene glycol) functionalization. Completed assemblies were coated and subjected to soak testing and animal surgical trials. Results: An assembly process utilizing commercially available techniques was developed. Initial investigation of packaging technologies/materials was collected in a database for continued accessibility. Soak testing of candidate materials and the completed assembly is an on–going process and new results will be presented at the meeting as will results of initial animal surgical trials. Conclusions: The use of commercially–available assembly techniques coupled with investigation of conventional and emerging packaging technologies/materials resulted in a viable assembly and packaging scheme for a retinal prosthesis. These technologies are expected to find application in other implantable prostheses such as in functional neural stimulation systems.

Keywords: age–related macular degeneration • retinal degenerations: hereditary • ocular irritancy/toxicity testing