Chapter 14
Accelerated Testing of Polyimide Coatings for Neural Prostheses J. McHardy, D. I. Basiulis, G. Angsten, L. R. Higley, and R. N. Leyden Downloaded via TUFTS UNIV on July 7, 2018 at 08:05:08 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
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Technology Support Division, Hughes Aircraft Company, El Segundo, CA 90245 The adhesion of polyimide insulator coatings to electronic materials was greatly enhanced by an alumina primer layer. Accelerated aging tests indicated that adhesion failure of alumina-primed polyimide coatings is unlikely to limit the functional l i f e of in vivo electronics. Factors contributing to adhesion loss can be physical, chemical or electrochemical. Measurements used to evaluate the effect of these factors on adhesion included mechanical peel strength and electrochemical pore resistance. The tests showed dramatic improvements in the adhesion of polyimide coatings, even to noble metal substrates, when the substrate was first treated with an aluminum chelate primer. Specimens survived for several weeks in boiling saline solution with no significant loss in adhesion strength. By comparison, unprimed specimens failed this test within a few hours. Applied voltage tests yielded similar distinctions: adhesion loss in primed specimens was induced only by treatments which attacked the underlying metal. Electronic components of neural prostheses must survive and function under challenging conditions. They are exposed not only to the corrosive e f f e c t s of saline f l u i d s but also to natural foreign-body reactions. Hermetic packaging can delay the attack but i t i s not p r a c t i c a l to seal the whole unit. The key to s u r v i v a l and r e l i a b l e performance of neural implants i s the s e l e c t i o n of i n s u l a t i n g materials that w i l l neither harm the body nor be harmed by i t . In a non-hermetic package, the primary moisture b a r r i e r i s t y p i c a l l y a thin, (
