In Vitro Reactive-Accelerated-Aging Assessment of Anisotropic Conductive Adhesive and Back-End Packaging for Electronic Neural Interfaces

Bioelectronic neural interfaces can fail in vivo due to water penetration and corrosion of the packaging technology used to protect sensitive portions of the device. Although anisotropic conductive adhesive (ACA) is gaining popularity in the neural interface community to connect fabricated electrode arrays with back-end packages, the durability of ACA in chronic implants is largely unknown. We have designed a platform that uses an aggressive reactive-accelerated aging (RAA) environment to rapidly assess the ability of ACA and silicone-rubber encapsulation to maintain electrical integrity in vitro. All RAA experiments were performed at 77°C, for 24 days, and with 10 to 20 mM H
₂
O
₂
, which approximates a 1 year implantation. Results from these experiments showed that ACA rapidly fails (i.e., 2 to 4 days RAA) due to water absorption through the silicone encapsulant. Electrical impedance spectroscopy (EIS) confirmed water penetration through the package and the resulting corrosion of the sensitive metallic components.