Accelerated-stress reliability evaluation for an encapsulated wireless cortical stimulator.

In preparing a wireless cortical stimulator for use in the Intracortical Visual Prosthesis (ICVP) project at the Illinois Institute of Technology (IIT), an accelerated environmental stress test is being performed on prototype stimulator modules. Stimulator devices, containing a custom application specific integrated circuit (ASIC), and encapsulated with PDMS, were soaked in an autoclave chamber at 121°C and 100% relative humidity for more than 2200 hours with and without power supplied to the ASIC. Experimental results showed no physical degradation of the stimulator devices after soaking. Reverse telemetry that measures the stimulator internal power supply, recorded periodically over the entire test time, verified that the devices were electrically functioning, as designed, without deterioration. Taking into consideration other standard reliability test environments, the accelerated moisture resistance-biased autoclave testing duration of 2200 hours, as conducted in this study, overwhelms other less-severe test conditions and demonstrates long term stability of the proposed vision prosthesis device with proven thermo-mechanical and electrical robustness.