Present techniques for assessing the reliability of active implantable medical devices (AIMDs) rely on testing one or two environmental conditions at a time. But the interaction of these environmental conditions may have a greater impact on reliability than what may be detectable from testing the individual conditions. Future generations of AIMDs will use conformal coatings rather than a titanium canister to effect a barrier between body fluids and the electronics, which could make them even more vulnerable to environmental conditions. The goal of this study is to measure the time-dependent effects of body temperature and chemistry, current density, and circuit geometry on the integrity of parylene conformal coating. To test the effectiveness of parylene as a barrier for AIMDs, test coupons made up of simple microcircuits were made. The entire device was first coated with <5nm Ag, and then conformally coated with parylene by a commercial laboratory. The coated devices are tested in a temperature-controlled bath (37 degrees C plus or minus 1 degree C) of physiological solution with the appropriate chemistry to represent body fluids; some of the baths contain additional concentrations of hydrogen peroxide and/or chlorine to represent the local immune response of the body. For each circuit we control the current density and measure the voltage over time. We sample the physiological solution weekly to look for trace amounts of Ag, an indication that the parylene coating has been compromised. The solution samples are tested in a mass spectrometer with a detection limit for Ag of 0.01 ppm.
Proceedings Title: Proceedings of Frontiers in Biomedical Devices Conference
Conference Dates: June 7-8, 2007
Conference Location: Irvine, CA
Conference Title: BioMed Frontiers in Biomedical Devices Conference 2nd Frontiers in Biomedical Devices Conference
Pub Type: Conferences
active implantable medical device, body chemistry, conformal coating, electrical conditions, parylene