Isolation Resistance of Encapsulated Electrical Conductors and Terminations for Biomedical Applications

Abstract

Implanted electronic medical devices are evolving into architectures that are comprised of multiple packages that require reliable, high density electrical interconnections. Both power and digital signals must be routed between devices on cables that are immersed in an ionic, electrically conductive medium. Electronics are typically housed in hermetic packages with electrical feed throughs that must also be protected from the implant environment. The polymer materials used to encapsulate cable conductors and terminations must be biocompatible, compliant and of minimal thickness. These requirements result in materials that are susceptible to ion diffusion and migration in electric fields. We have used finite element models to explore the effects of geometries, electric field intensity and material properties on the time dependent electrical isolation resistance of cables and terminations. Simple beaker tests have been used to evaluate the isolation resistance of samples under bias as a function of time to validate our finite element models.