A flexible polyimide-based package for silicon sensors

Abstract

This paper describes the development of a flexible polyimide-based package for silicon sensors. The fabrication process is compatible with standard integrated-circuit processes and produces a flexible package that sandwiches the metal leads between polyimide layers. Polyimide (DuPont PI-2611) is found to be resistant to the isotropic etchant (hydrofluoric acid/nitric acid) used to realize the sensing islands. Factors affecting package reliability, which include lead layout, island size and support material at the silicon/polyimide interface, are identified and investigated. Packages are tested in an automated test setup and on human subjects. A factor of three increase in lead width produces a two-fold increase in reliability. The use of epoxy as a support material between the rigid silicon island and the flexible polyimide produces a 50-fold increase in reliability on human subjects.