Silicone-based Chip-in-Foil System

Abstract

Abstract Aiming at devices for bioelectronic medicine, this paper proposes a die embedding process for the fabrication of flexible smart implants. By combining thinned bare dies with a polymeric encapsulation, completely flexible implants can be designed. The dies are encapsulated using a flip-chip process and a backfilling with silicone rubber. A completely even surface without detectable edge between the chip and the surrounding polymer substrate is achieved by gluing the chips face-down onto a polyimide-covered substrate. The backside is coated with silicone rubber and a second carrier substrate is attached. Removing the first substrate subsequent to curing of the silicone leads to chips located under a continuous polyimide layer, enabling the use of microtechnology for further processing steps. A custom-made test chip is proposed that enables the evaluation of the mechanical and chemical stability of the system.