A foldable multi-chip packaging technique with a polyimide platform and flexible PDMS assembly mold

A batch-scale low-profile assembly and packaging technique is developed and demonstrated using silicon chips representing ICs or micromachined transducers. Silicon and PDMS molds are prepared to contain and carry chips throughout the packaging process. A self-supported double polyimide layer is used as the main platform providing mechanical strength, electrical insulation, and flexibility. The packaged devices can be folded and twisted to make any desired shape and form required for various applications. In this paper, we will describe our initial efforts using the silicon mold followed by conversion to a PDMS mold having several advantages such as: 1) wider tolerance range for device placement and insertion, 2) easier release, and 3) lower manufacturing costs. A two-step polyimide curing process is developed to accommodate the low-temperature requirements of the PDMS mold. Initial polyimide curing at <140°C is followed by the release of the packaged devices which are then hard-baked at higher temperatures to fully cure the polyimide. The polyimide-PDMS integration process can be beneficial to several other polyimide-based technologies such as flexible recording and stimulating electrodes.