Microelectronic medical implants with superior performance are needed to improve quality of life for patients. For neuroelectronic applications, this will be enabled through miniaturisation of large numbers of high-density electrodes in bio-mimetic packages. The leading solution is to use ultra-thin silicon chips (UTCs) embedded in flexible polymers with small flexible ribbon cables. However, this technology creates a unique challenge of maintaining sufficient hermeticity, biocompatibility and biostability for decades-long implantation without the use of bulky, rigid glass/Ti boxes. The primary aim of THINPAC (Thin Hermetic Implantables using Novel Packaging of Active Chips) is to realize a robust technology platform for ultra-thin flexible hermetic packaging of UTCs using alternating layers of ceramic nanofilms and polyimide. Innovation beyond existing fabrication technology is needed (i.e. bonding for higher yield, thin-film noble metal patterns over chip edge topography, and hermetic connector strategies). THINPAC will aim to develop these technologies by solving remaining fabrication issues and in-depth in vitro evaluation of the developed technology to ensure long term hermeticity, biostability, and flexibility. New testing strategies will be developed towards highly reliable test protocols for real-time and accelerated testing to mimic long term evaluation of implants. Implant development is a highly multidisciplinary activity and in vivo testing in animals is indispensable. Discussion with medical people and initial tests with dummy devices are essential from the start of the project to avoid less suitable medical devices. Finally, functional probes for implantation into peripheral nerves will be fabricated and fully characterized in rats for foreign body reaction and electrophysiology. With this project, we aim to mature a technology platform for advanced implant fabrication and for the first time make it viable for clinical translation into humans.