Ultra-thin Parylene-based Printed Circuit Boards for the next generation of flexible electronics

Flexible electronics and sensors are a key enabler for current technology trends such as Industry 4.0 or the Internet of Things. Particularly, these flexible devices can be used for the realization of geometry adaptive devices, wearables or electronics that can be embedded into light weight structures. To enable the next generation of flexible electronics, a new approach for the fabrication of an ultra-thin and highly flexible printed circuit board (PCB) with a total thickness of only 20 µm or even less is presented.
This PCB bases on the thermoplastic polymer Parylene, which combines a variety of unique properties. For the realization of ultra-thin flexible PCBs, Parylene was used as a substrate, a dielectric between the metallic redistribution layers (RDL) as well as for the encapsulation. The RDL were deposited and patterned by standard microsystem technologies, such as sputtering, lithography and wet chemical etching using various metals, such as gold, copper, and aluminum. Additionally, printing technologies using screen printing and aerosol jet printing were investigated. Doing so, multiple RDL can be realized, which was tested for up to three RDL, but is scalable to even more. The electrical connection between the various RDL was realized by etching vertical vias through the Parylene using oxygen plasma. For the contact formation through the vias, different methods were investigated again including sputtering, printing and electrochemical deposition. Finally, the electrical properties were measured and found to be excellent for flat and bent conditions.

Besides the fabrication of the ultra-thin PCB itself, the integration of electronic and sensory components on this PCB is crucial. Doing so, the direct fabrication of components on the PCB was successfully demonstrated and, in parallel, the integration of discrete devices is investigated addressing several technologies such as soldering, wire bonding, and printing of conductive adhesives. Utilizing the unique properties of Parylene, also completely new integration approaches can be realized, which include the embedding of electronic components and the transfer of components.