Flip and Fuse: A New Technique for Diffusive Coating of Organic, Flexible, and Low-Transition-Temperature Substrates With Inorganic Materials in Roll-to-Roll Processes at Ambient Conditions

To enable polymer films to be used in manufacturing flexible systems, additive fabrication methods need to be adapted to the polymer material and to the roll-to-roll mass production process. In this regard, coating processes, such as sputter deposition, thermal evaporation, vapor deposition, and so on, are discarded because of the complex patterning processes and vacuum requirements on both coating material and deposition substrate. Other additive fabrication methods, such as screen printing, inkjet printing, microcontact printing, and so on, do not require vacuum environments. Yet, pure metals cannot be added without the addition of organic binders, which affect electrical properties and the surface finish of the end product. Laser-assisted techniques, such as selective laser sintering and laser-induced forward transfer, have been achieved at polymer-compatible temperatures (150 °C), but involve a complex design of the transfer of laser energy. Most of the aforementioned techniques deliver a purely mechanical adhesion between polymer film and coating. Inspired by flip-chip bonding, we developed an additive no-post-clean fabrication method, denominated by flip & fuse (F & F), based solely on thermocompression to enable a diffusive assembly between a stack of pure metals and a low-transition-temperature polymer at ambient conditions with a surface finish at industrial standards. F & F can be applied to the fabrication of electrical interconnects, soldering masks, high reflective coatings, and diffraction gratings, just to name a few.