Process Considerations for Ultraprecise Deposition Printing on Flexible Substrates

In this paper, process considerations for Ultra-Precise Deposition (UPD) printing of fine structures for the heterogeneous integration on flexible substrates are discussed. XTPL recently introduced UPD as an alternative to aerosol jet and ink jet printing technologies. It stands out as a printing technology that can achieve minimum feature sizes and precision on the order of 1 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu\mathrm{m}$</tex>. Printability on flexible substrates depends on the surface energy, the topology and the roughness of the substrate. The suitability of UPD for printing conductive traces on flexible substrates is showcased by the fabrication of packaging for chiplets, and printing coplanar waveguides with an air gap of 10 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu\mathrm{m}$</tex> on polyimide. A comparison is given between printability on unmetallized polyimide, polyimide with a galvanically grown copper layer and polyimide with a rolled copper layer, as well as the use of planarization layers to mitigate surface roughness.