Process Development Engineer MiQro Innovation Collaborative Center (C2Mi), QC, Canada
Printed electronic devices, both flexible and rigid, have garnered significant interest and adoption across multiple market segments, including aerospace, medical, IoT, automotive, energy and consumer electronics. The technology is highly adaptable and compatible with low cost, automated mass production processes, thereby attracting both industrial and academic applications.
To maximally exploit the opportunities of this technology, a hybrid printing solution using copper (Cu) inks is proposed that addresses both circuit density optimization and the integration of solderable, surface mount components. The hybrid approach leverages the respective strengths of two industrially pervasive printing processes, namely inkjet and screen-printing, on the same device. The inkjet technique enables fine lines and spacing of conductive traces with minimal ink consumption. Further, the technique does not rely on design-specific hard tooling, such as masks, thus allowing immediate correction or fine-tuning of device designs. On the other hand, the strength of screen-printing lies in its capability to cost-effectively print the thicker deposits necessary for reliable component connections. The use of a Cu ink renders these deposits compatible with the industry standard SAC305 solder used in high volume PCB surface mount assembly.
This presentation will first review the key process steps of the hybrid copper printing method as developed at the MiQro Innovation Collaboration Center (C2MI) in collaboration with École de Technologie Supérieure (ETS). Using an AWT High-Tech Micro clamshell flatbed screen printer and a Ceradrop F-Serie Inkjet printer, the resultant traces were simultaneously sintered using a photonic curing technology on a Novacentrix PulseForge Invent system. This curing method yielded prints with a resistivity of 3,5*10-7Ωm with the screen printed CP-009 Novacentrix ink and 2,4*10-7Ωm with the inkjet printed Dycotec DM-CUI-5002 ink while maintaining a 5B adhesion rating (ASTM D3359-17 method).
Surface mount assembly results are then presented. A no clean SAC 305 solder paste was applied to the Cu prints using an industrial scale ASM component attach assembly line (ASM DEC paste screener, ASM TX series component placement machine and Heller 1913 MK5 14 zones reflow oven) at C2MI. Solder join integrity and solder-copper interactions are discussed in the context of industry standard application requirements.