2025

Välimäki, Marja; Happonen, Tuomas; Karhu, Toni; Ontero, Pekka; Luoma, Enni; Ollila, Jyrki; Korhonen, Pentti; Takaluoma, Antti; Rooms, Harmen; Kraft, Thomas M.

A key aspect of printed electronics manufacturing is layer-layer registration and potential deformation of the substrate during processing (e.g. printing) which involves thermal treatment under tension or steps without any tension (e.g. surface mount hybrid integration of electronics). The influence of thermal processing on the registration control and material interfaces for printed and hybrid processing was evaluated on a pilot printing line using R2R screen-printed silver microflakes and PEDOT:PSS inks. The registration was not fully stabilized on PET whereas on thermally pre-treated PET (PET_t) it reached ±60 µm accuracy in machine direction (MD) and ±100 µm in cross-machine direction (CD) after settling. The print on PET deviated 0.18% in MD and -0.01% in CD, implying that the print dimensions were changing along the MD elongation whereas the changes on PET_t occurred during the pre-treatment thus, the print deviated only -0.01% in MD and 0.08% in CD. Silver-substrate interface obtained good adhesion, however partial delamination was detected after thermal post-treatment at zero tension, most likely due to substrate shrinkage. Differences in the thermal response may partially delaminate the silver. Delamination of PEDOT:PSS was not observed, which may be related to its polymeric nature. Silver resistance on PET was 8% higher than on PET_t in MD, due to the elongation of the PET that occurs during print curing. Respectively, the silver resistance on PET was 2% lower in CD, with the dimensions slightly below the nominal layout value. Thermal post-treatment at zero tension reduced the resistance on both substrates, being greater in the MD as well as the substrate shrinkage. The impacts of thermal treatment are particularly important if the hybrid electronics processing is utilizing manufacturing lines with different web tension, such as printing and SMT assembly, since the dimensional changes of the substrate can cause significant reduction in accuracy and reliability.