Multilayer Flexible Wiring Board based on screen printed Conductors

摘要

For high-volume products, such as, mobile terminals, low-cost techniques for multilayer polymer-based thick film wiring board manufacture are needed. Screen-printing is a cost-efficient technology candidate to build up approximately 6 conductor layers on both sides of a flexible substrate, for example. In order to experimentally evaluate the feasibility of screen-printing technique, the printing resolution was tested on different substrate materials, such as, polycarbonate (PC), polyethylene terephtalate (PET), polyimide (PI) and liquid crystal polymer (LCP). Conventional screen printed polymer thick film pastes were characterized on polymer substrates to form multilayer fine-line patterning and through hole vias. The final demonstrator was a double sided PI substrate having two conductor layers separated by dielectric layers on both sides of the substrate and through substrate vias. The screen-printed conductor material was an Ag based nanoparticle ink and the dielectric layer was a polyimide-based material. Several challenges were identified that might hinder the applicability of the technology for mass-production. The stability of the polyimide substrate is a problem if the curing temperature of the printed materials is above 20 ℃. Layer-to-layer alignment tolerances are feasible if the printed area is small, 5" × 5", in our case. The flatness of the substrate, however, is not very good after printing several layers on each other. The tested nanoparticle ink is a promising conductor system; however, lowering of the curing temperature from 230 ℃ below 200 ℃ would have a major impact on production friendliness.