Flexible embedded circuitry : a novel process for high density, cost effective electronics

Flexible electronics are starting to emerge with all-printed but also hybrid cost effective, smart electronic products that will find a wide range of applications in large quantities in our society. Such products have to be built on low cost substrate materials like PEN or PET foils. Because of the low thermal stability and limited chemical resistance of these foils, established interconnection technologies are not suitable. The current paper describes a novel technology for making electronic circuitry which does not need incompatible thermal and chemical processes during fabrication. The technology called ‘embedded circuitry’ uses laser ablation to write the circuitry patterns in the flexible foils. These patterns are subsequently filled with conductive pastes using mask-less squeegee filling techniques. Conducting lines in flexible PEN foil with widths down to 10 µm, line gaps down to 10 µm and resistances down to 0.1 O/mm are demonstrated. Finite element modeling and bending tests revealed good flexibility of this low cost circuitry. Also the circuitry can be directly used for chip attachment through flipchip bonding.