Ultrafast Laser Direct Writing of Conductive Patterns on Polyimide Substrate

Laser direct writing (LDW) is a fast and cost-effective method for printing conductive patterns in flexible polymer substrates. The electrical, chemical, and mechanical properties of polyimide (PI) make it an attractive material choice for laser writing of conductive circuits in such polymer. Electrically insulating PI has shown great potential for flexible printed electronics as LDW enables selective carbonization in the bulk of such material leading to the formation of conductive lines. However, existing studies in this area reveal a few key limitations of this approach including limited conductivity of written structures and fragility of carbonized PI. Therefore, more research is required to overcome those limitations and reap the benefits of the LDW approach in writing flexible electronic circuits in PI. The proposed study investigates potential approaches to enhance the electrical conductivity of femtosecond laser written bulk carbon structures in PI films. Deposition of laser energy was varied by changing key process parameters such as pulse energy, pulse picker divider, and hatch distance of laser scan to maximize the conductively of the carbon structure. The experimental findings show a strong dependency of laser energy deposition on the conductivity carbon structures in PI films. To further enhance the electrical conductivity of laser written structures, the feasibility of adding copper microparticles to the PI solution and subsequent laser carbonization was studied. The proposed LDW of conductive lines has potential in flexible electronic circuits and sensing applications.