Fabrication of wireless sensors on flexible film using screen printing and via filling

Wireless sensors are fabricated on flexible plastic films by means of screen printing and via-hole filling. The wireless sensors are battery free with data and power transmission functions. The sensors, fabricated on polyethylene terephtalate films, are designed based on RFID technology. Using an additive patterning process known as screen printing, metallization on polymer films is created. Both sides of a polymer film are printed with metallic patterns and connected with micro vias filled with conductive paste. One side of the film consists of printed electrical traces for discrete components like resistors and transistors that would be mounted onto it; the other side consists of a printed inductive coil used for wireless data and power transmission. The micro vias, which have a diameter of 120 mu m, are formed by mechanical punching and filled with conductive silver paste. The size of one sensor unit is approximately 2 cm x 1.5 cm; an array of 4 x 7 sensor units are printed over an area of 15 cm x 15 cm on a PET film. Details of manufacturing processes, component assembly and functionality test are presented in this paper.