Contactless inspection of electrically isolated electronic components of planar electronic devices by capacitive coupling

During the early steps of the production process, printed electronic circuits and devices such as flat panel displays and detector panels consist of a large number of electrically isolated components. Detection and thus inspection of isolated electronic parts by capacitive coupling only becomes possible if an appropriate sensor design is chosen. Therefore, the dependence of sensor performance on sensor design was analyzed by means of finite element simulations based on the nonmatching grid approach. A clear detection of individual components is achieved if the sensor imposes a non-uniform potential distribution along the boundary surface of the substrate that carries the electronic components. Sensor resolution can drastically be increased by shielding specific sensor electrode areas or employing an additional shielding encompassing the sensor electrode. From the analysis of the simulation results, design rules for sensor electrode and shielding geometry are deduced. Finally, the performances of a sensor obeying to the deduced design rules and a currently employed sensor are compared with regard to directly electrically accessible components.