A Compact High-Resolution Resonance-Based Capacitive Sensor for Defects Detection on PCBAs

Increased density of printed circuit board assembles (PCBAs) is diminishing physical contact test access of the in-circuit testing (ICT) solutions for defects detection. As a result, it is necessary to design contactless test solutions with high spatial resolution to overcome the current test limitations. In this paper, a compact contactless sensor is presented for monitoring the fabrication quality of PCBAs. The sensor consists of an inductor-capacitor-(LC)-based resonant circuit and it can detect defects on metallic traces of PCBAs in close proximity without a contact. The sensor is designed such that, strong electric field is confined around the sensor tip, which creates strong capacitive coupling between the sensor tip and devices under test (DUTs) within a small region for sensing, i.e. high resolution sensing. The sensitivity of the proposed sensor is verified by the simulated and experimental 2D surface mapping results with sample DUTs, and it shows that the sensor can detect the open or short defects with a size as small as 0.15 mm × 0.2 mm. Circuit models are proposed to predict the sensing behavior and for guiding the design. The proposed sensor shows great potential to be used in the real-time monitoring of defects along the manufacturing supply chain.