Microwave Photonic-Based Step Frequency Reflectometry for Electronic Circuit Defect Detection

In this study, a microwave photonic-based step frequency reflectometry (MPSR) system, with centimeter range resolution, is presented to identify the interconnect defects in electronic circuits. Interconnect defects encompass a range of issues, including faulty solder joints, damaged cables, and insufficient bonding, all of which can manifest as impedance mismatches within the circuit. The defect detection procedure consists of two main steps: wideband SF signal generation based on the optical frequency shift loop (OFSL) technique and the frequency response measurement of the device under test (DUT). The wideband SF signal generated from OFSL can be employed as the stimulus for frequency sweep measurement, facilitating the characterization of DUT by extracting its frequency response. The subsequent application of the inverse fast Fourier transform (IFFT) to the measured frequency response enables the derivation of time-domain information, which is inherently linked to the location of discontinuities within DUT. The mathematical expression for frequency response is developed, and simulations of electronic and photonic systems are used to analyze the performance of the proposed concept. Following this, a proof-of-concept experiment was conducted to validate the theoretical framework, demonstrating the practical viability. An SF signal with a bandwidth of 16 GHz is obtained, ensuring a high-range resolution of approximately 6.3 mm. The discontinuities of four fabricated circuits are further accurately identified, showing a high degree of concordance with the results from vector network analysis (VNA). Compared with existing methods, the proposed system presents a cost-effective solution for detecting defects in electronic circuits, offering a nondestructive and rapid technique for identifying and diagnosing faults.