Non-contact current reconstruction for fault detection in PCB circuits

With the increasing integration density of electronic circuits, the development of advanced failure analysis methods has become critically important. Traditional contact-based techniques are increasingly inadequate for diagnosing faults in densely packed and highly complex circuit layouts, highlighting the need for non-contact, accurate, and efficient diagnostic solutions. Here, we report a non-contact method for localizing electrical faults in printed circuit boards (PCBs) using tunnel magnetoresistance (TMR) sensors combined with a magnetic current imaging platform. A low-frequency (alternating current) AC excitation is applied to the PCB, generating a magnetic field that penetrates packaging materials and is captured by a compact TMR sensor probe. The magnetic signal, extracted via lock-in amplification, is processed using an inversion algorithm based on the Biot– Savart law to reconstruct a two-dimensional current density map. The technique achieves high sensitivity (below 1 nT at kilohertz frequencies) in a non-contact manner. Validation on both standard test structures and a functional low-noise amplifier PCB confirms the ability to image weak currents and accurately locate failing components. These results highlight the potential of TMR-enabled magnetic current imaging for precise, non-destructive failure analysis in modern electronic systems.