Abstract: Conventional detection methods for ball grid array (BGA) solder joints, such as X-ray or single-mode thermal imaging, often struggle to achieve precise identification and quantitative assessment when confronted with micron-level defects, due to insufficient differentiation and reliance on empirical thresholds. To address this challenge, this study developed a multiphysics simulation model based on COMSOL Multiphysics®. This model accurately represented the three-dimensional structure encompassing the chip, solder balls, and printed circuit board (PCB), and established a transient electrical-thermal coupling analysis framework. By incorporating differentiated contact resistance parameters to physically characterize the high - resistance of cold solder joints and the current-bypassing effect of solder bridging, and by applying a periodic alternating current for excitation, the study effectively revealed the unique response mechanisms of these defects under dynamic operating conditions. Based on these findings, a joint detection criterion combining localized electrical potential anomalies and temperature gradient features was proposed. This criterion effectively distinguished the localized hot-spot concentration associated with cold solder joints from the rapid thermal diffusion caused by solder bridging, thereby overcoming the insufficient differentiation capability of traditional methods for subtle defects. The study provides a quantitative non-destructive testing method for BGA solder joint defects, which is of significant importance for enhancing the reliability assessment of high-density packaging.