Time Domain Reflectometry technique for detecting the degradation of solder joints

Solder joints on the Printed-Circuit board (PCB) serve as mechanical and electrical connections. Their function maybe simple, but the reliability of the solder joints may affect the entire device or system. They are usually the weak links when the electronic products are exposed to a variety of load conditions from their operation and storage, such as temperature cycling, vibration, shock and humidity. One of the most important parameters of solder joints is electrical stability. The resistance or impedance will rise as the fracture spreads through the solder joints. The reliability of solder joints is often determined through continuous DC resistance measurement, but it not very accurate and sensitive. In recent years, Time Domain Reflectometry (TDR) technique has been found to be a better alternative that are required for monitoring the degradation of interconnects. A technique for prognosing solder joint degradation using TDR has been presented in this study. At high frequencies, signal propagation is concentrated at the surface of interconnects, a phenomenon known as the skin effect. Degradation of interconnects, such as cracking of solder joints due to fatigue or shock loading, also usually initiates at the surface and propagates inward. Therefore, even a small crack at the surface of a solder joint may change RF impedance. A physical crack initiated at the surface of the solder joints results in the increase of RF impedance and then senses interconnect degradation. This technology would create the opportunity for real-time detection and early warning of interconnect degradation, allow condition-based maintenance, and reduce unplanned downtime. This could bring potentially substantial savings in operation and repair costs, help to reduce the incidence of "no trouble found" failures due to intermittent contact behavior, and improve product safety and availability.