A study of solder joint degradation and detection using RF impedance analysis

The trend of many types of electronic products is toward higher operating frequencies. At high frequencies, the signal propagation is concentrated at the surface of interconnects, which is known as the skin effect. Therefore, even a samll crack at the surface of a solder joint may directly influence the performance of high speed electronic assemblies. Degradation of solder joints, such as cracking due to fatigue or stress, generally initiates at the surface where the strain range is maximized, and propagates inward. Traditional DC resistance measurements are not able to sense partial cracks in solder joints. RF impedance analysis, which is capable of detecting small cracks, offers an improved means of monitoring the degradation of solder joints of high speed electronic products. In this study, RF impedance changes are used as an early indicator of degradation of solder joints, due to the skin effect, compared with DC resistance measurements. Impedance-controlled circuit boards on which surface mount components were soldered have been developed. Partially and entirely cracked solder joints were produced for test in advance. The RF impedance was observed to increase in response to partial cracking of the solder joint, while the DC resistance did not indicate any anomalies. The technique of RF impedance analysis shows potential as a prognostic tool that can provide advanced warning of impending failures of solder joint. At last future research work in this field is suggested.