The role of impedance control in early detection of interconnect degradation using time domain reflectometry

A study was performed to investigate the feasibility of using impedance monitoring for early detection of interconnect degradation in circuits with poorly controlled impedance. The objective of this effort is to address one of the critical uncertainties affecting the implementation of interconnect monitoring in practical electronic products, including those not specifically designed for high frequencies. Time domain reflectometry (TDR) was used to monitor circuits on two different substrates, Rogers 4003 and FR4, during shear testing of solder joints. The test boards had a variety of circuit designs and ground configurations. It was found that early stages of solder joint degradation could be detected even on the circuits with poor impedance control, provided the initial healthy state of the test circuit was used as the reference condition during the calibration of the TDR instrument. This study thus opens the door to application of TDR to a wide variety of electronic products, including those without a dedicated ground plane, for interconnect monitoring.