An analytical model of the RF impedance change due to solder joint cracking

An analytical model is presented of the RF impedance change due to the cracking of a solder joint connecting a surface mount component to a transmission line (TL). This model provides insight into the underlying physical and electrical phenomena giving rise to the impedance changes which are experimentally observable. A distributed element model of a TL was developed which includes the geometrical parameters of a crack propagating through a solder fillet. The model was validated by comparison of the results to data obtained from laboratory measurements. In addition, a model of the DC resistance of the TL with a cracked solder joint was created. The two models were used to calculate and compare the sensitivity of the RF impedance and DC resistance to solder joint cracking as a function of crack geometry.