Torsional stiffness and fatigue study of surface-mounted compliant leaded systems

Circuit cards with surface soldered compliant leaded modules are often subjected to torque tests to ensure their structural integrity. The authors explore the stiffness and fatigue behavior of such structures. A torsional load tester was devised, exerting cyclic mechanical torque at a desired fixed amplitude and frequency. Twisting loads up into the nonlinear load range were applied. Lead forces were computed by structural analysis methods, and these were compared with finite element results. The Engel-Ling coupled plate theory was found to correspond well to finite element results. Fatigue failures occurred in the solder for J-leads and in the leads for gullwings. Fatigue curves resembled the Coffin-Manson law