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 present work explores 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