Stout hourglass – The ideal shape for robust solder joints

The optimum shape of solder joints in an electronic assembly that experienced differential thermal expansion between its constituting members was analysed using advanced beam analysis. The advanced beam analysis is capable of modeling the exact geometry of solder joints. The shearing and bending stresses in solder joints of multiple shapes: barrel, slender hourglass, and stout hourglass, were evaluated. The barrel-shape solder joints returned the highest magnitudes of shear stress, bending stress, and von mises stress. The slender-hourglass-shape solder joints that have superior in-plane shear compliance returned the lowest magnitude of shear stress at 10% that of the barrel-shape solder joints, and a von mises stress that is 27% that of the barrel-shape solder joints. The stout-hourglass-shape solder joints returned the lowest magnitude of bending stress at 13% that of the barrel-shape solder joints, and a von mises stress that is 14% that of the barrel-shape solder joints. The substantial reduction in the magnitude of von mises stress by the stout-hourglass-shape solder joints is estimated to give an eight-time improvement in the temperature cycling life of solder joints.