An investigation of solder joint fatigue using electrical resistance spectroscopy

Interconnect electrical resistance is examined as a possible bases for a reliability tool. Measurements are reported of the resistance change of lap shear (60% Sn-40% Pb) solder joints as a function of fatigue. The expected dependence of electrical resistance on elastic strain, plastic deformation, and cyclic fatigue is reviewed. An analytical framework is developed to examine the observed electrical resistance change. A technique called resistance spectroscopy was used to measure the small resistance change resulting from the strain and fatigue in the presence of much larger resistance changes resulting from temperature and other fluctuations. The level of the noise in the resistance measuring system used for the lap shear joints was less than one nano-ohm. The lap shear solder joints exhibited a systematic resistance change as the specimens were cycled toward failure. Initially the average resistance increased, followed by a much stronger decrease, and lastly increased markedly as crack propagation began. The decreasing-resistance portion of this signature occurs prior to crack initiation, and can be used to detect incipient solder joint failure more quickly and with greater ease than present techniques