Study of coupled thermal electric behavior of compliant micro-spring interconnects for next generation probing applications

Advances in integrated circuit fabrication have given rise to a need for an innovative, inexpensive, yet reliable probing technology with ultra-fine pitch capability. Flexible micro-spring structures that can exceed the probing needs of the next-generation microelectronic devices have been developed. Highly compliant cantilevered springs have been fabricated at pitches as small as 6μm. These micro-springs are designed to accommodate topological variation in probing surfaces while flexing within the elastic regime. Coupled thermal-electric numerical models have been developed to understand the thermal contours and current density developed across these springs. Based on the models and experiments, it is seen that the electrical resistance of the probe spring under study will be less than 1 Ω. Also, it is seen that the maximum temperature due to Joule heating is localized near the tip of the probe and can be about 93°C above the ambient temperature, when temperature dependent bulk material properties are used. Optimization of the spring geometry to reduce this maximum temperature is outlined. In addition, the role of scale effects on the thermal conductivity of the spring material is studied. Based on the work, it can be said that it is possible to design micro-contact springs for probing applications such that the electrical resistance and the temperature increase during probing will be within acceptable limits.