Experimental characterization of cryogenic contact resistance

Abstract

The thermal contact resistance associated with the interface made between high conductivity metals at cryogenic temperatures depends on several variables. Some of the primary factors include surface roughness, contact pressure, and the presence/type of thermal interface materials (TIMs). However, there are many secondary factors such as work-hardening, deformation, and pressure uniformity that can lead to inherent non-repeatability in the thermal performance of pressed contacts. This variability limits the value of measurements for predicting the resistance of similar contacts, or even the same contact when it is reassembled. This work presents careful thermal contact resistance measurements for copper–copper interfaces under high pressure with and without TIMs. In addition to these measurements, the paper presents the measurement of the bulk conductivity of the same samples that are used for the contact resistance measurements as well as detailed measurements of the surface topography, and the uniformity of the contact pressure. Finally, repeated contact resistance measurements for the same sample are presented; each measurement is made after a de-mating/mating cycle carried out at room temperature. In this way, the measurements presented here provide a detailed picture not only of the thermal contact resistance and its repeatability, but also of the properties of the materials and surfaces that are associated with the joint.