Characterization of the thermal properties of OFHC copper at cryogenic temperature

Advancements in electronics technology that operate at cryogenic temperature require the study of thermal properties of the materials and interfaces used to connect these systems to a source of cooling. A test facility has been developed to investigate thermal properties important to these applications, bulk conductivity and contact resistance, over the temperature range from 4 K to 40 K. Bulk conductivity tests were conducted on OFHC copper sourced from three different commercial vendors to determine the degree of variation between the commercial sources and the level of agreement with the values found in literature. Preliminary analysis found RRR values within the range of 50 to 75 for all sources examined. These results are in line with previous studies and confirm the consistency of copper conductivity regardless of the source. The contact resistance tests focus on measuring the variation of contact resistance with applied force over the range from 90 N to 161 N for gold-plated OFHC copper samples with surface roughness in the range of 1 to 2 micrometer. Results from these tests will provide insight into the significance of force on contact resistance. The results from both tests will help guide the design of heat paths in future cryogenic electronic technology.