Abstract
This research investigates the effects of thermal cycling from room to cryogenic temperatures (300K–4K) on the thermal expansion coefficient of two ceramic substrates of Silicon Nitride (Si3N4) and alpha-Alumina/Sapphire (α-Al2O3). Due to the shortage of available data, a comparative study with reference materials, Copper, AISI Carbon Steel 1008 and Molybdenum, are compared to the National Institute of Standards and Technology (NIST) property data as a proof of concept. Accurate thermal contraction data of materials at low temperatures are important in material selection and thermal design of engineered systems, such as, space electronic devices. Thermal expansion mismatch causes substantial problems in space electronic device reliability because of the various stresses imposed on the joint materials undergoing extreme thermal cycles. Theory supports the advantage of utilizing Sapphire (Al2O3) and Silicon Nitride (Si3N4) within microchip configuration. However, there is limited data available that confidently supports this assertion beyond theory. An electro-mechanical method for in-situ strain measurements is presented as a tool to characterize thermomechanical behavior of Sapphire and Silicon Nitride at temperatures below 50 K. The calculated coefficient of thermal expansion for silicon nitride is 1.35 · 10−6 1/K and 0.994 · 10−6 1/K for sapphire at 5.7 K. The results from this validation have a mean error percentage of less than 6 %.
