High-Temperature RF Transmission Loss Characteristics of Platinum–Inconel 600 and Platinum–304 Steel Interconnects

Abstract

Radio-frequency (RF) transmission losses that occur at electronic interconnects are currently an important limitation of wireless sensors and other electronic device packages that must operate in high-temperature environments. In this work, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> RF transmission losses were measured for two types of interconnects: platinum (Pt) wire bonded to an Inconel 600 coaxial cable, and Pt-wire bonded to a block of 304 steel. Heating the Pt wire/Inconel interconnects at 800 °C for up to 200 h was found to be very stable with no measurable transmission losses. In contrast, Pt wire/304 steel block interconnects examined over similar test periods at 800 °C exhibited gradual increases in transmission losses leveling off at 10, 38, and 85 mdB at 400, 700 MHz, and 1 GHz, respectively. Increasing the test temperature to 900 °C caused further elevated transmission losses of 30, 70, and 108 mdB at the same reported frequencies. By comparison, temperature cycling of the Pt wire/304 steel interconnects between room temperature and 900 °C was found to cause more significant degradation. In particular, four thermal cycles from room temperature to 900 °C resulted in losses of 75, 271, and 482 mdB at the same reported frequencies. Parabolic oxidation relative to the RF skin depth in the 304 steel block at the tested frequencies is discussed as a possible reason for the transmission losses during the isothermal soaks, whereas interconnect degradation due to differences in thermal expansion between Pt and 304 steel is primarily responsible for transmission losses caused by high-temperature cycling.