Thermal analysis, design, and characterization of a reconfigurable switch matrix based on LTCC technology for satellite communications

Abstract

The thermal characteristics of a reconfigurable switch matrix (RSM) module based on low temperature co-fired ceramic (LTCC) technology are presented. Owing to the PIN-diodes based design, a static power of 1.6 W is dissipated on the ceramic package; the double-sided mounting and integrated bias circuitry demands determination of the temperature distribution within the module. A finite-element thermal simulation model was validated by an infrared (IR) thermograph; the steady-state temperature distribution on the surface of the package estimated by the simulation model differs to the IR measurements by < 1%. This temperature distribution is the result of the thermal interaction among components on the multi-die package with different electrical power dissipation. The temperature on the multi-throw switch monolithic microwave integrated circuit (MMIC) is elevated by ~36.7 K relative to the ambient temperature. The peak temperature occurs on the current-limiting resistors in the bias circuitry; the peak temperature is estimated to be ~45 K above the ambient. In a later version of the RSM, the bias current was reduced by 50%, current-limiting resistor was replaced by two parallel resistors, and additional thermal vias and conductive pads were introduced on the ceramic package. The cumulative effect is a temperature distribution on the package with lowered values. Compared to its predecessor, the temperatures at the current-limiting resistor and the MMIC are reduced by ~20 K and ~14 K, respectively. With one heat source active on the ceramic package at a time, the resulting steady-state temperatures on this source and the remaining heat sources provided an estimate of the self- and transfer-thermal resistances, respectively. The reciprocity of the heat flow on the package and the three-dimensional symmetric layout required only ‘4’ thermal simulations to determine the symmetric thermal resistance matrix. The significantly reduced values of the computed matrix for the later version of the RSM module demonstrated lower thermal resistance to the ambient, compared to its predecessor. Lastly, the results of thermal measurements conducted with a vacuum wafer prober are presented, in order to validate RSM functionality for vacuum pressures (≤ 1 mPa) and temperatures between 248 K and 338 K; the control current and the transmission coefficient demonstrated variations of ≤ 0.5% and −0.015 dB/K, respectively.