Assessment of Thermal Pastes for Use in Space Electronics
Authors: Jeffrey Marcus Jennings, Susan M. Marlowe, and Peter F. Ruggiero Company: Harris Corporation Date Published: 9/27/2015
Abstract: As the aerospace electronics industry becomes increasingly more reliant on COTS surface mount processors (FPGAs, CPUs, etc.) with demanding thermal dissipation requirements and packaging optimized for convection cooling (top heat-sinked devices), thermal designers have been driven to broaden their search in the identification of suitable thermal interface materials. Thermal pastes, a material class traditionally avoided in high altitude or vacuum (space) hardware applications due to concerns over contamination and long term dimensional stability, are being considered with renewed interest for use in the adaptation of top heat-sinked devices into conductioncooled CCA applications. This trend is based on pastes’ ability to provide low interfacial thermal resistance often combined with minimal force transfer into the device preserving its long-term solder joint reliability. The current work reviews an assessment of numerous (non-electrically conductive) 1-part-silicone free thermal paste candidates for their potential use in space electronics and documents typical results (both positive and negative where applicable) for each evaluation performed. The thermal paste properties evaluated, many specific to space electronics, include: dimensional stability at high temperature (slump) and constant acceleration; mass loss and dimensional stability in vacuum; thermal conductivity before and after vacuum bake; material property change with extended high temperature and or thermal vacuum exposure; outgassing (per ASTM E-595); and thermal cycling. As a practical consideration ease of clean-up was also evaluated for a potential rework scenario requires full removal of any applied paste from the working area. The outcome of these evaluations are compared with results from paste materials in different material categories including silicone-based materials for determination of their relative performance and their applicability for use in the intended space electronics applications is discussed.
Thermal Paste, Thermal Putty, Thermal Gel, Thermal Interface Materials (TIMs), Thermal Management, COTS in Space Electronics, Material Characterization