Design Considerations for Miniaturized Steady-State Thermal Characterization Instruments

We use numerical simulations to design and optimize a set of miniaturized heat meter bars for high-resolution measurements of interfacial thermal transport across solid, contacting junctions (R
_T
) and thermal conductivity within low-resistivity materials (κ). We find that extreme care must be taken to design both the geometry of the heat meter bars and the cooling technique used to drive thermal transport across the junction. To reduce measurements of R
_T
down to 0.1 mm
²
·K/W, a channel heat sink is optimized to remove heat from the lower bar. Results suggest that in order to maintain a sufficient number of temperature measurements, the bar length can be no less than 3 mm in order to maintain a linear thermal gradient a sufficient distance away from the interface. Further reductions in heat meter bar length are insufficient to achieve corresponding reductions in R
_T
. To address this limitation, a jet impingement cooling technique is assessed. We find that a 2 × 3 array of jets (D = 1 mm) is sufficient to maintain a linear thermal gradient around the interface as the heat meter bar length is reduced below 5 mm. Using the jet impingement cooling technique described in this paper, measurements of R
_T
= 0.01 mm
²
· K/W are found to be theoretically possible. This would represent a two-orders-of-magnitude improvement in the resolution of interfacial thermal resistance measurements made with steady-state thermal characterization techniques. The thermal challenges explored in this paper are critical to the design of instruments that can directly characterize the magnitude of heat flow permitted across high-performance thermal interface materials in electronics packaging systems.