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Research Papers

Maximum Resolution of a Probe-Based, Steady-State Thermal Interface Material Characterization Instrument

[+] Author and Article Information
Ronald J. Warzoha

Assistant Professor
Mem. ASME
Heat and Mass Transfer Laboratory,
Department of Mechanical Engineering,
United States Naval Academy,
Annapolis, MD 21402
e-mail: warzoha@usna.edu

Andrew N. Smith

Professor
Mem. ASME
Heat and Mass Transfer Laboratory,
Department of Mechanical Engineering,
United States Naval Academy,
Annapolis, MD 21402
e-mail: ansmith@usna.edu

Maurice Harris

Department of Mechanical Engineering,
United States Naval Academy,
Annapolis, MD 21402

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received June 24, 2016; final manuscript received November 4, 2016; published online December 29, 2016. Assoc. Editor: Xiaobing Luo.This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.

J. Electron. Packag 139(1), 011004 (Dec 29, 2016) (8 pages) Paper No: EP-16-1075; doi: 10.1115/1.4035178 History: Received June 24, 2016; Revised November 04, 2016

Thermal interface materials (TIMs) constitute a critical component for heat dissipation in electronic packaging systems. However, the extent to which a conventional steady-state thermal characterization apparatus can resolve the interfacial thermal resistance across current high-performance interfaces (RT < 1 mm2⋅K/W) is not clear. In this work, we quantify the minimum value of RT that can be measured with this instrument. We find that in order to increase the resolution of the measurement, the thermal resistance through the instrument's reference bars must be minimized relative to RT. This is practically achieved by reducing reference bar length. However, we purport that the minimization of reference bar length is limited by the effects of thermal probe intrusion along the primary measurement pathway. Using numerical simulations, we find that the characteristics of the probes and surrounding filler material can significantly impact the measurement of temperature along each reference bar. Moreover, we find that probes must be spaced 15 diameters apart to maintain a uniform heat flux at the interface, which limits the number of thermal probes that can be used for a given reference bar length. Within practical constraints, the minimum thermal resistance that can be measured with an ideal instrument is found to be 3 mm2⋅K/W. To verify these results, the thermal resistance across an indium heat spring material with an expected thermal contact resistance of ∼1 mm2⋅K/W is experimentally measured and found to differ by more than 100% when compared to manufacturer-reported values.

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References

Figures

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Fig. 1

Thermal gradient within computational domain

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Fig. 2

Experimental apparatus

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Fig. 3

Effect of reference bar, thermal probe, and filler material k on Uy for each probe. rhole/rprobe = 5% was assumed.

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Fig. 4

Effect of probe hole radius to probe radius ratio and thermal probe to filler material thermal conductivity ratio on the location uncertainty for each individual probe. kbar/kprobe was assumed to be equal to 100.

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Fig. 5

(a) Average heat flux deviation from reference bars without embedded probes for varying W/D and (b) maximum range of heat flux values relative to expected heat flux at the interface without embedded probes for varying W/D

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Fig. 6

Heat flux ratio at interface for three different locations (bar edge, average distance between bar edge, and centerline and centerline) when W/D = 10

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Fig. 7

Uncertainty as a function of reference bar length forUT = ±0.01 K, Uy = 140 μm, Uk = ±20 W/m · K, and RT = 1 mm2⋅K/W

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Fig. 8

Uncertainty as a function of reference bar length for UT = ±0.001 K, Uy = 140 μm, Uk = ±20 W/m · K and varying RT

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Fig. 9

Thermal contact resistance at copper–copper (squares) and indium heat spring–copper (circles) interfaces

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