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Research Papers

Durability of Low Melt Alloys as Thermal Interface Materials

[+] Author and Article Information
Chandan K. Roy

Mem. ASME
Department of Mechanical Engineering,
Auburn University,
2420 Wiggins Hall,
Auburn, AL 36849
e-mail: ckr0005@auburn.edu

Sushil Bhavnani

Department of Mechanical Engineering,
Auburn University,
1418C Wiggins Hall,
Auburn, AL 36849
e-mail: bhavnsh@auburn.edu

Michael C. Hamilton

Department of Electrical and Computer Engineering,
Auburn University,
403 Broun Hall,
Auburn, AL 36849
e-mail: mch0021@auburn.edu

R. Wayne Johnson

Department of Electrical and Computer Engineering,
Tennessee Tech University,
217A Brown Hall,
Cookeville, TN 38505
e-mail: wjohnson@tntech.edu

Roy W. Knight

Department of Mechanical Engineering,
Auburn University,
3418B Wiggins Hall,
Auburn, AL 36849
e-mail: knighrw@auburn.edu

Daniel K. Harris

Department of Mechanical Engineering,
Auburn University,
2418B Wiggins Hall,
Auburn, AL 36849
e-mail: harridk@auburn.edu

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received October 6, 2015; final manuscript received December 28, 2015; published online March 10, 2016. Assoc. Editor: Xiaobing Luo.

J. Electron. Packag 138(1), 010913 (Mar 10, 2016) (7 pages) Paper No: EP-15-1108; doi: 10.1115/1.4032462 History: Received October 06, 2015; Revised December 28, 2015

This study investigates the reliability of low melt alloys (LMAs) containing gallium (Ga), indium (In), bismuth (Bi), and tin (Sn) for the application as Thermal interface materials (TIMs). The analysis described herein involved the in situ thermal performance of the LMAs as well as performance evaluation after accelerated life cycle testing, which included high temperature aging at 130 °C and thermal cycling from −40 °C to 80 °C. Three alloys (75.5Ga & 24.5In, 100Ga, and 51In, 32.5Bi & 16.5Sn) were chosen for testing the thermal performance. Testing methodologies used follow ASTM D5470 protocols and the performance of LMAs is compared with some high-performing commercially available TIMs. Results show that LMAs can offer extremely low (<0.01 cm2 °C/W) thermal resistance compared to any commercial TIMs. The LMA–substrate interactions were explored using different surface treatments (copper and tungsten). Measurements show that depending on the substrate–alloy combinations, the proposed alloys survive 1500 hrs of aging at 130 °C and 1000 cycles from −40 °C to 80 °C without significant performance degradation. The obtained results indicate the LMAs are very efficient as TIMs.

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References

Figures

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Fig. 1

(a) Testing of LMAs using the modified test-rig; the copper disks assembly with LMA TIM at the interface placed directly under the TIM tester surface. (b) Schematics of the testing methodology.

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Fig. 2

Tungsten (W) coated (about 2 μm) copper disk

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Fig. 3

Probe disturbance as a function of the probe location (distance from the TIM surface) for a TIM with a thermal resistance of 0.01 cm2 °C/W

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Fig. 4

Temperature distribution on the top surface of the TIM with a thermal resistance of 0.01 cm2 °C/W: (a) probes are perfectly aligned (ΔT = 0.04 °C) and (b) probes are at 90 deg (bottom probe is rotated) (ΔT = 0.26 °C) [17]

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Fig. 5

In situ thermal resistances of different substrate–alloy combinations at 138 kPa

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Fig. 6

Scanning electron microscopy (SEM) cross-sectional image of alloy 1 placed between bare Cu disks

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Fig. 7

Normalized thermal resistance of three alloys between bare Cu substrates as a function of aging time

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Fig. 8

Normalized thermal resistance of three alloys between W-coated substrates as a function of aging time

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Fig. 9

Thermal cycling of three alloys between bare Cu substrates

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Fig. 10

Thermal cycling of three alloys between W-coated substrates

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Fig. 11

Extrusion of alloy 3 (In–Bi–Sn) from the interface between W-coated disks upon thermal cycling

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Fig. 12

Alloy 2 (Ga) between bare Cu after 200 cycles, one side wetting

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Fig. 13

Performance comparison of a variety of commercial TIMs

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