Research Papers

Thermally Conductive and Highly Electrically Resistive Grease Through Homogeneously Dispersing Liquid Metal Droplets Inside Methyl Silicone Oil

[+] Author and Article Information
Shengfu Mei, Yunxia Gao, Zhongshan Deng

Key Lab of Cryogenics and Beijing Key Lab
of CryoBiomedical Engineering,
Technical Institute of Physics and Chemistry,
Chinese Academy of Sciences,
Beijing 100190, China

Jing Liu

Key Lab of Cryogenics and Beijing Key Lab
of CryoBiomedical Engineering,
Technical Institute of Physics and Chemistry,
Chinese Academy of Sciences,
Beijing 100190, China
e-mail: jliu@mail.ipc.ac.cn

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received August 15, 2013; final manuscript received December 25, 2013; published online January 24, 2014. Assoc. Editor: Masaru Ishizuka.

J. Electron. Packag 136(1), 011009 (Jan 24, 2014) (7 pages) Paper No: EP-13-1088; doi: 10.1115/1.4026414 History: Received August 15, 2013; Revised December 25, 2013

Thermal grease, as a thermal interface material (TIM), has been extensively applied in electronic packaging areas. Generally, thermal greases consist of highly thermally conductive solid fillers and matrix material that provides good surface wettability and compliance of the material during application. In this study, the room-temperature liquid metal (a gallium, indium and tin eutectic, also called Galinstan) was proposed as a new kind of liquid filler for making high performance TIMs with desired thermal and electrical behaviors. Through directly mixing and stirring in air, liquid metal micron-droplets were accidentally discovered capable to be homogeneously distributed and sealed in the matrix of methyl silicone oil. Along this way, four different volume ratios of the liquid metal poly (LMP) greases were fabricated. The thermal and electrical properties of the LMP greases were experimentally investigated, and the mechanisms were clarified by analyzing their surface morphologies. The experimental results indicate that the original highly electrically conductive liquid metal can be turned into a highly electrically resistive composite, by simply blending with methyl silicone oil. When the filler content comes up to 81.8 vol. %, the thermal conductivity, viscosity and volume resistivity read 5.27 W/(m · °C), 760 Pa · s and 1.07 × 107 Ω m, respectively. Furthermore, the LMP greases presented no obvious corrosion effect, compared with pure liquid metal. This study opens a new approach to flexibly modify the material behaviors of the room-temperature liquid metals. The resulted thermally conductive however highly electrically resistive LMP greases can be significant in a wide variety of electronic packaging applications.

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Fig. 1

A schematic diagram for the fabrication process of the LMP grease

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Fig. 2

(a) The contact angle measurement system (JC2000D3, Shanghai) and (b) contacting images of an oxidized liquid metal droplet with a bare copper surface and a silicone oil coated copper surface in air

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Fig. 3

(a)–(e) The sequential images of the first few minutes of the stirring process of making LMP greases. (f) The exhibition of the silicone oil, liquid metal and LMP grease; (g)–(i) the liquid metal, silicone oil, and LMP grease painted on copper plates, respectively.

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Fig. 4

(a) The Mathis TCi Thermal Analyzer Sensor, annular steel spacer (20 mm inner diameter, 15 mm depth) and 90 g steel cap and (b) experimentally measured and theoretically calculated thermal conductivities of the LMP thermal greases

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Fig. 5

Electrical resistivity of the LMP greases and liquid metal (inset: Agilent 34972A meg-ohm test system)

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Fig. 6

The viscosity of the pure silicone oil, LMP grease, air-oxidized liquid metal, and pure liquid metal

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Fig. 7

Plain-view ESEM images of (a) the pure liquid metal; (b) the air-oxidized liquid metal; and (c)–(f) the four different volume ratio LMP greases

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Fig. 8

(a) Corrosion test system; (b) the 6063 aluminum plates before corrosion; (c) the 6063 aluminum plates after corrosion (left: corroded by liquid metal, and right: by LMP grease); and (d)–(f) the energy-dispersive spectroscopy spectra of the clean 6063-aluminum plate, liquid metal corroded plate and the LMP grease corroded plate




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