Polymer materials are usually thermal insulators, but U.S. researchers have organized the polymer fibers into a neat array through electropolymerization processes to form a new type of thermal interface material. The thermal conductivity has been increased by 20 times over the original. The new material can operate reliably at temperatures up to 200°C and can be used in heat sinks to help dissipate heat from electronic devices in servers, automobiles, and high-brightness LEDs (light emitting diodes). The results of this research were published in advance in the online edition of the journal Nature Nanotechnology.
As electronic devices become more powerful and smaller, the heat dissipation problem becomes more and more complex. Engineers are always looking for better thermal interface materials to help electronic equipment effectively dissipate heat. Amorphous polymer materials are poor conductors of heat because their disordered states limit the transfer of thermal conduction phonons. Although thermal conductivity can be improved by creating a neatly arranged crystalline structure in the polymer, these structures are formed by a fiber drawing process, which can result in brittle materials.
According to Balatud Krath, an assistant professor at the George Woodruff School of Mechanical Engineering at the Georgia Institute of Technology, the new thermal interface material is made of conjugated polymer polythiophene. Its neat array of nanofibers facilitates the transfer of phonons. It also avoids the brittleness of the material. The new material has a thermal conductivity of 4.4 watts/m·Kelvin at room temperature and has undergone 80 thermal cycling tests at a temperature of 200°C. The performance is still stable; in comparison, the thermal interface between the chip and the heat sink is often used. The solder material may become unreliable when working at high temperatures during reflow.
The nanofiber array structure is fabricated in several steps: The researchers first applied a monomer-containing electrolyte to a microporous aluminum oxide template, and then applied a potential to the template. The electrodes in each pore attracted The monomers begin to form hollow nanofibers. The length and wall thickness of the fibers are controlled by the amount of current applied and the time, and the diameter of the fibers is determined by the size of the pores, ranging from 18 nm to 300 nm. Conventional thermal interface materials have a thickness of about 50 micrometers to 75 micrometers, and the new material obtained in this way can be as thin as 3 micrometers.
Carat stated that the technology still needs further improvement, but he believes that it can expand production and commercialization in the future. "Such materials with such high reliability are very attractive for solving heat dissipation problems. This material may eventually change the way we design electronic systems." (Chen Dan)
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