Taking the Heat Print E-mail
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Written by Dr. Renzhe Zhao   
Friday, 31 October 2008 19:00

Phase change materials offer an alternative to greases and pads.

Materials World When it comes to addressing thermal management demands of today’s advanced electronics devices, newer technologies are offering much-needed alternatives for varying requirements. Different applications, user preferences and performance requirements dictate the material type to be selected. One thing is universal, however: effective thermal management – especially at the TIM2 level – is more critical than ever as devices shrink in footprint and increase in functionality and, therefore, get hotter. Recognizing that robust, cost-effective heat management must also cater to differing applications and user requirements, leading materials companies have developed a range of solutions to meet numerous specifications.

Traditionally, thermal interface materials have been supplied in two forms: thermal greases or paste or solid pads. Pads have generally been preferred for their ease of use and long-term stability while pastes or greases tend to offer better wetting and, therefore, improved overall thermal performance. But, selection of a particular class of material often comes down to preference for whatever reason – comfort level with a particular material, the most important performance criteria or, of course, cost. One thermal management film-based technology that has become increasingly popular are phase change materials. These products are solid at room temperature, but become liquid once the device’s heat moves the material to its melt point. This efficiency and ease of use has encouraged widespread adoption of phase change thermal interface products.

But, while phase change film technologies are regarded for their performance, there are some drawbacks. Films come in a variety of thicknesses but extremely thin films are difficult to manufacture and often do not release cleanly from the liner. To address these hurdles, liquid systems that offer similar performance characteristics to that of film technologies have been developed. The new materials come in liquid form and provide many of the advantages of thermal greases in terms of usability and throughput without some of the challenges inherent with greases in some applications. These novel liquid format products are pastes that can either be dispensed or screen-printed and, over time, the paste will dry and yield a phase change pad. The reliability and performance of these materials are consistent with film phase change materials but, because they are liquid mediums, thickness can be adjusted depending on the requirement. As the liquid material can be fully automated, throughput is improved and adaptable to current equipment, permitting manufacturers to use standard dispensers or screen printers. In addition, liquid-based phase change materials deliver more control for deviations in surface flatness with the ability to fill voids with varying thicknesses.

For manufacturers that prefer to use thermal greases, new materials with improved characteristics are an option for devices that have flatness or coplanarity issues, as greases have a tendency to easily compensate for voids. While phase change liquids have to undergo a step whereby they flash off prior to achieving desired performance, greases are functional as soon as applied. Greases offer a viable alternative for manufacturers who want to avoid the extra processing requirements associated with phase change materials and silicone-based, water washable formulations deliver improved ease of use while conferring the known benefits of greases. Although phase change products generally offer better long-term reliability because they don’t pump out over time like greases, there are extra process steps required. One must carefully evaluate each specific application to determine the most appropriate thermal solution.

As designers continue to push the functionality envelope – cramming ever greater capability into smaller and smaller devices – high performance thermal management systems will be critical components to in-field success. While there are several proven thermal management materials commercially available, new materials that afford simpler processing with equally robust results may be in order. Take time to carefully evaluate personal preferences, the pros and cons of usability and performance for all TIM2 thermal products and taking off the heat may not be as difficult as you think!

Dr. Renzhe Zhao is technical manager, applications engineering at the electronics group of Henkel (henkel.com); This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

 

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