Microscopic texturing is a method to increase the effective How to increase a heat sinks surface area without increasing the heat sink size. We’ll explore this compelling strategy for making heat sinks more efficient in this two part article series. Part 1 covers what this technology is, options to apply, and under what conditions it is effective.
Microscopic texturing not only increases the surface area, it also increases the emissivity of the surfaces at the same time. However, while this surface enhancement can be used for boiling heat transfer, it is of little importance for air cooling. This is due to the fact that radiation heat transfer is primarily a surface phenomenon and certain texturing processes that provide sufficient control over surface feature morphology could increase surface emissivity [6].
There are several surface texturing methods. A common one is chemical etching. Another is ion beam texturing where ion beam bombardment is used to selectively etch materials in applications from electronics substrate pattering to the creation of high surface-area pace maker electrode tips. It is based on a phenomenon known as sputtering, which is the process of removing material from a surface at the atomic level through collisions between energetic ions and substrate atoms. Because it is done on such a fine scale, this process provides a great degree of control over surface features. In principal, it is used to create almost any type of surface topography, whether smoother or rougher than the original surface [6]. Examples of ion beam texturing are shown in the following figure:
Ion beam textured surfaces typically absorb over 90% of the incident light across a wide range of wavelengths, implying that the surface is highly emissive. Such textured surfaces would be ideal for electronics cooling using liquids in boiling mode due to its significantly increased surface area. Increased surface area would enhance radiation as well as convection heat transfer provided that the texturing will provide excellent surface for pool boiling heat transfer often seen in cooling of high power electronics. Surface texturing will not be useful for applications using unducted low-speed airflow, since air cannot flow easily in the microstructures.
In part 2 we’ll cover accurate surface texture characterization.
References:
- Radiation Heat Transfer and Surface Area Treatment ,Qpedia Thermal eMagazine, June 2008.
- Edwards, J., Coating and Surface Treatment Systems for Metals, Finishing Publications Ltd. and ASM International, 1997.
- Aluminum Anodizer Council Web Forum, http://www.anodizing.org/index.html.
- Gustavsen, A., Berdahl, P. Spectral Emissivity Of Anodized Aluminum And Thermal Transmittance Of Aluminum Windows Frames, Nordic Jounnal Of Building Physics, Vol.3, 2003.
- Ozisik Necati, M., Heat Transfer A Basic Approach, McGraw Hill, 1985.
- Highly Emissive Ion Beam Textured Surfaces For Improved Cooling Of Electronic Devices, Electronics Cooling Magazine, September 1997.
- Chi, T. , Ballinger, R., Olds, R., Zecchino, M., Surface Texture analysis using Dektak Stylus Profilers, Veeco Instrument Inc.http://www.veeco.com/pdfs/appnotes/an525%20_dektak_surface_97.pdf