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The thermal interface material is another important factor in cooling equipment design. It is of particular importance when the heat flux (W/cm2) is high. A detailed example follows, however, it is important to remember that when the heat flux is low (relatively low power over a large area), then the impact of the thermal interface material will not be significant. However, when the opposite is true (high heat load over a small area - ex. LED application, IGBT, high power CPU, RF components, etc), then the choice of thermal interface material will be critical to the design of the cooling solution.

 

If we consider that Q = A/Rth*∆T, we can then write: ∆T = Q*Rth/A. If we let Q = 10W, Rth = 2 C*cm2/W (as provided from thermal interface material supplier), and A = 1 cm2 (heat flux of 10W/cm2), it follows that ∆T will be 20C across the thermal interface material. If on the other hand, the heat source is spread over a much larger surface (say 6 cm2 - heat flux of 1.66 W/cm2), then the ∆T will only be 3.3C. It can be seen then that higher the heat flux, the greater the impact of the thermal interface material will be. In the case where we have a heat flux of 1.66 W/cm2, we can probably not expect more than a few degrees reduction in IC temperature by optimizing the thermal interface material. On the other hand, in the case where we have a heat flux of 10 W/cm2, it is very possible that we can reduce IC temperatures 10C or more by using a better thermal interface material. There are various types of thermal interface materials from thermal paste, to gap fillers, thermal adhesive pads, and phase change materials. All have their strengths and weaknesses depending on the application in question.
 

If you have any questions regarding the above or for a specific design question which you may have, please contact us and we will be pleased to help you.

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