Conduction cooling provides both the least expensive and the most expensive types of passive cooling.
The three types of conduction cooling are:
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Aluminum Plate
- Least expensive cooling method, when suitable
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Heat Spreaders/Thermal Doublers
- Materials like diamond and diamond composites. They are mounted directly under the chip, and are very thin, and have high thermal conductivity. They have a much smaller scale than the other technologies discussed in these web pages, hence won’t be discussed further.
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Encapsulated Conduction Plates
- Aluminum layer encapsulating a higher thermal conductivity material. They are the most expensive passive cooling technology and are discussed on a separate web page.
6063 and 6061 aluminum plates are commonly used to cool electronics and also provide structural support. 6063 Aluminum Alloy has a thermal conductivity of ~ 200 W/m K, while 6061 has a thermal conductivity of ~ 170 W/m K. Even though copper has a thermal conductivity ~ 400 W/m K, it is generally not used for conduction cooling. While the conductivity is twice that of aluminum, the density is 3.3 times higher, so copper has a lower specific thermal conductivity.
Baseline Aluminum Plate Uses and Benefits
The benefits and limitations of baseline aluminum plate conduction cooling are shown in Table 2. Aluminum plates are both the lowest-performing and the cheapest solution for thermal management. Due to their lower conductivity, they are generally suited for low-power systems. When analysis shows that the peak temperature or mass is too high for a simple aluminum plate, then Spot Cooling Heat Pipes, HiK™ Plates. Vapor Chambers, and Encapsulated Conduction Cooling, should be considered. These devices are more expensive but have higher performance.
Table 2. Benefits and Limitations of Baseline Aluminum Plates.
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Benefits |
Limitations |
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Thermal conductivity of 200 W/m K |
Lower thermal conductivity than two-phase thermal devices and encapsulated conduction cooling |
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Lowest cost for passive thermal management |
Lowest performance for passive thermal management |
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Lower density than two-phase systems |
Lower specific thermal conductivity than two-phase systems |
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Thermal performance unaffected by acceleration |
Lower maximum heat flux than two-phase devices |
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Operates over a wide temperature range (Water heat pipes have low effective conductivities below 25°C) |
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No length limitation in the vertical direction |
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Short lead times |
Baseline Aluminum Plate Selection Parameters
Selection parameters for the baseline aluminum plate are given in Table 3. Unlike many of the other devices, most of the selection parameters are application-specific. For example, there is no set maximum heat flux that can be applied to an aluminum plate. Instead, the maximum heat flux is set by the maximum allowable temperature of the component to be cooled (Note that due to its lower thermal conductivity, this heat flux is almost always lower than for the other devices discussed here. Similarly, the minimum thickness is set by structural considerations.
Table 3. Baseline Aluminum Plate Selection Parameters.
|
Parameter |
|
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Maximum Heat Flux |
Depends on Geometry |
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Effective Thermal Conductivity |
200 W/m-K |
|
Density vs. Al |
1 |
|
Spreading |
2 dimensional |
|
Minimum thickness |
Depends on Structural Considerations |
|
Maximum Dimensions |
N.A. |
|
Maximum Acceleration |
Depends on stresses |
|
Minimum Temperature |
N.A. |
|
Maximum Temperature |
N.A. |
|
Typical Delivery Times |
3-4 weeks |
More information on When to Use Heat Pipes, HiK™ Plates, Vapor Chambers, and Conduction Cooling: