[Amps] making aluminum heat sinks black

[Will Matney]

Paul,

The black color only has to do with infrared radiation, the same as white, and nothing to do with the heat transfer from the device to the heatsink. The black absorbs this radiation and white reflects it. Anodizing is an electro-chemical coating which uses a die for the color. The surface is etched, then dipped in the electro-chemical bath containing the die which is a similar process to plating. This forms a skin on the aluminum about 1 mil or so thick similar to the way they make the anode foil in an electrolytic capacitor. That forms an insulator which combined with the electrolyte acts similar to a diode in function (unless it's a non-polarized type of cap). The term insulator is the key word here (electrical or heat) where I think it can actually impede the thermal transfer between the device and heatsink by some amount. I would rather have that junction be bare aluminum, but the rest could be colored. Most heatsinks though used to mount power RF devices have a series of tall fins which really should be fan cooled where they're spaced close together. Ones for other power devices (regulators, pass transistors, etc) are made to dissapate heat into the air by the fin design.

Best,

Will

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On 7/22/06 at 4:28 PM Paul Christensen wrote:

>> It could be that they think the same as I do. Any time you anodize
>> aluminum, there is actually a coating formed 1-2 mils deep on the
>> aluminum.
>
>Anodizing aluminum increases themicity and results in a substantially
>better
>heat radiator over that of bare aluminum.  The vast majority of heat-sinks
>are anodized, usually black or gold.  The anodizing process is a job best
>left for the experts.   There should be someone in your area that
>specializes in the procedure.
>
>Paul, W9AC
>
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