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topic 12121

Any plating suggestions for max conductive heat transfer--aluminum?


 

I have an aluminum 6061 frame mounted on a PCB for conductive heat dissipation into a cold wall. The plating needs: -to transfer heat effectively -abrasion protection (from shock and vibration, maintenance) -corrosion protection (the enclosure will be susceptible to salt water environments, humidity)

The dimensions are 6"x9"x.5". 100/year. Anodizing acts more like an insulator and cannot be used. Electroless nickel is probably an obvious solution but I would like to know if I have any other options such as alloys (nickel gold, nickel copper, diamond chips etc) that will give it better protection in harsh environments. Cost isn't necessarily a limitation but is always a consideration.

Also, is there any cadmium or magnesium in the nickel plating because the chemical composition is a factor since it may be used in military applications?

Thanks,

Matt d'Artenay
electronic solutions - San Diego, California, USA


 

There is an electroless nickel diamond composite available that will conduct heat better than plain EN. Medium phos EN contains about 75ppm cadmium in the deposit. There will soon be some medium phos EN available without the cadmium.

Todd Osmolski
- Charlotte, North Carolina, USA


 

A 100% pure PVD aluminum coating is frequently used, on aluminum heat sinks you describe, in DoD circuit board applications. You may contact us for more information.

Mandar Sunthankar
- Fort Collins, Colorado


 

Actually, anodizing aluminum leaves an outer layer of mostly aluminum oxide. Although aluminum oxide is not a good conductor of electricity, it is a good conductor of heat, with 27.21 W/mK at 300K (27C). The effect is not typical of other metal oxides and the conductivity stems from lattice phonon effects, which are not important for this discussion. Many heat sinks made of aluminum are anodized to protect the surface from environmental interaction, and the oxide layer which works well at improving abrasion resistance.

Anodizing, which can be done by any of the anodizing job shops at www.finishing.com/shops/ should be more than sufficient in this application and a whole lot cheaper than vacuum coating or other vapor deposition processing. If you need an electrical contact, simply abrade the contact surface to base metal.

As always, If you have any specific questions (we do not anodize), feel free to write us at SCSC.

Dale Woika
- Bellefonte, Pennsylvania, US


 

Just a quick word to say you can get cadmium free medium phos electroless in the UK and you should be able to get the same in the US. Also ever thought of silver over ENP?

Martin Trigg-Hogarth
Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England



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