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-----Coatings for aluminum heat sinks
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(this entry appended to this thread by editor in lieu of spawning a duplicative thread)
Q. I've been asked by a customer to help direct them in finding an immersion style coating for high volume aluminum stamping that will enhance thermal dissipation on LED heat sinks. We're a hard chrome plater so I have very limited knowledge of conversion coatings or other available choices, I'm just trying to put options in front of them. I would think with volumes exceeding 2M units/yr that anodizing and other electroplated (racked) coatings would be a non-starter due to economics. Thanks for your time! ⇦ Answer?
Jeff~
President - Meadville, PA
November 21, 2025
A. Hi Jeff,
As you'll see in this thread, electroless nickel and anodizing are the usual coatings for heat sinks. Conversion coatings have temperature limits which don't align well with heat sink applications.
But you are right that individual racking may not be necessary. Electroless nickel can be done in a basket or barrel, and if cosmetic appearance isn'r required, they can probably be 'bulk anodized' / 'basket anodized'
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
Thank you for the comment, Ted... Appreciated!
- Meadville, Pa
⇩ Similar, related, Q&As -- oldest first ⇩
Q. I have an aluminum heat sink used in a cleanroom environment and therefore the surface needs to sealed to prevent oxidation and contamination to sensitive materials. Will a chromate coating have sufficient thermal conductivity to ensure good heat transfer? And is chromate a sacrificial coating or will it resist oxidation even if scratched? If the answer to these questions is 'no' than what would be the best coating to use?
Jim SbrognaSemiconductor Equipment Engineer - Natick , Massachusetts
2004
A. Heat sinks can be anodized. Chromate coatings will not cause thermal conductivity problems; they are electrically conductive, which could be a problem or not. Chromate is not a sacrificial coating but it is "self healing" so it is helpful even in an environment where scratching is possible.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
Aluminum How-To
"Chromating - Anodizing - Hardcoating"
by Robert Probert
You'll love this book. Finishing.com has sold a thousand copies without a return request 🙂
A. In addition to all the accurate advice Ted sent to you, you may need also to know that bare unpainted chromate conversion coatings are limited to a surface temperature of 140 °F, above which the coatings disintegrate. Absolutely not suitable for a very hot sink.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
A. The coating of choice for heat sinks has been electroless nickel forever. Corrosion resistant, conductive, both thermal and electrical. Even looks good.
Dan Weaver- Toccoa, Georgia
2004
Treatment &
Finishing of
Aluminium and
Its Alloys"
by Wernick, Pinner
& Sheasby
on Amazon or eBay
or AbeBooks
(affil link)
A. Anodizing should be fine. Aluminum oxide is tough, proven, and is thermally a good conductor due to lattice phonon effects.
Dale Woika- Bellefonte, Pennsylvania, USA
A. Electroless nickel is the best coating if you want maximum heat transfer. Anodize coatings are dielectric and have poor heat transfer characteristics. They are very corrosion resistant as is electroless nickel.
Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics"
and "Plating ABS Plastics" eBay or AbeBooks affil links])
Ed. note: The ratings in the poll so far: Electroless Nickel 5 stars; Anodizing 3 stars; Chromating 1 star.
Multiple threads merged: please forgive chronology errors and repetition 🙂
Best plating on porous aluminum castings
Q. Hi Friends,
Can you please suggest the best plating that can be done on a porous die-cast aluminium Heat Sink. It should withstand 72 hours of salt spray.
vendor development - Bangalaore, Karnataka, India
2004
A. Hi Suman. I'd say poor plating is the best plating that can be done on a porous die-cast aluminum part 🙂
Seriously though, any plateable metal can be plated on virtually any substrate -- the choice is based on why you are plating the part -- not on finding a plating that works on porous parts.
It's possible to vacuum impregnate the castings to render them non-porous or at least much less porous. It's possible to anodize them, or paint them, or plate them with almost anything, but I think anodizing and electroless nickel are the most common choices. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
Q. Hi Ted, thanks for your reply. We cannot avoid porosity on castings. Vacuum impregnation was a good idea. I tried doing ENP on it. ENP doesn't stick on impregnated area. I tried Zinc. Zinc is not penetrating deep into the fins. I tried anodizing. I am not happy with the finish. Is there any other alternate. On porous surface, plating fails very quickly. Corrosion starts from the porous surface; ultrasonic cleaning helps a bit but not 100%.
Regards,
vendor development - Bangalore, Karnataka, India
2004
A. What is wrong with chem film (Alodine, Iridite, etc.)? What is wrong with anodize. Both are cheaper and should work for a heat sink.
James Watts- Navarre, Florida
A. Suman,
It should be obvious that porous parts will retain the plating solution and bleed after plating. As you are in B'lore, suggest contacting Mr K Vahanvala who is a professional plater and runs Saify Ind [a finishing.com supporting advertiser]. He is your last hope of success.
Asif Nurie [deceased]
- New Delhi, India
With deep sadness we acknowledge the passing of Asif on Jan 24, 2016
Hi Asif,
I just saw this and had a rollicking good laugh over it! I'm already on Suman's black list as a plater who can't plate on porous parts! But Suman, to answer your question: zincate, EN and Zinc Cobalt, seems to be the way to go ahead on this.
Khozem Vahaanwala
Saify Ind
Bengaluru, Karnataka, India
A. Hi
Although Khozem has suggested a good plan, if the parts can be buffed mid-cycle you might consider a heavy layer of cyanide copper plating in lieu of electroless nickel because it is possible, at least under favorable circumstances, to "mush buff" to push copper into the porosity.
Luck & Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
Q. Vahanwala my Friend.
Need is the mother of invention. Everyone knows porous Surface will bleed after plating. We need to come out with a solution to overcome this. Please take back the word Blacklisted - I am still doing business with you & coming for all R&D work. No doubt you are the right person to give solution to my problem. Vahanwala, I want to come out of ENP fully.
Hi James, Anodizing & Chromating meets my functional requirements. But doesn't meet aesthetic requirements. Can I do some plating on top of anodized / chromated surface.
Regards,
vendor development - Bangalaore, Karnataka, India
A. You appear to have tried nearly everything and nothing is satisfactory. A zincate followed by a copper strike followed by a copper build followed by nickel may work, but that is a lot more expense and time and places for failure.
Better castings might be a more affordable way to go. Another thought would be to zincate and alkaline EN strike followed by a conventional EN. I doubt if it will meet your needs, but it is a last effort to try. PS, I hate castings and am not in love with bad extrusions.
- Navarre, Florida
A. If you were sand casting your situation would be hopeless but aluminum die casting MUST render a part with integrity and soundness. There must be something or many things wrong in your casting process. A quality management program for your castings is the answer not finding a miracle plater.
Guillermo MarrufoMonterrey, NL, Mexico
Hi. My vote is for Guillermo's answer! Quality management of the die casting step is essential. Sometimes, although costly, it's a matter of inspecting each casting and throwing each poor one back into the melt pot until better dies, better metal, or better methods are available.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
A. For porous aluminium castings, vacuum impregnation is best idea. It can withstand 250 degree temperature, 72-hour salt spray, etc.
Sandeep Nandra- Chandigarh, India
2005
Q. Sir, if I want to increase heat transfer capacity of heat sink, electroless nickel coating will be okay, or you can suggest any other coating? ⇦ Answer?
Hemant Jakhwal- Udaipur, Rajasthan, India
April 8, 2011
Q. Hi
I have a sealed aluminium case (with chromate conversion coating CL3) containing a PCB that can reach temperatures up to 110 °C (230 °F). The case has a finned area on the outer-upper face, and the PCB is fixed to A LOT of stumps or columns on the inner upper-face through copper-plated brass bolts. During some thermal tests I have discovered that the heat transfer between PCB and the case is quite bad, I guess that the conversion acts like a heat barrier. The question is: is there any other conversion/plating/anything that can improve this heat transfer while keeping the corrosion protection? I contacted a metal finishing service and they told me that nickel would do the job better, but I'm not quite sure about that since they have similar thermal conductivity... Any ideas?
Thank you in advance!
- Madrid, Spain
February 14, 2013
A. (1) The chromate conversion coating is not interfering with the heat transfer, but
(2) if the chromate is bare, at that temperature you are completely dehydrating the chromate coating and destroying it.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
Q. I am working on a similar project. What would your recommendations be for the following.
Aluminum Heat Sink.
Completely submerged in salt and freshwater.
Best recommended protection for coating, while still maintaining thermal conductivity. For a high powered heat generating light. Temperatures around 230 °F
Avoiding corrosion. I know it can be anodized as one option, but I feel coating would be optimal.
Input would be greatly appreciated!
- Atlanta Georgia
March 27, 2014
A. Hi. As long as the coating will not be mechanically damaged, electroless nickel plating sounds ideal. But nickel is far more noble than aluminum, and will greatly accelerate the corrosion of the aluminum if the plating is porous, pinholed, or scratched, and aluminum is exposed. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
⇦ Tip: Readers like to learn from others' situations;
some readers skip abstract questions.
Q. Can anyone please tell me some disadvantages of aluminium coated heat sink for PCB. According to environmental effect.
Kushang Dankhara- Melbourne, VIC, Australia
September 24, 2015
? Hi Kushang. Hopefully someone will fully understand your question and reply to it, but personally I would need you to offer more detail as I do not quite understand. Please try to be as specific as possible in describing your own situation. Thanks.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
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by Runge & Kaufman
on Amazon or eBay
or AbeBooks
(affil link)
A. If you truly mean aluminum coated, the drawback is the price of vapor deposition or the highly specialized electroplating from an organic media.
If you mean coated aluminum, the thickness of the coating will reduce the effectiveness of the heat sink giving up heat to the atmosphere.
Hexavalent chromium coating is a problem in many countries, but trivalent is available and is nearly as corrosion resistant but a bit more expensive.
Thin anodize is an option.
- Navarre, Florida
A. Hey, kushang, what particular application you were looking for you have not mentioned. For the cons you need to elaborate your Q's first.
Thank you.
Control Systems Engineer - Surat,Gujarat, INDIA.
October 25, 2016
If you would like to increase heat transfer, for a heatsink made of aluminum, with direct heaters beneath, we have a patent pending solution. Our current test results show 100-150% increase based on thickness of metal, and type. You can look up US patent US 9,265,092 which is for alufoils. Our solution for industrial coatings is based on this.
I realise this does not answer the issue regarding the surface, however it will help in terms of heat transfer.
- Copenhagen, Denmark
October 26, 2017
Q. Hello
I'm looking at ways to have dual finishes on a die cast aluminium heatsink.
Neither side is cosmetic (internal part).
One side should be black + dielectric + a rough surface for improving heat dissipation.
The other should be natural color + conductive + polished surface, as it is used for EMC shielding.
My actual process is painting with masking.
I'm looking if a surface treatment (like anodization on one side, and chrome finishing on other) will do in a more industrialized way (more automated).
Thanks for your help
Regards
product engineer - RUEIL, FRANCE
October 5, 2016
A. Hi Dominique. Anything is possible, but automation of plating is not easier than automation of painting. Further, painting is usually more tolerant of poor diecastings than plating is.
If you wish to chrome plate one side and black anodize the other side, it is possible with a masking sequence, but nickel plating rather than chrome plating would probably be better and easier.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
Readers may also be interested in this related thread:
• Topic #280/42 "Best Heat Sink Finishes / Surface Treatments"
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