Heat conductive silicone glue.

Hi guys, I don't think I have posted here many times so hello to you all.

Anyway, I am throwing together some cheap lighting for my workshop. Its 180m2 and I will use 30 20w $2 led chips from eBay like these ones. (*Link removed - please find another way to describe the product)

And a couple of cheap switching supplies with current control etc etc.

My question is regarding silicone glues to fix them to there heat sinks. The base of my chips measure 47x47mm so there's plenty of surface area to conduct the heat. I understand there are purpose made silicone glues for this application and some are cheap and some are expensive.

Are these much different from just any old silicone that I could get at the local hardware store?

Could I get away with using something not specifically designed for this application?

Here are a couple of links to cheap stuff on eBay that looks designed for this application, does anybody have any experience with this stuff?

Any advise/info will be appreciated.

Many thanks and sorry for my bad spelling.

There are a lot of thermally conductive adhesives out in the world. 3M and Dow Corning list some on their web sites....

http://solutions.3m.com/wps/portal/...cs/Products/Product_Catalog/~?N=7234484&rt=c3

http://www.dowcorning.com/content/etronics/etronicswet/etronics_wet_adhov.asp

To compare them, you'll want to use the values for thermal conductivity.

Are they much different from plain silicone RTV? Yes.
Can you get away with using plain silicone RTV? It depends. Why not try it and find out? The worst that can happen is you'll damage $60 of questionable ebay LEDs.

You might try just mounting one or two of the LEDs and running them for a few weeks. Measure the temperature of the LED too. If it is getting to 85C, that would be a sign that it is probably too warm. The hotter it gets, the faster you'll kill the LEDs.

There are alternatives to thermal adhesive. I'm fond of using a thin layer of thermal grease (a.k.a. heatsink grease) and bolting the LED to the heatsink. Thermal grease tends to be quite a bit cheaper than good thermal adhesive.

Thermal paste, for connecting heat sinks to CPUs in computers, is also widely available and pretty cheap. You'd probably want to also screw them down however. (opps, just saw this was already suggested)
Also there are pre-made self adhesive LED strips. Which save on both the glue and the wiring.

Also in my experience, many of the LEDs sold on E-bay are fakes and /or frauds. They don't match the claim wattage, nor the lumen output. Needless to say, the cheaper ones tend to be the worst offenders.

Artic Silver works wonders but its not silicone based. It's an epoxy but if you want silicone than there is Fujik. Good stuff. I like to use it for potting my LED drivers.

Thanks for the replies guys.

I guess I should have outlined one key aspect to the project although it should have been obvious;-) This is to be done on a shoe string, time and money wise. Hence trying to find a cheap glue as opposed to drilling 120 holes and nuts in bolts etc.. The aluminium for sinking comes from scrap/offcuts bins. The cable I use will come from the the scrap yard etc. This project is a pure and simple get the job done project not one that I am interested in taking GREAT pride in. It is simply to cast good bright shadow free efficient light over my dusty and dirty workshop.

Regarding LED strip lights, I want to keep the line losses down, other than that they were certainly considered.

As for the chips questionable quality, I have not seen any of this style fail yet. In any case I will be down tuning them slightly for longevity and further electrical efficiency. When it comes to them not being as efficient as higher quality items that cost relatively a LOT more, I would love to see a comparison. My understanding is that it will take many years to get the extra investment back.

3M, Dow Corning and arctic silver all out of the question due to premium prices tags. No doubt these are premium products that do premium jobs. Given the high foot print/wattage ratio my led chips have I cannot see any reason to spend the extra money. The fujik looks fair priced. But I wonder if any of the cheap glues I linked could be similar products?

In any case I just brought one of these I have been meaning to for AGES! Hopefully it turns up quickly though! Will be most interesting to compare some general thermal grease to some cheap silicone with some 10 watt chips I have laying around. http://www.ebay.com/itm/New-LCD-Non...619?pt=LH_DefaultDomain_0&hash=item3a90bbe303

If anybody has any more info regarding cheap thermal adhesive compounds I am all ears.

Thank everybody for your suggestions, they are all good suggestions and I hope I have not ruffled anybodies feathers by disregarding basically all of them. As I stated I have my own objectives for this project. I do love some of the projects people have done on this site, some real master pieces there is.

I see some of my links did not make it to print. I will try to rectify this. It would be nice to be able to describe the led chips more accurately but I've no idea where to start with finding a brand name or data sheet for these cheap generic and mega mas produced chinese chips. They are the same as these ones anyway. http://www.lohas-led.com/index.php/led-chip-20w-900-1000lm-integrated-chip.html#.U71cm_75t0w

Not sure if my links got removed or not but these are the cheap thermal glues I had come accross so far. Although I get the feeling this one is not actually glue but just typical old heat conductivity paspte. http://www.ebay.com/itm/Silicone-Th...hermal_Compounds_Supplies&hash=item1c356b3b22

menace said:

Not sure if my links got removed or not but these are the cheap thermal glues I had come accross so far. Although I get the feeling this one is not actually glue but just typical old heat conductivity paspte. http://www.ebay.com/itm/Silicone-Th...hermal_Compounds_Supplies&hash=item1c356b3b22

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I like the part where the ebay page's text says that it can also be used on wood..... I think that's where the user should realize that this stuff isn't any sort of thermal compound at all.

If you want to build something cheap, then use parts from ebay. If you want to build something well, then buy parts from trusted suppliers.

Steve K said:

If you want to build something cheap, then use parts from ebay. If you want to build something well, then buy parts from trusted suppliers.

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This statement is simply not true, I have brought hundreds of things from ebay. I always do my research I always received exactly what I expected(except 2 times, on both occasions I got a full refund and on one of those occasions i got to keep the goods which were still perfectly usable). Thanks for your suggestion/opinion though.

well, as a person involved in the design and production of electronics for 3 decades, I can assure you that no one builds commercial electronics with parts purchased from ebay.

I do buy a few items from ebay, but not from Chinese sources. I suppose it depends on your tolerance for risk.

What type of LEDs are they? If they are a square shape with the yellow emitting area also a square-ish shape in various wattages, then don't drive them hard. They are known for the strings of LEDs inside failing open circuit. I'd drive them at around 50% max current to be safe. Better to use Bridgelux or Cree CXA series LEDs in your lighting project rather than the cheap junk. The Good LEDs are not so highly priced.

JohnR66 said:

What type of LEDs are they? If they are a square shape with the yellow emitting area also a square-ish shape in various wattages, then don't drive them hard. They are known for the strings of LEDs inside failing open circuit. I'd drive them at around 50% max current to be safe. Better to use Bridgelux or Cree CXA series LEDs in your lighting project rather than the cheap junk. The Good LEDs are not so highly priced.

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Im using these ones.

Lumens for watt would have to be a lot different for me to get my investment back if I went teh more exspensive route. As for being known for going open circuit, perhaps they are "known" for this but I know of a lot of them that have not done that so I am happy to wait and see if my experiance is any different. In any case its a very small investment to loose out on and seems like a good punt to me. Cree and bridgelux certainly do look a lot darer by comparison on ebay. As I said earlier I would be keen to see some testing/review on these cheap ebay chips im using. I have googled to find such articles but have not found any.


Is it possible to put a picture in a post with out linking to it? As in upload it to CPF I mean?

I must say though that these look interesting for flooding the yard.

http://www.dx.com/p/hzled-20-cree-x...ed-warm-light-lamp-28-36v-298190#.U8BTUP75t0w

Update.

Just a wee update. I have done a quick prelimernary test using cheap RTV with a ten watt led chip. Test was a success. Running at 9 watts seemed well cool enough(30 minutes-ambient temps:high teens celsius). At ten watts it was running a little warm for my liking, maybe still permissibly but Ill stick with 9 watts.

Now I will wait for the rest of my ebay purchases to turn up and I will test 4 or five materials and see how much differents there is in there heat transfering abilities. This is gonna be interesting I think.

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Re: Update.

While run-of-the-mill RTV adhesive can make a passable heat transfer compound in non-critical applications, like this. It's a lousy adhesive for this. You should use screws. Then, a TINY dab of RTV will be all that's needed.

Re: Update.

brickbat said:

While run-of-the-mill RTV adhesive can make a passable heat transfer compound in non-critical applications, like this. It's a lousy adhesive for this. You should use screws. Then, a TINY dab of RTV will be all that's needed.

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I tried as hard as I can with my bare hands to get it off and absolutley no chance, so it seems it is thoroughly strong enough.

Out doors with repedative frost situation may be another story from what I have seen from this type of material in the past, but for my aplication I can't see where i might need any more strngth that this.

Am I missing somehting? Will this material degrade over time with the low heat it will indure or?

Can you explain furthar as to why it is a lousy adhesive?

Re: Update.

Its not a lousy adhesive in general, just not a good choice for a metal-to-metal bond that needs to last a long time. I've seen RTV lose its grip over time in this type of application. Screws also have the huge advantage of applying a high compressive force, which will keep the LED-to-heatsink spacing minimal. A key to a good LED-to-heatsink thermal bond is for the adhesive (or paste) to be as thin as possible.