Fastening a High Brightness LED to a Heat Sink Using Arctic Silver

Fastening a High Brightness LED to a Heat Sink Using Arctic Silver


One option for fastening an LED assembly
to a heatsink is to use Arctic Silver two part adhesive. When applied correctly, Arctic Silver
adhesive will create a very efficient, permanent bond between the assembly
and the heat sink. Key to creating a thermally efficient
bond is to create as thin a bond line as possible between the LED and the top
of the heat sink. At most you don’t want to epoxy layer to be more
than .004″ (0.1mm) thick, with .002″ to .003″ (0.05 to 0.08mm)
being easily achievable if this is done correctly. To begin you need to make sure you have
all of the items close at hand. You are going to need both parts
of the Arctic Silver. A mixing pallet, something with a plastic surface so that
the adhesive does not soak into it. Mixing wand. Isopropyl alcohol. Clean wipes. LED assembly press, which we now include with each shipment of Arctic Silver. The heat sink you are going to be bonding to. And of course the LED assembly itself. So you want to start be ensuring
that the surfaces are thoroughly clean and free of any oils or greases. So I will clean them off with isopropyl alcohol. And will clean off the back of the LED as well. Make sure that both surfaces
are impeccably clean. Next we need to mix up the adhesive. Now the amounts you are going to
need are actually very small, and it can be a bit tricky to judge this. So I have made up this little pallet showing droplets of the amount of adhesive that you will need
for different types of assemblies. For the star assembly this drop represents about how much
you are going to need to fasten the LED to the top of the heatsink. if you’re a fastening a 10mm square LED assembly, then this is all you will need. And if you are fastening a larger 40mm 7 LED assembly, then this will be all you need. So we are going to start by mixing
up some adhesive on our mixing pallet. Squeeze out a small amount of the first part. And then an equal amount of the second part. Mix that up. Now this is more than what we will need. But we will mix this up and just use exactly
what we need for this assembly. Mix the epoxy very thoroughly. Stirring for about thirty seconds or so. Put a small drop where we want the center of the LED On the heatsink. We want this LED on the center
of this heatsink, so we will put a drop right in the center. Not very much. Avoid the temptation to spread the adhesive around.
Just put a small drop in the center. That should be about right. Take the LED and drop it right on top, and carefully push it down. Aligning the LED to the center. Take the LED press set it on top with the LED in the opening, making sure that it all lined up. You want to put as much pressure as you can on top for about 30 seconds. Now leave this in place and then just use it to position the LED where you want it on the heatsink. You have time as it takes 5 to 10 minutes for the
epoxy to set up, so there is time to do this. Get it into position. Don’t worry about the epoxy that squeezes out, and avoid the temptation to try and wipe it off.
Just leave it alone. And when you are satisfied with the positioning you need to weight or clamp this in
place while it sets up. I prefer to use a clamp. You want to very carefully position the press in the middle being careful that you don’t move the LED around. And then very gently drop your clamp in place. Make sure that everything is still in position. And then let that sit for about 10 to 15 minutes to setup It will take about 24 hours to fully cure but you can have a look at it after
about 10 to 15 minutes as it won’t move after that. So it has been about 20 minutes since we clamped this up. It takes about 24 hours
for the epoxy to fully cure, but it firms up after about 20 minutes so we can
take the clamp off to have a look at it. Looking here we can see that the epoxy is all the way around the edge of the LED, which means that we have
good coverage underneath the the bottom of the assembly. Now if you were to measure the thickness
of the epoxy we’d find that it is about .002″ to .003″ (0.05mm to 0.08mm) thick, so this assembly will perform very well and provide excellent thermal efficiency when it is put into service.

11 Comments

  1. Informative, but some questions remain:
    1) What tolerance is there on the epoxy mix ratio – hard to judge "equal' at this scale.
    2) Epoxy joints are notorious for gliding out of position especially under clamping pressure, you make it seem no problem but it is an issue.
    3) How long will the Arctic Silver epoxy last once opened, & what does it cost?
    4) You don't show any surface prep other than cleaning, what about checking at least for flatness of the emitter assembly?
    5) Mechanical fixing ?

  2. This is in response to a post that was submitted some time ago but somehow got snagged by YouTube's spam filters.

    1) What tolerance is there on the epoxy mix ratio – hard to judge "equal' at this scale.
    I am not sure about the mixing tolerance. I suspect it is generous, but you would need to contact the makers of Arctic Silver to get accurate information.

    2) Epoxy joints are notorious for sliding out of position especially under clamping pressure, you make it seem no problem but it is an issue.
    If the parts are sliding around a lot when clamped, then that is a sign that too much compound is being used. The objective is to create as thin a bond line as possible in order to create a thermally efficient joint. So if you find that the parts are moving when clamped, reduce the amount of Arctic Silver you are using.

    3) How long will the Arctic Silver epoxy last once opened, & what does it cost?
    The manufacturer does not state an unmixed shelf life that I have seen, but I suspect it is fairly long. Probably a year or more at least. As of today, a 7 gram package of Arctic Silver is priced at $19.85 on our website.

    4) You don't show any surface prep other than cleaning, what about checking at least for flatness of the emitter assembly?
    It goes without saying that the surfaces do need to be as flat as possible. Commercially produced heat sinks will already have a very flat surface. Most LED assemblies will also have a flat surface as they are designed to be mounted to a cooling surface. So for the most part just being sure that the surfaces are free of contamination and moisture is, usually, sufficient.

    5) Mechanical fixing?
    Many of the LED assemblies that we offer can be mounted with mechanical fasteners, however we have found that both thermal tape and Arctic Silver perform very well and are much easier to use than screws or spring clips. Mechanical fasteners can be a bit trickier as it is very easy to over torque the screws, distorting the assembly.

  3. Luxeon, I am looking for a 8 to 10mm base with an LED installed.  Do you have any suggestions where I can procure such a small assembly?

  4. Hope you don't mind that i share my opinion , but i think it would be better to use this staff (ARCTIC SILVER GLUE PASTE)  only on the edges , to make it stay where you want  and in the middle area a good high quality thermal paste , as this, once it goes like glue it will not transfer the heat as good as a normal thermal paste (witch doesn't get dry''solid'').I think that better heat transfer will be obtained in this way .
    Best thermal paste's are the ''COPPER OXIDE'' thermal paste . one with the best results , and the best i ever used in my projects . here's a link with one that i used and was much better than Arctic silver 5 , and Cooler-Master E2 ,
     http://www.ebay.co.uk/itm/E2-GOLD-THERMAL-PASTE-BETTER-THAN-ARCTIC-SILVER-5-ARCTIC-COOLING-COOLER-MASTER-/321834264786?hash=item4aeed128d2

  5. @Luxeon Star Leds : Is it ok to solder the electrical wires to the LED AFTER fastening the LED to the Heatsink with the arctic silver? Will the heat of the iron not damage the Arctic Silver?

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