does arctic silver thermal adhesive smoke?

[Bauer]

I used some to direct mount an xm-l emitter to copper and after about 10 seconds it starts to smoke. The led/copper isn't hot to the touch, so does this stuff smoke a bit at first?

 

[AmperSand]

Are you using arctic silver alumina thermal adhesive?

 

[Bauer]

Are you using arctic silver alumina thermal adhesive?

yes

 

[AmperSand]

Just checking!
I have used it quite a few times but never for direct mount, always on a star and never had any smoking issues so can't really add much more. So long as its not electrically conductive that's about all I could think of and you have that covered.

 

[DellSuperman]

direct mount an xm-l emitter to copper

Sorry, my interpretation of this sentence is that you are using the arctic silver adhesive between the emitter & mount (star).
Or did I interpret it wrongly.

I only know of 1 method to mount the emitters to the mount (solder reflow) but never heard of using adhesive to mount them.

 

[MikeAusC]

The temperature between the emitter and the star will be much higher than between the star and the heatsink so I'm not surprised it's smoking.

I don't have a datasheet but I suspect it's not intended to be used at these temperatures.

 

[DellSuperman]

Thats why im asking if he is using it between the emitters & star or star & pill/mount...

If its the latter, it shouldn't be a problem since its designed to work that way.
If its the former, than I'm curious to find out if it can work this way or not.

- JonK

 

[Epsilon]

Thats why im asking if he is using it between the emitters & star or star & pill/mount...

If its the latter, it shouldn't be a problem since its designed to work that way.
If its the former, than I'm curious to find out if it can work this way or not.

- JonK

If it is used to glue the emitter to a star/heatsink:

I have used Artic Silver adhesive (silver variant) on SST-90 builds, which does the job fine if both surfaces are very flat and a very thin layer of adhesive is applied.

But with an XM-L, this is very difficult due to the small form factor. When the layer is only a little thick, the heat will not be transferred good enough to the heatsink/star which will result in a dead LED. It is fine for big surfaces but not for such small ones. The thermal interface when using the AA or AS adhesive is a lot worse than soldering it.

 

[Bauer]

The emitter is direct mounted, no star. After being on high @ around 3A I get some smoke but very little heat. I used to have it flowed on a star and then AS'd to the copper but it was producing a lot of heat but no smoke.

 

[Epsilon]

If the heatsink is getting hot, this is a good sign of good thermal transfer. If it doesn't get warm, the heat is trapped in the LED and will kill it eventually.

The LED is producing a certain amount of heat that has to be transferred. The smoke indicates that it gets very, very hot.

 

[DellSuperman]

The emitter is direct mounted, no star. After being on high @ around 3A I get some smoke but very little heat. I used to have it flowed on a star and then AS'd to the copper but it was producing a lot of heat but no smoke.

If your copper mount is not hot after running it at 3A, then I believe that your thermal contact is very poor & the heat might be trapped in the emitter, which will eventually kill it.
I recently tested a XM-L2 on a copper star direct from a DC power supply at 4A.
After 10 secs, the whole copper star because too hot to touch.

You might wanna check the contact surface between your emitter & copper mount.
Like Epsilon said, the 2 surfaces gotta be very flat in order for them to have good contact.

 

[LilKevin715]

Did you use a very thin layer when mounting the emitter? Did you squeeze out any excess by pressing down on the emitter? Ideally you want a layer that is less than the thickness of a sheet of paper.

I've used arctic silver alumina thermal adhesive for mounting LED's with larger center thermal pads such as SST-50/90, but not for a smaller emitter such as a XM-L. Since you were mounting a emitter to copper wouldn't it be easier to reflow solder it instead:thinking:? If you have a soldering iron you can reflow. Solder paste makes it much easier but it can be done with regular 60/40 rosin core solder as well.

 

[DellSuperman]

If you have a soldering iron you can reflow. Solder paste makes it much easier but it can be done with regular 60/40 rosin core solder as well.

Hey Lilkevin715, care to share how you reflow using soldering iron?
Can it work with normal MCPCB stars?

 

[LilKevin715]

Hey Lilkevin715, care to share how you reflow using soldering iron?
Can it work with normal MCPCB stars?

http://www.youtube.com/watch?v=0ZcOqYFtzo4

My method is similar to what is done in the video.

Bauer any updates?

 

[Bauer]

I went ahead and ordered a couple h22a's for my maglites. I will probably just toss this one in the spare parts box and go with a warmer tint xm-l.