Thermally Conductive / electrically isolated Epoxy

[RDTech]

For all lasers I have built, either with Axixz, O-like or custom, I have used a thermally conductive / electrically isolated potting material for heat dissipation. This is, IMHO how to keep laser diodes running longer. When I keep laser modules / pointers unpotted, there is an air gapp which does not allow adequate thermal conduction. Most of the heat from laser diodes is dissipated out the rear and through the pin attached to grounded housing. Addionally, potting the driver circuit right next to the LD irself may add to the laser diode temperature. I usually purchase 60g epoxyies from Arctic Silver. NOT the silver adhesive, but slow or medium cure Arctic Alumina. It has worked for years. The only issue wit this method is that your laser diode and host/heatsink are bonded Permanently.

 

[RA_pierce]

Be careful when using arctic silver or arctic alumina over electrical components or near diode pins.
It is designed to be an electrical insulator but it can conduct very slightly.

I use a silicone adhesive when needed. I generally use press-fits for best thermal conduction, since it is not permanent and adhesives can be messy.

 

[HIMNL9]

DealExtreme: $7.23 FUJIK Silicone Thermal Glue (50ml Grease-Like)

I use this one for my assemblies ..... it conduct heat decently, is totally insulant, and in case that your diode burn, you can dismantle the assembly with some efforts ..... sometimes, for specific assemblies, i also use it for fill all the space between the driver and the body, so also the driver become heatsinked .....

In some specific case i also used arctic silver alumina, but only when i need assemblies that have not to be dismantled in any case

 

[Benm]

Does that stuff from DX harden/set to a solid, or does it remain liquid?

The reviews and information are a bit confusing - it says grease-like, but reviewers say it becomes elastic, non rock-solid, but its like glue (which usually becomes quite solid).

 

[HIMNL9]

It become solid like silicone, but less elastic and a bit more breakable ..... it don't glue well like normal silicone sealant, anyway remains elastic and glue parts together.

Edit: i figured what you mean about their reviews ..... no, the "grease-like" is cause, when it's liquid, it look like the normal thermally conductive grease, but once it harden, it become solid ..... only it need some time, if you use a lot of it ..... mean, using it for glue a pair of surfaces, probably in an hour or few more is completely dried, but for filling spaces, it need to rest 24 hours for completely harden.

 

[Benm]

Ah right, so thats what they mean with 'not completely solid': it does try out to a solid state, but not as hard as, say, the plastic a keyboard is made out of.

Do you use it in thick (several milimeter) layers to fill the space between a module and host, and does it conduct reasonably well in that case?

 

[HIMNL9]

For aixiz modules, when i need to couple the whole driver with the body, i just "inject" it slowly, til it fill all the space ..... with different hosts, where the space is more high, i always try to made some "intermediate" filler ..... how can explain better ?

I mean, suppose that you have to couple an LM1117 (flat) to the inside wall of a host (round), and that the regulator is at 15mm from the wall ..... in a similar case, i always try to shape a piece of aluminium or copper, flat on one side, and round on the other, a pair of millimeters more small of the space that i have to fill ..... then first i glue this "filler" on the circuit, wait that the glue is hardened, then slide the assembly inside the host space and fill all the rest of the empty space with the glue .....

I've seen that this glue still conduct heat good enough, for being a glue, but, anyway, is not metal, and cause metal is always better than any glue, i try to reduce the glue thickness all the times where i can do that ..... but, yes, if is matter of 3 or 4 mm, i use just the glue, only if i have more space to fill, i made metal fillers.

 

[RDTech]

Arctic Alumina has such a low electrical resistance, it will and has never for me (over 8 years) affected any circuit. We purchase their products regularly and get discounts. Maybe we should offer here at discounted rate. There are 3 types, slow, med and fast cure. Yes, it will harden to a point where you could conceivably get it apart, but some SMT parts will/may come with it. The adhesive is especially good from the rear & connected pin for heat dissipation. I always heat shrink the leads coming from the Anode & Cathode anyway.

 

[Benm]

but, yes, if is matter of 3 or 4 mm, i use just the glue, only if i have more space to fill, i made metal fillers.

Thats actually pretty good and practical... say you would want to mount an aixiz module to a heatsink, you could effectively just drill a 13 mm hole through it and fill the gap with the stuff. I doubt it would be mechanically stable, but interesting none the less.

 

[Flaminpyro]

You are being confusing by saying it has a low resistance ! if it has a low resistance like say 1 ohm isn't that a good conductor....

Arctic Alumina has such a low electrical resistance, it will and has never for me (over 8 years) affected any circuit. We purchase their products regularly and get discounts. Maybe we should offer here at discounted rate. There are 3 types, slow, med and fast cure. Yes, it will harden to a point where you could conceivably get it apart, but some SMT parts will/may come with it. The adhesive is especially good from the rear & connected pin for heat dissipation. I always heat shrink the leads coming from the Anode & Cathode anyway.

 

[HIMNL9]

Thats actually pretty good and practical... say you would want to mount an aixiz module to a heatsink, you could effectively just drill a 13 mm hole through it and fill the gap with the stuff. I doubt it would be mechanically stable, but interesting none the less.

Uhm, yes, this can work, but in these cases i try to keep the gaps as low as possible ..... as i've said, tthis glue is a good heat conductor, but is not like metal ..... i use it for place, as example, aixiz modules in pen hosts or heatsinks, but always try to keep the hole the more close possible to the 12mm diameter of the aixiz module ..... in this sense, yes, the thing works better than bare set screw, cause with a set screw, the module is "pushed" against a wall (better thermal conductive point of the assembly), but at the same time, pushed away from the side where the set screw is (lefting a gap, also if thin) ..... in this sense, it improve the thermal coupling, filling all the space around the module. (also, in this way, when i fill also the inside of the aixiz module around the driver, the driver itself become heatsinked ..... the only disadvantage, in this, is that you cannot disassemble it, or better said, disassembling it for recover the aixiz module when the diode dies, you also destroy the driver, normally)

And, yes, glueing a 12mm module inside a 12,1 / 12,2 mm hole for all the lenght, it give you also a decent mechanical stability, cause also if that glue don't become hard like dual components epoxy, is still glue ..... it remain a little elastic, but still do a damn good keeping force, and is more hard of common silicone ..... i glued a side of a green module on the flat surface of an heatsink, cause i was needing it on-the-fly for a long test ..... at the end, i was unable to take it away with only fingers, had to place a screwdriver blade under it and make lever, for detach it, and was not easy the same ..... so, mechanically, yes, you can use a 13mm hole for fit a 12mm module without too much problems, probably, you only need to wait 24 or 48 hours for left all the glue set hard .....

 

[kiyoukan]

As far as trying to get good thermal conductivity inside the aixiz modules i tend to fill them with mineral oil and then plug up the end.
I use goop to plug the end of the modules.
This seems to work very good, never had an issue and mine don't leak although i never thought about pressure build up...
i also have it set into a 12.7 aluminum housing stretched closed to 12mm.
Never had an overheat on any lasers or a temp change greater than 10F, and this was a long run.

 

[HIMNL9]

I suggest you to be careful, using this system with open can diodes ..... not all the LD are fitting perfectly in the aixiz modules, sometimes can remain some very thin space, or scratches, and for some types of oils it's enough for slowly leak out to the diode ..... it anyway depend from the oil type, i have one that flow and leak everywhere, so is fluid, and another that you can use it for glue a paper on the wall, so is thick ..... so this can happen or not .....

But, basically, all the oils tend to infiltrate and leak from small spaces or capillarity, more or less ..... and, if you're using a LOC diode (Long Open Can), you risk that, after a month or two, you end with a OSLOC diode (Oil Soaked Long Open Can ), that is not the better working condition, for a laser diode chip .....

 

[RDTech]

It has negligible electrical resistance but very slight capacitance. Having a slight capacitor across the leads of the laser diode is not bad anyway. The electrical resistance is orders of magnitude lower than 1 Ohm. I'm just saying it has worked very well for me for a long time. Potting is a very good way to heat-sink and bond the entire assembly together. I have found some other 2 parts epoxies which are made expressly for electrical potting. Just my 2 cents.

 

[Benm]

Pooring in mineral oil seems a bit odd, i'd rather go for this thermal compound then.

Then again, i dont usually insist on having the driver inside of the aixiz module at all, but i can imagine you would want that for compact builds.

 

[kiyoukan]

Me and mineral oil do everything together.
I did have a few ld leak in the beginning but i sealed them up.
And i don't have the driver in the housing i am always paranoid about heat and my electronics.
Also for long run times of over 1 hour i need to make sure everything is always cool, now that i am getting into more expensive lasers.
Mineral oil has so many uses from cpus to fish tanks to lasers heck anything that is heat sensitive.