Hi all,
I currently have the following work in progress:
What I want to know is should I have thermal paste between the star and the copper heat sink underneath, or should I just sand (I believe the term is 'lap') the crap out of both surfaces to get everything as smooth as possible before tightening those bolts up?
- Matt
Paste, but only a tiny tiny amount, just enough to spread out to cover the whole mating surface.
Lap it and then add just a tiny amount of the best quality paste you have.
That looks pretty sweet.
OK, so it seems a tiny bit of arctic silver would do the trick then?
It's slow progress and I have a few weeks to wait for my new driver but it'll be sweet when it's done:
It is controversial here, but comes from own experience: with those four (!! 
) screws, don't spoil that maximum metal-metal contact by using too much thermal paste, the heatpath is great anyway, much better than the bottleneck at the led solder pads.
Illustration: I reflow my leds using a heatblock at (estimated) 250degC. When I place a ledboard on top of it (no screws, no paste, just gravity pushing the surfaces together) the solder paste starts bubbling almost instantly, indicating that there is virtually no heat barrier between board and heat block.
Perhaps best is: apply thermal paste and then scrape it off completely with a razor blade, do this for both surfaces, then screw the board down.
Wow...that little hey? I'll go with that. As you say I may have more than enough transfer as it is so anything extra might be more detrimental than beneficial.
There were some tests that demonstrated toothpaste was the better heat paste. Its all so controversial. If the surfaces mate nicely, and you use screws, paste will be useless Id think. But if you have imperfections, then paste will work better than air pockets even if tiny.
What sort of distance are you shooting for with that aspheric on the 1100? XP-G I assume?
Does the shinyness of the aluminum affect the beam?
Could you put a drop of solder paste on that and reflow the star to the block? Or, are you hoping to tear this one open again in the near future? Even then, a little heat and it’s loose. Silver solder paste might even improve the thermal properties, since silver is a better heat conductor than copper.
Could do so I plan on hiding the heatsink once its ready to roll. Either with black paint or a cover.
Probably a step too far too be honest. The benefits may just not be worth it. I'll be driving the emitter at around 5.5-6A. Noctigon + copper heatsink + well lapped surfaces and those 4 screws should keep things as cool as they are realistically going to get. In theory.
That’s going to be a beast.
practically impossible to make the surfaces “mate nicely” so a TIM (thermal interface material) is always necessary
That came together very well indeed, as much as I don’t care for aspherics I truly do love the look…especially with a quality lens like that one in a light such as that.
Let me know when you get tired of it, :bigsmile:
IMO this not true for led boards and a pill surface without rim, like the build above. If you have a flat surface as a backing for the sandpaper (I have a perfectly flattened block of casting iron for that, a piece of thick Trespa plate can be used as well), and apply careful sanding, surfaces can be mated very well in my experience.
That build in Post 3 looks awesome.
Wait is there copper in that sink that the Noctigon is touching? I assumed it was solid Al, of there is copper I would definitely reflow to it, even at 3A current builds I reflow all my builds with copper sinks.
Matt, I am currently trying a new (to me) product from Cool Laboratories called Liquid Pro that uses an all metal alloy made with gallium and several other exotics. Using a qtip you smear it into the copper and it fills the microscopic voids with an ultra thin layer, leaving a shiny near mirror finish. “plating” both surfaces this way gives the ultimate heat transfer path, being better than solder or paste by a pretty good margin. Silver solder might be an even better answer, but this stuff is easy, and seems to work well. Cheap enough too for as little that is actually used.
You might want to check it out.
I should note, it’s not to be used on aluminum surfaces, it will destroy the aluminum. Copper to copper is what it’s for, you have ample copper surface to use this, but it would be prudent to mask off the aluminum when applying to the copper sink.
But microscopically they simply don’t mate
Sandpaper no matter how fine simply makes hills and valleys on the surfaces. When you put them together they only make contact at the hills. Thermal interface materials fill the gaps
LEDs aren’t very high power so you could probably get away with it but with 200w chips the size of your thumbnail, cant run them without TIM
I would use thermal paste, but that's just me. I would never even polish to a mirror finish, (lapped), either. It's just not enough of a gain, to do that, but then again, it's just my preference. Nothing is perfectly smooth. There are always gaps you cannot see, but "Microscopic" is just way too much about nothing, to be concerned at all, from my point of view. I've never had a led fry because of too much heat. Copper stars aren't really necessary either. It's just taking simple things to extremes, which we all love to do. Beating a dead horse is futile, but a heck of a lot of fun most of the time.
This can't be true,low temp metals have low thermal conductivity,low temp alloys are even worse.They are better than thermal pastes,but Sn-Pb solder has several times better conductivity than both.