I vaguely remember a discussion that concluded that copper PCB’s with a dielectric layer was similar to an aluminium PCB rather than a SinkPad/Noctigon.
I have 10 sinkpads that I got as free samples, some aluminum and some copper. Does anyone want a copper XM-L and an aluminum XM-L bare sinkpad for some testing? Shoot me a PM, and I’ll try and hook you up.
I see a little project coming up: a kind BLF-er (Slim Pickens) has just this week offered me some aluminium Sinkpads for the Luxeon TX (that I do not posess as yet, by the way). and I would not mind finding out what the aluminium ones do compared to copper, so yes, I would like them, but I do have a spare 20mm copper Sinkpad, so unless it is not going to be used anyway (I will never say no to an extra Sinkpad :-) ) I am already happy with just the aluminium one. PM sent.
Test the board as is, the way the emitter will see it. If you have continuity then you should also have a direct thermal path. And that board is not the one they showed in the link.
i think what he is saying is that when you hit the board with a dremel , you are grinding down to the copper, and now you have no idea if it was direct to copper before you dremeled it.
If there is a separate dielectric layer, it is the dielectric that determines the thermal properties, not what it is on top of. A diamond board with no dielectric layer would not have a separate dielectric layer, just like a direct copper board has no dielectric layer... hence why on purpose I included the words 'and a dielectric layer' in there.
Honestly I was just to lazy to scratch it by hand and my train of thought was a dielectric layer would be easy to see anyway. I did a dremel scratch on the original sst-50 board to double check myself.
I could be wrong about this, so I am asking, should you have scratched it at all. ? If you test to see if the led goes thermally direct to copper, don’t you test from where the led would be, instead of scratching down to the copper ?
Conventional MCPCB is just a very very thin PCB on top of a metal backing
Noctigon and sinkpad, they remove the center heatsink area (between the + and - solder points) to provide a direct solderable path of heat to the hunk of metal underneath http://www.pcb007.com/pages/zone.cgi?a=59637
sinkpad actually punched the center portion out then pressed in a plug of copper underneath (or as above diagram shows presses a slug upwards to the base of the emitter), noctigon cuts the pcb BEFORE they machine out the stars…is one better than the other…maybe but they BOTH are heads and shoulders above the heat insulative layer of the PCB
A solution to those crappy MCPCB’s is to figure out a way to cut and remove the center PCB material and then solder directly to the star underneath
Thermodynamics
Thermal conductivity of fiberglass (standard pcb material correct?)…horrendous compared to solder
Thermal conductivity of solder
Which do you think would be “better” at moving the heat generated by the LED?
so the above star with the PCB on it made out of copper or diamond or aluminum…until the heat can force it’s way thru the very low thermally conductive PCB…it doesn’t matter what the star is made out of.
So basically there is little point filling that void in Noctigons/Sinkpads with solder and filing/lapping flat as Ive seen done? Its just a lack of faith to do so?
well not entirely no…the heat is going to travel the path of least resistance (same as electricity)…it will fan out from the center solder point then into the star, then into the pill…the beautiful thing is now it takes that teeny 1/8” square (the thermal slug the emitter is mounted on) and turns it into an effective 10/16/20mm square surface (whatever the size of the star)…then it has to force it’s way thru the RTV/epoxy which has a lower thermal conductive rating as the metal above it
The filling in and lapping just ensures you have MORE metal to metal contact rather than uneven surface
this is what it looks like “microscopically” between the star and the pill, the RTV/epoxy fills that space, yes it’s lower thermal resistance that copper or aluminum but MUCH MUCH better than static air
This is why you use a VERY thin layer of the mounting compound…just to fill the gap…NOT to create a gasket