if you’re not willing to drill a couple holes and screw it down then you’ll need an adhesive one
slightly cheaper on ebay or walmart, but i like newegg
Lapped might be superior when done professional. With home tools? I'm unsure..
How could soldering have any negative effect? You already have a layer of solder between LED and PCB, but the layer between PCB and heatsink would have 10times the area -> better heat conduction. If you have a 1" pipe at the source it doesnt matter how many 1" pipes you add in the path, even if some are 3"..
Actually aluminium PCBs would be great if you could solder the LED directly on the aluminium, without the dielectric layer and all that stuff inbetween. Thats the main advantage of copper pcbs. I think even brass PCBs would be better if its a good alloy.
And I dont think the gold layer has any influence on thermal conductivity at all. Its there so the copper doesnt oxidate. Also, even those copper PCBs from LED-tech are uneven because they are punched out..
@ChimpOnABike: CPU heatsinks arent lapped because you need both parts for lapping. They are sometimes sanded pretty good, but often far from a mirror-like finish. Its an easy improvement actually.
Something with powdered diamond in it. Diamond powder is actually not too expensive. Check Ebay:
Shop by Category | eBay%28dust%2Cpowder%29&_sacat=3213&_odkw=diamond%28dust%2Cpowder%29+mesh&_sac=1&_osacat=3213&_from=R40
ah, yes, I dont’ own either.
probably a good idea to remove.
I’ll be using some mother’s polish as a last step next time I do a pcb…
well, I have lapped machined parts professionally, but I don’t think someone else needs to have been paid to do a good job. it does take some patience.
there isn’t any fluid mechanics involved here, so fluid in pipes isn’t a good analogy.
i’m not sure how to explain it differently. Maybe we’ll have to agree to disagree.
the thermal conductivity of solder is lower than the metals involved, so putting it in between them reduces thermal conductivity if they have very good contact before soldering - what happens before or after that can change the temperature gradient in operation, but not the properties of the materials at the junction.
I guess we’ll have to agree disagree.
you can solder aluminum, but it requires a different solder, or at least a different flux, and it is a PITA
any material will have ‘some’ influence but it’d be near impossible to measure
anyway, I didn’t mean to imply that’s why gold shouldn’t be removed…I meant you don’t want the copper to tarnish…which would surely reduce contact area as well as thermal conductivity…
anyway, let me know when you find copper PCBs, I’d be happy to test this scenario.
I meant with the proper tools, not necessarily paying someone to do that..
Its the easiest I could think of.. I'm not good at calculating, but as there already is solder involved right under the LED, it cant really get worse. Maybe someone who knows how to calculate that stuff can chime in..
Metal to metal is of course superior, but if someone doesnt have the tools or patience, soldering is as good as he can get. Agreed? :D
I know, I did it before.. but as you said, not easy and therefore (I guess) rather expensive to produce. So they dont..
Well, gold is worse than copper, so.. :P
And yes, its there so the copper wont tarnish and its easier to solder to. But if you plan on using the copper stars from LED-tech, you better sand them, because they arent much better (regarding how even they are) than all those aluminium stars.
You guys gave me an idea on how to lap the insides of the pill very flat
I currently lap my stars on a flat piece of glass using wet/dry sandpaper progresively up to 2000 grit.
For the pill I am thinking on using a steel bolt like this
And lap the bolt’s head flat on a glass using wet / dry sandpaper up to 2000 grit and then glue wet / dry sandpaper to the bolt’s head and lap the inside of the pill up to 2000 grit using a drill, IMHO it should produce really good results, what do you guys think?
I’m familiar with the calculations, although admittedly not as familiar as when I passed thermodynamics w/ an A grade 16 years ago…
The problem with calculating this is, interfacial thermal resistance is empirical.
I like this stuff, so I spent a couple hours last night looking for test data. ( No mystery why I’m single 
)
I couldn’t find a study of ‘copper to copper’ vs ‘copper to solder’ interfaces. The closest I could find, in different studies, was that a milled copper to copper interface (1.6um roughness…not lapped), with no thermal compound, is has an order of magnitude lower thermal conductance than a copper-solder-copper sandwich where the solder is <30um thick and has above average (for solder) thermal conductivity. Of note, a copper-copper interface that is ground (3.6um) is 3x worse than milled…
So…I find that data interesting, and pointing in the direction of solder being superior…but ultimately inconclusive…
If you’re good at soldering
I definitely think soldering is easier - although it doesn’t preclude lapping…in fact the copper solder sandwich study used lapped copper discs….
I picked up a good tip from that study. calculate the amount required to cover the contact area with 10um layer, use a little excess, press the parts together while still hot to squeeze out excess.
anyway, maybe some day we’ll get to test this. unfortunately, the studies I found use a laser for heating and very accurate measuring equipment…which to me implies, even if we get the chance to test, we’d be hard pressed to tell the difference w/ ‘amateur’ test equipment :bigsmile:
Lets recap, I was hoping for some consensus or side by side testing, but so far it seems to be a contest between
http://www.frys.com/product/6274350
http://www.intl-outdoor.com/shinetsu-x237783d-thermal-grease-5-pcs-p-480.html
same product, different numbers
http://www.wakefield.com/Catalog/tabid/92/CategoryID/110/ProductID/362/Default.aspx
and
http://www.amazon.com/Innovation-Cooling-Diamond-Thermal-Compound/dp/B0042IEVD8
finally, according to this don’t use cheese
Thermal Paste Shootout!!
Also a suggestion to use as little compound as possible just to fill in air gaps (if the compound is more conductive then the metals then this advice may be mute?)
Can somebody wade through these and figure out the best 3?
sorry for distracting your thread 0:)
yes as far as use as little compound as possible, the compound will not be superior to metal.
if you’re not going to screw down the PCB, then you will need adhesive compound.
the technique (or at least my technique) is different for adhesive compound.
Since I flatten/lap the surface, I apply grease-like compound to both surfaces, rub it in to eliminate air, then scrape it off with something flat.
For adhesive, I apply to both surfaces, rub it in, then clamp the two parts together, so that excess squeezes out, and pressure is maintained while the adhesive sets.
i’ll look at the links then reply more 
the last two links did work for me
the first two links are not adhesive.
the only adhesive thermal compounds I’m familiar with are fujik and arctic silver adhesive.
Start at the top of the chart you linked, search the product name (ie the products that don’t say they’re a grease) and when you find one that’s adhesive, and above arctic silver adhesive in the chart…you’ve got your answer 
adhesive is not necessary, just superior thermal transfer
Awwww..^^
So.. if grounding (=sanding?) isnt that good, would lapping be between sanding and milling then?
Oh and I read somewhere that the thickness of solder wouldnt really matter.. I dont really know about that.
Well, for the regular home-modder soldering is a good choice if copper pcbs are available.. and some soldering skills. :D
Yup, some soldering skills might be helpful anyways for modding. :D
But I think its great that we have found a point where we might lack test equipment to see whats better for home users.. not too bad IMO.
It depends on which compound you use as some are worse than others. Anything with high levels of silver and given enough of it you run the risk of Argyria, although I totally accept this is low risk unless you’re using it on a daily basis. I can’t find the link (it was back in my PC modding days several years back) but I have seen dermatology people talk about problems with the very fine particle size and skin reactions. Either way it’s best not to eat it or get it on skin, although you won’t drop dead on the spot if you do.
after some searching…
mirror polish aluminum surface roughness approaches .0005 um.
amateur polishing is more like .4 um
the copper-solder-copper study found a ~20% improvement in thermal interface conductance by reducing solder layer from 30um to 10um.
absolutely.
hot rodding flashlights! pun intended 
Anyone tried to use the “liquid metalpad” for LED mounting?
Its a thin foil of some metal mixture that has a melting point of (iirc) 60 degrees celsius,
and usually you put it between CPU and heatsink and then drive the CPU until the stuff melts.
Somewhere i saw a comparison chart of different thermal “greases” and this one had the lowest thermal bulk resistance.
Now using that + lapping both the copper MCPCB and the heatsink to also reduce the interface resistance
seems to me like a very good way of keeping the LED cool.
And regarding solder: how good is the thermal conductivity of silver solder? (googling around i found that
you use this to hard-solder copper pieces, and it is more than 60% copper and silver, which conducts heat even better
than copper)
It probably can’t be used do mount MCPCB to heatsink because it takes too much heat to solder, which the led wouldn’t survive.
But reading around in the forums i learned that some people actually build their own copper heatsinks without a lathe,
by hard-soldering flat sheets of copper together. With this kind of solder, the resulting heatsink should be close to pure copper, right?
Not really. Copper is around 350W/m.K while even silver solder is below 100W/m.K IIRC. Still far better than most heatsinks tho.
And those metal pads.. they are very expensive right?
Ok, those metalpads probably don’t count as “budget” stuff.
But on ebay you can find them at a “reasonable” price, like 3x CPU pad for less than 12 euros (roughly $16).
I believe a CPU pad is 38mmx38mm, so you would easily get 4 pads for a 16mm PCB out of one CPU pad.
Not a steal, but at less than 1 euro per light it’s not a big part of a flashlight mod/build. I assume that you won’t add those
pads to stock flashlights.
I think i will try those pads some time…
Not bad these pads, 82W/m.K, thats better than most solder. But you have to apply constant pressure.