to be clear, I mate the pill and pcb when lapping, I don’t just flatten them. though judging from the pcbs I’ve lapped, even just flattening them would be a significant improvement.
If you have a copper pcb and a brass pill, soldering those together is superior to almost anything except for extremly tight lapped surfaces.. there is already a solder connection between the heat source (=LED) and the heatsink (=PCB), so adding another one to connect the PCB to a larger heatsink cant have a negative influence. On cpf I read that someone grinded down the bottom of emitters and glued them on with something really good.. I mean there is stuff with better thermal conductivity than aluminium, its just very expensive. I think it was linked in the "lets discuss heatsinking" thread.
But yes, stock PCBs have very poor connection because they are so uneven.
For P60 pills: I wouldnt mind removing the rim, havent noticed any negative effects so far.
As for lapping: I find it easier to flatten pcb and heatsink first with sandpaper and bring them to a mirror-like finish, going up to 2500 grid. Then some lapping and you are done, although its better to be good at sanding than to be bad at lapping. ;)
Nice tips, guys. I usually use 000/0000 steel wool followed by Brasso or Mother’s until both the PCB and heatsink shine.
like I said, well lapped is superior.
soldering them together DOES have a negative influence vs lapped….it adds an additional layer of metal that has a lower thermal conductivity…
there is stuff w/ better thermal conductivity than aluminum, but it sure isn’t solder.
would soldering be better than unlapped pcb with thermal paste. sure, unless you use way too much solder.
now, with a copper pcb, that likely has a gold coating to resist tarnish, solder might be wiser than lapping in the long term, since you’d remove the gold when lapping…
have you ever lapped a pcb? try it 
Of course, the whole discussion is sort of a mute point. Real world, single emitter lights don't have to go to extremes, just clean the surfaces and apply whatever you want, either thermal compound or thermal adhesive and give it some pressure. Good enough for 95% of the lights out there and only a highly modded "hot light", would really need the extra attention.
Even with those, most of us would use it a few times, for short periond and then put it on the shelf, sell it, trade it, or give it away, so in 99% of the cases, it's not really a big issue, it's just an issue in our minds.
yup
mating parts by lapping takes too long to ever be used in production, or by people that aren’t as silly as I am. soldering would takes seconds…
I always wondered how good a baby soothing creme with zinc oxide would work as a heatsink grease. They look and feel like thick thermal greases.
was it viffer that tested toothpaste?
i think the best thermal grease is the one you have on hand, and apply properly
I dunno, a lot of the performance CPU heatsinks out there are pretty much lapped out of the box. If you automate the process the time overhead is really fairly small. Coming from a computing background I’m surprised just how badly heat is managed in flashlights, the amount of thermal gunk in my bike lights suggests that they never read the instructions as it’s far to thick to be effective.
You really want to avoid getting thermal paste on your skin. The AS stuff can be quite toxic and is a bugger to remove as it really gets into the pores.
didn’t know it is toxic!
but certainly found out it is a bugger to get off of just about anything.
I use a credit card (or similar piece of flat edge plastic) to scrape off excess, and acetone to clean up.
hah! But if we weren’t OCD, we’d just buy a Craftsman LED torch from Walmart and be happy with it, wouldn’t we
I’d wager that most of the single emitter lights on here would benefit greatly from better thermal management, given how much heat they’re producing in such a small place. You only have to look at the output drop from switch on to +15min to see how ineffective they are at dissipating heat. I’m not saying cleaning up just one thermal interface (between star and pill) is going to magically solve that problem, but it’ll help.
All this has really got me thinking about the Jacob a60 and ke-5 I just nodded, on both I sanded then wire wooled the anodizing off and polished the stars, now perhaps, I should go further next time.
I’m also thinking I need to get an hd2010 to play with…
you sanded off the anodizing from the outside?!
Check their MSDS (material safety data sheet)… it’s rather benign. Don’t spread it on crackers, though.
Pretty much all thermal compounds perform the same! The main difference between a good and poor compound is the long term stability of the carrier fluid used to make up the paste.
Lots of interesting info in this thread, for my application i want to replace the star in this photo
with this in xm-l2 when it becomes available
So i want the best thermal transfer compound made by man, economically achievable
Sorry, I’m thinking everyone knows what I’m on about, on both the Jacobs and the ke-5, there is no pill, the light engine is part of the host, as such, its anodized just like the rest of the host, so I sanded and polished under where the star will sit, so the star was pasted direct to the host alu, rather than there being an anodized layer between the base of the star and the aluminium of the light engine, now I see, I should have also polished the base of the star flat too, something I’ve wondered about.
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.