Yeah, or ceramic screws which are super expensive.
Another way is to use some sort of hold-down plate with screws outside the MCPCB area.
The easiest way is to use thermal epoxy and just remove the screws once it is dry.
Small insulating fiber washers + insulated sleeves work for other applications. There is no reason they shouldn’t work to insulate screws from an MCPCB.
How do you keep the threaded shaft of the screw from contacting the MCPCB inside the hole? The walls of the screw hole? Easiest to use a non-conductive screw. Or none at all.
“+ insulated sleeves”
Better if insulated washer and sleeve are one unit, but probably hard to find.
…or get some Laird thermal sheet stuff.
Various thicknesses available.
I tried putting the Black Flat in a Shooter 2X today. The driver I had in it is an original MaxToch Buck driver for 2 cells at 6A. Poof! went my little jewel. So I heated up the 32mm Noctigon, inside the light, (difficult!) and removed the fried one to put a new one in it’s place. Worked fine in testing, was in the light with the 32mm board glued with Arctic Alumina Thermal Adhesive. I reduced the output of the driver to 4.22A pushing an old XM-L T6 on a test board with 2 18350 cells. Got it back together and working, tested 424Kcd in the 2X, but wanted to try a centering ring to see if I could dial in focus. Centering ring ripped off the emitter. UGH! Managed to remove the 32mm MCPCB and clean it up, re-flow the emitter properly and it worked fine on my bench. Put the light back together with new thermal adhesive, everything checked out fine, assembled it, fired it up…. pooof! goes a second little jewel. :person_facepalming:
To insulate the non isolated board I use this method successfully:
- Non conductive thermal paste, I use Arctic MX-4
- Lapped he MCPCB on #320 grit SiC to give some grittiness to the base of the MCPCB. Too shiny and most of the thermal paste will squeezed off the base.
- Apply thin MX-4 to the base of the MCPCB.
- Sprinkle the pasted MCPCB with #320 grit SiC powder. SiC is a relatively good conductor at 20W/MK and a very effective insulator. Much better than AlO3. This SiC powder serves as the thickness guide and separator while still provide decent thermal conductivity in between the paste. The same technique is used by some manufacturers by adding micro glass beads to their TIM.
- Gently, blow the excess powder.
- Place it on the heatsink. Move it SLOWLY in XY direction while firmly press on it. Make sure you spread the paste and SiC powder well.
- I use PEEK screws to fasten the MCPCB. It’s a very strong plastic screw with service temp up to 270C. It’s not cheap but still far below ceramic screws.
Note:
SiC powder is extremely cheap. I got mine for $3 for 1 kg, last for years. If you don’t have some, you can get some by soaking abrasive paper in the warm gasoline.
PEEK screws are available through online stores such as Ebay, Aliexpress. I paid $50 for 25pcs (M3 x 5)
MX-4 on the other hand is relatively expensive but works extremely well. Also very easy to apply. It’s rated at 8,5W/MK I guess.
- Clemence
I really like your story… Weird things happened to me before and they will probably happen again. Weird things like driver fail after I tested it, emitter burnout without any special reason driven on low current draw, shortcuts when reflector managed to peel 2 layers of kapton tape, UFO specks of dirt on emitter etc.
Plenty of weird things can happen… Maybe because of that some of us like modding stuff?
Oh! Another good one… Once I mixed to much flux into solder paste(some guys were giving this kind of advice for soldering paste refreshment 
) - I tried that same paste for reflowing emitter - I had put emitter on top of that, reflowing started and puff! Emitter flew away over whole room and of course it did not survived.
I also had that flying LED moments with my home brewed solder paste. If the flux you’re using is too thin and has low boiling point, it will pops the LED off the board. Slow heating can prevent this. But the better fix is to use proper tacky honey like consistency flux.
- Clemence
Moisture in flux is cause, it starts to boil over 100C and expand rapidly > parts flying.
Is it bad that I still don’t use flux to reflow LEDs after all that years of modding ?
I don’t use flux for anything I do X3, I mean, I use flux core solder from Kester and good Kester solder paste, but never put additional flux on anything.
I found that flux is must especially for nice and shiny solder joints. Also used without flux several years ago… I use dense honey like flux for driver to pill soldering and classic not so dense for wire soldering. Premium quality flux from Topnik, and I also use premium stuff Stanoll Sn60Pb39CU1 recently used with some Osram leds and it works perfect, and it looks solid and shiny. But of course I will never use flux with solder paste When solder paste drys it goes straight to the junk… Btw I use that mechanic solder paste cause I can’t get any better than that. I use needle injecting package.
I tried the Mechanics a long time ago and it was just too thick, too dry. The Kester solder paste in a syringe flows so smooth and easy, love it!
I don’t care about a shiny solder joint, it’s going to be inside the light anyway! 
I have plenty of other things to be OCD about. lol At least I never have to wash a board, or otherwise clean it. Well, once in a great while if a light is giving trouble and it has to be soldered several times in the overall process it can get kind of messy and then I’ll clean the board up. Building drivers, and I’ve built hundreds, I just don’t usually find a need to clean em up. I use solder paste masks and it leaves a nice neat finished driver.
I would like to try that Koester solder paste but on ebay cheapest solution is 43$ S&H to Europe(plus potential 20% of customs tax on that ), and yes mechanic solder paste is thick and it drys fast if left exposed. It does not look like premium stuff at all… That needle mechanic package is a bit better than box one which will dry a lot faster because of packing itself…
Yes sometimes after fluxing something washout is necessary(like driver to pill). But it is easy. Just few drops of isoproprly alcohol and compressed air resolves that in a second with one good blow.
But flux applicator(like flux pen for example) is also important. If it can put thin layer of flux than no cleaning will be necessary. For wires soldering for example. I like thicker layer of flux for driver to pill soldering, and for that I use thin brush applicator.
Yes… I need premium solder paste in arsenal so I could compare it to mechanic sp and see the difference.
Ok… but I also find that I don’t need solder paste for reflow.
I just use soldering wire :nerd_face:
Which solder wire?
Generic chinese one from a long time ago…
It says “xinfa gao ji han xi zhi pin” :partying_face:
Ok… I’ll try to believe you It can be done with a lot more heat than with solder paste and with low melting point solder wire. My personal opinion that solder paste will be less stressful for emitter.
Anyone tried Sekisui 5760 under a non-isolated thermal pad MCPCB? It's pretty thin and it is said to work well.
Cheers ^:)