Fujik is a thermal adhesive, not a thermal paste, or grease. One sticks, the other doesn't.
Arctic Silver is a great non adhesive paste, but lately I've gone back to Fujik for modding multi emitter lights. It's almost impossible to get the LEDs centered on these lights if you don't align them before you start, and tighten down the reflector until they are glued in place.
Some reflectors are easier to align, so I paint Fujik around the outside with a drop of AS in the center. Other big reflectors are a lot of work and shifting around the MCPCBs just makes a smeary mess.
Arctic silver and alumina both come in two part epoxy versions, but if you need to change an emitter, it's not coming off without a lot of destruction or damage to nearby emitters. Fujik adheres well, and can be removed without a lot of fuss.
I've been painting a thin coat of Fujik to the bottoms of the MCPCBs, then screwing down the reflector as tight as it can, and leave it until it cures. This leaves a super thin, even bond.
You can show me all the graphs you want, but when running LEDs at 5A+, a very thin film of Fujik on a direct thermal path copper MCPCB is not stopping that heat from transferring to the pill. It's an instantaneous transfer.
If you're using an aluminum MCPCB, I'd rather have a direct thermal path of toothpaste than the fiberglass dielectric layer that is under the LED. You can use all the high end thermal pastes you want, but as long as the heat has to pass through that dielectric layer first, it's too little too late.
Sure, I'd like a an adhesive with a higher thermal transfer specs, but not if the bond is permanent and not easily removed.
