Bare LS Emitter Technique

I am Interested in all methods of attaching bare LS emitters to aluminum and or copper. Any tips, advice and pitfalls to avoid will be much appreciated.

For instance, how do I keep positive terminal insulated from aluminum heat sink? Is it just a dab of epoxy on the underside between heat sink and emitter or should I use something else?

Do you need to solder leads on before gluing to heat sink?

What is the best mix of Artic Silver and Epoxy? Will other glues or tape work better?

Do you clamp emitter to aluminum while glue dries?

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by startravel:
I am Interested in all methods of attaching bare LS emitters to aluminum and or copper. Any tips, advice and pitfalls to avoid will be much appreciated.

For instance, how do I keep positive terminal insulated from aluminum heat sink? Is it just a dab of epoxy on the underside between heat sink and emitter or should I use something else?

Do you need to solder leads on before gluing to heat sink?

What is the best mix of Artic Silver and Epoxy? Will other glues or tape work better?

Do you clamp emitter to aluminum while glue dries?<HR></BLOCKQUOTE>

Both the pos and neg lead need to be insulated from the heatsink if it is grounded. When attaching to aluminum heatsinks, use Artic Silver epoxy for best results. The Luxeon leads can be bent up, and folded over on themselves to make sturdy wire connections after the epoxy sets up. You don't need to clamp, but press down to make the epoxy under the emitter as thin as possible.

I don't know the best mix, as I use straight Artic Silver epoxy and use mixes for potting.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by startravel:
What is the best mix of Artic Silver and Epoxy? Will other glues or tape work better?

Do you clamp emitter to aluminum while glue dries?<HR></BLOCKQUOTE>

For heatsinking epoxy I use Arctic Alumina. For potting I mix in (half the amount) Arctic Silver 3 thermal compound with a slow-cure (overnight) epoxy. Slow cure tends to be thinner and will flow out better.

For clamping the emitter, I put the assembly in the flashlight and screw down the head to use the collumator as a clamp and to ensure it's centered.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by lambda:
[QB]Both the pos and neg lead need to be insulated from the heatsink if it is grounded.[QB]<HR></BLOCKQUOTE>

do they? someone posted a picture awhile back that had the negative lead and the heatsink joined near the diode. also, any aluminum light that heat sinks to the case and uses the aluminum housing to conduct to the negative lead would charge the heatsink, wounldn't they?

hmm...just got out my meter and tested ohms between ground and heatsink. infinite. tried powering the LS with the positive hooked up and the negative to the heatsink. nada. so i guess they were mistaken, whoever posted the diagram. _but_ i ran it with the positive hooked up and the negative lead jumped to the heatsink and it worked fine.

now that i think about it there were several posts where people were trying to revive dead LSes and did so by putting hi voltage through the heatsink and positive leads. hmm...

I think it is more critical for the red/amber lower voltage Luxeons, but the tech documents at LumiLeds state it for the white also. Regular Artic Silver epoxy will insulate the Luxeon heat slug from the heatsink anyway, so I've not worried about it too much.

ahh, i checked on an LS/O, now i realize that you guys are talking the bare emitters specifically (perhaps it was the title that gave it away?). i'm guessing that the bonding agent luxeon uses to mount their emitters to their heatsinks are non-conductive.

** edit **

interesting. the bare amber HD sitting here says that positive is internally connected to the heatsink, not negative. odd, i thought that most of the heat whicked off of the negative lead, at least on traditional LEDs.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by papasan:
i'm guessing that the bonding agent luxeon uses to mount their emitters to their heatsinks are non-conductive.
<HR></BLOCKQUOTE>

Actually, the Luxeon w/o has the heat stud glued to a thin layer of copper cladding in a + pattern that is seperated from the aluminum heatsink by a layer of fiberglass; it's well insulated.

a well insulated heatsink is interesting in and of itself.