Metal Core Circuit Board material - Where to find??

Does anyone know of a source for metal core printed circuit board material??

This is the same board material that Lumileds uses to mount their stars on.

Essentially, I need a board material that is thermally conductive WITHOUT being electrically conductive.

Any ideas?

The narrow answer to your question is that metal core FR-4 doesn't exist. The FR-4 specification is for an epoxy-fiberglass laminate.

Thanks for the clarification, Doug. I mistakenly had thought "FR4" was the laminate that was applied over aluminum sheeting to produce the product.

So, I guess what I'm looking for is just plain old "metal core printed circut board"..

Is there anyway that you could coat your own Al sheeting?

Slick, check Lumileds Application Brief AB10. It lists a supplier [in France]. A call to Lumileds may be useful.

I have AB10 and saw that Lumileds was getting thiers from France, I had hoped to find something a little easier to obtain (in the US).

One thing I had considered doing was to use a light coat of "red insulating laquer" that is used for coating windings... I just don't know how that would stand up tho. Another option is to find some heavily anodized aluminum sheet that I could have heatsinks punched from. The black anodized CPU heatsink I use on the Luxeon test bench is completely NON-conductive, so that approach may work.

My need for this non-conductive heatsink will permit me to build some Red/Orange Luxeon mods. The die slug on the R/O MUST be isolated (electrically).

For most people who would build a R/O mod, I would recommend using an LS/o to avoid this exact "complication". I've pretty much reached the point where I most just build with bare emitters, since this tends to be a more flexible approach to engineering my solutions.

Originally posted by Slick:
I have AB10 and saw that Lumileds was getting thiers from France, I had hoped to find something a little easier to obtain (in the US).

One thing I had considered doing was to use a light coat of "red insulating laquer" that is used for coating windings... I just don't know how that would stand up tho. Another option is to find some heavily anodized aluminum sheet that I could have heatsinks punched from. The black anodized CPU heatsink I use on the Luxeon test bench is completely NON-conductive, so that approach may work.

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<font size="2" face="Verdana, Arial">Both of these ideas seem well worth a try. The various PCB "conformal coating" compounds might be worth looking at too. Also worth considering are the various insulating wafers that are used to isolate power semiconductors from sinkheats. BeO2 is especially good though toxic.

I have a suggestion: you could try placing a mica sheet between the LS and the metal heatsink. Mica, or a similar material, is used for electrically isolating power transistors from heatsinks. Since the application here is the same, it should be a viable solution.

hotfoot pointed out to me that a problem with this is that the mica sheet might not allow heat transfer away from the LS slug fast enough. In this case, you could try bonding the LS to a small copper disc first (like the ones you described in your buy/sell post ) and then using mica between that disc and the heatsink. The copper disc should help "pull" the heat out from the LS slug quicker, and its larger size would mean the mica would be less of a problem.

Slick,
I had two red HD emitters short to ground with my standard attachment process of using the Arctic Silver epoxy. My solution was to put a thin coat of the Arctic Silver epoxy on the sink lug of the emitter and let it partially cure. I then used a second coat for bonding the LED to the heat sink. This has worked fine for me and I feel that I have the best thermal path available, under the circumstances.
- Don

What about using thin double-sided circuit board material (5 mil) and laminating it with thermally-conductive epoxy to a metal substrate? This has the advantage of using easy-to-find materials and can be done with no special tools (clamp it together with two pieces of wood?).

Thanks for all the suggestions & ideas. I've decided to pursue having some heatsinks punched from some heavily annodized .125 thick aluminum. I can sand the annodize off of the bottom of the heatsink so I can still use it as my negative power pick-up. I will then remove a small patch of annodize from the top of the slug and connect the negative emitter lead using electrically conductive epoxy. With the annodize remaining under the emitter's die slug, I should be safely insulated.

I'm currently in the process of obtaining additional samples of heatsinks in various sizes, so I will report on the success or failure of using an annodized heatsink for this purpose.