PCB Schematic with Philips Rebel LEDs

Are these the ones?

ttps://www.sparkfun.com/datasheets/Components/LED/SMD/COM-09636-DS65.pdf

I've not read it in detail but there might be something regarding if you need to attach it to anything other than a polygon.

The thermal pad design looks complex.

Yes those are the LEDs, & that is the thermal pad view that they provide. But I am still in the schematic layout & can't seem to figure out where these thermal pins need to be connected to?

It would normally say in the data sheet if it needs to be connected to something specific such as GND.

I have a similar task in that I need to connect up some capacitive sensors which exist only as PCB shapes. My plan was to add them as new library components and then wire my circuit to a "pad" on that new component.

So I found in the data sheet that "all thermal pins need to be connected to a net named TH", which I did, & it removed the ERC error. But now when I go to the board layout, the autorouter adds a trace connecting all the thermal pads. What is the function of this?

I built a board with Philips Luxeon LEDs and the thermal pad contact to the ground plane.  The board works and the "isolated" claim for the thermal pad seems correct.

So late last night I added a "TH" ground-connection to all the thermal pins of the LEDS. Then on the board layout I connected all these "TH" connections to a bottom layer ground/thermal plane. All the errors went away! The only question is, did I do this correctly? Guess I will get the board made & find out...

Electrically this should not be a problem because thermal pad is isolated. So it's all about if you've put down enough copper to disipate the heat generated.

If I want to make a metal core PCB on eagle cad, how do I distribute the layers. Do I just tell my board house that I want a certain layer to be aluminum?

The ground plane covers most of the back of my board, so there's a fair amount of copper.  I placed a cut-out in the ground plane solder mask behind the LEDs so I can make a good connection to a heat sink, but I haven't used one yet.  With 3 LEDs at full power (about 6W total supply) the contact area gets quite hot to the touch.  I wouldn't be comfortable running it that way for an extended time but heat does not seem excessive.  I expect a modest heat sink to do the job.