Thoughts on new LED board

[jlforester]

I'm looking to start using superflux LEDs in my color-changing landsape lighting projects.  I bought a bunch of them, and threw together a prototype on simple perf board.  I was pleased with the results, so I fired up Eagle to lay out a new board.  From the many discussions here, I wanted to pay attention to thermal considerations in the design, so I really went crazy with the polygons.  This is my new design.  I'd like some (gentle) opinions on the new layout.  I used the top layer mainly to sink heat.  The actual signals, as well as the current limiting resistors I put on the bottom layer.

[justDIY]

that's a nice looking board, but I have to disagree with your led choice.  if this is for lighting and not indicating, then you need a lighting class LED.  The superflux leds make great indicators, and the auto industry is slowly adopting them in place of hotwire bulbs.  However, the superflux is not a lighting class led.  You'd need a lot more than nine to throw even a faint amount of illumination into any sort of landscape.  They only look bright when viewed directly on axis.

However, three little rebels or something like a ZLed P5-II would far outshine a board full of superflux, and give you better color mixing and an easier design.

If you're going to have PC boards made up, you can take advantage of the rebel's isolated thermal pad, and use some power pore vias and a solid 2oz copper backplane, and the top layer can be mostly solid copper with only a few divisions for your six signal wires (or four if you go common anode/cathode.)

The ZLed makes things even more interesting, as it's only one part to mount, and lower power than the rebels, you could get away with a single sided board given you've met the 3 sq in per watt rule.

Optics wise, you can go cheap with some sort of frosted diffuser assembly, or there's a number of computer modeled light-guide type lenses that provide excellent mixing from three discrete rebels.  The ZLed would probably fit a regular power led optic.

[jlforester]

Thanks for the feedback on the board.  I agree with you that the superflux LEDs wouldn't be good for illumination.  These, however, are going to be for pathway lights.  The ones I have installed right now are using 5MM LEDs, and they do a good job in this application.  The superflux LEDs I just bought have a wider viewing angle and do a respectable job of color mixing in this particular application (much better than the 5MM LEDs).  I wanted to try the superflux because they're brighter, and can sink heat better.  I've had a high failure rate with the blue 5MM LEDs, and I'm about ready to blame that on heat.  If I ever want to cast light on something, I'd definitely consider something other than the superfluxes.  I've got a driver board that can handle the higher current needed.  I've driven Luxeon III stars with it.

The Z-Power P5-II looks interesting.  Doesn't look like something I can hand-solder, though.

[justDIY]

what drive current are you expecting to operate at? 

That pcb should have plenty of mass to sink heat, but what happens when the sink is saturated?  What kind of ventilation is available for convection to whisk the heat away?  As I recall, eagle has a script that tells you the total area of the copper mass, some clever math could tell you if you have enough or not, based on the led's datasheet info.

you could include pads for an smt transistor or thermistor, so you can tie in a thermal feedback circuit.