FR4 for Rebel or a good MCPCB star vendor - a summery please?

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oakgraphics

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I just finished reading all the discussions between FR4 and MCPCB, and all, but I didn't see an outcome.

Things I learned from the threads:

1: FR4 is possible to use for mounting Luxeon Rebels - with proper via count and high oz. copper with a thin substrate. (but will it handle 700ma type loads?) As far as I have read - nobody on the forums have tried Philips's Rebel suggestion pattern, but they have found some alternatives.

2: There are some bad stars out there (like the endor star) - but there was no summery or suggestions on what stars 'worked'.

3: the AS round 6x circle seemed like it might be okay after all even though it was FR4 based.

4: MCPCB is difficult to find a shop that can produce prototypes for without tossing 3x the cost for development.

What I am Ultimately trying to do is make some RGB(+W? / +A?) theater lighting that will be low wattage as we are stuck on how much power we can use. Of course I could buy pro lighting - but at what I figure to be 10x the cost. I can do the circuits to control the PWM and DMX just fine, but I am trying to manage the big 'heat' issue for the Luxeon Rebels.

I would also like to use this for some fun holiday stuff like halloween and the like. The Halloween stuff requires small power and small size because the garage we use for the maze is pretty small. (2 car garage)
 
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SemiMan

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Oh to have the luxury of your time being worth nothing.... ;-) .... as long as you have 100's of hours for testing, layout, s/w, debug, optics, etc....

Rebel on FR4 works great if you follow the guidelines. I would suggest 2oz min copper.... and it takes a good MCPCB to compete with it. That is from experience. Think of differences measured in a few degree C/watt.

Semiman
 
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oakgraphics

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Yeah - I hear ya on the hours - this 'hobby' seems to take a bunch just to get a grasp on what the heck can be done. :) The lighting is for a community theater - which means community budget (or practically nothing) so it's probably my passion for the cause that will allow the result to happen. :)

I am currently designing a FR4 board that would be 4oz copper and I am thinking of trying a thin pcb to boot. My working theory is 16 rebels (4 serial channels) on a 120x120 square pcb that will be bolted to a heatsink and then a forced-air 120mm fan on to of that. For optics - I thought I would try the dialight lumidrives optics as they seem fun and all. I will have to get some samples of that though I guess. :) Looking for a good 'flood' type optic, not really a 'spot' - so if you know any good difuser/flood optics that would be cool.
 
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BillyNoMates

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I've been using my own FR4 PCB layout with 1oz copper without any problems - I regularly run the rebels to 800mA with no problems.

I usually try to surround each rebel by at least 20 vias and estimate I'm getting <10K/W even with 1.6mm thick substrate.

Here is an example of the last board layout I did:

Rebelx5_Top_SurfaceFinish.jpg


I've got a few going spare if anyone is interested... Layout pattern fits Ledil RER-5-M or GT4 optics.
 
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oakgraphics

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I would most definitely be interested in a few. :) It will help me understand some concepts I am trying for sure.
 
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SemiMan

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I've been using my own FR4 PCB layout with 1oz copper without any problems - I regularly run the rebels to 800mA with no problems.

I usually try to surround each rebel by at least 20 vias and estimate I'm getting <10K/W even with 1.6mm thick substrate.

Here is an example of the last board layout I did:

Rebelx5_Top_SurfaceFinish.jpg


I've got a few going spare if anyone is interested... Layout pattern fits Ledil RER-5-M or GT4 optics.

I have done a lot of simulations (and designs) and hence why I have gone with 2 ounce and I have gone more where my via space was limited. You can certainly get away with 1 ounce and my prototype more often than not are 1 ounce since I get them practically overnight.

In general, I get 3-5C/watt better on 2 ounce. That 10-15C at 3 watts can give a surprising amount of extra headroom in meeting product lifetimes.

Semiman
 
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oakgraphics

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That brings up a good question (about 2oz copper) - what's a good prototype pcb company that can let you use 2oz? I am familiar with pcbcart - and the prices are not bad for repeat orders, but the tooling costs jumps pretty high for the first order. :-(

If I go for the gusto - and get 4oz, what's a good thickness to use for the pcb? Normally they are 1.6mm but the above can go down to .5mm for not much more. (after the tooling cost that is)

I would love to crank out 2 or so of my boards for testing, then generate probably 20 more once it looks good. :)
 
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BillyNoMates

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Getting the best possible thermal performance is always a good target, but sometimes one is limited by other factors - like getting proto runs done at reasonable cost. I haven't done any detailed simulations, but I've estimated the thermal resistance of the vias and top surface copper - using 0.8mm substrate would help almost as much as 2oz copper.
 

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