Best way to heatsink high power SMT LEDs?

[bh4017]

Hello all, I am new around here.

I am trying to build a custom light for a particular application. I have got myself one of these from Ebay. All I want from it is the enclosure; I have taken out the little LED and driver PCB inside it and I want to roll my own replacement to install inside.

The LEDs I want to use come in a rather awkward SMT package, as most of them do nowadays. My plan is to design my own PCB for the LEDs, but I am wondering what is the best way to heatsink these things. If I make a double-sided PCB then I'm thinking that my best bet is to try to transfer the heat from the LED's SMT footprint to the copper plane on the bottom-side of the PCB using lots of small vias (which is a standard heatsinking practice that I have seen used with power FETs). I would then find a suitable heatsink to contact with the bottom side of the PCB to conduct the heat away. I've never attempted this sort of design before, and I wonder if anyone here has useful advice in this regard.

I can purchase the same kind of LED in a convenient "heatsink package", for want of a better phrase, like this one. My first idea was to use these, since the heatsinking method is already taken care of for me and all I have to do is bolt a suitable heatsink to the underside. The problem is they are physically too large in circumference - five of them would not fit together inside my enclosure. I am open with regard to enclosures, so I tried to find a larger one with a suitable torch head to accommodate 5 LEDs (or some similar number) in this package. But I couldn't find one about, so I abandoned this idea.
The package that these LEDs come in interests me, though. It's not simply a regular PCB with an LED fitted, the package is a kind of thick aluminium piece with what looks like a very thin top layer PCB for the tracks.
This is obviously the optimum way to provide heatsinking. But how does it work? And if I wanted to do something similar with my own PCB, how could I achieve it?


Thanks in advance for any advice that is offered.

Cheers,

bh4017.

 

[HarryN]

The LED Engine LED package is pretty nice, as is the star.

If you are careful, sometimes you can trim away at potions of the star to make it fit into your desired shape without impacting the electrical aspects. The yield is not 100%, but for a one off hobby project, it is usually acceptable.

For a light I built, I had a custom board made using a thick copper (rather than Al) heat spreader, and came up with a trick method of directly soldering the LED heat sink area to it, through the multiple layers of the pcb. (no vias, a full size opening)

I have a specialty, low volume PCB shop that makes them for me, as needed. It is really a "price is no object" kind of arrangement though, so it is right on the edge of eccentricity to do it. I have some of the core board material left from my last project still at the shop, so if you are really serious and willing to throw at least $500 at the solution, send a PM. The big challenge with PCB technology is that low volume / low tech boards are cheap, and high volume / high tech boards are reasonable, but low volume / high tech boards are super expensive.

Honestly, I would try to trim some stars first and see if that can work for you.

 

[TexLite]

Are you set on using that particular emitter?

There are others available in 850-940nm that use a standard pattern PCB/Star, some even work with the copper PCB's like Sinkpads.

It would most likely be an easy swap, I'm guessing the light you purchased uses one of the standard size PCB's.

Also, I don't want to be "that" guy, but hopefully you're aware you should be careful with IR emitters.

 

[bh4017]

Thanks for the replies both; I ended up dropping this project for a while but now I am picking it back up and I am revisiting this issue of PCB design for an SMT LED.

Regarding Harry's idea to take some existing STAR packages and trim them to fit, I already tried that before posting here but unfortunately it isn't really feasible for this particular application. Which is a shame.

Regarding Harry's idea to have a piece of copper and then have openings on the PCB to allow a connection from the LEDs... OK that makes sense, and Perhaps it's an option for me. I don't want to throw lots of cash at this project, so I would prefer to purchase an off-the-shelf heatsink in the right package and then try to implement this idea on it.
In order for the "openings" to be useful the PCB would have to be really thin. I'll have to look into that as I've never ordered thin PCBs before.

Regarding TexLite's advice:

Unfortunately I can't use LEDs with the standard STAR pattern as I need to fit a few of these into the enclosure and the star PCBs are too large. That's why I'm down this custom design road.

Regarding safety I must admit my knowledge is not that great. I read the datasheet for the LEDs themselves and it mentioned the potential for eye damage. I'm skeptical about that if I'm honest, for a few reasons, but I've got no intension of placing any risk on my eyesight so I will simply adhere to the recommendations in the datasheet regardless of my doubts.