Heatsinking 5mm LEDs?

[Elijah]

So Luxeons are easy to heat sink... glue it on a chunk of Al/Cu. But how about heat sinking 5mm LEDs? I know leaving as much copper on the PCB as posible will help disapate some heat from the leads, but can you heat sink by direct contact with the Epoxy body of the LED? Here is what I am thinking: Machine a pice of Al flat stock with holes in it big enough to fit the LED through so that the top of the Al stock is level with the top of the reflector cup within the LED (so that about half the LED sticks out above the Al stock). I was also thinking of using a little thermal glue to make a better thermal contact between the outside of the LED and the inside of the hole. Would this provide sufficiant heat sinking for a 5mm aray, or are the leads the only place worth heat sinking?
Thanks, Eli

 

[The_LED_Museum]

The LED's epoxy body is a poor conductor of heat.
IMO, the best way to heatsink a 5mm LED is to increase the mass of the cathode (-) connection (the lead that goes to the bowl inside the LED body). As I understand, some users have had success soldering a penny to the cathode lead of the LED to help keep the bowl (and consequently, the die or light-emitting chip) cooler.
This is about the best you can heatsink a 5mm round LED in an epoxy body.

My 2¢ here; individual opinions may vary.

 

[idleprocess]

Craig is right - there's not much that can be done with standard 5mm LEDs for heatsinking. The typical thru-hole LED package (epoxy+leadframe) is an old design from when LEDs were relatively dim indicators, not illuminators. Thermal management just isn't a consideration.

I have seen LED array PCBs with large quantities of unetched copper left on the board where the LED cathode connects - presumably for heatsinking since they overdrive the arrays.

Bear in mind that pennies are a thin layer of copper over a zinc core.

 

[Doug S]

I agree with the above comments by Craig and IP. Almost all of the heat exits via the cathode (-) lead. Thermal resistance from the die to about .1" down the lead is on the order of 240C/W. Heatsinking this lead definitely helps but 240C/W is the best you can do even with an "infinite" heatsink.

 

[Elijah]

crap! /ubbthreads/images/graemlins/frown.gif Oh well. So much for that idea. Thanks for the input.
Peace, Eli

 

[3rd_shift]

I have a nice 31 led 3d mag adapter that used to be 32, before one of the leds overheated and started strobing, and then quit working. /ubbthreads/images/graemlins/thumbsdown.gif
I was hitting it kinda hard with 3 nimh D cell batteries at 30+ milliamps per led. /ubbthreads/images/graemlins/icon15.gif
I got it from www.goldengadgets.com .
As good a heatsink system as possible is recommended for these when overdriving them can only help.
Otherwise, keep the current per led down to about 20 or so milliamps.

 

[INRETECH]

Unfort, the small wire coming out the LED case really doesn't allow much heat transfer; the 5mm device just wasn't designed for heatsinking

I will try and take some thermal pictures as soon as I can get access to the camera again