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# LEDs at the die level

#### sophie MC

Aug 26, 2013
3
Hey guys,

I need to found a LED, SMD type, with very small dimensions (for example, package 0402 or 0603) that produces high power output.

I read about LEDs at the die level, but I don't understand what does "at the die level" means. Are they a good choice?

Can any one help me with this???

Thank you so much for any information at all

#### GreenGiant

Feb 9, 2012
842
They are just talking about what size they are made.
For example an indicator LED may have a typical die size of 250 microns, meaning when it is made it will be about 250 microns across.

#### davenn

Moderator
Sep 5, 2009
14,260
what's your definition of hi power ?
as in what wattage are you needing ?
very small and hi power out don't go together too well as the hi power LEDs require a substantial heatsink

Dave

#### sophie MC

Aug 26, 2013
3
Thank so much for answering.

What I need is a LED with an optical power output of 100 or 150 or 200 mW/cm2. I know that this values in mW/cm2 depend on the area and that if I have an area of 1 cm2, to obtain 100 mW/cm2, I need a source of 100 mW. If I have an area of 50 cm2, to obtain 100 mW/cm2, i need a source of 5 W, and so on. My problem here is that I don't know the area because I think that the area depends of the beam area of the LED. Is this right?
Another problem is that I have to soldering the LED in a very small space (like, 1.5 mm x 1.5 mm) in a PCB.

Imagine that I have this LED: http://doc.chipfind.ru/osram/f1998a.htm

The information of optical output comes in lumens. How do I know what is the optical output in watts? Is this LED suitable to soldering in a PCB? What is the area the the beam of this LED can illuminate?

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Input power is in watts, output intensity is in lumens.

#### BobK

Jan 5, 2010
7,682
That chip is .3mm(.0118 in) square! And it has contacts on top and bottom. I don't think you could possibly find a way to use it.

What are you trying to build? (I think I know already, a device for doing skin treatments, right?)

Edited: too many zeros in my inches. About 1/100 of an inch.

Bob

Last edited:

#### sophie MC

Aug 26, 2013
3
I am trying to built a device for doing skin treatments. I have a batery of 3V and 160 mAh. The device is small and as I said I have litle space to put the LEDs for illuminating tissue. The light source has to have some output power so it can penetrate into tissue.
I think that output power from LEDs can be in watts to. It is call radiant flux in watts and luminous flux in lumens. When I am refering to watts I'm not refering to the power that is consumed by de LED but the power radiated by the LED that is gone to penetrate in the tissue.

I have read something about to use LEDs at the die level for my aplication. They refer to a silicon diode in forward bias in series with the LED should be sufficient. But I don't urderstand wath they want to say with this.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Radiant flux for LEDs is maybe 5% of the input power.

Actually it is quoted as being between 4.2% and 35%, although in practice they are only slightly more efficient than CFL.

"Using LEDs at the die level" is a fairly meaningless statement unless you're a manufacturer of the LEDs themselves. Even COB LED's come with a substantial substrate and a protective (and possibly phosphor) coating on top.

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