woohoo! Reflowed my first LED :)- Mtbr.com
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  1. #1
    mtbr member
    Reputation: mattthemuppet's Avatar
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    Jul 2004

    woohoo! Reflowed my first LED :)

    nothing particularly major to report, but I was incredibly chuffed I didn't screw this up, so I thought I'd share it I got a NW XM-L from Chinaqualitygoods a while back with a poorly reflowed emitter (it was tilted up a few degrees on one edge). Not willing to let that stop me, I figured I'd reflow it myself with the help of a few tutorials on BLF.

    Long story short:

    1. put star on electric hob, setting 2 (gas mark equivalent not known)
    2. watch carefully until the solder goes liquid
    3. lift off emitter with tweezers, being careful to forget which way round it was on originally
    4. put it on the counter top
    5. suck off old solder from star, put fresh stuff on
    6. look up Cree's datasheet to figure out which way emitter goes
    7. pay careful attention to datasheet
    8. stick LED on star, squish down with tweezers (don't touch dome) until solder squeezes out the side
    9. lift star off hob with tweezers and put on another hob (that's off), blow on it until it cools down
    10. cross fingers and check with a spare 18650 cell

    amazingly, it worked! Now to swap it into a CW+Regina powered commuter/ handout light with one of the LED DNA optics.
    Last edited by mattthemuppet; 10-31-2012 at 06:17 AM.

  2. #2
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    May 2005
    Too cool Matt! I'm certain if I tried that it would be fubar.

  3. #3
    Rolling on 650b
    Reputation: Clipless in PA's Avatar
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    May 2009
    Matt, you're nuts. Congrats though, I have a hard time soldering wires to a 10mm board without nudging the emitter.

  4. #4
    mtbr member
    Reputation: mattthemuppet's Avatar
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    Jul 2004
    I dunno - I think that if you can use a pair of tweezers it's actually simpler than a lot of the fiddly soldering jobs we do routinely. It was certainly a lot more straight forward than I'd feared It's not a job I can see myself doing routinely, but it's nice to know that I can if I need to.

    Now I just have to get a Nichia 219 to reflow onto my camping lantern XP-G star, that would make such a sweet light..

  5. #5
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    Reputation: troutie-mtb's Avatar
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    Sep 2007
    Cracking job and good it worked out but I am not too sure about the pressing the led down bit what if the solder squeezed the wrong way and shorted underneath the led .

    it should self centre its self when the solder flows watch this and you will see some of the leds move into position

    Swopping leds at home - YouTube

  6. #6
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    Jul 2004
    you're right, it did self centre itself, but it didn't suck itself down completely as I've seen on other vids, hence the pressure. The excess solder came out the side of the centre pad in a little blob, much like I've seen on other LEDs I've used. I don't think there's much of a risk of shorting the pads as the solder really won't want to cross that non-metallic gap, which is I think why it pops out the side instead.

    No way on earth would I want to do a 7-up myself though - you'd have to be so quick to get them all done within the time specified (60-120s max going by the datasheets).

  7. #7
    Reputation: mhahn@hvc.rr.com's Avatar
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    Mar 2007
    The trick to doing this with more than one LED is to use a thin layer of solder paste that is stenciled over just the pads the LED sits on. You can make your own stencil using acetate or mylar film (gives you a 3 or 4 mill thick layer of paste). This also gives pretty reproducible results doing just a single LED.

    Use a very sharp exacto knife with the smallest blade you can find. Photocopy your star. Lay the mylar over the photocopy. Cut out tiny little squares where you want the solder paste to go.

    Tape the mylar over your cleaned star. Apply paste. Squeegee off the excess using a credit card (an old one as it will become covered in lead paste). Gently peel the mylar off the star. Then carefully place the LED on the paste. It should be sticky enuff to hold the LED in place.

    I usually use an electric skillet for heating the star up for soldering. Get one with as flat a bottom as you can. Set the star a bit off center, as the center is sometimes a bit cooler. Turn the skillet on high. Watch the LED till the solder starts to flow. Count to 5 and turn the skillet off. Wait 5 minutes or so for everything to cool off.

    I've done dozens of surface mount LED driver boards this way and a few LEDs (when I couldn't find them on a star).

    Try the technique out on some parts you don't care about the first times you try it. The first times you try it you'll probably make a mistake or two. So practice with cheap stuff first.

    You can find mylar, acetate, and exacto knives at most art supply stores.

    Wear disposable gloves while doing this. Do the soldering part outside. Wipe up any left over paste with rubbing alcohol and paper towels (dispose of properly). Lead is bad for you so try to not get it all over you. Don't use a skillet you intend to use for cooking

    Nimium est melior!

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