• 01-04-2013
    roxtar
    Help with attaching a bare XM-L to a star MCPCB
    I guess the correct term is reflowing.
    How to?
  • 01-04-2013
    troutie-mtb
    Heres how I did this one

    http://i199.photobucket.com/albums/a...ps9fa59eb0.jpg

    Clean all the solderpads on the bottom of the led and the star
    lightly flux and lightly tin each one .

    then pop on a plate of aluminium with the led positioned correctly on the stove
    mine is a gas stove

    I also put a small bit of solder on the plate to act as an indication when it melts

    apply heat slowly to the base and when your bit of solder melts you should see the led centre its self on the solder
    turn off the heat and let cool down .

    dont heat too fast as it will still heat up a bit when you turn it off more so if its an electric hob maybe test first with a bit of solder to give you an idea how fast it heats up .

    There are other ways and I do use a multi meter with heat probe to keep an eye on the temp you dont want to go above 220 c

    I should have used my heat gun as in this video but cound not find the aluminium platter
    Swopping leds at home - YouTube
  • 01-04-2013
    adleysh
    Cree-XRE-Solder - YouTube

    Here is a youtube video of someone swapping led's on a star which will show you the idea. Although they managed to burn there star a little bit so practise makes perfect.

    adleysh

    *EDIT* As troutie says above, I shouldn't have taken so long to find video haha
  • 01-04-2013
    mattthemuppet
    I use an electric hob. Very lightly tin star - I tin the + and - pads I'm going to solder too later and use those as an indicator as Troutie suggested. Put star and LED onto hob. Turn to no. 2. When solder on pads melts, I gently press down on either side of the LED with a pair of tweezers to push out any excess solder and make sure the LED sits flat. Pull off hob and put on the one next to it to cool down.

    Main thing to avoid is putting too much solder on the LED contact pads and leaving it on the heat too long. It's slightly terrifying the first time, but it's really rather simple.
  • 01-04-2013
    MtbMacgyver
    You guys are making this way too hard. Buy some solder paste intended for reflow soldering. Flux is part of the paste and it holds the LED in place until heated. Simply apply a very small amount of the paste to the copper pads, stick the LED down, lay the assembled LED+MCPCB on 500-600 degree metal surface for a few seconds until the paste turns metallic, and you're done.

    You can apply the paste by hand if you get a nozzle with the solder paste. Solder paste typically comes in a syringe. Heated metal surface can be a hot plate or really anything that can get up to 500-600 degrees. Put a small patches of solder paste on a piece of scrap MCPCB or copper sheet and experiment with the heating process before you try a real LED. Be careful taking the MCPCB off the heated surface, the led can slide around until it cools enough for the solder to solidify.

    If you want to get really fancy, make a solder template. It's a thin sheet of plastic or metal with cut-outs that match up with the copper pads on the PCB. Then you lay the template over the PCB so the cut-outs line up with the pads and you use a squeegee to apply the solder paste. The thickness of the solder template determine how much paste is applied, but we're talking thin like 1-2 thousandths of an inch. I've always made them using an automated plasma cutter, but it can probably be done on a mill.
  • 01-04-2013
    mattthemuppet
    Quote:

    Originally Posted by MtbMacgyver View Post
    You guys are making this way too hard. ...

    If you want to get really fancy, make a solder template. ... I've always made them using an automated plasma cutter, but it can probably be done on a mill.

    :D

    Couple of minutes with a soldering iron and an electric hob really isn't that hard :)
  • 01-04-2013
    MtbMacgyver
    Quote:

    Originally Posted by mattthemuppet View Post
    :D

    Couple of minutes with a soldering iron and an electric hob really isn't that hard :)

    What makes using the paste easier is the LED lays perfectly flat, you don't have much trouble with too much solder, and it makes cold solder joints much less likely.

    The solder template is really only needed if you're doing a bunch of the same thing and you need a fast and consistent process. It becomes necessary, from a practical perspective, when you start doing boards with lots of electronic components.
  • 01-04-2013
    mtbikerTi
    Sparkfun sells small quantities of solder paste, in both leaded and unleaded varieties.

    https://www.sparkfun.com/products/10605

    I haven't checked places like Digi-Key or Mouser lately, but last time I checked they didn't sell any solder paste in small quantities.
  • 01-05-2013
    scar
    Easier than I expected
    Just reflowed a couple of XM-L2 samples I got onto stars. I used our flat top stop. :thumbsup:

    ****
  • 01-06-2013
    mattthemuppet
    Quote:

    Originally Posted by MtbMacgyver View Post
    What makes using the paste easier is the LED lays perfectly flat, you don't have much trouble with too much solder, and it makes cold solder joints much less likely.

    The solder template is really only needed if you're doing a bunch of the same thing and you need a fast and consistent process. It becomes necessary, from a practical perspective, when you start doing boards with lots of electronic components.

    sorry, I was just pulling your leg :) Paste would certainly make it easier and take some of the guess work out of how much solder is needed on each pad. Still, if you add a little too much solder, it'll just pop out the side when you press the LED down - you sometimes see this on LEDs from China, a little bobble of solder at the side of the LED.
  • 01-07-2013
    roxtar
    WTF
    How the hell do you keep the damn solder in those tiny spaces?
    This **** feels like I'm doing laser surgery.
    Now I've got the entire bottom of the LED one solid blob of solder. Probably not the best way to keep positive away from negative.
  • 01-07-2013
    mattthemuppet
    don't solder the bottom of the LED! Solder the pads on the star, place the LED (no solder) onto the pads and heat the star. As the solder melts, it'll suck the LED down - if not, just press lightly on diagonally opposite corners with a pair of tweezers.

    Use a solder sucker to get the solder of the bottom of the LED and try again :)
  • 01-07-2013
    roxtar
    Quote:

    Originally Posted by mattthemuppet View Post
    don't solder the bottom of the LED! Solder the pads on the star, place the LED (no solder) onto the pads and heat the star. As the solder melts, it'll suck the LED down - if not, just press lightly on diagonally opposite corners with a pair of tweezers.

    Use a solder sucker to get the solder of the bottom of the LED and try again :)

    I did only solder the star. Apparently, I got a bit too much solder on the star and when it melted it was just one solid connection, not three. :madman:

    I do think the paste is the way to go with my obviously limited soldering skills.
  • 01-08-2013
    mattthemuppet
    ah. You need just the barest covering of solder. Heat the pad with your iron tip, melt a small blob of solder, spread it around with the iron so the pad is just covered and that's enough. If it starts curving up (like you would do on a +ve or -ve power pad) then you've used too much and need to solder sucker it off.

    just clean off the pads and LED and start again :)
  • 01-08-2013
    adrenalnjunky
    Using very fine solder helps too - I have really fallen in love with this particular roll I got at Radio Shack - it is very fine .022 and is silver-bearing, which I've found to flow much better - they call it "High tech solder":
    High-Tech Rosin Core Silver-Bearing Solder (1.5 Oz.) : Soldering Tools & Supplies | RadioShack.com

    Also - get a roll of desoldering braid/solder wick - this stuff absorbs solder from places where you don't want it - like when you solder up the hole on a Lflex, and then can't get your lead to push through.:
    Desoldering Braid : Soldering Tools & Supplies | RadioShack.com


    and if you're not using flux on your wire ends, and tinning them before you try attaching them to whatever you're working on, get a tub of flux:
    2 oz. Non-Spill Rosin Soldering Paste Flux : Soldering Tools & Supplies | RadioShack.com
  • 01-08-2013
    roxtar
    Success!!!
    Well, two out of three. The one I over-soldered was a total loss, must have overheated it while desoldering and the round cover dropped off.
    Thanks all
  • 01-08-2013
    mattthemuppet
    nice job! As for the de-domed one, it might still work and if it does then it might make a nice thrower paired with something like a Regina. There was a lot of discussion on BLF about de-doming LEDs and the consensus (although somewhat disputed) was that it decreased spot size/ increased throw while shifting the colour temp warmer and reducing output by ~20%.

    worth a try anyway :)
  • 01-11-2013
    WeLight
    We have a good video on the Cutter youtube site which covers this pretty well,specifically XML
    Soldering Cree Leds - YouTube
  • 01-15-2013
    mattthemuppet
    not in the same class as Cutter's video, but here are a few photos of a reflow I just did.

    http://i451.photobucket.com/albums/q...psed2f829c.jpg

    http://i451.photobucket.com/albums/q...pse644ed85.jpg

    http://i451.photobucket.com/albums/q...psd1d64875.jpg

    http://i451.photobucket.com/albums/q...ps09784070.jpg

    You can see the excess solder (blobs) that was pushed out from under the LED and that was with the barest "dusting" of solder on the pads - you really don't need much. To press down on the LED, I take it off the heated stove plate and put it on the unheated one next to it then press down on either side of the LED with a pair of tweezers. You have to be quick though as the solder will set v. quickly. Don't try pressing down with it on the heat as you risk punting the LED off the pads.

    Each pad was tested for continuity with each other and the centre pad - from plus to minus should be some millions of ohms, from either pad to centre should be open line. XM-L was tested with a very brief contact with a bare mostly discharged 18650.

    It's ever so slightly terrifying, but also surprisingly easy :)
  • 01-17-2013
    plugp7
    If you have one of those 60w or so trigger solder guns, the ones with the bent wire tips, resoldering can be easily done without annoying the wife, from your work bench.
    Tape the trigger closed, lay the gun on it's side and clamp down so the wire tip is parallel to the bench. Simply rest the star and emitter one the wire tip, as per other posts. Switch on at mains and follow what other posts say about the soldering. Switch off at mains and wait to cool down. Leave it about a minute before you move it. I find this way the application and removal of heat is more or less instant.
  • 01-17-2013
    roxtar
    BTW, side question here.
    What's the benefit to lead free solder over leaded?
  • 01-17-2013
    MtbMacgyver
    Quote:

    Originally Posted by roxtar View Post
    BTW, side question here.
    What's the benefit to lead free solder over leaded?

    Lead is bad for the environment and the European Union's ROHS directives have gone into effect prohibiting the sale of consumer electronics with added lead. So if you're building something you want to sell internationally, you need to use lead-free solder. ROHS has been a pretty big deal in the electronics industry because it goes way beyond just solder. You also have to make sure all the electronic components that go into the products are ROHS certified.

    The trade-off is that it's harder to use and is less proven in terms of the effects on things like long term reliability.
  • 01-17-2013
    roxtar
    IOW, no benefit to me whatsoever.
  • 01-17-2013
    adrenalnjunky
    another side question. What is the center pad for? Adhesion only? Doesn't appear to be electrically connected to anything on either board.
  • 01-17-2013
    Vancbiker
    Quote:

    Originally Posted by adrenalnjunky View Post
    another side question. What is the center pad for? Adhesion only? Doesn't appear to be electrically connected to anything on either board.

    It's for conducting heat away from the die. The best performance comes when the center pad is directly soldered to a copper heatsink. That is essentially what Troutie shows in post 2. Matt also posted a thread about a direct to copper star group buy on BLF recently.

    The standard aluminum MCPCB has an insulating layer between the center pad and the aluminum. This slightly inhibits heat transmission.