# Help with attaching a bare XM-L to a star MCPCB



## roxtar (Sep 7, 2009)

I guess the correct term is reflowing.
How to?


----------



## troutie-mtb (Sep 20, 2007)

Heres how I did this one










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


----------



## adleysh (Jun 4, 2012)

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


----------



## mattthemuppet (Jul 16, 2004)

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.


----------



## MtbMacgyver (Jan 23, 2007)

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.


----------



## mattthemuppet (Jul 16, 2004)

MtbMacgyver said:


> 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.




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


----------



## MtbMacgyver (Jan 23, 2007)

mattthemuppet said:


> 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.


----------



## mtbikerTi (Jan 15, 2004)

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.


----------



## scar (Jun 2, 2005)

*Easier than I expected*

Just reflowed a couple of XM-L2 samples I got onto stars. I used our flat top stop. :thumbsup:

****


----------



## mattthemuppet (Jul 16, 2004)

MtbMacgyver said:


> 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.


----------



## roxtar (Sep 7, 2009)

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.


----------



## mattthemuppet (Jul 16, 2004)

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


----------



## roxtar (Sep 7, 2009)

mattthemuppet said:


> 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.


----------



## mattthemuppet (Jul 16, 2004)

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


----------



## adrenalnjunky (Jul 28, 2007)

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


----------



## roxtar (Sep 7, 2009)

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


----------



## mattthemuppet (Jul 16, 2004)

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


----------



## WeLight (Aug 12, 2007)

We have a good video on the Cutter youtube site which covers this pretty well,specifically XML
Soldering Cree Leds - YouTube


----------



## mattthemuppet (Jul 16, 2004)

not in the same class as Cutter's video, but here are a few photos of a reflow I just did.





































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


----------



## plugp7 (Oct 8, 2011)

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.


----------



## roxtar (Sep 7, 2009)

BTW, side question here.
What's the benefit to lead free solder over leaded?


----------



## MtbMacgyver (Jan 23, 2007)

roxtar said:


> 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.


----------



## roxtar (Sep 7, 2009)

IOW, no benefit to me whatsoever.


----------



## adrenalnjunky (Jul 28, 2007)

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


----------



## Vancbiker (May 25, 2005)

adrenalnjunky said:


> 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.


----------



## plugp7 (Oct 8, 2011)

Vancbiker said:


> The best performance comes when the center pad is directly soldered to a copper heatsink.


I use copper heatsinks and am wondering how to attach a bare emitter directly to these copper heatsink! How do you electrically insulate the 2 contacts on the underside of the emitter?


----------



## MtbMacgyver (Jan 23, 2007)

roxtar said:


> IOW, no benefit to me whatsoever.


Not unless you're messy with the solder paste and have a habit of licking your fingers.


----------



## Vancbiker (May 25, 2005)

plugp7 said:


> I use copper heatsinks and am wondering how to attach a bare emitter directly to these copper heatsink! How do you electrically insulate the 2 contacts on the underside of the emitter?


Easiest way would be to get in on the group buy Matt linked in this thread...

http://forums.mtbr.com/lights-diy-do-yourself/sinkpad-copper-xm-l-xp-g-20mm-stars-gb-blf-833110.html

Otherwise do it like Troutie did in the second post in this thread.


----------



## mattthemuppet (Jul 16, 2004)

plugp7 said:


> I use copper heatsinks and am wondering how to attach a bare emitter directly to these copper heatsink! How do you electrically insulate the 2 contacts on the underside of the emitter?


most of the ones I've seen either mount it on a high enough pedestal that the + and - contacts hang in free air and leave space for the wires to be soldered OR grind off those pads and solder to the contact points on the top of the LED. You could even do a hybrid - grind off/ high mount one and solder the other one to the heatsink, using it as an electrical path.

It'd be easier to buy one of those stars though  PM Nitro direct as the group buy is closed.


----------



## MtbMacgyver (Jan 23, 2007)

plugp7 said:


> I use copper heatsinks and am wondering how to attach a bare emitter directly to these copper heatsink! How do you electrically insulate the 2 contacts on the underside of the emitter?


I made a PCB with pads that matched the 2 electrical contacts on the outer edge of the LED and a cutout the exact size of the thermal pad in the middle of the LED. Then I machined the copper heatsink with a raised area the exact height and size of the cutout in the PCB. Slipped the PCB over the post on the heat sink and then reflowed the LED to both the heatsink and PCB at the same time.

In theory this could be even better than the solid copper mcpcbs because you can eliminate the joint between the mcpcb and the case if you're willing to have an all copper or brass case. There was an improvement in performance, but it wasn't dramatic in terms of perceived light level. I ended up deciding the improvement wasn't dramatic enough to justify all the extra work compared to a well designed normal mcpcb and case. But that's somewhat personal preference.


----------



## mattthemuppet (Jul 16, 2004)

I've seen that before - looks really cool, but very fiddly. I saw a really neat twist on that on BLF recently. Instead of machining matching posts on the heatsink, the poster mounted the 4-up PCB and drilled _through_ the centre pads of the PCB into the copper heatsink, then pressed and soldered matching copper rod into the holes. The rod was then cut down to the right height so that it was level with the top of the PCB.

Not as good as machining the posts, as there's another part metal/ part solder interface, but easier and probably better than copper PCBs. I thought it was pretty neat.


----------



## adrenalnjunky (Jul 28, 2007)

I just read this thread on BLF - thoguht I would cross post it here:

Match's Mods: Emitter to Copper Reflow in a 1C mag mod (How To) | BudgetLightForum.com

If you read it - notice that this beamshot was done _DURING THE FREAKIN DAY!!!_


----------



## mattthemuppet (Jul 16, 2004)

just showing off 

got a bunch of Xx-x2 LEDs, some copper sink pad stars and a tube of solder paste (which rocks)









into









XM-L2 on sinkpad and XP-E/G2 parallel triple is going to Ofroad'bent, hopefully he'll be able to give us some feedback when they're done!


----------

