How to reflow solder an LED emitter on a PCB or MCPCB. Cree XML2, XHP70, XHP50, XPG2, XPG3.

YouTube Matt from Adventure Sport andwant to make a quick video today about how to reflow solder an led emitter.

I get a lot of questions about this, so I figured I might as well make avideo, and hopefully clear some of this up for people.

There are several waysthat you can do it and none of the ways I'm gonna show you involve owning$10, 000 pieces of equipment.

These are all pretty simple things that anybodycan do, and we're going to start with the way I think is a really good way to do it.

Then move to some of themore unconventional ways of doing it, that will also work.

Ok so we've got our MCPCB, this happens to be the copperdirect thermal path which I always use, and I'm gonna do some Cree XHP70s today becausethey're a little bit bigger, and their kind of easier to see.

But it's the samemethod for for any of them.

First thing you need to do is figure out theorientation of your your positive contact or your negative.

Youfigure out which way sits on there, for the XHP70 if you look on the bottomthere is kind of like a little arrow in the center.

You see that that little "T"thing is pointing to the left on this particular emitter, that is how you'regonna know what is the positive.

That arrow points to positive things, so youwant to make sure that it's gonna go on there in that direction.

Next thing that we're gonna need issolder paste and I'm using this kester EP256 that I got CMLsupply.

com, andit is a no clean solder paste which just means that it won't leave behind an acidresidue that will eat at your connections.

All we've gotta do is just takethis syringe and I've got the bigger tip that's on there, and you just go across thesecontacts and put a little bit of your paste.

Get enough to kind of cover anddon't get crazy, if you get a little too much thats ok, if you get not enough, stuff can happen so you don't want to do that.

Now we're all set there and we'll putour emitters on in the correct orientation, and what I've got this sitting on here isan electric skillet a hot plate or whatever.

Anything will work and I likethis because you can control the temperature on it very very well.

Youcan get it just hot enough.

All you want is just to wet the solderto melt it and not enough to burn up the led.

This substrate layer can actually peel off of there if you get this too hot.

On my particular skillet I turn it to right about 400degrees on there, which is what it takes to get this this part to where it wetsthe solder about right and doesn't cook things to death.

Basically what will happen is these willjust sit there until the time the solder melts.

You'll be able to seeit as soon as it does the emitter will start to move.

If they'resitting out here not quite perfect what'll happen is when it whenthe solder does melt they just kind of suck into place.

There areways you can do this that would be a little bit faster but that's notnecessarily better I like to start with a cold skill it or at least not a raginghot one because that gives the LED emitter time to heat up more slowly andthings to heat up evenly as opposed to shocking the emitter and that isn't ahuge problem with XHP 70 LEDs.

Cree has a formula about how many degreesper second they're suppose to heat up.

I don't worry about that too much because I'venever had anything that I know of happen doing it this way.

Some of the olderemitters, like luminus SST90 emitters, when those were more popular, and we used those the dome would pop off on those like crazy andyou know a lot of times let's not what you want.

So it was a little morecritical then but you still don't want to shock the emitter too fast that's whyI think the electric skillet is really an ideal way to do this.

And there you go just like magic they kind of slide intoplace.

Now the next thing you want to do is move the emitter around on their justa little bit and I'll show you why.

You need to make sure the solderis spread evenly between the little pads on the sides and the one in the middle.

Otherwise your led can be sitting upfunny and it's not going to be right.

Now if you've got enough solder on therewhat's gonna happen is this this.

You saw the LED slide into place earlier.

It'sgonna bounce like a rubber band if you try to move it is toing to go Boing BoingBoing Boing.

You see that means we've got enough solder it's notsitting down on this it's good.

We've gone cross ways to make sure that thosesolder bubbles are even height and I'm also gonna show you what you don't want.

I did another one of these and hopefully I got it right here.

If you did not get enough solder what'll happen is it just kinda sits there.

There's no Boing Boing Boing Boing like that.

Even if I go this way no Boing okthat's a bad thing, it means you have one or more of the pads where there'snot enough solder.

I intentionally left it out of the middle section on this one.

You can just put more onthere and then spread it around.

Now justbecause you get a bounce does not mean you're solder is spread evenlyif you've got the two pads on the right left loaded up and nothing in the middleit can still bounce like that that's why we do this.

Now the next thing you needto do is you don't want the LED riding high on on this you don't want itfloating in the air.

I mean it's good that we bounce like let but you don'twant to be riding high on several thousands of an inch of solder.

We want to be as close to that copperMCPCB be as possible so what we do is this.

Just give the top of thatdome a little tap.

See how that kind of pushes out.

Ok itpopped out the extra solder, do it just a little bit faster than that just pop onthe top and it'll kind of shoot it out.

Makesure that you're still sitting on their square.

Sometimes doing that can makeit sit funny.

If you plan to put a gasket around thatsome led gaskets for like an XML they fit right around the edges of thatand you don't want those saolder bubbles in your way holding the gasket up youcan just take a toothpick and hold it down and push those bubbles out.

Just makesure that when you flip the bubbles out you don't slide your MCPCB over the topof it or they'll stick to it then you've gotta send off the bottom.

Now thatwe have that, all you gotta do is turn your heat back off and let the emitterscool.

While we happen to have this skillet hot before I shut itoff, I will show you one other thing.

We did that fresh with allbrand new things but a lot of times flashlight modders are in a situationwhere they want to recycle some of their old parts.

They want to put a new LEDemitter inside of a flashlight that they bought so that they can get more output.

Maybe they've either tried before or they're just they're trying touse some other parts and so I'm gonna go ahead and show you real quick how to dothat while we're still in the skillet here.

Say maybe for example you hada copper MCPCB and you had this LED.

There's already some solder on itsince this is a recycled PCB that's one of the copper ones.

Let's say I wantedto put this emitter on it.

Maybe it's a neutral emitter and the only way I couldorder this emitter it was on one of these little cheap aluminum stars.

Basically what you wanna do then is get your orientation again and for the XMLthat little black dot in the corner denotes the negative side.

This has already got some solder onit because it was used.

We pulled the emitter off that somethingelse it's already got some solder on it.

Now that solder will re-wet on its ownmost of the time but it's not great.

So if you're working with that CML sells this right here this RF741 they call it rework flux it's on their website and it's actually reallygood.

If you just tried to use regular liquid no clean flux it pops andsplashes and as soon as you put it there it just it goes crazy anddoesn't really do its job.

It just kind of beads, it would do that same thing if Iput it there in the center of that pad.

With this it's kind of a thickerslime and I think it's probably higher a higher acid than the other stuff.

Anyway that helps this solder wet at alower temperature and it's going to make our lives a lot easier to transfer that.

It's gonna cause that that other solder will be kinda dry and crunchy.

if not sowe pull this one here and just stick it on there like that and we're actuallypretty springy with this particular one already.

See it drew back so we're good there.

We've got an enough solder on things so wedon't need to add any and of course we give it the tap.

Flick that little beadout of there and we're gonna go on that.

Now we're gonna turn off or skilletand just leave the LEDs right there where they're at and let them cool.

Just like they are until youcan tell they're almost cool enough to touch.

You can pull them out a littlebefore.

LEDs are now cooed down and they're ready to testand if you're doing a whole bunch of these rather than having to hook all ofthem up to find out if you did a good job of reflowing it and if you've got electricalcontact and everything and easy way to do it is you can use your multimeter.

Basically what you do is turn it to the continuity setting which is thatright there on mine and if you touch the Leeds together it'll make that little ringing noise.

For thethree voltmeters like XML and XPG and everything youjust touch it and there you go your LED lights up.

So that means we're good thisDMM is not gonna have enough voltage to do the XHP70 or other six volt emitters so I just use my bench power supply.

I've got a couple ofleads hooked up to that and I just test it like this.

Put about 4.

8 volts orso on there and it lights up so we're good to go on these.

Both of those worked out.

Now you can see on there there's a lot ofkind of a nasty residue around the edges its easier to see on the XHP'scause they're white.

That isn't gonna hurt because wedid use no clean flux but if you're in a situation where that's going to bevisible and you want to get rid of it what you can do is just clean it offwith some of this this goof off.

Its just a cleaner and I put some on a Q-tip.

Rubbing alcohol and stuff is not really a strong enough acid.

I suppose youcould use gasoline or something but just make sure you don't touch the dome ofthat led with this.

All you gotta do is just wipe along the side and you can seethere on that side over there where snow white again.

But like I said make sureyou do not touch the dome of your led with that.

You could actually usethis to deme emitters.

If you touch the dome with that goof off it it turns it whiteand cloudy and it makes the dome dry and crackly.

It's really really a bad thing so if you wanna clean the dome part of youremitter just get a Q-tip with rubbing alcohol and that'll be good.

But you're really not gonna get that much flux on on the top of that unlesssomething went wrong.

Now if you don't happen to have anelectric skillet, I understand that doesn't mean you're outside theloop this, means you know you gotta think outside the box little.

There aresome other ways that you can you can still do this.

Using things that you may already have.

I will show you a couple of those ways.

This is probably my next favorite way if you don't have a skillet.

What you can do is just take a wide piece of aluminum bar and put it in a clamp or something, a vice or whatever youhappen to have.

And you can set your MCPCB on here just as if it wasthe skillet.

I like this because it gives you the same opportunity to heatthings up slowly.

What I would do then is just take my my torchlike this and put your solder paste in your your led on there and thenyou heat it up like this until the solder wets and that gives you asimilar effect of the kind of slow heat up as what the electric skillet.

This will heat things up slowly because your not putting the heat directly on the PCB.

If you don't have this medal and a torch you're still not outside theloop, there's still plenty of other ways that you can do this.

This is one we're gonna do real quick.

Just get you some hemos or a pair of vice grips orsomething and clamp this in something you don't have to use a vice justwhatever and put your solder paste just like normal.

XML time and show the little black dotsfacing the right side negative side.

And then you've got a couple of choices heressomething that probably a lot of people have is a heat gun.

Youcan even do these from the top but you kinda risk blowing the emitter away.

You can use this and that will actually get the bottom of that and it doesit cause it to melt almost instantly.

Also if you really really have nothing else, a good olddollar $1.

29 cigarette lighter from the grocery store and you can pull off thesame thing.

That's really my least favorite way to do it but you know what, do what you gotta do.

There you go see just like that we're wet.

Popped out the extra and you're done.

The thing I don't like about that iskind of how fast it does I guess you could hold the lighter little furtherbut really XML and most of the Cree LEDs actually are pretty tough and like Isaid I don't know anything that I've ever had happened because of it doing doing this you know like I saidusually what will happen if we do shocked the emitter is the dome comesloose on him and that's pretty much it hope you guys enjoy the video good lux.

on your projects.


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