How to reflow solder an LED emitter on a PCB or MCPCB.

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BrianK
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I’m betting everything on that sinkpad that isn’t copper actually “repels” the solder. It has to, otherwise yes, it would short out.

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BrianK wrote:
I'm betting everything on that sinkpad that isn't copper actually "repels" the solder. It has to, otherwise yes, it would short out.

Of course, whatever is in between the contact pads and the thermal one “repels” the solder.

When converting a non-DTP copper board to DTP via milling the thermal/central pad even to the very edge of the contact ones, the same behaviour can be observed: it's the dielectric layer, of course.

Take a look at these base plates:

These look like… unbranded Sinkpads!

I bet you my kingdom they come from the same OEM, but the Sinkpads undergo custom tailoring.

 

By the way, just had some more reflowing practice:

This time it went really shiny. That small heatsink (which once cooled the northbridge of an 8KHA+) is my new reflowing pan, thanks to it I've been able to carefully monitor the reflowing temp. 

 

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vestureofblood
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Kusie wrote:
Good video! You got your hand/fingers in the way a few times when it gets interesting but hey… no problem Wink

There is one thing I was always very curious about: the LED and pad have 3 connection points, two for + and – connections and one large pad that is resposible only for heat transfer from the LED to the sinkpad, right? Now you took A LOT of that solder paste on that first pad. now what happens if you take so much that the solder under the LED creates a electric connection between + and headpad, or – and heatpad, or even between all 3 of them? When connecting this to power it should create a short and destroy the LED, right?

How do you make sure this does not happen? You seem to be very tolerant and even move the LED around on the pad when the hot solder is fluid, I don´t get why it works anyway.

EDIT: those DTP boards like the sinkpad also have some kind of “cavity” or pit where the solder can “flow in”, while cheap aluminium stars like this don´t. Does this affect the process?

K.

Hi Kusie,

Yes, your correct. 3 pads one for + and – and one for heat. I do put extra solder in the center, and then move the LED from side to side to make sure all pads are covered. When you tap on the top of the dome fast like shown in the video the extra solder will eject from under the LED. Pushing down on the emitter like that to get rid of the extra will ensure there are no shorts. Its very very rare that you will ever get a short doing it this way.

You are correct about the cavity in the center of a sinkpad. The reason that cheap LED stars do not have that cavity is because they fill it with substrate material. This material is a very poor conductor of heat. In the sinkpad that little gap is filled with solder which is a much better conductor of heat.

The process for re flowing will be the same on either type of board.

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Thank you very much for your detailed answer, much appreciated!
K.

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bump..

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Tks for ur sharing!
If need mcpcb, pls conact me: brightchen802@163.com

Good at designing and making MCPCB of thermoelectric separation! My email is brightchen802@163.com.

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vestureofblood wrote:
I do put extra solder in the center, and then move the LED from side to side to make sure all pads are covered. When you tap on the top of the dome fast like shown in the video the extra solder will eject from under the LED. Pushing down on the emitter like that to get rid of the extra will ensure there are no shorts. Its very very rare that you will ever get a short doing it this way.

Though one should be careful doing this and without shaky hand. When I reflowed Photo Red XP-Es to a 3XP board (and soldering it to the triple spacer and stock pill) over a hot plate while being ill, I ripped off the silicone dome when trying to adjust the LED. It did survive the experience though I harbour suspicions that its light output is worse than its brethren.
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Xoden wrote:
vestureofblood wrote:
I do put extra solder in the center, and then move the LED from side to side to make sure all pads are covered. When you tap on the top of the dome fast like shown in the video the extra solder will eject from under the LED. Pushing down on the emitter like that to get rid of the extra will ensure there are no shorts. Its very very rare that you will ever get a short doing it this way.

Though one should be careful doing this and without shaky hand. When I reflowed Photo Red XP-Es to a 3XP board (and soldering it to the triple spacer and stock pill) over a hot plate while being ill, I ripped off the silicone dome when trying to adjust the LED. It did survive the experience though I harbour suspicions that its light output is worse than its brethren.

Hot de-dome is a method used by several around here. I don’t know about XP-E, but the XP-E2 R3 that I have are very easy to de-dome with heat. Any time you de-dome an LED, you will lose lumens, but I doubt there was any damage done. Maybe you should de-dome the brethren so that they are all the same. Crazy

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gi.lumens
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Taught an old dog a new trick. Wonderfull video thanks for you time. Thumbs Up

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VoB

really excellent

needs to be a sticky

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dittos.

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Thank you everyone. Hearing that my work has helped someone makes this very worth while to me.

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Very nice, thanks a lot! Sticky’d.

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Ronin42 wrote:
VoB

really excellent

needs to be a sticky


BrianK wrote:
dittos.

sb56637 wrote:
Very nice, thanks a lot! Sticky’d.

WoooHoooo!

Thank you!

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I’m planning to do my first emitter reflow in the next week or two, this video was incredibly useful. Thanks a ton.

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Good luck on the reflow sac. Quality solder paste goes along way to a perfect job if your going that way and dont forget to get the + and – in the correct orientation. Silly

 

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sac02 wrote:
I’m planning to do my first emitter reflow in the next week or two, this video was incredibly useful. Thanks a ton.

Thank you, and good lux!

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If you have flux soldering tin you can do the same as with paste

Its best to add some mass so the temperature does not raise too quick, I used a 12mm iron plate and on top 6mm black anodisated aluminium plate on my induction stove

On the Aluminium I use a IR thermometer but it works great if I heat up till solder melts and then reduce the power of the stove

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My very first reflow using a sinkpad an XHP70 with a skillet and hot plate. I will purchase a Infrared thermometer from Harbor Freight to do some testing and also see how hot the sinkpad gets as soon as the solder paste turns into liquid solder. Smile
BTW, Harbor Freight is having a good sale right now in my area, so I can purchase an Infrared thermometer with a coupon for $17.99! I guess that’s a good deal..lol.. Question

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Nice job Willie. That looks pretty darn good for a first attempt. Looks like the emitter is sitting down all the way. I see the extra solder beads were pushed out the sides, and the dome is still in tact. What more could a guy ask for Smile

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vestureofblood wrote:
Nice job Willie. That looks pretty darn good for a first attempt. Looks like the emitter is sitting down all the way. I see the extra solder beads were pushed out the sides, and the dome is still in tact. What more could a guy ask for Smile

Thanks! Appreciate the compliment! I just followed what you had said in your video and it came out almost as good as yours..hehehe I did test it afterwards using a 3.7V lion, but that wasn’t enough voltage. So I put another cell in series and that did the trick..lol Only ran it for a few seconds. Wow, I touched the bottom of the sinkpad to see how warm it was and my it gets hot..lol Crazy BTW, Thanks for your tips and videos! Thumbs Up

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This is really very helpful to me.
Thank you for the video!

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Thanks for the tutorial. Saved it to my favorites for future reference.

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I was curious how the emitter was centered then I found your vid, duh, it's the BOING BOING BOING of course!  LOL   Thanks for great vid and details man!

Cheers!

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Huge thank you for this video! Looking forward to to doing my first emitter swap and now I feel (relatively) confident. Smile

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Mitko wrote:

Something else that is important and worth mentioning: sometimes the emitter + pad and the core pad could solder toghether yet the emitter will work( xml, xpl, xpg est).

It will work even if you connect the proper driver for testing outside the flashlight, but then inserted in the host the MCPCB will contact the host body and ofc this will cause a short connection.

Thats valid for DTP MCPCBs, non dtp in this case wont suffer that issue yet the emitter core isnt electricaly neutral: sometimes it could affect driver memory mode and/or correct driver modes

Hi there :)…

I had “Curious cases of Benjamin Button” recently with newest batch of noctigons. Symptoms were that after re flowing everything was tested and works flawlessly(mode selection and everything) and when you assemble it to flashlight I got High mode only Crazy
So atiny is trying to change modes(i can hear high pitch noise) but high mode still remains…

That happened around 5 times out of 50 emitters so I guess it could be that what Mitko mentioned.

I did not try yet but I think electrical insulating thermal glue like AA or Fujik(if it really must be used) can resolve this issues if they ever happen to you.

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Indeed, sometimes you wont be having a short connection but just a modes lost( it stucks on high), or like on some of my drivers offtime memory function disabled

luminarium iaculator
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Mitko wrote:
Indeed, sometimes you wont be having a short connection but just a modes lost( it stucks on high), or like on some of my drivers offtime memory function disabled

That is so irritating… A lot of effort to assemble everything and than wtf happens! Sad

Mitko what is your method of correcting this issue?

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luminarium iaculator wrote:
Mitko wrote:
Indeed, sometimes you wont be having a short connection but just a modes lost( it stucks on high), or like on some of my drivers offtime memory function disabled

That is so irritating… A lot of effort to assemble everything and than wtf happens! Sad

Mitko what is your method of correcting this issue?

I’ve had a similar result when there is power bleeding off to ground to led negative on the driver board. High mode always.

If there is a short of some kind in the MCPCB the best solution would be to just dump the mcpcb and use another one. Trying to prevent a short with thermal epoxy would likely result in having to use a layer so thick it would negatively effect the thermal path.

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