LED Reflow gone wrong

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LichtAn
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LED Reflow gone wrong

Hello everyone,

I just tried my second reflow job with a Nichia SST-10 UV. And so far it doesn’t look like a success. I heated the MCPCB added solder and let it cool down to 100°C again. Put the LED on top and heated to 250°C and waited for the LED to slide in place like it did on my first reflow job with a XP-L. Nothing happening…
The solder on the + and – pad is quiet liquid. So the temperature seems to be enough. I tried moving around a bit and then pressing onto it. The excess solder comes out of the side…still no bouncing LED…
I took it of the heating plate and the solder instantly went dull. What am I doing wrong?
I’m kind of frustrated since it worked so well the first time and now I got a 9$ LED on the line. Facepalm

duramax
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not entirely sure what happened, but my guesses would be:
1) not enough flux or the wrong type (never seen that having such an impact but you never know)
2) LED misaligned (ie 90° rotated and won’t jump into place – I did that once)
3) sometimes things don’t “bounce” (or not as strong as we have seen it before, on Youtube, etc)

Did you check for shorts? Does the emitter light up when you check with a DMM?

LichtAn
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duramax wrote:
not entirely sure what happened, but my guesses would be:
1) not enough flux or the wrong type (never seen that having such an impact but you never know)
2) LED misaligned (ie 90° rotated and won’t jump into place – I did that once)
3) sometimes things don’t “bounce” (or not as strong as we have seen it before, on Youtube, etc)

Did you check for shorts? Does the emitter light up when you check with a DMM?

1) At first I thought it wasn’t enough, then I added some more. (which was too much at that point)
2) I triple checked before putting it on
3) I’m confused since it worked so well on my first try

I doesn’t, but the XP-L I reflowed also didn’t light up with DMM. Guess it doesn’t have enough power?

goshdogit
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Too much solder can create a bridge between the emitter’s contacts.

Check for continuity between the MCPCB’s + and – pads.

LichtAn
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goshdogit wrote:
Too much solder can create a bridge between the emitter’s contacts.

Check for continuity between the MCPCB’s + and – pads.

Nope, no continuity.

LichtAn
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Oh well. Went into an almost dark room. It does light up. Cool
So I should be just satisfied with the way it is? Also I’m a bit pi**ed off, that it looks how it looks now. Not a nice soldering job.

goshdogit
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I once overheated an XHP 70.2 while reflowing. It lit up, but only very dimly.

moderator007
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http://budgetlightforum.com/node/46443
Might help if you haven’t seen it already. Thumbs Up
If it only lights very dim that usually means bad reflow connection.
I have had them work fine until all of a sudden they go dim without warning. I assumed it was a bad reflow that was good enough until the led made some real heat and broke the solder connection. Reflowed it again and no problems after.

TheOnlyDocc
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I only use solderpaste if i reflow LED´s. At the beginning most of the time something went wrong i used to much solder or to much/wrong flux.
Since i use solderpaste everything is going like it should. It is still possible to use to much paste but after some LED´s you learn to use the right amount.
I would not recomend to start with pricy LED´s. Buy some old dirt cheap LED´s and some old cheap boards and get a feeling for it.

BLF D 80 LT and Longer D80 Tubes for Sale http://budgetlightforum.com/node/62463

LichtAn
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I got the light finished! I was about to throw my soldering iron in the trash, when I had an idea. I wasn’t even able to properly pre-tin my wires. I mean I’m not good at soldering, but not THAT bad. Big Smile
I tried some new tin I got from Banggood. This
I switched back to the rest I had leftover from my old tin and oh what a surprise. The tin on the MCPCB was shiny, I put the LED on it and it bounced like crazy. Reflow looked perfect all of a sudden!
Now getting the new tin of the wires and putting the old back on…works like a charm.
I’m wondering the Banggood tin got 2200 5 star reviews. Am I just to stupid to use it or what? Old tin is Sn60Pb38Cu2 if that helps anyone to help me.

P.S.: Can I use that SST-10 UV without any eye protection? I have no idea how hazardous it is. This thing puts out an insane amount of UV. Doesn’t compare to anything I had before for geocaching.

goshdogit
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Good to hear your project was successful! Thumbs Up

I think the general consensus is to wear protection with all UV lights.

Most polycarbonate blocks UV. I only use UV for a couple minutes at a time, but I wear wrap-around safety glasses that fit snugly to my face.

To test polycarbonate glasses, illuminate an item with UV, then move the lens in front of the light. If effective, the item will no longer fluoresce because the UV light is being blocked.

I didn’t know geocaching could involve UV light! Tell me more.

LichtAn
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goshdogit wrote:
I didn’t know geocaching could involve UV light! Tell me more.

Especially for geocaches that are meant to be done at night or have stages in dark places it’s not uncommon to have hints written with UV reactive paint.

vt2nv
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I use solder paste, which requires less heat that solder does, and which is the best way to solder a part onto pads that are covered by the part.

1) apply solder paste on the pads that the part will sit on
2) gently place emitter into the solder paste. Don’t push hard enough to squeeze out the solder paste
3) heat sinkpad from underneath using a hot air gun or a blow dryer or whatever

So there you have it.

If there’s a large courtyard around the part you can solder the traditional way. If the part covers the pads then use solder paste. Much better than hand soldering.

LichtAn
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vt2nv wrote:
I use solder paste, which requires less heat that solder does, and which is the best way to solder a part onto pads that are covered by the part.

1) apply solder paste on the pads that the part will sit on
2) gently place emitter into the solder paste. Don’t push hard enough to squeeze out the solder paste
3) heat sinkpad from underneath using a hot air gun or a blow dryer or whatever

So there you have it.

If there’s a large courtyard around the part you can solder the traditional way. If the part covers the pads then use solder paste. Much better than hand soldering.

Yeah I will be getting paste for this kind of stuff.
But why does the Banggood tin suck so hard? Or do I just need to use it differently? Even with the iron it was very hard for me to work with.

vt2nv
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Working with solder paste can be tricky if you’re unfamiliar with the process or the material. The CM (CM = Contract Manufacturer. )uses a temperature profile specific to the boards they’re running. They pre-heat the board, then the board is heated just enough to flow the solder paste, then the board is slowly cooled. The process is a bit more involved than heating a board with a blow dryer, but a blow dryer can do the job.

Practice working with paste using boards you don’t care about.

1) heat the board form underneath (or from above if it’s a double sided board).
2) gently nudge the part with tweezers, until the part moves
3) remove the part using tweezers
4) remove heat
5) clean the pads using solder wick with a soldering iron.
6) use an acid brush with alcohol to clean to complete the cleaning operation

From there the board is ready for installation of the new part. Worth noting is that most electronic assemblies are “RoHS” (lead-free) compliant. This keeps lead out of our landfills, but RoHS (lead free) solder is a pain in the *()&)( to work with. Go with leaded solder which is easier to work with.

Good luck

LichtAn wrote:
vt2nv wrote:
I use solder paste, which requires less heat that solder does, and which is the best way to solder a part onto pads that are covered by the part.

1) apply solder paste on the pads that the part will sit on
2) gently place emitter into the solder paste. Don’t push hard enough to squeeze out the solder paste
3) heat sinkpad from underneath using a hot air gun or a blow dryer or whatever

So there you have it.

If there’s a large courtyard around the part you can solder the traditional way. If the part covers the pads then use solder paste. Much better than hand soldering.

Yeah I will be getting paste for this kind of stuff.
But why does the Banggood tin suck so hard? Or do I just need to use it differently? Even with the iron it was very hard for me to work with.

Lexel
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I also had bad solder wire from Aliexpress no matter what i did it went dull, did not flow good ext.
finally I threw it away totally useless crap

I would never buy lead free solder, to get the reflow temperature for good flow temperature with lead free is like 40°C lower
and you are not literally just a few °C away from overcoocking the LED and ruin it

Manufactirers like Cree give you only 45 seconds above 220°C and 10 seconds on 240°C, with lead free solder you literally have to heat to 230-235°C to get it melt good
while with lead free I can reflow for minutes safely at 190-200°C

for example
old quad board with LEDs

1. picking off old LEDs
2. removing with cotton tips all old solder
3. puting some solder wire or past on the pads
4. place the preheated LEds carefully on it
5. move em around to make sure solder bonds on full surface
6. puch out too much solder
7. remove nasty solder bubbles on the side of LED with a sharp knive or needed

try this all in 10 seconds, you cant do it

vt2nv
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Solder paste requires less heat than the solder most of us use. Solder paste will flow both pads at the same time. This type of rework can be done by hand soldering, or with an air knife or a heat gun. The folks that make the boards inspect the boards when they come out of the oven. . This inspection is initially done using a microscope, or by AOI. You can be certain that problems will be identified when a large board with a thousand (or more) parts is inspected. Tombstoned or missing components. Components improperly placed or in backwards. Components off-center. All of these defects are manually repaired, so it can be done.

Dogginit, misclocked or misaligned BGA’a can be manually reworked (it is a truly amazing process, really complex optics). Inspection of BGA solder is done using an X-Ray machine. If the part is off-center, or voids are identified, the required rework is manually done. It’s either deal with the problem or scrap a board that can be worth thousands. This is the world I live in, at least until retire in a few years.

So yes, we can all solder a single component to a board without burning the board or the component, while making quality solder connections.

Whatever. Please don’t say it can’t be done.

Lexel wrote:
I also had bad solder wire from Aliexpress no matter what i did it went dull, did not flow good ext.
finally I threw it away totally useless crap

I would never buy lead free solder, to get the reflow temperature for good flow temperature with lead free is like 40°C lower
and you are not literally just a few °C away from overcoocking the LED and ruin it

Manufactirers like Cree give you only 45 seconds above 220°C and 10 seconds on 240°C, with lead free solder you literally have to heat to 230-235°C to get it melt good
while with lead free I can reflow for minutes safely at 190-200°C

for example
old quad board with LEDs

1. picking off old LEDs
2. removing with cotton tips all old solder
3. puting some solder wire or past on the pads
4. place the preheated LEds carefully on it
5. move em around to make sure solder bonds on full surface
6. puch out too much solder
7. remove nasty solder bubbles on the side of LED with a sharp knive or needed

try this all in 10 seconds, you cant do it