Hand-soldering 0402 LEDs... Total failure!

tetsujin · Post by **tetsujin** » Mon Aug 16, 2010 4:38 pm

Hiya!

So I use 0603-size (1.6mm x 0.8mm) surface mount LEDs a lot in my projects - they're great 'cause they can fit almost anywhere... I've gotten pretty good at soldering them. But I thought I'd relate my experiences trying to solder the next size down - 0402 LEDs (1.0mm x 0.5mm)...

Basically, I failed. Completely. I had ten of the little buggers, and one of the first things I noticed was that my usual approach to holding 0603 LEDs as I solder on the first wire doesn't work. Normally I wrap a rubber band around the handle of a pair of fine-nose pliers and use that to hold on to the LED... Probably half the LEDs I tried this on simply jumped out of the pliers' grip and were never seen again. At least one other actually broke (one of the terminals snapped off). I finally managed to get one wire soldered to one of the LEDs, but I think something happened to the other terminal - maybe the pad got overheated and broke off, or maybe it just got gunked up from all the soldering attempts - anyway, I couldn't attach the second wire.

Really, it's pretty dramatic, the difference between trying to solder 0603's and 0402's. I wouldn't have expected it would be so much more difficult.

Ultimately, I found a way to do what I was trying to do using 0603's instead of 0402's... Basically I had been trying to fit a 0402 directly underneath a small lens at the end of a 1.5mm metal tube. My solution was to use a 0603 and put it at the other end of the "tube", and replace the tube with a piece of clear plastic painted to look metallic (and block light from escaping...) I haven't fully tested this solution yet - hopefully it will work nicely. But the upshot of this approach is that it was far easier to solder and install the LED...

Kylwell · Post by **Kylwell** » Mon Aug 16, 2010 4:51 pm

Why not stick them down with some double-stick tape to a surface to work on them?

Mouser has some extremely fine multi strand wire. 32g IIRC.

tetsujin · Post by **tetsujin** » Mon Aug 16, 2010 5:42 pm

Kylwell wrote:Why not stick them down with some double-stick tape to a surface to work on them?

The heat on the terminal would melt the tape's adhesive enough that the LED would stick to the soldering iron instead of the tape... I think so anyway. I tried a couple with whatever tape I had handy (not double-stick, didn't seem necessary) and it was too hard to get the LED stuck securely to the tape but still have access to the terminal I was trying to solder.

Mouser has some extremely fine multi strand wire. 32g IIRC.

I was attempting to solder on enameled magnet wire... But I don't think the wire was the problem. Have you hand-soldered 0402 LEDs? Maybe I could give it another try sometime - 10 red LEDs isn't a huge loss, but I'm not too eager to repeat it. :)

Kylwell · Post by **Kylwell** » Mon Aug 16, 2010 5:49 pm

I haven't but you've given me a reason to try it.

http://www.mouser.com/ProductDetail/Alp ... 1D7skPE%3d

Is what I use.

USS Atlantis · Post by **USS Atlantis** » Mon Aug 16, 2010 6:19 pm

I'm fond of "wacky" ideas - reason I got the title "Master of the Makeshift" back in my Air Force days

Anywho - my off the wall suggestion

1) Get one toothpick (round or flat, doesn't matter)

2) Put some clay (Klean Klay?) on the end of the toothpick

3) Touch clay to LED face - LED is picked up by clay

4) Lock other end of toothpick in pliers/mini-vise/etc

5) Solder leads

6) Take LED off toothpick, wipe clay off

Rinse-repeat

tetsujin · Post by **tetsujin** » Mon Aug 16, 2010 6:46 pm

Kylwell wrote:I haven't but you've given me a reason to try it.

:D

I will be appropriately impressed and inspired if you succeed. :)

For most stuff I used 30 AWG stranded wire - the only reason I was using magnet wire was because it was the only stuff thin enough to fit two strands through my metal tube. There's other ways I could have done it, like not run the wires inside the tube, or use the tube itself as one of the conductors, but that would have been more complicated...

As for the clay suggestion - I think it would still be a real challenge to get the LED to stay put without burying it so deep that you have no access to the terminal... I thought about maybe super-gluing the LED to something and then breaking it off when finished... It could have worked... Though I believe super glue breaks down under heat as well so I'm not entirely sure.

Right now I'm basking in the feeling of relief from finding a solution that doesn't require 0402's. :) But if I get the urge to try again, I have another ten LEDs (green, though, rather than red) so a "round 2" is a possibility.

Tchail · Post by **Tchail** » Tue Aug 17, 2010 11:21 pm

I picked up several 0603 SMDs with an eye towards using at least one of them on an Enterprise-D model.

But I'll be buggered if I can figure out a way of soldering those tiny things (1.6mm x 0.8mm x 0.6mm).

The last time I was in the SF Bay Area, I stopped by Al Lasham's and picked up some of what the guy behind the counter called "wire gauge" wire. I take it that it's the thinnest wire that they sell.

-Tchail

Mr. Engineer · Post by **Mr. Engineer** » Wed Aug 18, 2010 12:00 am

I've tried that before but what I did was to use those wire-wrapping wires.

-I remove the plastic sheath about 2mm, then tin it.
-Stick one end of the LED (vertically) to a double sticky foam tape and try to tin its connector.
-Put the tinned wire on top of the LED and quickly use the (sharp) tip of the soldering iron to melt the two solder joints together. This must be less than 2 seconds, the most.
-Repeat for the other end. But bear in mind, the wire-wrapping tapes are very fragile especially at the area where you removed the plastic sheath as there is a microscopic nick which weakens the wire when bent too much.

tetsujin · Post by **tetsujin** » Wed Aug 18, 2010 2:49 am

Tchail wrote:I picked up several 0603 SMDs with an eye towards using at least one of them on an Enterprise-D model.

But I'll be buggered if I can figure out a way of soldering those tiny things (1.6mm x 0.8mm x 0.6mm).

I work with 0603's a lot... In fact, immediately after my total failure with the ten 0402 LEDs, I tried a 0603 and got it the first try.

My approach is to wrap a rubber band around the handles of small-tip pliers, grab the LED with those, and get the first wire on. Once the first wire's on the LED is a lot easier to handle.

Of course, I've had a lot of practice with the 0603's at this point - and I've lost or destroyed a significant number of surface-mount LEDs while working on various projects - but I consider them to be quite easy to work with. Getting to the same point with 0402's may require finer tools, or just more practice, I'm not sure...

Madman Lighting · Post by **Madman Lighting** » Thu Sep 30, 2010 11:42 am

I do stuff with 0402s, but its tough and you need a different mindset.

The little buggers are so tiny that almost anything knocks them off their pad or overheats them.

I get a flux pen for organic solder and use "red" label organic flux solder. I also use very thin solder wire, .40mm diameter.

First I tin the pads the part has to sit on with a little solder, just so there's a little bump on the pad. Then I flux the part so it has excellent solderability with the flux pen. You need tiny tweezers to get them down right. Then I use a temperature controlled heat gun, and heat from the bottom of the board until the solder flows. This is a poor man's reflow rig but once the solder flows the part self aligns on the pad and sits well. Clean up soon after with lots of clean water to remove the acidic flux.

-John

Mr. Engineer · Post by **Mr. Engineer** » Fri Oct 01, 2010 6:18 am

Heat gun is a great idea! Why did I not think of that! Maybe I'll get one when I have a VQFN chip to play with. Until then, yes, its tweezers and solder bumps.

But I never tried flux pens before, mainly they do not sell them where I live.

Madman Lighting · Post by **Madman Lighting** » Fri Oct 01, 2010 11:15 am

Mouser sells flux pens, just a few bucks each. Make sure the flux is the same type as the solder you're using. Rosin, Organic or whatever.

Make sure its a temperature controlled heat gun, otherwise you'll just roast the poor thing.

I cant take complete credit for the idea, its what we do here in the lab at work...

The Arbiter · Post by **The Arbiter** » Mon Oct 04, 2010 12:16 am

If these are SMA LEDS, why not just get two soldering pencils with teensy tips and hit both sides at the same time?

Back in the late nineties, I worked at Ericsson building power amps for the cell towers and that is how we repaired SMA components . Granted, being able to look thru a Bausch and Lamb stereo microscope was nice, but a magnifier will suffice.

Use tweezers to place the LED on the pads and hit both ends with the soldering irons. It takes a bit of practice but it gets pretty easy after a while.