Help with Ngineering Micro LEDs

[mike_lawyer]

I am working on preparing Ngineering Micro LEDs for use in steam locomotive headlights, and I am having the hardest time getting the wires soldered to soldering pads on the LEDs.  I have all the tools (the holder, the micro-tip soldering gun, and the silver solder) and have been following the online PDF instructions, and I am having a real difficulty soldering the small wires to the soldering tabs.  Any tips on the best method to get the soldering to work?  I have pre-tinned the wires and everything.  Thanks.

[MK]

Are you using any flux?  If not, just a touch of it to the pads will make a world of difference.  And why silver solder?  No need to use high strength solder for LEDs.  Normal solder would work just fine and they have a lower melting point than silver solder (I think).

[RBrodzinsky]

Yes, flux is what makes the difference.  I use a liquid flux, and put a tiny amount (toothpick tip, dipped in the liquid, then touched to the LED) on the pad.  Drape the pre-tinned magnet wire over the pad, then, with small amount of solder on tip of iron, touch the wire and pad. 

[JMaurer1]

I wouldn't use silver solder, doesn't that use acid flux? In the past I bought micro LEDs and tried to solder leads to them, and in spite of me being great at soldering, it was VERY HARD to do. Now I buy the LEDs with the leads already attached but what worked best was to use solder paste. Line everything up (LED and wire), apply a dab of paste with a toothpick, heat with the iron (just heat, no need to actually touch the LED or wire), let cool, done. Good luck!

[mmagliaro]

I just stick the LED to a small square of double-sided tape on my workbench.  Then apply a tiny drop of that gooey paste flux they used to sell at Radio Shack to the pad, then touch for an instant with the point of the soldering iron, already having a little drop of solder hanging on the tip.  That immediately tins the pad on the LED. 

Do the same thing for the wire.

Then place the wire in position, sticking it to the double-sided tape so the stripped, tinned wire end is right against the LED pad and won't move.  Now get a tiny drop of solder on the soldering iron tip again, and touch it to the joint.   The wire should bond to the pad instantly.

You have to just touch the joint for an INSTANT and immediately pull away.  Anything longer will destroy the LED.
So both surfaces have to be tinned, the iron tip has to be clean and tinned, with just a tiny micro drop of wetted solder hanging on the tip.

I admit, it's tedious.  But it does work.
However, there are now so many cheap sources of 0603 and 0402 LEDs with pre-soldered leads, that I do avoid this task if at all possible.

[mike_lawyer]

Great idea on the flux, I had not even thought about that!  I totally missed that in the instructions (it is there, I just missed it).  Should help things tremendously. 

[mike_lawyer]

I just stick the LED to a small square of double-sided tape on my workbench.  Then apply a tiny drop of that gooey paste flux they used to sell at Radio Shack to the pad, then touch for an instant with the point of the soldering iron, already having a little drop of solder hanging on the tip.  That immediately tins the pad on the LED. 

Do the same thing for the wire.

Then place the wire in position, sticking it to the double-sided tape so the stripped, tinned wire end is right against the LED pad and won't move.  Now get a tiny drop of solder on the soldering iron tip again, and touch it to the joint.   The wire should bond to the pad instantly.

You have to just touch the joint for an INSTANT and immediately pull away.  Anything longer will destroy the LED.
So both surfaces have to be tinned, the iron tip has to be clean and tinned, with just a tiny micro drop of wetted solder hanging on the tip.

I admit, it's tedious.  But it does work.
However, there are now so many cheap sources of 0603 and 0402 LEDs with pre-soldered leads, that I do avoid this task if at all possible.

Max -

Do you have any particular sources you like to use?  I must admit, this is really tedious to do, and if I can find a cheap source with leads attached, I might purchase some of those in the future.

[Lemosteam]

First I assume you are burning the coating off of the magnet wire.  Tinning the pads AND the wire is the secret I have found.  After you tin the wire snip off all but just a bit of exposed wire. Like Max says, having the wire and the pads tinned maks the solder flow instantly.

I use two sided tape as well.  This frees one had for holding the short exposed end of the wie and th the other for the soldering iron. I dip the wire end into the flux and hold it on the pad, and a fast touch of the iron and boom.

I use flux-free silver solder in 0.025" diameter from Radio Shack- not sure if it is still available.

Max mentioned in another thread a solder that instantly solidifies.  I need to get some because sometimes I find that even after I flow the solder, I can still move the wire off the pad and cussing ensues.

[C855B]

... Max mentioned in another thread a solder that instantly solidifies. ...

Eutectic solder. I don't know if Max's recommendation is a lead-free alloy, but I use 63/37 tin/lead. Crucial for tiny stuff where you need to hold your breath while the joint cools.

[u18b]

Even better, there are 603 LEDs of places like ebay that are prewired.  I've bough some before.

like these:  https://www.ebay.com/itm/3pcs-MICRO-Nano-LEDs-WARM-WHITE-Pre-Wired-402-SMDs-Model-RR-DIY-18wm/312854138319?hash=item48d78f4dcf:g:cIoAAOSwAGdczgZI

Searching the terms: micro leds prewired
returns lots more hits.
https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=micro+leds+prewired&_sacat=0&LH_TitleDesc=0&_sop=10&_osacat=0&_odkw=402+leds+prewired


And BTW.... you can feel like you're losing your mind trying to solder these.

[mmagliaro]

Eutectic solder. I don't know if Max's recommendation is a lead-free alloy, but I use 63/37 tin/lead. Crucial for tiny stuff where you need to hold your breath while the joint cools.

And for the record... it wasn't me... It was Peteski who has alerted us to the importance of using that solder.  I confess that I still do not have any.

Notice... I stick the wire down to the double-sided tape WITH the LED, as I described.  Then I don't have to hold it, nothing moves, and I can just touch with the iron, pull away, and the joint cools however it has to without being disturbed by clumsy fingers.

As for the pre-wired LEDs on eBay... here is one that I like:
https://www.ebay.com/itm/10pcs-0402-SMD-LED-Warm-White-Pre-wired-micro-litz-wired-Soldered-20CM-Line/292783752859?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

10 warm white 0402, prewired, for under 8 bucks.   Yes, you can do it cheaper if you buy them in bulk, unwired, and solder yourself.  I just don't use enough of them to make that worthwhile.

[Sokramiketes]

Also don't be afraid to chop up your solder into small bits, picking a single bit up with your iron for each solder connection. 

That's the secret to tinning the tip consistently with just the right amount of solder.

[RBrodzinsky]

I wired up 10 0603 and 10 0402 LEDs a couple days ago (hadn't done them in a long time). Only took about 2 hours, in all, but that was it for that day.  As per Ron, the mind needs to clear after that.

[Lemosteam]

And for the record... it wasn't me... It was Peteski who has alerted us to the importance of using that solder.  I confess that I still do not have any.

Notice... I stick the wire down to the double-sided tape WITH the LED, as I described.  Then I don't have to hold it, nothing moves, and I can just touch with the iron, pull away, and the joint cools however it has to without being disturbed by clumsy fingers.

As for the pre-wired LEDs on eBay... here is one that I like:
https://www.ebay.com/itm/10pcs-0402-SMD-LED-Warm-White-Pre-wired-micro-litz-wired-Soldered-20CM-Line/292783752859?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

10 warm white 0402, prewired, for under 8 bucks.   Yes, you can do it cheaper if you buy them in bulk, unwired, and solder yourself.  I just don't use enough of them to make that worthwhile.

Unfortunately, I have not found any pre-wired with 38 gauge green and red magnet wire, which I really like for threading into small holes.

[C855B]

Unfortunately, I have not found any pre-wired with 38 gauge green and red magnet wire, which I really like for threading into small holes.

Yeah, that's the issue for me as well in my messing with signals. #36 is the largest possible to feed 12 wires - 3 heads * (3 colors + common) - through 0.032 thin-wall SS tubing.