How to solder very thin leads?

Thread Starter

djsfantasi

Joined Apr 11, 2010
9,186
I have many SMD LEDs with pre-wired leads attached. The leads are insulated stranded wire and almost as thin as a thick hair.

Soldering these is a nightmare. They are so light that the slightest breeze or tremor moves them. That’s if I can manipulate them into position in the first place.

I have essential tremor and that makes it worse. I’ve tried with a wrist weight but the wire is too flimsy.

I made a tool with nested heat shrink tubing that helps me hold them while installing the LED. But I can’t use it when soldering because the tool would be trapped.

Any ideas that might help me? A799F3A0-43A3-4660-8DE9-0B425517ECE9.jpeg
 

dl324

Joined Mar 30, 2015
17,110
How about using 1 or 2 third hands. From the Arduino forums:
thirdHand.jpeg
holders1.jpeg
Or using springs as on the right.

Or using reverse grip ceramic pliers tweezers?

Is twisting the wires before soldering an option?
 
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nsaspook

Joined Aug 27, 2009
13,545
I've used blutack to hold small wires and components.

You can use a small ball on the wire , then stick, solder, remove tack.
 
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MrSoftware

Joined Oct 29, 2013
2,212
What are you soldering them TO? At work sometimes we use really tiny (40awg, 3-thousandths thick) wire for reworking some circuit boards and I do the work under a microscope. I do some 0201 SMD parts too, haven't tried 01005 parts yet. A microscope helps a ton. If you've got the pockets, the stereo optical microscopes like this style (click here) are by far the best. That's not the same model we have at work, that's just the general idea. Good magnification, light ring around the bottom and a long arm that attaches to the back of your workbench. I've got this one (click here) at home, it's a little more awkward to use, but a ton better than no microscope. It also helps to have an iron with a small curved pointy tip like this one. Use a lot of flux (this is my personal favorite) and leaded or low temp solder. Also use a good set of stainless (so they will not magnetize) tweezers and keep them clean. When things start sticking to them, clean them up good with alcohol. Flux gets sticky after it gets hot so you'll be cleaning them often. Helping hands like mentioned above are also extremely helpful.

All of that said, if you can explain what you're trying to solder the wires to then I'll try to give tips if I can. It sounds like the wires are already attached to the LEDs and you're now trying to attach the other end to something else, is that correct?
 
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Thread Starter

djsfantasi

Joined Apr 11, 2010
9,186
What are you soldering them TO? At work sometimes we use really tiny (40awg, 3-thousandths thick) wire for reworking some circuit boards and I do the work under a microscope. I do some 0201 SMD parts too, haven't tried 01005 parts yet. A microscope helps a ton. If you've got the pockets, the stereo optical microscopes like this style (click here) are by far the best. That's not the same model we have at work, that's just the general idea. Good magnification, light ring around the bottom and a long arm that attaches to the back of your workbench. I've got this one (click here) at home, it's a little more awkward to use, but a ton better than no microscope. It also helps to have an iron with a small curved pointy tip like this one. Use a lot of flux (this is my personal favorite) and leaded or low temp solder. Also use a good set of stainless (so they will not magnetize) tweezers and keep them clean. When things start sticking to them, clean them up good with alcohol. Flux gets sticky after it gets hot so you'll be cleaning them often.

All of that said, if you can explain what you're trying to solder the wires to then I'll try to give tips if I can. It sounds like the wires are already attached to the LEDs and you're now trying to attach the other end to something else, is that correct?
I’m soldering the wires to a PCB. I’ve tried holding them with tweezers, but they slip out. Thanks for responding, though.
 
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MrSoftware

Joined Oct 29, 2013
2,212
I’m soldering the wires to a PCB. I’ve tried holding them with tweezers, but the slip out. Thanks for responding, though.
You might need better tweezers. What size is the pad and how much copper is under it (a small trace or a big plane)? Try this: tin the pad with a little bit of solder then flood the pad with flux. Twist and tin the end of the wire if you can. Hold the iron on the edge of the pad, the solder will melt. With the tweezers touch the wire to the pad then remove the iron. Or option B: tin the pad, tin the wire, flood the pad with flux. With the tweezers hold the wire on top of the pad then lightly press the wire into the pad with the tip of the iron for just half a second, just a touch really. If that doesn't help, can you post pictures?
 

Thread Starter

djsfantasi

Joined Apr 11, 2010
9,186
You might need better tweezers. What size is the pad and how much copper is under it (a small trace or a big plane)? Try this: tin the pad with a little bit of solder then flood the pad with flux. Twist and tin the end of the wire if you can. Hold the iron on the edge of the pad, the solder will melt. With the tweezers touch the wire to the pad then remove the iron. Or option B: tin the pad, tin the wire, flood the pad with flux. With the tweezers hold the wire on top of the pad then lightly press the wire into the pad with the tip of the iron for just half a second, just a touch really. If that doesn't help, can you post pictures?
I don’t need better tweezers; I need better hands.

It’s a pad, not a plane. Since this is a universal modular PCB, the holes can accept 22g wire. The pads that do connect to a plane are made with “spider” connections to make it easier to solder. Here is a picture. The connections are made to the matrix of pads.
07BA3551-F4B1-414A-A937-386881BF65B5.jpeg
 

MrSoftware

Joined Oct 29, 2013
2,212
OK those are through hole, so add option C to my above suggestions: slip the wire through the hole, pin it there with the tip of the iron then touch the solder to the pad or tip of the iron where the iron meets the pad. It should flow right into the hole.
 

nsaspook

Joined Aug 27, 2009
13,545
This has potential! I’ll pick some BluTack up in a day or two…
What's nice is it's possible to tack separate tiny wires in separate PCB holes, flip the PCB and solder them all in one operation. Just be sure the tack surface is clean and clean up any tiny residue left after removal with IPA.

It's also very useful for holding odd shapes that need fine soldering.
1673757861152.png1673758276188.png
 
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Thread Starter

djsfantasi

Joined Apr 11, 2010
9,186
slip the wire through the hole, pin it there with the tip of the iron then touch the solder to the pad or tip of the iron where the iron meets the pad. It should flow right into the hole.
Exactly what I was trying to do! The problem I was having is getting the wires to stay in place long enough to tack them. My essential tremors always pulled them out before I could get the soldering iron. Normally, I have no problem soldering. I use all the techniques you’ve mentioned.

What's nice is it's possible to tack separate tiny wires in separate PCB holes, flip the PCB and solder them all in one operation. Just be sure the tack surface is clean and clean up any tiny residue left after removal with IPA.
Perfect! I think this will solve all of my issues. I’ve heard of using BluTack but have not tried it yet.

Reverse tweezers with ceramic tips could be used to hold the wire in place and solder won't adhere to them.
Any solution using tweezers will not work for me. My fine motor control is almost gone. I can hold something for a second or two before my hand shakes badly. Modeling in N scale takes me a long time.

I can insert the wire beyond what is needed, hold it with BluTack and slide the tinned end to the hole.
 

Thread Starter

djsfantasi

Joined Apr 11, 2010
9,186
@nsaspook
So, I completed soldering my first set of drivers. The BluTack was a great help.

However, the thin leads are still difficult. They have a 1/8” uninsulated tinned termination. It’s difficult to just position that 1/8” end.

I bought a tin pot. I was wondering if I dipped the ends into the molten solder if it would melt off the insulation and create a longer lead?

The BluTack works great for soldering the components (resistors and 2N7000s) and wires. And does hold the thin leads, but positioning the short tinned ends is still a problem.
 

nsaspook

Joined Aug 27, 2009
13,545
@nsaspook
So, I completed soldering my first set of drivers. The BluTack was a great help.

However, the thin leads are still difficult. They have a 1/8” uninsulated tinned termination. It’s difficult to just position that 1/8” end.

I bought a tin pot. I was wondering if I dipped the ends into the molten solder if it would melt off the insulation and create a longer lead?

The BluTack works great for soldering the components (resistors and 2N7000s) and wires. And does hold the thin leads, but positioning the short tinned ends is still a problem.
As we get older our physical limitations make even simple things difficult.

I'm so happy to help.
 

Ya’akov

Joined Jan 27, 2019
9,264
The problem with the solder pot approach is two fold: depending on the composition of the insulation the result might be contamination of the leads with the melted/burned results. and dipping them could be fraught, for the same reasons positioning is. If the insulation is amenable to melting without thermal damage to the part, you might be able to do the removal in situ with the working solder—I’ve done that successfully.

An alternative to the blue tack that you probably have around is fast, thin cyanoacrylate cement. Applied with a needle (exceedingly small amounts) you can position the part and it will stay for soldering.

One more possibility is tacky flux. You can get the no-clean sort (though you will want to clean it, the residue isn’t harmful so you don’t have to be perfect at removing it). It has a surprising ability to hold small parts in place and can actually improve the soldering results including reducing solder bridges by making the affinity of the solder to a pad much greater than the air between them.

If you can create a lead forming jig that bends the wires to the correct angles so the lengths align with the uninsulated sections, you might be able to consistently place them. I didn’t notice that you were or were not using magnification, are you?
 

Ya’akov

Joined Jan 27, 2019
9,264
I did a quick and dirty test by tacking some 26AWG magnet wire onto the ends of an SMD zener as leads. I formed them (with tweezers, but a purpose built form would be a lot easier and probably simpl(ish).

IMG_0150.jpeg
The leads are projecting into the hole just the right amount so the ⅛” tinned portion just emerge from the other side.

IMG_0156.jpeg
Applying some tacky flux (Amtech MC-559-V2-TF), which holds the part to the board, even flipped over.

IMG_0158.jpeg
It helps to have a vise like this Panavise that can easily be flipped over to access the other side.​
 
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