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Desoldering technique

falter

falter

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Just something I'm curious about as I work to desolder something. I don't have a desoldering gun - I just have a fancy solder sucker with replaceable silcone tips. And for the most part, it works well - sucking up 95% of the solder in one go. However, I'm always challenged with solder between the leg and pad, especially when the original assembler folds the leg down to hold it in place for soldering. I've not yet found a good solution for this and sometimes have had to resort to moving the leg with the solderirng iron tip to get it away from the pad before the solder reconnects it, which is not good for the tip or chip.

Is there a better way? I find the copper braid stuff doesn't help much here. Time for a desoldering gun?
 
Desoldering needles might be a good intermediate step here. They are essentially hollow needles that solder won't stick to. You heat up the joint with your regular iron, liquefy the solder, and then pop the needle over the leg and pull it.

I've used them to pull/push legs on caps and resistors straight, but it does take some dexterity. You can also clear plugged through-holes with them but it is slower than doing it any sane way.

They cost about six bucks shipped for a pack on AliExpress.
 
I've found soldering braid to work better than a solder sucker, though I have both. The best tip I ever received about desoldering was to get a bottle of flux with a brush cap, and brush some flux on the desoldering braid before using it. It makes the braid slurp up solder like nothing I've ever seen.
 
falter said:
Time for a desoldering gun?
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I would say yes, in general.

You seem committed to the hobby, so you will get a lot of mileage out of a desoldering gun. If you get a quality tool and maintain it (not hard), it will last you for many years.

You can build skills with simpler and cheaper tools, and those skills are valuable, but your time has value, too. A desoldering gun will save you a lot of time.

Remember too my remark from months ago about how having a good tool will change your outlook on doing rework. Things that you would have decided not to do, because they're too much hassle or because the risk of damage seems too great, suddenly become possible. This can keep projects from collecting dust on a high shelf.

When you finally get a desoldering gun, as I suspect you eventually will, you'll probably find that you can separate your experience as a technician into B.G. ("before gun") and A.G. eras. It makes a real difference.

I say: just do it!
 
That said, even with the desoldering gun, you can still run into trouble with through-hole legs sticking to pads with just a bit of leftover solder :)
Adding fresh solder and attacking the joint again with the gun can help.
 
If you don't need to reuse the ic, I usually chop off the legs as close to the ic body as you can, and then heat and lift the pin out with a bit of help from a fine flatblade screwdriver pressing it to the iron tip.
 
Some good advice in this thread. +1 for the desoldering needles, they are not very popular I believe but I've found them to be the best way to clean stubborn holes, especially on big ground planes. They can't help much with IC legs though.

A desoldering gun also won't do wonders with bent legs that are soldered on the pad. You'll need to release and straighten them first as you've found out. And while I've seen videos of braid soaked in flux absorbing solder like crazy as @cjs wrote, I've never managed to make it work like that.

My tip is to add fresh leaded solder before attempting to desolder. And if the first attempt doesn't succeed and you are left with a bit of solder that you can't get rid of, add more fresh solder and repeat. Also be careful when cutting legs to do it in a way that doesn't apply twisting force or you might lift the pad.
 
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Non-corrosive desoldering flux can be very helpful at making sure oxidised solder melts and flows without excess heat application
Use proper lead low temperature solder whenever you have to resolder after a non-clean suck
Never pull until free but gentle twisting can often break the join between leg and plated hole. Use of pliers to squeeze the either side of a DIL then apply gentle twisting can often give good results (I said GENTLE !).
0V pads are often the worst as they can have very large tracks which dissipates the heat.
the temp of the iron, I tend to use 300°C these days as it quickly melts the solder and allows me to suck before the heat has spread too much and it generally works, but can be too hot for some tracks. Apply the heat to the leg not the pad if you can as the mechanical contact of the iron can damage a hot pad.
Ensure the hole has melted through, you can often see it 'pop' as it breaks through to the other side. If it hasn't melted through, you wont suck it.

I have done more damage over the years with a vacuum tool than I have with a sucker. I have even gone back to my vintage RS green sucker and can probably desolder quicker with this than I can with my vacuum tool in anything but simple jobs

Dont rush.
 
stepleton said:
That said, even with the desoldering gun, you can still run into trouble with through-hole legs sticking to pads with just a bit of leftover solder :)
Adding fresh solder and attacking the joint again with the gun can help.
Click to expand...

This is true; one technique I use when using the vacuum desoldering gun is to move the tip in a small circle while desoldering/pumping to try to pull all the solder possible out. It seems to do a better job that way. Also, if it is the smallest amount of connection after that, using something to push on the pin to break it free seems to work ok and I haven't had any pcb damage doing that as long as there was barely any connection. Sometimes there is the smallest amount of "stick". The circular depumping usually works pretty well though.
 
Here's another voice for desoldering needles. When you need them nothing else works anywhere near as effectively. They work best in conjunction with other tools; you want to remove all excess solder before using the needle to separate the leg from the plated through hole.
 
So once a desoldering needle has sucked up some solder inside it, how do you get it back out?
 
You run a wire down the inside of the needle. Steel music wire works best.

If you're on the cheap, get the big Soldapullt clone from Temu for desoldering. Most of the smaller clones just don't have enough suction.
 
cjs said:
So once a desoldering needle has sucked up some solder inside it, how do you get it back out?
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That's not the way they work, actually.

The needle just provides a physical barrier the solder won't easily wet so that when the solder solidifies the two solid pieces of solder are no longer physically joined; you then pull the needle out, and the solder won't have stuck to it, if you've been quick enough. If you let the needle get too hot or if you have a lot of leftover flux on or in the joint the solder can wet the needle and things get trickier, and you'll have to pull the needle out with heat on it and clean the solder and flux off. If you get too good a wet on the needle it's time for a new needle.
 
I have a set of metric precision drill bits, starting at 0.1mm and going up to 3mm in 0.1mm increments. Not sure of the shank size, probably close to 1/8", since it will chuck in a Dremel.
 
konc said:
I've never managed to make it work like that.
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Good quality flux and braid make all the difference. Cheap braid is mostly useless on anything but single sided boards.

For the bent legs, I use flat blade tweezers (the rounded one from the iFixit toolkit) to lift them up while I melt the solder with the iron.

+1 for getting a desoldering gun, especially if you desolder many ICs
 
lowen said:
I have a set of metric precision drill bits, starting at 0.1mm and going up to 3mm in 0.1mm increments. Not sure of the shank size, probably close to 1/8", since it will chuck in a Dremel.
Click to expand...
Given the price of a set of SS hollow needles, I wouldn't risk a drill bit on one. Music wire (say, .006" is cheap). Heat the needle and run a hunk of wire through. Simple--and very difficult to break.
www.ebay.com

8pcs Stainless Steel Non-stick Tin Hollow Core Needle For Soldering Assist Tools | eBay

8Pcs desoldering Hollow needles. Material:Stainless Steel.
www.ebay.com
I haven't looked but I suspect that they're even cheaper on Temu or Aliexpress.
 
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