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Desoldering how to?

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Ian Parkin24/01/2020 12:20:25
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How do people desolder components?

i have a circuit board with a couple of small switches that i want to remove and place remotely...so not wanting to use the removed switches..

the board is double sided

the switches have 6 wires all told on a 8mm square grid

how best to go about it?

I’ve got a solder sucker and desoldering tape but never had much luck with using either

Ian Parkin24/01/2020 12:25:49
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1017 forum posts
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This is the board in question as you can see the switches are hard to the board

7acd6ae7-7331-426d-99c5-f31b28b6277f.jpeg

b19baaa3-f3f6-4859-b787-09c07afe1889.jpeg

Stuart Bridger24/01/2020 12:30:54
538 forum posts
29 photos

QUALITY desoldering braid combined with a decent iron would be my answer.

If it was an IC or other component, I would recommend snipping the legs, then working one joint at a time. That said I have desoldered quite large pin count ICs complete with success. It will be fiddly to get all 6 connections to the switch loose, but you should be able to do it.

Mike Poole24/01/2020 12:30:58
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Soderwick fluxed braid works well for me after a sucker has removed most of the solder. Sometimes it helps to add some fresh solder then desolder. If you have very deep pockets then people like Weller make professional desoldering stations with vacuum pumps and heating dies for various chips. You would have to be making a living from board repair to use that sort of gear though.

Mike

duncan webster24/01/2020 12:31:31
3946 forum posts
63 photos

With dfficulty! What I usually do is grip the board in a vice, then put a thin blade under the component to lever it out and run the soldering iron round and round so it comes out a bit at a time. If you have a biggish soldering iron you can probably get all 3 pins on one side melted at the same time which helps.

Then you have the problem of getting the solder out of the holes, the only way I've succeeded is by applying the solder sucker to one side and the iron to the other

not done it yet24/01/2020 12:41:53
6749 forum posts
20 photos

I’ve used my trusty desoldering spring pump for more than the last thirty years. Not used often, but has done all I have needed to do. That said, if this is soldered from both sides it may be more of a challenge. A tiny soldering iron tip helps.

Farmboy24/01/2020 12:54:51
167 forum posts
2 photos

If they are normally open switches you could leave them in place and just solder the leads for the remote switches to the pins. Hard to be sure but they appear to only use two pins of each switch so it should be fairly simple.

Edited By Farmboy on 24/01/2020 12:57:01

IanT24/01/2020 12:56:40
1989 forum posts
212 photos

Agree with most of the above and I've been 'soldering' for over 50 years (having first learned in the Royal Signals) and I thought solder suckers were great when I first came across one about 40 years ago. Then I discovered de-soldering braid about 20 years ago and thought that was pretty good too. My latest 'discovery' is a hot-air soldering station that I purchased early last year when I finally decided I needed to use (more) SMD components - and the price was also now affordable (about £30).

However, it is also very useful in some situations when de-soldering - sometimes better than using a soldering iron. It's also usually much easier to clean up & re-solder if you can cut the old component out and then simply remove the old 'legs' of course.

Regards,

IanT

Ian Parkin24/01/2020 12:57:28
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1017 forum posts
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It’s double sided with very small tracks and it’s a dpco switch

Mike Poole24/01/2020 12:57:51
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After removing as much solder as possible the component legs will often still be soldered to the wall of plated through holes, I heat the leg and use a suitable tool to move the leg away from the wall. If you are out of earshot then swearing and abuse helps, it probably doesn’t make a positive contribution to the task but you will feel better.

Mike

SillyOldDuffer24/01/2020 14:09:41
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Posted by IanT on 24/01/2020 12:56:40:

... It's also usually much easier to clean up & re-solder if you can cut the old component out and then simply remove the old 'legs' of course.

...

Half a century I've been de-soldering and never thought of that! What a good idea.

It helped me to match the pump and iron to the problem. I threw away a pump because it didn't generate enough vacuum. It's slightly larger replacement works much better provided the nozzle is in good nick. When there's space, the new pump works best with a 25W iron. I guess a larger iron melts more solder around the joint and inside plated holes, and then supplies enough heat to keep the solder wet as it's sucked off the joint.

Desoldering isn't my idea of fun, and SMD is too much...

Dave

Nicholas Farr24/01/2020 14:47:14
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3330 forum posts
1531 photos

Hi, I always find the de-soldering braid works better if you paste a little flux on the solder you want to remove first. In my case, I use Frys Fluxite. I have used the braided outer of TV downlead with some flux on, at times when I've run out of the ready made stuff.

Regards Nick.

Andrew Johnston24/01/2020 14:56:35
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6577 forum posts
701 photos

Like many things in engineering desoldering is counter-intuitive.

To start with use a proper soldering iron at a good temperature. My Weller iron is 80W and I run at 360°C. Forget solder suckers and braid for desoldering. It doesn't look like the switch leads can be cut to start with. First add solder in two beads down both sides, each covering three pins. Then melt one bead and push on the switch, it should tilt slightly. By melting alternating sides you can work the switch out far enough to get one side completely out, or at least cut the leads on one side. A high wattage iron helps as you want to go in, melt the solder and be out again in a few seconds. A low power iron that takes ages to heat up is useless. Although not relevant in this case a multilayer board with internal planes will need even more heat to melt the solder quickly. Once the leads are seperated it is simple to remove them one by one.

After the switches are removed you can clean up the board. Solder braid is great for surface mount pads, but isn't that useful for thru hole. To clean up with a solder sucker add solder until the hole is full. Then melt the solder and suck! Solder suckers are ineffective at cleaning partially filled holes as it isn't always easy to get the solder properly melted. Filling the hole first makes it easy to melt all the solder.

Note to SoD: Come on! Meet the challenge and get those SM devices soldered. For ICs down to around 0.05" pitch it's simple to solder individual pins. Below that we need to be counter-intuitive again. I use a liquid flux and add a big blob of solder covering several pins. If you then melt the blob of solder and slowly move the iron along the row of pins the solder will follow and amazingly it will leave the pins soldered while surface tension ensures there is no solder bridging between pins.

Andrew

Stuart Bridger24/01/2020 15:29:16
538 forum posts
29 photos

Whwn I worked in electronic repair, I had a VERY fine pair of stainless steel pointed tweezers, so fine I was always stabbing myself with them. But they were pefect for working the hole to free stuff up after desoldering

Edited By Stuart Bridger on 24/01/2020 15:30:42

Nicholas Farr24/01/2020 15:33:42
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3330 forum posts
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Hi Andrew, this one hot enough! ? devil

hot-stuff.jpg

Regards Nick. teeth 2

Stuart Bridger24/01/2020 15:35:06
538 forum posts
29 photos

The positive thing is that the OP's PCB is not too dense, with good size tracks and pads so could be a lot worse!

Simon Williams 324/01/2020 16:34:00
652 forum posts
82 photos

Solder sucker every time, unless you can spring for a de-soldering station. Never got on with de-solder wick, just can't get the hang of it.

I know nothing about working with SMD, plated through holes are quite fiddly enough. As others have said, best option is to accept that the removing component is scrap, so cut it to bits in situ.

Two tricks you need to know with a sucker, firstly (exactly as Andrew says) use a hot iron and add solder first.

Then put a Hellerman sleeve (butyl sleeve) over the end of the sucker nozzle so it seals to the plated through hole. A bit of silicon tube would be even better, Some sucker have a soft tip and work much much better than the old type with a hard plastic nozzle. Now get the heat in there, suck and get out. There's a knack to the "heat - suck - leave" co-ordination that needs a bit of practice. You definitely need the board clamped in something so it doesn't run away when you press in with the tip of the sucker. Empty the sucker out each stroke.

With plated through holes you usually have to grab the end of the pin with needle pliers and give it a good wriggle to get the last remnant of solder to let go. Soemtimes adding a little bit more solder and having a second go helps.

As Andrew has said, the trick is adding solder (and hence flux) first.

Brian G24/01/2020 16:47:23
839 forum posts
37 photos

Has anybody tried stainless steel desoldering tubes? I ordered a set after seeing them described (but not used) on YouTube, but haven't had occasion to use them yet. The idea is that the solder is melted and the tube slid over the component wire. The solder doesn't stick to the tube, so when it solidifies the tube can be pulled out, leaving the component wire loose and a hold in the PCB.

Brian G

(Edit, found a video showing use)

 

Edited By Brian G on 24/01/2020 16:50:35

Neil Wyatt24/01/2020 17:20:53
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What Andrew J. says.

Although now I've got a proper Antex reworkstation I'd use the hot air gun on that.

Neil

Mike Poole24/01/2020 17:42:13
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3308 forum posts
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Desoldering high quality glass fibre boards is a hell of a lot easier than the old SRBP boards, a moment too long and the track lifted, time to get the Kynar wire out and bodge ( I mean repair) the board.

Mike

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