Glue before soldering

[soup]

I am repairing a Corsa key this involves soldering a couple of microswitches to a PCB. Now these switches are soldered onto lands rather than holes through the board a la :-

He seems to have a great deal of difficulty holding the switches in position, he actually ends up putting his finger on them . I don't want to do this as I KNOW I would burn my finger. Can I use a VERY small drop of CA to attach the centre body of the switch to the PCB , then solder the ends?

Will the CA damage in any way the PCB or the switch body? Obviously I would be very careful putting glue on as I don't want any on any moving part of the switch.

Have heard some horror stories of people gluing the leads on then soldering them thereby heating the CA until it off-gases producing VERY toxic fumes. But any glue I put on will be in the middle of the switch so away from the ends where any soldering would be.

[Andy Burns]

As long as the glue can't wick inside the switch and affect the operation, but why not use tweezers or a lolly stick to hold it in place?

[Clive Arthur]

That guy shouldn't be allowed near a soldering iron. It's not a shovel.

Yes, glue is fine.

Cheers

[soup]

Don't know if he was shaky because he was on camera but (what I assume was a processional) seemed to have a great deal of difficulty holding it steady with tweezers

[John Rumm]

I think the main difficulty is poor technique for that type of soldering...

The "rules" for surface mount device soldering need to be tweaked a bit from those for normal soldering...

You could, but with a more appropriate technique you probably won't need to.

A couple of ways to try it:

Clean and flux the original pads, and then tin them with a small amount of solder. Next tin the leads on the new switch. Then flux the board again, and place the switch in the right location, and hold in place with light downward pressure from a small tool (tweezer, screwdriver, whatever). Now just touch each terminal in turn with the iron to reflow the solder that is already there to make your joint.

For a more "sticky" option, start with clean pads and switch, apply a blob of solder paste to each pad, and place the switch into position. The mixture of solder and flux in the paste will stick the switch into position by surface tension well enough to hold it in place. Now, apply some downward pressure to the switch and touch each end with the tip of the iron to fuse the solder paste.

[The Natural Philosopher]

shpuld be OK. CA fumes are incredibly acrid. But not as far as I know toxic unless you suffer from really bad asthma

Hot glue is another possible

[alan_m]

Liquid flux is often the key to good surface mount soldering

See the soldering of the resistor in

[Dave Plowman (News)]

Surface mount components are often glued before soldering during manufacture.

But to replace one, I use a 'helping hand' with a scribe in the jaws to hold the component in place. Allows you to move it slightly to the correct position. Then solder. I have very fine multi-core for this, and a fine bit on the iron. But with a processor etc with lots of closely spaced pins the correct solder paste and hot air is best.

[Adrian Caspersz]

No glue required. As long as you have a very hot iron and good leaded solder ...

With the iron, put a small fresh dab of solder on one of the pads. Holding the part with tweezers in one hand, and the soldering iron in the other, melt the dab and place the switch accurately in place. Solder the other side, and then redo the first.

[Theo]

Also using solder paste helps - provides flux and solder in one go. Though the short shelf life means it's less practical for occasional soldering.

For something large like this I wouldn't worry about using your finger to hold it: if you're holding it long enough for the body to get hot, you're doing it wrong. If the pads are properly fluxed, it shouldn't need more than a dab of the iron to mechanically secure it. There's no need for glue, which will just make a problem next time you need to remove it. (in production, most components aren't glued unless there's a good reason, like mounting on both sides of the board)

I'd recommend soldering one end with a tiny dab of solder to provide mechanical support, then solder the other end properly (iron and solder wire applied at the same time), then go back and solder the first end properly.

Theo

[soup]

I didn't mean the switch itself would get so hot it would burn me, I more meant the iron would slip and the end of it would contact my finger.

[soup]

I hadn't thought of that.

[Brian Gaff]

I think you are worrying unduly from botht the fumes and getting inside point of view. My only worry is that if/when the glue gives up if the switches are only secured by their ends, this might both allow movement and possible stress the swittch. Is this really all that holds them in? Seems bad design to me. Even on cheapo washing machines you find a little clip of plastic wheich goes through holes in the pcb and is melted on the other sde to hold the swich stable. Brian

[Theo]

Usually the plastic housing provides support such that the only movement the switch can see is up or down. All the other pressure is taken by the housing or by the rubber/plastic pad that the user presses. The switches are slim so there's comparatively little bending moment on them. It's common for such switches to be soldered without glue. In the worst case the soldering will fracture before damaging the PCB.

Theo

[Dave Plowman (News)]

You're very optimistic. ;-)

[Fredxxx]

Becoming very rare, and haven't seen it for a while. Normally the solder paste holds components sufficiently in place in any automatic or semi-automatic process.

There are some components where there isn't any room to put glue. QFNs come to mind.

[Fredxxx]

A professional would have used some palm or hand support to stop the shakes. The video doesn't give me much confidence to the repair company.

I might use a finger if the part is large enough, but in general I have a couple of sets of tweezers I use for this type of work.

I also use re-work flux so as not to rely on the solder core flux.

One thing this missed out is the cleaning of pads. I would suggest you get some solder wick if you don't have any.

Take care in getting the old switches off. Its very, very easy to damage the PCB. If you do, it is then a glue and wire job.

Good luck.

[soup]

Never heard of that, I will be using the cored stuff supplied with the iron

He cleans the pads earlier on in the video. I have a de-solder pump . But was reading that this wasn't as effective as other methods until you get 'the knack'. I have got some de-solder wick coming (1.5mm)

I already have the old switches off (without damaging anything YAY!!!)

So just the clean up when I get the wick and a wee wipe (FSVOwipe) with 99% alcohol then solder the new switches on, reassemble and bob's your uncle. Doesn't sound much when I say it quick .

[Dave Plowman (News)]

Most standard multicore is far too large for surface mount stuff. And indeed for many ordinary PCBs. Smaller gauge is easier to use - and less chance of solder bridges. Something like 0.7mm diameter. Same applies to many bits as fitted as standard to an iron.

Not saying it can't be done - but using the correct tools makes things easier.

[soup]

Smallest solder I have is 0.8 (this is not the stuff supplied with the iron but some I found in my FIL's tool box [he is in a care home now so has no need for it])so shall have to try that, luckily the board isn't too crowded at that point so this should be OK as long as I take care. Iron has quite the selection of interchangeable bits so the smallest point one will have to do.

Isn't that always the case.

I realise this is a non event to any body who has soldered before but to me this is a big deal.