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.
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.
Never heard of that, I will be using the cored stuff supplied with the
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 .
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
*If you don't pay your exorcist you get repossessed.*
Dave Plowman firstname.lastname@example.org London SW
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.
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
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.
Also using solder paste helps - provides flux and solder in one go.
Though the short shelf life means it's less practical for occasional
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.
Surface mount components are often glued before soldering during
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.
*Learn from your parents' mistakes - use birth control
Dave Plowman email@example.com London SW
Becoming very rare, and haven't seen it for a while. Normally the solder
paste holds components sufficiently in place in any automatic or
There are some components where there isn't any room to put glue. QFNs
come to mind.
No glue required. As long as you have a very hot iron and good leaded
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.
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.
This newsgroup posting comes to you directly from...
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.
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