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PICList Thread
'[EE] SMT soldering manually'
2006\10\20@054242 by Tamas Rudnai

face picon face
Currently I am facing to solder some SM capacitors that are around half size
as an SOT23. My problem is that I can't put too small amount of solder to
the tip of the iron. So that the two pads have a good chance to get
connected. I can't use my desolder pump to remove the exceeds as it could
pick up the capacitor as well :-). Is there any good solution for that
(without buying solder paste)?

Thanks
Tamas

2006\10\20@060238 by Steven Howes

picon face
> Currently I am facing to solder some SM capacitors that are around
half
> size
> as an SOT23. My problem is that I can't put too small amount of solder
to
> the tip of the iron. So that the two pads have a good chance to get
> connected. I can't use my desolder pump to remove the exceeds as it
could
> pick up the capacitor as well :-). Is there any good solution for that
> (without buying solder paste)?

Put solder on the pads, then suck it off so they are left with a coating
of solder. Remove any solder from your iron, put the SMT on it and heat
either end. Might not give a perfect join first time but it works.

2006\10\20@063748 by Bob Axtell

face picon face
Tamas Rudnai wrote:
> Currently I am facing to solder some SM capacitors that are around half size
> as an SOT23. My problem is that I can't put too small amount of solder to
> the tip of the iron. So that the two pads have a good chance to get
> connected. I can't use my desolder pump to remove the exceeds as it could
> pick up the capacitor as well :-). Is there any good solution for that
> (without buying solder paste)?
>
> Thanks
> Tamas
>  
Yes. Purchase the smallest diameter braid of "Solder Wick". Solder Wick
allows you to gently remove
excess solder without removing the device.

If the problem is that the device moves around, use an adhesive to keep
the device in place. This is available
in a syringe; just squirt out a tiny drop and place the device into
place, and allow it to harden for a few minutes.
Then you can solder without worrying about it scooting all over the PCB.

If you need to clean the PCB surface, use "liquid solder flux", not
paste. The  liquid flux can be applied very evenly.

--Bob

2006\10\20@064605 by Chris Gavin-Egan

flavicon
face
>From experience of doing a fair amount of SMT repair work I would say
that a solder pump is far to clumsy for the sort of thing. I use
de-solder braid for everything other than large quantities of desoldering.

As for pick and placing - I normally clean the position with deflux -
then add a little "smt - rework flux", tin the soldering iron with a
little solder, hold the item down with the tip of a scalpel (i know you
can get special smt holders too) and simply touch your iron on points to
solder. You may need to re-clean and re-tin the iron in the process.

The solder will flow on to the joint with ease and in about .5 of a
second so the job doesn't get hot at all

If necessary spray some deflux over it after.

Just my 2 pennth worth

Chris
{Quote hidden}

2006\10\20@064753 by Jinx

face picon face
> Is there any good solution for that

What sort of tip are you using ? For general soldering and
large SMT I have an iron with a 3mm chisel tip, but for the
finer SMT I've an iron with a pointed tip. One advantage of
that is that it is less prone to have a pool of solder on it. A
recent challenge was some 60-pin 0.5mm pitch sockets. Takes
a steady and rested hand, magnifier and letting the solder wick
and flow, but it can be done. (not too often hopefully)

2006\10\20@072742 by Tamas Rudnai

face picon face
I have a pointed tip, the smallest I could buy, but still much larger than
the component. When I touch the solder most of the times the melted solder
goes around 1 - 1.5 mm behind the edge of it so that's why I could not put
too small amount of it -- I may have to buy a better iron or have to make a
tip for myself, I do not know. With soldering the SOT23-6 sized PIC it is no
problem -- using the similar technique Steven described above. Will try to
stick it first as Bob advised.

Thanks for everyone!
Tamas




On 20/10/06, Jinx <spam_OUTjoecolquittTakeThisOuTspamclear.net.nz> wrote:
{Quote hidden}

> -

2006\10\20@073729 by Tomas Larsson

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face
> -----Original Message-----
> From: .....piclist-bouncesKILLspamspam@spam@mit.edu
> [piclist-bouncesspamKILLspammit.edu] On Behalf Of Jinx
> Sent: Friday, October 20, 2006 12:47 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] SMT soldering manually
>
> > Is there any good solution for that
>
> What sort of tip are you using ? For general soldering and
> large SMT I have an iron with a 3mm chisel tip, but for the
> finer SMT I've an iron with a pointed tip. One advantage of
> that is that it is less prone to have a pool of solder on it.
> A recent challenge was some 60-pin 0.5mm pitch sockets. Takes
> a steady and rested hand, magnifier and letting the solder
> wick and flow, but it can be done. (not too often hopefully)
>
> -

2006\10\20@082536 by Vasile Surducan

face picon face
35ml of no wash solder paste is around $40
or 0.4mm diameter standard solder wire, you'll need no other solder
wick or whatever...

Vasile

On 10/20/06, Tamas Rudnai <.....tamas.rudnaiKILLspamspam.....gmail.com> wrote:
> Currently I am facing to solder some SM capacitors that are around half size
> as an SOT23. My problem is that I can't put too small amount of solder to
> the tip of the iron. So that the two pads have a good chance to get
> connected. I can't use my desolder pump to remove the exceeds as it could
> pick up the capacitor as well :-). Is there any good solution for that
> (without buying solder paste)?
>
> Thanks
> Tamas
> -

2006\10\20@153124 by Art

picon face
I used to use a standard Weller soldering station with a fine tip
(pointed). I'd file off the tip, using leaving the tinned sides and a
flat untinned tip. I would then wrap silver wire around the remaining
tip so that it would absorb the heat. Use real silver, not coinage
silver which is much more common.

Then I could squeeze or flatten the silver wire to make a tip as fine
as I like. With solid silver wire, you almost never have to re-tin the thing!

Used it for quite a few years until the newest fine pitched chips
became so common.

I recently switched to a Weller Pyro-pen, which is a butane powered
heater with a hot air tip. The hot air is oxygen free (due to a
catalyst in the special tip), and it does great with paste. I almost
never get any solder shorts and the same hardware works for rework as
well. Having oxygen starved hot air does not oxidize the solder, so
the flux can really do it's job well. I have liquid flux, but never
need it. Having the oxygen starved hot air is the secret.

For me, this was the answer.

Your mileage will vary.

You can buy solder paste in very small quantities from several hams
who buy large tubes and split them up. Also, with paste, you can put
it in a sealed container (I use an old thermos)....since it's
airtight, it is safe to refrigerate (with food), so I throw it in the
freezer till I need it. It greatly extends the life of the paste
without endangering your health. I never tried refrigerating it, not
sure if that works as well or not. My paste is going on 2 years old
now and shows no sign of going stale. Don't even think about storing
it with food unless you use an absolutely air tight container.

Enjoy,

Art



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