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'[EE]: Desoldering'
2006\08\27@081135 by Dave King

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face
Just wondering about how much success anyone has had desoldering SMT parts
for reuse. Actually wondering which of the various methods work or don't.

I'm trying to get a air rework station but for now I have my normal
soldering
station and a spool of wick. I've had one person suggest to forget the
wick and just alternate the iron tip from side to side on say a resistor
until
it comes loose. And supposedly this works fine until trying to do flat packs
and larger chips.

Just curious

Dave

2006\08\27@082859 by Wouter van Ooijen

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> I've had one person suggest to forget the
> wick and just alternate the iron tip from side to side on say
> a resistor until it comes loose.

Reality check: what is the cost of one SMD resistor?

And yes, I do remove SMD resistors from PCBs this way, but only to
replace them. I would not dream of using that resistor again.

I guess this will be a bit more difficult with lead-free soldered
PCBs...

> And supposedly this works fine until trying to do flat packs and
larger chips.

If you realy want to go this way: get a hot-air (electrical) paint
stripper, heat an area of the PCB, hold it with that area down, give the
top a knock, and gather what comes loose. A bit like olive harvesting.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2006\08\27@101430 by Tamas Rudnai

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Wouter,

Does not get those parts overheated this way?

Tamas


On 27/08/06, Wouter van Ooijen <spam_OUTwouterTakeThisOuTspamvoti.nl> wrote:
{Quote hidden}

> -

2006\08\27@101729 by Vasile Surducan

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On 8/27/06, Wouter van Ooijen <.....wouterKILLspamspam@spam@voti.nl> wrote:
> > I've had one person suggest to forget the
> > wick and just alternate the iron tip from side to side on say
> > a resistor until it comes loose.
>
> Reality check: what is the cost of one SMD resistor?

Invaluable if you need desperate ONE, just now, of particular value
and/or tolerance and/or size. Tested this affirmation in the USA, so
this problem does not depend the country you live in...

There are two successfuly methodes:
1. hot air rework, advantage:is fast, disadvantage:if does not have a
fine air blow , will blow the component to a wrong direction that you
want. Use an autoholder tweezer for the component.
2. use a manufactured iron copper tip for different SMD sized, one
touch with two simetrical desolder, it's the best solution. SMD
smaller than 0603 will be automatic taken off and remains soldered on
the tip

BTW, a SMD may be used many times if the first solder failed, as long
the temperature desolder does not destroy metalisations.

greetings,
Vasile

2006\08\27@104645 by Wouter van Ooijen

face picon face
> Does not get those parts overheated this way?

if you do it quickly not (much) more than by hot air soldering (that is
what you are doing!)

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2006\08\27@111731 by Marcel Duchamp

picon face
Dave King wrote:
> Just wondering about how much success anyone has had desoldering SMT parts
> for reuse. Actually wondering which of the various methods work or don't.
>
> I'm trying to get a air rework station but for now I have my normal
> soldering
> station and a spool of wick. I've had one person suggest to forget the
> wick and just alternate the iron tip from side to side on say a resistor
> until
> it comes loose. And supposedly this works fine until trying to do flat packs
> and larger chips.
>
> Just curious
>
> Dave
>
For passives, this is a bad idea unless you have really good equipment.

If you read the data sheets for resistors and capacitors you will find
they recommend against *ever* touching the component directly with a
soldering iron.  The reason is thermal stresses cause micro-cracks in
the component that lead to subsequent failure.  The actual failure rate
is low; boards I stuffed with an iron years ago still work - mostly.
But we had one experience where many of the parts did fail.  They were
.1uf - hundreds of them.  Those used as bypass caps were not noticed;
those used as filters in RC networks were disasters.

For IC's, reuse has better success.  Still, we throw away 99.9% of parts
that we remove and just put new ones on.  Why bet the company fortunes
on bad parts?  Of course, for hobby use, the story is not so bad.



2006\08\27@112758 by Vasile Surducan

face picon face
On 8/27/06, Marcel Duchamp <marcel.duchampspamKILLspamsbcglobal.net> wrote:
{Quote hidden}

What make you think there would be no failures of the same type you've
mention when you'll use hot air (or even wave soldering) and a large
ground (without thermals) on one side of the SMD and a very thin
microstrip route on the other side of the SMD ?. Sometimes the
"micro-cracks" are good visible even with open eye... and trying a few
times with a good preheating of the whole board  does not help at
all...

greetings,
Vasile

2006\08\27@175013 by Herbert Graf

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face
On Sun, 2006-08-27 at 05:11 -0700, Dave King wrote:
> Just wondering about how much success anyone has had desoldering SMT parts
> for reuse. Actually wondering which of the various methods work or don't.
>
> I'm trying to get a air rework station but for now I have my normal
> soldering
> station and a spool of wick. I've had one person suggest to forget the
> wick and just alternate the iron tip from side to side on say a resistor
> until
> it comes loose. And supposedly this works fine until trying to do flat packs
> and larger chips.

Reusing something as cheap as an smt resistor or cap doesn't make much
sense to me personally. That said, yes, the "alternate from side to
side" method works very well and I can get parts from 1206 down to 0201
off without much difficulty these days.

For larger packages the only way by hand IMHO is hot air. With a good
nozzle you can get nearly any smaller (say 48pin or lower) chip off
without much trouble. Larger chips take more skill, but are certainly
possible.

TTYL

2006\08\27@184338 by Dave King

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face
My desire to try an salvage a few parts is not a matter of money, its
a simple matter of time. I somehow live in the electronic middle of
nowhere and have to order in everything. Whats funny is they try to
promote this hole as the new sillycon valley of the north.... Just
try to find common transistors here. Anyway I need to have a couple
of proto boards running by mid week to do a show n tell and so far
no parts in sight.

Just hoping some manual desoldering technique will give me a greater
chance of having usable parts to use. I did look at a few 20x parts(specs
of dust) for cracks as one person suggested, and they still metered out
right after taking them off with the wick method. It is rather tempting
to fire up the torch and give the board a rap or two though.

Dave

{Quote hidden}

> -

2006\08\27@191842 by Richard Prosser

picon face
Dave,
One technique that can be a bit risky is to add a solder blob to one
side & then loosen the component using an iron from the other. - ie
use the thermal capacity of the solder blob in place of another iron.
You run the risk of overheating the component but if it's just for
removal that's no issue. OTOH I've use the same technique when
salvaging quad packaged microcontrollers many times and not had many
failures at all - maybe one or two. (Prototyping use only - NOT
reccomended for production).

RP

On 28/08/06, Dave King <.....KingDWSKILLspamspam.....shaw.ca> wrote:
{Quote hidden}

2006\08\27@214816 by Gaston Gagnon

face
flavicon
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Herbert,

Herbert Graf wrote:
> Reusing something as cheap as an smt resistor or cap doesn't make much
> sense to me personally. That said, yes, the "alternate from side to
> side" method works very well and I can get parts from 1206 down to 0201
> off without much difficulty these days.
>
> For larger packages the only way by hand IMHO is hot air. With a good
> nozzle
Can you provide a pointer to an image (or model number) of what do you
call a good nozzle to unsolder chip like 48pin?
Gaston

2006\08\27@214941 by Charles Craft

picon face
I've been trying to work the word "olive" into a PIClist post for years.  :-)

>
>If you realy want to go this way: get a hot-air (electrical) paint
>stripper, heat an area of the PCB, hold it with that area down, give the
>top a knock, and gather what comes loose. A bit like olive harvesting.
>
>Wouter van Ooijen
>
>-- -------------------------------------------
>Van Ooijen Technische Informatica: http://www.voti.nl
>consultancy, development, PICmicro products
>docent Hogeschool van Utrecht: http://www.voti.nl/hvu
>
>
>-

2006\08\27@215446 by Herbert Graf

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face
On Sun, 2006-08-27 at 21:48 -0400, Gaston Gagnon wrote:
> Herbert,
>
> Herbert Graf wrote:
> > Reusing something as cheap as an smt resistor or cap doesn't make much
> > sense to me personally. That said, yes, the "alternate from side to
> > side" method works very well and I can get parts from 1206 down to 0201
> > off without much difficulty these days.
> >
> > For larger packages the only way by hand IMHO is hot air. With a good
> > nozzle
> Can you provide a pointer to an image (or model number) of what do you
> call a good nozzle to unsolder chip like 48pin?

Not really, I just use the heat gun we have a work, it comes with a few
nozzles.

Generally use a nozzle that covers just the part in question. TTYL

2006\08\27@222557 by Gaston Gagnon

face
flavicon
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Herbert Graf wrote:
{Quote hidden}

Heat gun, I see. I had in mind Hot-Air pencil :-[ .
Thank you.
Gaston

2006\08\28@015650 by PicDude

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face
Alternately touching both pads of resistors and caps (I've only tried 1206's
and 0805's this way) works, but I've never tried to re-use these.  For 28
SSOPs, I worry about lifting pads (as I've done a few times) when heating it
a lot to desolder, so I destroy the chip to protect the pads.  Also, don't
want to trust a previously-soldered and unsoldered chip.  So I use an
ultra-fine-tipped pair of tweezers and heat one pin at a time while lifting
(bending backwards) the pin.  Then the same for all but one pin on that row.  
Then the other side.  The final two diagonal pins are easy to desolder and
remove after that.  I just replace the part though.

Cheers,
-Neil.



On Sunday 27 August 2006 07:11, Dave King wrote:
{Quote hidden}

2006\08\28@210030 by Dwayne Reid

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At 09:17 AM 8/27/2006, Marcel Duchamp wrote:

>If you read the data sheets for resistors and capacitors you will find
>they recommend against *ever* touching the component directly with a
>soldering iron.  The reason is thermal stresses cause micro-cracks in
>the component that lead to subsequent failure.  The actual failure rate
>is low; boards I stuffed with an iron years ago still work - mostly.
>But we had one experience where many of the parts did fail.  They were
>.1uf - hundreds of them.  Those used as bypass caps were not noticed;
>those used as filters in RC networks were disasters.

We solder a fair number of smt parts by hand without much
problem.  However, we bake any moisture-susceptible parts
first.  These include any ceramic capacitors and most
epoxy-encapsulated parts (ICs, transistors).

We had one board run with an enormous failure rate (shorted or leaky
100n mono caps) - sure enough, parts not baked first.  Oops.

dwayne

--
Dwayne Reid   <EraseMEdwaynerspam_OUTspamTakeThisOuTplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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2006\08\29@130447 by M. Adam Davis

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For small components a tweezer style soldering iron works ok, though
I'm just as liable to heat one side a lot, then apply heat and force
to the other side quickly.  Typically it overheats the part, but it
may still be good.

The multi leg SMT parts are trickier.  A hot air rework station with
the appropiate nozzle works very well.  If that's not available then I
have used solder wick along with an x-acto blade to lift each pin up
while it cools.  Takes a long time, the pins don't ever really lay
flat again, but the parts are generally usable.

Good luck!

-Adam

On 8/27/06, Dave King <KingDWSspamspam_OUTshaw.ca> wrote:
{Quote hidden}

> -

2006\08\29@141221 by Vasile Surducan

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On 8/29/06, M. Adam Davis <@spam@stienmanKILLspamspamgmail.com> wrote:
> For small components a tweezer style soldering iron works ok, though
> I'm just as liable to heat one side a lot, then apply heat and force
> to the other side quickly.  Typically it overheats the part, but it
> may still be good.

My english is not too good so maybe no one understand my last email on
this topic.
Imagine that you split in two the tip of the soldering iron. You need
an ordinary one euro chinese soldering iron and a piece of copper for
the tip. "Tip"  means for me the copper part of the iron. Using a
hammer, make the copper cilinder flat at the top. Using a cutting
device make two separate flat parts. Using a file adjust those parts
to be sharpen and position those like a real desoldering tweezer.
Adjust distances between those for 1206, 805, 603 or 402 (even 201
works).
One heating, two points desoldering.

>
> The multi leg SMT parts are trickier.  A hot air rework station with
> the appropiate nozzle works very well.

Yes, the air flow control is the most important.

greetings,
Vasile

2006\08\29@213936 by Dave King

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face
Vasile

That is an excellent idea! On my soldering station the tips are held
in place with a set screw so I just need to find some copper rod
and I can make several tip sizes and be able to change them. It would
minimize the amount of heat by quite a bit.

Now to find some copper rod. ;-]

Cheers

Dave

{Quote hidden}

> --

2006\08\29@221935 by Denny Esterline

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> That is an excellent idea! On my soldering station the tips are held
> in place with a set screw so I just need to find some copper rod
> and I can make several tip sizes and be able to change them. It would
> minimize the amount of heat by quite a bit.
>
> Now to find some copper rod. ;-]
>
> Cheers

Depends on what you consider "rod". My local home center has some #4 solid conductor ground wire - it's about 1/4 inch in diameter and sold by the foot.

-Denny


2006\08\30@002217 by Dave King

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face

> > That is an excellent idea! On my soldering station the tips are held
> > in place with a set screw so I just need to find some copper rod
> > and I can make several tip sizes and be able to change them. It would
> > minimize the amount of heat by quite a bit.
> >
> > Now to find some copper rod. ;-]
> >
> > Cheers
>
> Depends on what you consider "rod". My local home center has some
> #4 solid conductor ground wire - it's about 1/4 inch in diameter
> and sold by the foot.
>
> -Denny

I know the stuff you are talking about. I'm not sure I've seen it in
rod more like thick stranded wire. It's definitly worth a trip to
the hardware store to check to find some.

Thanks

Dave

2006\08\30@005543 by Vasile Surducan

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On 8/30/06, Dave King <KILLspamKingDWSKILLspamspamshaw.ca> wrote:
> Vasile
>
> That is an excellent idea! On my soldering station the tips are held
> in place with a set screw so I just need to find some copper rod
> and I can make several tip sizes and be able to change them. It would
> minimize the amount of heat by quite a bit.
>
> Now to find some copper rod. ;-]

In California will be difficult... (no joke).
On my last visit to US, I discovered you have almost the same problem
finding small part quantities like the rest of the world...

greetings,
Vasile

2006\08\30@035419 by Robert Ammerman

picon face
>
> I know the stuff you are talking about. I'm not sure I've seen it in
> rod more like thick stranded wire. It's definitly worth a trip to
> the hardware store to check to find some.
>
> Thanks

Measure the diameter your existing tips and take a micrometer or caliper
with you to the store. (Or just drill a hole or two in a scrap board that
just fit the existing tips and use that as a guide.)

Bob Ammerman

2006\08\31@103911 by Gerhard Fiedler

picon face
Charles Craft wrote:

> Wouter van Ooijen:
>> A bit like olive harvesting.

> I've been trying to work the word "olive" into a PIClist post for years.
> :-)

That wasn't the first time in recent years:

http://search.gmane.org/?query=olive&group=gmane.comp.hardware.microcontrollers.pic

Olives are more universally used than one might think :)

Gerhard

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