Hi all,

I have a small surface mount amplifer/filter chip on a packed PCB that
I need to replace. In order to solder in the new one I obviously need
to desolder the old one first being as careful as possible not to
damage anything else on the board. I've never desoldered before and
was wondering if someone could give me the basics or atleast point me
to a tutorial for desoldering in this type of application. Thanks so
much for any advice,

Kev

wrote:
Hi all,

I have a small surface mount amplifer/filter chip on a packed PCB that
I need to replace. In order to solder in the new one I obviously need
to desolder the old one first being as careful as possible not to
damage anything else on the board. I've never desoldered before and
was wondering if someone could give me the basics or atleast point me
to a tutorial for desoldering in this type of application. Thanks so
much for any advice,

Kev

What type of package?

In article . com,
wrote:
I have a small surface mount amplifer/filter chip on a packed PCB that
I need to replace. In order to solder in the new one I obviously need
to desolder the old one first being as careful as possible not to
damage anything else on the board. I've never desoldered before and
was wondering if someone could give me the basics or atleast point me
to a tutorial for desoldering in this type of application. Thanks so
much for any advice,

It's often worth crunching up the faulty chip with cutters to remove most
of it before applying heat. Sounds brutal but the important thing is not
to damage the PCB and prolonged desoldering is likely to. Once you've
reduced it to just the soldered 'tails', remove each one individually
using solder braid.

--
*If I throw a stick, will you leave?

Dave Plowman London SW
To e-mail, change noise into sound.

wrote in message
ups.com...
Hi all,

I have a small surface mount amplifer/filter chip on a packed PCB that
I need to replace. In order to solder in the new one I obviously need
to desolder the old one first being as careful as possible not to
damage anything else on the board. I've never desoldered before and
was wondering if someone could give me the basics or atleast point me
to a tutorial for desoldering in this type of application. Thanks so
much for any advice,

Kev

If you really have no experience of desoldering, then I would venture to
suggest that you are dicing with death to attempt successful removal of a
surface mount chip on a packed board, as a first project ...

You really will need to practice first on a scrap board. I usually start by
flooding the pins with new solder, then wicking off as much as possible.
This will remove much more solder than just going for it with the existing
solder, which will not melt and flow up into the solder wick very well. I
then slide a length of single strand rework wire under all the pins down one
side, and tack solder the end to any convenient solder pad. If you then
gently pull on the free end of the wire, away from the chip body, whilst
applying heat to each pin in turn, they will come up off the board cleanly,
as the wire passes below them.

When most of the pins are separated from the board, you may see the chip
body start to move. Be careful then that the removal of the last couple of
pins does not twist the IC and pull the last couple of pads off the board.
If you do not see the IC moving, it is likely glued to the board. The glue
bond is usually easily fractured by inserting a blunt scalpel blade under
the edge of the IC body, and twisting. When the IC is off the board, re-wick
the pads to make sure that they are very flat, and remove any traces of
glue.

Position the new IC very carefully, making sure that it is the right way
round, then tack two pins at opposite corners. Check the pin alignment again
with a strong magnifying glass. When you are satisfied that it is aligned
correctly, apply some liquid flux to one row of pins, then just go ahead and
solder with the smallest iron tip and finest gauge solder that you have.
Don't worry about solder-flooding bridging the pins at this point. If you
are using a good quality liquid flux, this should be minimal anyway, if you
are not going mad at applying solder. Repeat for the other one or three rows
of pins, depending on package type.

When you have finished, examine your work with your magnifying glass again -
a jeweller's loupe is ideal for this - and then go back to any pins that
have bridged, and apply your solder wick with your iron tip to the vertical
faces of the affected pins. This will remove the excess solder causing the
bridge, without compromising the joint. Clean down with flux remover and an
old toothbrush, and recheck the work with the magnifier. You should find
that the job you have done is nearly as good as the original flow soldered
product.

Arfa

wrote in message
ups.com...
Hi all,

I have a small surface mount amplifer/filter chip on a packed PCB that
I need to replace. In order to solder in the new one I obviously need
to desolder the old one first being as careful as possible not to
damage anything else on the board. I've never desoldered before and
was wondering if someone could give me the basics or atleast point me
to a tutorial for desoldering in this type of application. Thanks so
much for any advice,

Kev


Hint for de-soldering surface mount ICs.
Use a hot-air paint-stripper,1400W,500 degree centigrade,with 2 level heat
control to prolong element life.
Form a ring of silicone covered wire around the IC{to isolate the remaing
components on the pcb.Push a thin piece of wire
under one side of the IC and form a loop around the IC,repeat on the other
side;this is to remove the IC when the solder melts, tug on these wires
while heating up to ensure minimum heating contact time.
Place a slab of PTFE with right size hole cut into and
clip pcb and slab together with clothes pegs/Bulldog clips etc.
If the IC is for re-use then cover body of IC with heat insulating material
or blast IC with freezer spray.Allow the hot-air gun to get up to heat{say 1
minute}before applying to IC.
For more crowded boards make "conical" shrouds to surround the IC. I used
some PTFE strip that i had but thin paxolin or similar but drilled and wired
together would probably do. Cut 4 small trapezoids from the PTFE strip.
Fixed together with all long edges one side and short edges adjascent on the
other side. Fixed together with paper staples but for the smallest shroud
for 8 pin SM had to wire together the final join. Forms a sort of truncated
cone, frustrum, in shape. Tie to the PTFE cone (to stop the blower blowing
it off) with
copper wire or temporarily solder to distant points.
When practised the heated contact time should be less than
2 seconds - no board distortion or collateral damage surprisingly.
If you can't get the tugging wires under the IC then pass
under a few pins at each corner.
Because this tugging frees the IC at the earliest moment, the solder
on the board is not fully melted and leaves a profile for localising
the new IC in place and then solder pin by pin.
SAFETY NOTE:- ensure good ventilation, use safety goggles,and beware of very
slight risk of combustion.

other hints and tips on

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

Meat Plow wrote in message
news
On Mon, 18 Dec 2006 11:09:27 -0800, kevin.pavin Has Frothed:

Hi all,

I have a small surface mount amplifer/filter chip on a packed PCB that
I need to replace. In order to solder in the new one I obviously need
to desolder the old one first being as careful as possible not to
damage anything else on the board. I've never desoldered before and
was wondering if someone could give me the basics or atleast point me
to a tutorial for desoldering in this type of application. Thanks so
much for any advice,

Kev

google

http://www.scienceprog.com/ease-way-to-desolder-smd/
--
Pierre Salinger Memorial Hook, Line & Sinker, June 2004

COOSN-266-06-25794

And for those of us without broadband, an outline of that method is ?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"N Cook" wrote in message
...

And for those of us without broadband, an outline of that method is ?

--

Hope you've got a single-sided, single layer PCB, put the flat side on an
upside-down hot iron, remove SMD's (all of them 'cuz they all melt) from
board. Doesn't go into replacement of said parts.

Dave wrote in message
news:LfUhh.71438$YV4.51840@edtnps89...

"N Cook" wrote in message
...

And for those of us without broadband, an outline of that method is ?

--

Hope you've got a single-sided, single layer PCB, put the flat side on an
upside-down hot iron, remove SMD's (all of them 'cuz they all melt) from
board. Doesn't go into replacement of said parts.




so a no-no , i take it

Hi!

so a no-no , i take it

Probably a site of questionable reputation...I see a sign of the video and
then get redirected promptly to a "DMV lemon law" page or something.

William

do it the RIGHT way and either

(a). throw it out & buy a new one.

(b). get a PACE or Weller hot gas bonder/debonder
tool/station and do it the way the manufacturer
(and repair depot) would.

All these methods are half ass "poor man" approaches
that might work, but it's highly dependent on your
skill level (and if you have to ask how to remove an
SMT chip, you don't have the skill level).

the other question is, if you have no desoldering
experience whatsoever - what kind of hands on electronics
troubleshooting have you done to arrive at the conclusion
that particular chip needs replacement ?

Go look on E-bay and you'll find many hot gas
debonding tools to rework SMT boards.



"Dave Plowman (News)" wrote in message
...
In article . com,
wrote:
I have a small surface mount amplifer/filter chip on a packed PCB that
I need to replace. In order to solder in the new one I obviously need
to desolder the old one first being as careful as possible not to
damage anything else on the board. I've never desoldered before and
was wondering if someone could give me the basics or atleast point me
to a tutorial for desoldering in this type of application. Thanks so
much for any advice,

It's often worth crunching up the faulty chip with cutters to remove most
of it before applying heat. Sounds brutal but the important thing is not
to damage the PCB and prolonged desoldering is likely to. Once you've
reduced it to just the soldered 'tails', remove each one individually
using solder braid.

--
*If I throw a stick, will you leave?

Dave Plowman London SW
To e-mail, change noise into sound.