TIP: A simple and safe way to desolder SMD SOICS etc

N

N_Cook

Guest
I discovered this via needing to isolate Vcc of a SOIC where the trace
is under the IC and a multilayer board.
I have a reel of 0.08mm diameter tungsten wire , tungsten probably not
critical and diameter only needs to be small enough to go under SOIC pins.
I've since tried, pin by pin, of an 8p SOIC on a scrap board with a
success rate of 8 out of 8 isolating each pin , first time. Leaded
solder, PbF situation not tried yet

Feed length of the wire under a pin , long enough to grab hold of both
ends. Pull outwards and slightly upward while quick soldering iron melt
of the pin solder. The wire pulls through, but surprisingly , 8 out out
8 times so far, the solder has not rejoined across the gap. Then a
sliver of mica under the pin , in my Vcc situation, to fully
isolate for testing purposes.
But of course where hot air is out of the question , the IC is required
for salvaged re-use etc, this method pin by pin could be used even in
restricted space,
to salvage a whole SMD IC. I wonder if a single loop per side of a DIL
or quad footprint IC , and progressive single pin melting , would work
with 8 or more pins in one operation - worth trying some time
 
Surface-mounted stuffs are not supposed to be repaired as traditional
chips, right? :)

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On 07/24/2013 07:59 AM, N_Cook wrote:
I discovered this via needing to isolate Vcc of a SOIC where the trace
is under the IC and a multilayer board.
I have a reel of 0.08mm diameter tungsten wire , tungsten probably not
critical and diameter only needs to be small enough to go under SOIC pins.
I've since tried, pin by pin, of an 8p SOIC on a scrap board with a
success rate of 8 out of 8 isolating each pin , first time. Leaded
solder, PbF situation not tried yet

Feed length of the wire under a pin , long enough to grab hold of both
ends. Pull outwards and slightly upward while quick soldering iron melt
of the pin solder. The wire pulls through, but surprisingly , 8 out out
8 times so far, the solder has not rejoined across the gap. Then a
sliver of mica under the pin , in my Vcc situation, to fully
isolate for testing purposes.
But of course where hot air is out of the question , the IC is required
for salvaged re-use etc, this method pin by pin could be used even in
restricted space,
to salvage a whole SMD IC. I wonder if a single loop per side of a DIL
or quad footprint IC , and progressive single pin melting , would work
with 8 or more pins in one operation - worth trying some time
Click to expand...
I'd try to break the trace leading from the pad first.
 
On 07/24/2013 08:02 AM, Mr. Man-wai Chang wrote:
Surface-mounted stuffs are not supposed to be repaired as traditional
chips, right? :)
Click to expand...
I believe he was describing a diagnostic procedure, not a chip repair.
 
On 24/07/2013 16:22, dave wrote:
On 07/24/2013 07:59 AM, N_Cook wrote:
I discovered this via needing to isolate Vcc of a SOIC where the trace
is under the IC and a multilayer board.
I have a reel of 0.08mm diameter tungsten wire , tungsten probably not
critical and diameter only needs to be small enough to go under SOIC
pins.
I've since tried, pin by pin, of an 8p SOIC on a scrap board with a
success rate of 8 out of 8 isolating each pin , first time. Leaded
solder, PbF situation not tried yet

Feed length of the wire under a pin , long enough to grab hold of both
ends. Pull outwards and slightly upward while quick soldering iron melt
of the pin solder. The wire pulls through, but surprisingly , 8 out out
8 times so far, the solder has not rejoined across the gap. Then a
sliver of mica under the pin , in my Vcc situation, to fully
isolate for testing purposes.
But of course where hot air is out of the question , the IC is required
for salvaged re-use etc, this method pin by pin could be used even in
restricted space,
to salvage a whole SMD IC. I wonder if a single loop per side of a DIL
or quad footprint IC , and progressive single pin melting , would work
with 8 or more pins in one operation - worth trying some time

I'd try to break the trace leading from the pad first.
Click to expand...
Not accessible in tnis case, its buried inside the board somewhere unknown.
While at it for traces that are accessible. Sometimes in those sets of
Cintride/"diamond" abrasive addons for Dremmels, a diabolo shaped one.
Like 2 cones back-to-back, the 3mm or so diameter outermost cone base is
excellent for cutting neat + tight slots in fine pcb copper traces.

I will try kevlar fibre from an optical data link instead of tungsten
wire, to see if that works also
 
A twist of kevlar fibres works if you can get the cord under and around
the pin
 
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ksopo3$p5q$1@dont-email.me...
I discovered this via needing to isolate Vcc of a SOIC where the trace is
under the IC and a multilayer board.
I have a reel of 0.08mm diameter tungsten wire , tungsten probably not
critical and diameter only needs to be small enough to go under SOIC pins.
I've since tried, pin by pin, of an 8p SOIC on a scrap board with a
success rate of 8 out of 8 isolating each pin , first time. Leaded solder,
PbF situation not tried yet

Feed length of the wire under a pin , long enough to grab hold of both
ends. Pull outwards and slightly upward while quick soldering iron melt of
the pin solder. The wire pulls through, but surprisingly , 8 out out 8
times so far, the solder has not rejoined across the gap. Then a sliver of
mica under the pin , in my Vcc situation, to fully
isolate for testing purposes.
But of course where hot air is out of the question , the IC is required
for salvaged re-use etc, this method pin by pin could be used even in
restricted space,
to salvage a whole SMD IC. I wonder if a single loop per side of a DIL or
quad footprint IC , and progressive single pin melting , would work with 8
or more pins in one operation - worth trying some time
Click to expand...
I detailed this procedure a long long time ago on here. I use etch-revision
wire, fed under the pins, and tacked to a convenient solder point at the far
end. With the wire pulled against the first pin, and slightly upwards,
applying the tip of the iron to the pins in quick succession results in them
popping off the board remarkably easily and cleanly. I have used this
technique with total success to remove SM ICs without physically damaging
them , and where hot air cannot be used, for many years now.

Arfa
 
On 25/07/2013 01:43, Arfa Daily wrote:
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ksopo3$p5q$1@dont-email.me...
I discovered this via needing to isolate Vcc of a SOIC where the trace
is under the IC and a multilayer board.
I have a reel of 0.08mm diameter tungsten wire , tungsten probably
not critical and diameter only needs to be small enough to go under
SOIC pins.
I've since tried, pin by pin, of an 8p SOIC on a scrap board with a
success rate of 8 out of 8 isolating each pin , first time. Leaded
solder, PbF situation not tried yet

Feed length of the wire under a pin , long enough to grab hold of both
ends. Pull outwards and slightly upward while quick soldering iron
melt of the pin solder. The wire pulls through, but surprisingly , 8
out out 8 times so far, the solder has not rejoined across the gap.
Then a sliver of mica under the pin , in my Vcc situation, to fully
isolate for testing purposes.
But of course where hot air is out of the question , the IC is
required for salvaged re-use etc, this method pin by pin could be used
even in restricted space,
to salvage a whole SMD IC. I wonder if a single loop per side of a DIL
or quad footprint IC , and progressive single pin melting , would work
with 8 or more pins in one operation - worth trying some time


I detailed this procedure a long long time ago on here. I use
etch-revision wire, fed under the pins, and tacked to a convenient
solder point at the far end. With the wire pulled against the first pin,
and slightly upwards, applying the tip of the iron to the pins in quick
succession results in them popping off the board remarkably easily and
cleanly. I have used this technique with total success to remove SM ICs
without physically damaging them , and where hot air cannot be used, for
many years now.

Arfa
Click to expand...
Etch revision wire must be compatible with solder, I would have thought
the technique would require an incompatible material
 
On 25/07/2013 01:43, Arfa Daily wrote:
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ksopo3$p5q$1@dont-email.me...
I discovered this via needing to isolate Vcc of a SOIC where the trace
is under the IC and a multilayer board.
I have a reel of 0.08mm diameter tungsten wire , tungsten probably
not critical and diameter only needs to be small enough to go under
SOIC pins.
I've since tried, pin by pin, of an 8p SOIC on a scrap board with a
success rate of 8 out of 8 isolating each pin , first time. Leaded
solder, PbF situation not tried yet

Feed length of the wire under a pin , long enough to grab hold of both
ends. Pull outwards and slightly upward while quick soldering iron
melt of the pin solder. The wire pulls through, but surprisingly , 8
out out 8 times so far, the solder has not rejoined across the gap.
Then a sliver of mica under the pin , in my Vcc situation, to fully
isolate for testing purposes.
But of course where hot air is out of the question , the IC is
required for salvaged re-use etc, this method pin by pin could be used
even in restricted space,
to salvage a whole SMD IC. I wonder if a single loop per side of a DIL
or quad footprint IC , and progressive single pin melting , would work
with 8 or more pins in one operation - worth trying some time


I detailed this procedure a long long time ago on here. I use
etch-revision wire, fed under the pins, and tacked to a convenient
solder point at the far end. With the wire pulled against the first pin,
and slightly upwards, applying the tip of the iron to the pins in quick
succession results in them popping off the board remarkably easily and
cleanly. I have used this technique with total success to remove SM ICs
without physically damaging them , and where hot air cannot be used, for
many years now.

Arfa
Click to expand...
Must have been on a thread I was not following. I think I would have
tried it myself if I'd seen it.
Just tried removing a 50 pin quad format SMD IC. Convenient tiny plated
hollow vias all over the board to pass the tungsten wire through. First
run I decided to run flux over the pins to assist desoldering but that
made the solder recoalesce on half the pins. As tungsten wire is awkward
to handle, used an artery forceps to clamp the wire under the pcb via
and another to hold the free end of the wire, and tension angles just
slightly off line to avoid bending the pins.
Tried another 50 pinner and 4 runs with satisfying twang on release each
time, with only 2 pins having rejoined solder under , which of course is
no difficulty to deal with individually when the other 48 are released.
Only a couple of minutes to desolder a 50 pin SMD
 
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ksr923$109$1@dont-email.me...
On 25/07/2013 01:43, Arfa Daily wrote:


"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ksopo3$p5q$1@dont-email.me...
I discovered this via needing to isolate Vcc of a SOIC where the trace
is under the IC and a multilayer board.
I have a reel of 0.08mm diameter tungsten wire , tungsten probably
not critical and diameter only needs to be small enough to go under
SOIC pins.
I've since tried, pin by pin, of an 8p SOIC on a scrap board with a
success rate of 8 out of 8 isolating each pin , first time. Leaded
solder, PbF situation not tried yet

Feed length of the wire under a pin , long enough to grab hold of both
ends. Pull outwards and slightly upward while quick soldering iron
melt of the pin solder. The wire pulls through, but surprisingly , 8
out out 8 times so far, the solder has not rejoined across the gap.
Then a sliver of mica under the pin , in my Vcc situation, to fully
isolate for testing purposes.
But of course where hot air is out of the question , the IC is
required for salvaged re-use etc, this method pin by pin could be used
even in restricted space,
to salvage a whole SMD IC. I wonder if a single loop per side of a DIL
or quad footprint IC , and progressive single pin melting , would work
with 8 or more pins in one operation - worth trying some time


I detailed this procedure a long long time ago on here. I use
etch-revision wire, fed under the pins, and tacked to a convenient
solder point at the far end. With the wire pulled against the first pin,
and slightly upwards, applying the tip of the iron to the pins in quick
succession results in them popping off the board remarkably easily and
cleanly. I have used this technique with total success to remove SM ICs
without physically damaging them , and where hot air cannot be used, for
many years now.

Arfa

Must have been on a thread I was not following. I think I would have tried
it myself if I'd seen it.
Just tried removing a 50 pin quad format SMD IC. Convenient tiny plated
hollow vias all over the board to pass the tungsten wire through. First
run I decided to run flux over the pins to assist desoldering but that
made the solder recoalesce on half the pins. As tungsten wire is awkward
to handle, used an artery forceps to clamp the wire under the pcb via and
another to hold the free end of the wire, and tension angles just slightly
off line to avoid bending the pins.
Tried another 50 pinner and 4 runs with satisfying twang on release each
time, with only 2 pins having rejoined solder under , which of course is
no difficulty to deal with individually when the other 48 are released.
Only a couple of minutes to desolder a 50 pin SMD
Click to expand...
If by 'compatible' you mean solderable, then yes, etch revision wire is. It
is a thin silver wire with a Teflon sleeve. I don't know what metal it is
made of, but it certainly does solder well, as you presumed. By why would
that be a problem to the procedure ? It's definitely not, anyway. I just
strip a couple of inches back, feed it behind a pin row, tack it down
somewhere convenient, put the tension on it with my left hand, and start
applying the iron tip to the vertical faces of the IC pins. Once you get a
'feel' for it and get going, the pins will pop off the board at a rate of a
couple a second. The only place that you have to be careful, is with the
last few pins on the last row. I usually stop pulling on the wire when I get
to that point, and just place the flat of the iron tip across those last two
or three pins to just melt them all at once. This avoids putting twist
strain on the tracks, and risking losing the last couple of fingers.

Once the IC is off the board, I just make sure that the pads are absolutely
flat by going round with a bit of solder wick, although there is generally
precious little solder left on the pads, anyway.

Arfa
 
On 26/07/2013 01:43, Arfa Daily wrote:
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ksr923$109$1@dont-email.me...
On 25/07/2013 01:43, Arfa Daily wrote:


"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ksopo3$p5q$1@dont-email.me...
Click to expand...

I've not come across the term or actuality of revision wire, only pcb
trace repair copper foil of various thicknesses/widths. Tungsten is
surprisingly strong for only 1/10mm diameter, which is probably an
advantage for this use and quite rigid for the insertion under the pins
process. Ill probably ditch the masking off and hot air desoldering of
ICs and move over to this method. I used tungsten wire there but only to
apply lift-off force to the IC while applying hot air.
 
On 26/07/2013 08:41, N_Cook wrote:
On 26/07/2013 01:43, Arfa Daily wrote:


"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ksr923$109$1@dont-email.me...
On 25/07/2013 01:43, Arfa Daily wrote:


"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ksopo3$p5q$1@dont-email.me...
Click to expand...
I find solder perfidious stuff. Cut a trace for diagnosis purposes and
the solder will not bridge the gap when it comes to repairing the cut.
Resolder one pin of a SMD and there is a good chance of soldering to
the neighbouring pin and for good measure some of the solder migrating
under the IC. I would never of believed that running a wire between pcb
pad and pin of a SMD swathed in molten solder , would split the solder
into 2, the vast majority of times, so would never have considered
trying it.
 
On 25/07/2013 01:43, Arfa Daily wrote:
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ksopo3$p5q$1@dont-email.me...
I discovered this via needing to isolate Vcc of a SOIC where the trace
is under the IC and a multilayer board.
I have a reel of 0.08mm diameter tungsten wire , tungsten probably
not critical and diameter only needs to be small enough to go under
SOIC pins.
I've since tried, pin by pin, of an 8p SOIC on a scrap board with a
success rate of 8 out of 8 isolating each pin , first time. Leaded
solder, PbF situation not tried yet

Feed length of the wire under a pin , long enough to grab hold of both
ends. Pull outwards and slightly upward while quick soldering iron
melt of the pin solder. The wire pulls through, but surprisingly , 8
out out 8 times so far, the solder has not rejoined across the gap.
Then a sliver of mica under the pin , in my Vcc situation, to fully
isolate for testing purposes.
But of course where hot air is out of the question , the IC is
required for salvaged re-use etc, this method pin by pin could be used
even in restricted space,
to salvage a whole SMD IC. I wonder if a single loop per side of a DIL
or quad footprint IC , and progressive single pin melting , would work
with 8 or more pins in one operation - worth trying some time


I detailed this procedure a long long time ago on here. I use
etch-revision wire, fed under the pins, and tacked to a convenient
solder point at the far end. With the wire pulled against the first pin,
and slightly upwards, applying the tip of the iron to the pins in quick
succession results in them popping off the board remarkably easily and
cleanly. I have used this technique with total success to remove SM ICs
without physically damaging them , and where hot air cannot be used, for
many years now.

Arfa
Click to expand...
"here" being usenet but on uk.d-i-y, end apr 2013, a place I rarely
visit except to post a buildings type query
 
I just noticed the production date on my roll of tungsten wire - 1954, I
think it came from auction sell off of stuff at CEGB Marchwood,Hampshire
labs
 
Arfa Daily wrote:
If by 'compatible' you mean solderable, then yes, etch revision wire is.
Click to expand...
That sounds like the 30 AWG wire that used to be used to wrap wire
backplanes. I have several rolls of solid wire in that size that is
tinned, and has a thermoplastic insulator, commonly used for ECOs
(Engineering Change Order)


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
 
On 26/07/2013 20:54, Michael A. Terrell wrote:
Arfa Daily wrote:

If by 'compatible' you mean solderable, then yes, etch revision wire is.

That sounds like the 30 AWG wire that used to be used to wrap wire
backplanes. I have several rolls of solid wire in that size that is
tinned, and has a thermoplastic insulator, commonly used for ECOs
(Engineering Change Order)
Click to expand...
or even just plain old wire-wrap wire, it has to be strong enough to be
pulled tight over those square corners of the pins without fracturing.
If I can remember where it is I'll dig out some of it and see how
solderable it is and whether it works for this SOIC removal purpose
 
On 26/07/2013 20:54, Michael A. Terrell wrote:
Arfa Daily wrote:

If by 'compatible' you mean solderable, then yes, etch revision wire is.

That sounds like the 30 AWG wire that used to be used to wrap wire
backplanes. I have several rolls of solid wire in that size that is
tinned, and has a thermoplastic insulator, commonly used for ECOs
(Engineering Change Order)
Click to expand...

Tried some ancient Bicc-Vero wire-wrap wire (Kynar sleeving stated on
the drum, order code faded with age), surprisingly as made just down the
road from me, stated as 30AWG. I don't know how to strip off long
lengths of the sleeving but for 6 inch length, grab stripped wire end in
pliers and compress by pushing with fingernail+finger, the Kynar/ptfe?
along and off the wire. Incidently , by heating and stretching this , in
effect sleeving, will form even finer spaghetti tube. The wire does take
solder and I can confirm can be used for SMD SOIC removal
 
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:kst8r9$2sc$1@dont-email.me...
On 26/07/2013 01:43, Arfa Daily wrote:


"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ksr923$109$1@dont-email.me...
On 25/07/2013 01:43, Arfa Daily wrote:


"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ksopo3$p5q$1@dont-email.me...


I've not come across the term or actuality of revision wire, only pcb
trace repair copper foil of various thicknesses/widths. Tungsten is
surprisingly strong for only 1/10mm diameter, which is probably an
advantage for this use and quite rigid for the insertion under the pins
process. Ill probably ditch the masking off and hot air desoldering of ICs
and move over to this method. I used tungsten wire there but only to apply
lift-off force to the IC while applying hot air.
Click to expand...
That's perhaps an 'Americanism' that I picked up when I worked for an
American computer company many moons ago. It was very common back then for
logic functions on cards to be revised, and this was invariably done by
cutting traces, and running thin blue wires (sometimes pale yellow) between
chip pins to 'insert' a spare gate from another package. Longer runs were
almost always stuck down to the PCB with little dabs of hot melt, or RTV. It
actually appears to be genuinely known as wire wrap wire here in the UK, and
indeed, we used to use it for this as well. Again, it was common to custom
configure bespoke multi-card systems by having a backplane covered in wire
wrapping posts, which you then used to route bus signals between cards. The
insulation is actually Kynar not Teflon as I originally thought. This is the
stuff

http://uk.farnell.com/pro-power/100-26b/wire-kynar-26awg-blue-100m/dp/150085

Check out

https://en.wikipedia.org/wiki/File:pDP-8I-backplane.jpg

Arfa
 
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ksthkc$cbq$1@dont-email.me...
On 26/07/2013 08:41, N_Cook wrote:
On 26/07/2013 01:43, Arfa Daily wrote:


"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ksr923$109$1@dont-email.me...
On 25/07/2013 01:43, Arfa Daily wrote:


"N_Cook" <diverse@tcp.co.uk> wrote in message
news:ksopo3$p5q$1@dont-email.me...


I find solder perfidious stuff. Cut a trace for diagnosis purposes and the
solder will not bridge the gap when it comes to repairing the cut.
Resolder one pin of a SMD and there is a good chance of soldering to the
neighbouring pin and for good measure some of the solder migrating under
the IC. I would never of believed that running a wire between pcb pad and
pin of a SMD swathed in molten solder , would split the solder into 2, the
vast majority of times, so would never have considered trying it.
Click to expand...
Solder does not run between pins or migrate under pins, if you use liquid
flux during the soldering process ...

Arfa
 
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