Surface mount chip problem

[jamma-plusser]

I have a board with a large QFP surface mount IC - something had been
smashed into a few pins of this IC, so bending them and causing them
to short against each other. Managed to straighten them all, except
for one which broke right against the main body of the chip.

Argh!

I can get just about get a connection to the infinitessimally small
pin stub using some very fine wire, but the connection is erratic to
say the least.

Have tried gently carving back some of the plastic around where the
pin stub enters the body of the chip to expose more to solder onto,
but no luck there really.

The pin spacing is pretty tight, so making things even more awkward.

Any tips please on how to salvage this?

Thanks

 

[jamma-plusser]

On Wed, 19 Nov 2008 10:31:57 GMT, jamma-plusser@hotmail.com
(jamma-plusser) wrote:

I should add that I've got the right equipment for SMT reworking and
have successfully removed and replaced quite a number of SMT chips,
but this is a rather new problem.

 

[N_Cook]

jamma-plusser <jamma-plusser@hotmail.com> wrote in message
news:4923eb02.517312234@news.zen.co.uk...

I have a board with a large QFP surface mount IC - something had been
smashed into a few pins of this IC, so bending them and causing them
to short against each other. Managed to straighten them all, except
for one which broke right against the main body of the chip.

Argh!

I can get just about get a connection to the infinitessimally small
pin stub using some very fine wire, but the connection is erratic to
say the least.

Have tried gently carving back some of the plastic around where the
pin stub enters the body of the chip to expose more to solder onto,
but no luck there really.

The pin spacing is pretty tight, so making things even more awkward.

Any tips please on how to salvage this?

Thanks

Tiniest of blobs of conductive epoxy on the cut end of some 40 gauge or less
copper wire , then other end soldered to the trace, while heatsinking the
middle?
How to get a tiny blob ? warm up the epoxy slightly and heat up the wire
prior to epoxying ? don't know have not tried it at any time


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

 

[jamma-plusser]

On Wed, 19 Nov 2008 10:58:21 -0000, "N_Cook" <diverse@tcp.co.uk>
wrote:

Tiniest of blobs of conductive epoxy on the cut end of some 40 gauge or less
copper wire , then other end soldered to the trace, while heatsinking the
middle?
How to get a tiny blob ? warm up the epoxy slightly and heat up the wire
prior to epoxying ? don't know have not tried it at any time

Thanks, I really like that idea. Only problem is that conductive epoxy
is very expensive (due to the silver content) so is there a cheaper
and equally effective alternative?

 

[Dave]

"jamma-plusser" <jamma-plusser@hotmail.com> wrote in message
news:4923fe74.522359468@news.zen.co.uk...

On Wed, 19 Nov 2008 10:58:21 -0000, "N_Cook" <diverse@tcp.co.uk
wrote:



Tiniest of blobs of conductive epoxy on the cut end of some 40 gauge or
less
copper wire , then other end soldered to the trace, while heatsinking the
middle?
How to get a tiny blob ? warm up the epoxy slightly and heat up the wire
prior to epoxying ? don't know have not tried it at any time

Thanks, I really like that idea. Only problem is that conductive epoxy
is very expensive (due to the silver content) so is there a cheaper
and equally effective alternative?

Think I would try to blob a small amount of solder onto the tiny lead
remains, and then solder a piece of #32 wire (pretinned on both ends) to the
blob and the trace, with a heat-sink of course. Would try to use a
light-duty soldering iron with just enough heat to melt the solder. The
Weller Cold-Heat Pro cordless soldering iron would come in handy here...
(my experience. YMMV)

Good luck.

Dave

 

[PeterD]

On Wed, 19 Nov 2008 10:31:57 GMT, jamma-plusser@hotmail.com
(jamma-plusser) wrote:

I have a board with a large QFP surface mount IC - something had been
smashed into a few pins of this IC, so bending them and causing them
to short against each other. Managed to straighten them all, except
for one which broke right against the main body of the chip.

Argh!

I can get just about get a connection to the infinitessimally small
pin stub using some very fine wire, but the connection is erratic to
say the least.

Have tried gently carving back some of the plastic around where the
pin stub enters the body of the chip to expose more to solder onto,
but no luck there really.

The pin spacing is pretty tight, so making things even more awkward.

Any tips please on how to salvage this?

Thanks

Have any friends who are *good* dentists? If so see if one of them can
use their fine tools to eat away a bit fo the plastic. They will need
to understand what they are doing, and how much you want to remove but
I'm sure it can be done.

 

[Arfa Daily]

"PeterD" <peter2@hipson.net> wrote in message
news:ed88i45d114i80lssihqe5pdq8t2s87sqn@4ax.com...

On Wed, 19 Nov 2008 10:31:57 GMT, jamma-plusser@hotmail.com
(jamma-plusser) wrote:

I have a board with a large QFP surface mount IC - something had been
smashed into a few pins of this IC, so bending them and causing them
to short against each other. Managed to straighten them all, except
for one which broke right against the main body of the chip.

Argh!

I can get just about get a connection to the infinitessimally small
pin stub using some very fine wire, but the connection is erratic to
say the least.

Have tried gently carving back some of the plastic around where the
pin stub enters the body of the chip to expose more to solder onto,
but no luck there really.

The pin spacing is pretty tight, so making things even more awkward.

Any tips please on how to salvage this?

Thanks


Have any friends who are *good* dentists? If so see if one of them can
use their fine tools to eat away a bit fo the plastic. They will need
to understand what they are doing, and how much you want to remove but
I'm sure it can be done.

Are you able to check what the damaged pin does ? If you are incredibly
lucky, it might just be common with another pin or just have an internal
resistor or diode to another pin. Sod's Law says that you won't be that
lucky, but you never know - the gods of electronic accidents might just be
smiling in your direction today. They certainly weren't looking my way when
I had a flash-bang encounter with a Pioneer amp that I had just finished
working on ... :-(

Arfa

 

[msg]

jamma-plusser wrote:

I have a board with a large QFP surface mount IC - something had been
smashed into a few pins of this IC, so bending them and causing them
to short against each other. Managed to straighten them all, except
for one which broke right against the main body of the chip.

Argh!

I can get just about get a connection to the infinitessimally small
pin stub using some very fine wire, but the connection is erratic to
say the least.

Have tried gently carving back some of the plastic around where the
pin stub enters the body of the chip to expose more to solder onto,
but no luck there really.

The pin spacing is pretty tight, so making things even more awkward.

Any tips please on how to salvage this?

I would suspect that most folks working with SMT have experienced this
problem. My solution was to use a tiny sewing needle pressed against the
remaining pin metal on the device and secured (under pressure) with
non-conductive epoxy. You can even see a magnified example of this
approach in photos of my mods to the Zipit Wireless Messenger (takes
a little site drilling to get to the appropriate photo, but it is
there) at: http://www.cybertheque.org/homebrew/zipit

Michael

 

[bz]

jamma-plusser@hotmail.com (jamma-plusser) wrote in
news:4923fe74.522359468@news.zen.co.uk:

On Wed, 19 Nov 2008 10:58:21 -0000, "N_Cook" <diverse@tcp.co.uk
wrote:



Tiniest of blobs of conductive epoxy on the cut end of some 40 gauge or
less copper wire , then other end soldered to the trace, while
heatsinking the middle?
How to get a tiny blob ? warm up the epoxy slightly and heat up the wire
prior to epoxying ? don't know have not tried it at any time

Thanks, I really like that idea. Only problem is that conductive epoxy
is very expensive (due to the silver content) so is there a cheaper
and equally effective alternative?

You could spot weld a small wire to the end. IC makers spot weld gold wires
to the IC's all the time.

Of course the equipment to do that might be a bit more expensive than
conductive epoxy

You could try some silver bearing conductive ink from radioshack.






--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

bz+spr@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap

 

[N_Cook]

jamma-plusser <jamma-plusser@hotmail.com> wrote in message
news:4923fe74.522359468@news.zen.co.uk...

On Wed, 19 Nov 2008 10:58:21 -0000, "N_Cook" <diverse@tcp.co.uk
wrote:



Tiniest of blobs of conductive epoxy on the cut end of some 40 gauge or
less
copper wire , then other end soldered to the trace, while heatsinking the
middle?
How to get a tiny blob ? warm up the epoxy slightly and heat up the wire
prior to epoxying ? don't know have not tried it at any time

Thanks, I really like that idea. Only problem is that conductive epoxy
is very expensive (due to the silver content) so is there a cheaper
and equally effective alternative?

Has anyone ever tried grinding gold of 70s TTL board edge connectors and
mixing the sieved dust with standard epoxy? I know graphite does not work.
Mercury and epoxy? would mercury amalgam stick to things ?


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

 

[jamma-plusser]

On Wed, 19 Nov 2008 13:16:48 -0600, msg <msg@_cybertheque.org_> wrote:

Thanks all. I'm afraid that the leg in question carries a needed
signal so no chance of doing anything but repairing it.

I'm going to attack the chip with a dremel tomorrow and see if I can
very carefully expose enough of the leg stub to solder to. If I fail
then nothing lost as the chip is no good as it is anyhow.

 

[bz]

"N_Cook" <diverse@tcp.co.uk> wrote in
news:gg22od$2f3$1@news.motzarella.org:

jamma-plusser <jamma-plusser@hotmail.com> wrote in message
news:4923fe74.522359468@news.zen.co.uk...
On Wed, 19 Nov 2008 10:58:21 -0000, "N_Cook" <diverse@tcp.co.uk
wrote:



Tiniest of blobs of conductive epoxy on the cut end of some 40 gauge
or
less
copper wire , then other end soldered to the trace, while heatsinking
the middle?
How to get a tiny blob ? warm up the epoxy slightly and heat up the
wire prior to epoxying ? don't know have not tried it at any time

Thanks, I really like that idea. Only problem is that conductive epoxy
is very expensive (due to the silver content) so is there a cheaper
and equally effective alternative?


Has anyone ever tried grinding gold of 70s TTL board edge connectors and
mixing the sieved dust with standard epoxy? I know graphite does not
work. Mercury and epoxy? would mercury amalgam stick to things ?

You do NOT want mercury anywhere near electronic equipment.

Back in the late 70's I saw a mini-computer that had mercury (a manometer
was laid down on top of it) all over the circuit boards.

We had to scrap it.

Attempting to replace a part would have been fatal.
Mercury vapor is highly toxic and would have been released in large
quantities by any heating such as soldering.

Mercury is bad enough at room temperature! If you work in a room where
mercury has been spilled and not properly cleaned up, you can accumulate
enought mercury in your body from breathing the mercury vapor to make you
very sick or dead.

Not to mention the fact that many parts get rather warm during normal
operation.

Attempting to use that computer would have been deadly.



--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

bz+spr@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap

 

[bz]

jamma-plusser@hotmail.com (jamma-plusser) wrote in news:49248d7c.559184421
@news.zen.co.uk:

On Wed, 19 Nov 2008 13:16:48 -0600, msg <msg@_cybertheque.org_> wrote:

Thanks all. I'm afraid that the leg in question carries a needed
signal so no chance of doing anything but repairing it.

I'm going to attack the chip with a dremel tomorrow and see if I can
very carefully expose enough of the leg stub to solder to. If I fail
then nothing lost as the chip is no good as it is anyhow.

I DID fix a surface mount chip that I broke a leg off of by using the
conductive paint I mentioned earlier.
After it cures it can be soldered to.

I replaced the chip later even though it was still working, not trusting it
to be reliable.

Good luck to you.





--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

bz+spr@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap

 

[F Murtz]

jamma-plusser wrote:

I have a board with a large QFP surface mount IC - something had been
smashed into a few pins of this IC, so bending them and causing them
to short against each other. Managed to straighten them all, except
for one which broke right against the main body of the chip.

Argh!

I can get just about get a connection to the infinitessimally small
pin stub using some very fine wire, but the connection is erratic to
say the least.

Have tried gently carving back some of the plastic around where the
pin stub enters the body of the chip to expose more to solder onto,
but no luck there really.

The pin spacing is pretty tight, so making things even more awkward.

Any tips please on how to salvage this?

Thanks

jaycar has some silver conductive paint in very small bottle

 

[F Murtz]

jamma-plusser wrote:

I have a board with a large QFP surface mount IC - something had been
smashed into a few pins of this IC, so bending them and causing them
to short against each other. Managed to straighten them all, except
for one which broke right against the main body of the chip.

Argh!

I can get just about get a connection to the infinitessimally small
pin stub using some very fine wire, but the connection is erratic to
say the least.

Have tried gently carving back some of the plastic around where the
pin stub enters the body of the chip to expose more to solder onto,
but no luck there really.

The pin spacing is pretty tight, so making things even more awkward.

Any tips please on how to salvage this?

Thanks

jaycar has some silver conductive paint in very small bottle

oops jaycar is australian maybee radio shack might have same thing

 

[N_Cook]

F Murtz <haggisz@hotmail.com> wrote in message
news:4926a2ae$1@dnews.tpgi.com.au...

jamma-plusser wrote:
I have a board with a large QFP surface mount IC - something had been
smashed into a few pins of this IC, so bending them and causing them
to short against each other. Managed to straighten them all, except
for one which broke right against the main body of the chip.

Argh!

I can get just about get a connection to the infinitessimally small
pin stub using some very fine wire, but the connection is erratic to
say the least.

Have tried gently carving back some of the plastic around where the
pin stub enters the body of the chip to expose more to solder onto,
but no luck there really.

The pin spacing is pretty tight, so making things even more awkward.

Any tips please on how to salvage this?

Thanks

jaycar has some silver conductive paint in very small bottle
oops jaycar is australian maybee radio shack might have same thing

See new thread
title
TIP: Poor man's conductive epoxy


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

 

[Michael A. Terrell]

F Murtz wrote:

jamma-plusser wrote:
I have a board with a large QFP surface mount IC - something had been
smashed into a few pins of this IC, so bending them and causing them
to short against each other. Managed to straighten them all, except
for one which broke right against the main body of the chip.

Argh!

I can get just about get a connection to the infinitessimally small
pin stub using some very fine wire, but the connection is erratic to
say the least.

Have tried gently carving back some of the plastic around where the
pin stub enters the body of the chip to expose more to solder onto,
but no luck there really.

The pin spacing is pretty tight, so making things even more awkward.

Any tips please on how to salvage this?

Thanks

jaycar has some silver conductive paint in very small bottle
oops jaycar is australian maybee radio shack might have same thing.

General Cement makes both 'Copper Print" & 'Silver Print' for the US
market.


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