Topics

SMT chip replacement


Ted Rook
 

I wish to replace a defective SMT linear IC (28pin), something I haven't done before. I have experience with thru-hole analogue assembly. This is a hobby project (fixing a CD player) and not having the professional SMT rework tools I plan to use a solder pot to get the old chip off. Is this method likely to prove successful? Do chips float in solder, or do I need to improvise a "scoop" for the chip? Any recommendations for a cheap solder pot? I only have this single project in mind, it doesn't need a long life, I would probably sell it again after this is done.


Best
Ted NY USA


 

Since the chip is bad, you should just cut all the leads close to the chip package. Then just remove each lead one at a time using a fine tip soldering iron. You can then clean up the track pads with some solder wick. Now you are ready to install the new chip.

----- Original Message -----
From: rooknrol@... [TekScopes]
To: TekScopes@...
Sent: Saturday, May 16, 2015 11:29 AM
Subject: [TekScopes] SMT chip replacement



I wish to replace a defective SMT linear IC (28pin), something I haven't done before. I have experience with thru-hole analogue assembly. This is a hobby project (fixing a CD player) and not having the professional SMT rework tools I plan to use a solder pot to get the old chip off. Is this method likely to prove successful? Do chips float in solder, or do I need to improvise a "scoop" for the chip? Any recommendations for a cheap solder pot? I only have this single project in mind, it doesn't need a long life, I would probably sell it again after this is done.


Best
Ted NY USA


Gary Robert Bosworth
 

Is this a dual-in-line package? Can you state the package style from the
manufacturer's datasheet?

Gary
On May 16, 2015 8:29 AM, "rooknrol@... [TekScopes]" <
TekScopes@...> wrote:



I wish to replace a defective SMT linear IC (28pin), something I haven't
done before. I have experience with thru-hole analogue assembly. This is a
hobby project (fixing a CD player) and not having the professional SMT
rework tools I plan to use a solder pot to get the old chip off. Is this
method likely to prove successful? Do chips float in solder, or do I need
to improvise a "scoop" for the chip? Any recommendations for a cheap solder
pot? I only have this single project in mind, it doesn't need a long life,
I would probably sell it again after this is done.


Best
Ted NY USA

[Non-text portions of this message have been removed]



[Non-text portions of this message have been removed]


Ted Rook
 

Thank you Gary, 28-SSOPH-375 approx 0.75in x 0.375in Fairchild KA9258 discontinued

Thank you Tom, I wish it were that simple, unfortunately the "new IC" is actually a used one
on a second, scrap, board, and has to be removed intact.

Ted NY USA

On 16 May 2015 at 8:46, Gary Robert Bosworth @grbosworth wrote:


Is this a dual-in-line package? Can you state the package style from the
manufacturer's datasheet?

Gary
On May 16, 2015 8:29 AM, "rooknrol@... [TekScopes]" <
TekScopes@...> wrote:



I wish to replace a defective SMT linear IC (28pin), something I haven't
done before. I have experience with thru-hole analogue assembly. This is a
hobby project (fixing a CD player) and not having the professional SMT
rework tools I plan to use a solder pot to get the old chip off. Is this
method likely to prove successful? Do chips float in solder, or do I need
to improvise a "scoop" for the chip? Any recommendations for a cheap solder
pot? I only have this single project in mind, it doesn't need a long life,
I would probably sell it again after this is done.


Best
Ted NY USA





stefan_trethan
 

Hot air really works best in situations like that.
Normally I only recommend to buy high end hot air guns or stations,
with closed loop temperature control, but you might get away once with
a cheapie if you set it just right, hold the right distance, and cross
your fingers.

Practice on a scrap board from the junk, there is a fine line between
melting the solder and overheating the board. Pull only very lightly
on the chip.

It helps to apply some fresh solder, leaded if possible to lower the
melting point. Chipquick low temperature alloy would make it even
easier, might be worth it for someone who only needs to do this once
instead of learning how to do it properly.

ST


On Sat, May 16, 2015 at 5:29 PM, rooknrol@... [TekScopes]
<TekScopes@...> wrote:
I wish to replace a defective SMT linear IC (28pin), something I haven't done before. I have experience with thru-hole analogue assembly. This is a hobby project (fixing a CD player) and not having the professional SMT rework tools I plan to use a solder pot to get the old chip off. Is this method likely to prove successful? Do chips float in solder, or do I need to improvise a "scoop" for the chip? Any recommendations for a cheap solder pot? I only have this single project in mind, it doesn't need a long life, I would probably sell it again after this is done.


Best
Ted NY USA


David DiGiacomo
 

On Sat, May 16, 2015 at 9:29 AM, <rooknrol@...> wrote:

I wish to replace a defective SMT linear IC (28pin), something I haven't done before. I have experience with thru-hole analogue assembly. This is a hobby project (fixing a CD player) and not having the professional SMT rework tools I plan to use a solder pot to get the old chip off. Is this method likely to prove successful? Do chips float in solder, or do I need to improvise a "scoop" for the chip? Any recommendations for a cheap solder pot? I only have this single project in mind, it doesn't need a long life, I would probably sell it again after this is done.
No, a solder pot is not a good tool for this. You can buy a cheap hot
air tool, or if you don't want to spend that much, you can use
Chip-Quik, or piano wire.

I think every method is covered in this old Usenet thread:

https://groups.google.com/forum/#!topic/sci.electronics.repair/4tW3cvBpzQ8


Gary Robert Bosworth
 

This IC was also manufactured by Samsung.

Since you do not have a hot-air tool, I would use copper solderwick braid
and get as much of the solder off of all of the leads as possible. Then I
would rapidly slide the soldering iron along the leads on one side of the
IC while gently prying the IC off of the board with a small screwdriver
underneath the IC. You have to make sure you do not damage any of the
traces under the IC. You can usually lay the copper solderwick along the
side to help heat all of the leads simultaneously.

Gary
On May 16, 2015 9:08 AM, "'Ted Rook' rooknrol@... [TekScopes]" <
TekScopes@...> wrote:



Thank you Gary, 28-SSOPH-375 approx 0.75in x 0.375in Fairchild KA9258
discontinued

Thank you Tom, I wish it were that simple, unfortunately the "new IC" is
actually a used one
on a second, scrap, board, and has to be removed intact.

Ted NY USA

On 16 May 2015 at 8:46, Gary Robert Bosworth @grbosworth wrote:

Is this a dual-in-line package? Can you state the package style from the
manufacturer's datasheet?

Gary
On May 16, 2015 8:29 AM, "rooknrol@... [TekScopes]" <
TekScopes@...> wrote:



I wish to replace a defective SMT linear IC (28pin), something I haven't
done before. I have experience with thru-hole analogue assembly. This is
a
hobby project (fixing a CD player) and not having the professional SMT
rework tools I plan to use a solder pot to get the old chip off. Is this
method likely to prove successful? Do chips float in solder, or do I need
to improvise a "scoop" for the chip? Any recommendations for a cheap
solder
pot? I only have this single project in mind, it doesn't need a long
life,
I would probably sell it again after this is done.


Best
Ted NY USA

[Non-text portions of this message have been removed]


[Non-text portions of this message have been removed]



[Non-text portions of this message have been removed]


Bert Haskins
 

On 5/16/2015 12:08 PM, 'Ted Rook' rooknrol@... [TekScopes] wrote:

Thank you Gary, 28-SSOPH-375 approx 0.75in x 0.375in Fairchild KA9258
discontinued

Thank you Tom, I wish it were that simple, unfortunately the "new IC"
is actually a used one
on a second, scrap, board, and has to be removed intact.

Ted NY USA
Just a suggestion:
Pick up one of those cheap heat guns from Harbor Freight and try melting
a few chips off of the scrap board while working your way to the one you
want to salvage.
You can try a tin foil deflector on the end of the gun to focus the hot
air stream.
I actually got away with doing this for a few years before buying a hot
air rework station.
I practiced on scrap boards first.
BE CAREFUL!!! hot air that is hot enough to melt solder can do a real
nasty number on flesh and/or eyes.


On 16 May 2015 at 8:46, Gary Robert Bosworth @grbosworth wrote:

Is this a dual-in-line package? Can you state the package style from the
manufacturer's datasheet?

Gary
On May 16, 2015 8:29 AM, "rooknrol@... [TekScopes]" <
TekScopes@...> wrote:



I wish to replace a defective SMT linear IC (28pin), something I haven't
done before. I have experience with thru-hole analogue assembly.
This is a
hobby project (fixing a CD player) and not having the professional SMT
rework tools I plan to use a solder pot to get the old chip off. Is this
method likely to prove successful? Do chips float in solder, or do I
need
to improvise a "scoop" for the chip? Any recommendations for a cheap
solder
pot? I only have this single project in mind, it doesn't need a long
life,
I would probably sell it again after this is done.


Best
Ted NY USA

[Non-text portions of this message have been removed]


[Non-text portions of this message have been removed]



[Non-text portions of this message have been removed]


stefan_trethan
 

Removing as much solder as possible usually does not help unless you
can get it all, which you can't with braid. Since the solder acts as a
heat bridge between the iron and joint, and thermal mass to store
heat, removing any is counter productive.

I do not favour this method, especially on such large ICs, but have
used it often enough to know that it works much better if I add a lot
of solder to brigde all the pins.

ST

On Sat, May 16, 2015 at 6:25 PM, Gary Robert Bosworth @grbosworth

Since you do not have a hot-air tool, I would use copper solderwick braid
and get as much of the solder off of all of the leads as possible. Then I
would rapidly slide the soldering iron along the leads on one side of the
IC while gently prying the IC off of the board with a small screwdriver
underneath the IC. You have to make sure you do not damage any of the
traces under the IC. You can usually lay the copper solderwick along the
side to help heat all of the leads simultaneously.


Mirco Boschi
 

I agree with stefan;
Just make two huge solder blobs, one on each side of ic.
Use a flat head screwdriver to lift up ic a little from one side, then heat
the other side and lift again. Repeat until the ic is actually lifted from
the board and is keep firm only by these solder blobs; then you can remove
the solder as you like.
Be gentle, and try it before on another board.
I've removed and resolder a lot of so8 ic with this technique; done that
even on my tds420 to fix traces under that ic.
Il 16/Mag/2015 18:43, "Stefan Trethan stefan_trethan@... [TekScopes]" <
TekScopes@...> ha scritto:



Removing as much solder as possible usually does not help unless you
can get it all, which you can't with braid. Since the solder acts as a
heat bridge between the iron and joint, and thermal mass to store
heat, removing any is counter productive.

I do not favour this method, especially on such large ICs, but have
used it often enough to know that it works much better if I add a lot
of solder to brigde all the pins.

ST

On Sat, May 16, 2015 at 6:25 PM, Gary Robert Bosworth @grbosworth

Since you do not have a hot-air tool, I would use copper solderwick braid
and get as much of the solder off of all of the leads as possible. Then I
would rapidly slide the soldering iron along the leads on one side of the
IC while gently prying the IC off of the board with a small screwdriver
underneath the IC. You have to make sure you do not damage any of the
traces under the IC. You can usually lay the copper solderwick along the
side to help heat all of the leads simultaneously.


Ted Rook
 

Thank you gentlemen. I am concerned about heat damage to the IC, my iron is a Curie point
thermostat type that has a minimum temperature rating of 600F (the tip is the
thermo-element), whereas the IC has a rating of about 450F for 10 seconds. Same deal with
hot-air guns, isn't the chip just going to fry inside? The attraction of a solder pot is the
controlled temperature, with reduced risk of damaging the "unobtainium" chip.

Ted NY USA

On 16 May 2015 at 18:43, Stefan Trethan stefan_trethan@... [TekSRe: [TekScopes]
SMT chip replacement wrote:


Removing as much solder as possible usually does not help unless you
can get it all, which you can't with braid. Since the solder acts as a
heat bridge between the iron and joint, and thermal mass to store
heat, removing any is counter productive.

I do not favour this method, especially on such large ICs, but have
used it often enough to know that it works much better if I add a lot
of solder to brigde all the pins.

ST

On Sat, May 16, 2015 at 6:25 PM, Gary Robert Bosworth @grbosworth

Since you do not have a hot-air tool, I would use copper solderwick braid
and get as much of the solder off of all of the leads as possible. Then I
would rapidly slide the soldering iron along the leads on one side of the
IC while gently prying the IC off of the board with a small screwdriver
underneath the IC. You have to make sure you do not damage any of the
traces under the IC. You can usually lay the copper solderwick along the
side to help heat all of the leads simultaneously.


David DiGiacomo
 

On Sat, May 16, 2015 at 10:51 AM, Ted Rook <rooknrol@...> wrote:

Thank you gentlemen. I am concerned about heat damage to the IC, my iron is a Curie point
thermostat type that has a minimum temperature rating of 600F (the tip is the
thermo-element), whereas the IC has a rating of about 450F for 10 seconds. Same deal with
hot-air guns, isn't the chip just going to fry inside? The attraction of a solder pot is the
controlled temperature, with reduced risk of damaging the "unobtainium" chip.


No. A solder pot won't work, and you won't fry the chip if you work
reasonably quickly.


Gary Robert Bosworth
 

When they solder the board at the factory, the entire IC cooks very hot.
The leads inside the IC are micro-welded. Any soldering that you do with a
25W soldering iron is child's play to the IC.

Gary
On May 16, 2015 10:03 AM, "David DiGiacomo telists@... [TekScopes]"
<TekScopes@...> wrote:



On Sat, May 16, 2015 at 10:51 AM, Ted Rook <rooknrol@...> wrote:

Thank you gentlemen. I am concerned about heat damage to the IC, my iron
is a Curie point
thermostat type that has a minimum temperature rating of 600F (the tip
is the
thermo-element), whereas the IC has a rating of about 450F for 10
seconds. Same deal with
hot-air guns, isn't the chip just going to fry inside? The attraction of
a solder pot is the
controlled temperature, with reduced risk of damaging the "unobtainium"
chip.

No. A solder pot won't work, and you won't fry the chip if you work
reasonably quickly.


[Non-text portions of this message have been removed]


ykochcal
 

I would split the job in to two parts.


Save the good board:

To take the bad chip off I would cut the pins and use a soldering iron and
solder wick to clean/wipe the old pins off

Save the good chip three possible ways:

You don't say what type of solder was used. If it's the new high melting
temp lead free stuff I would "resolder" the pins and add a bunch of 60-40
first to lower the melting temp. of the solder.

If you are not removing a motor control IC with a big heat sink, Once it's
flooded and all pins are connected on a small chip it is possible to keep
one side melted on all the pins and pry up one side and then the other.

From the scrap board, If I had a heat gun I would heat the back side of the
board and gently pull the chip off with tweezers, because the heat is
uncontrolled it might be best to do it outside as the board will cook if it
is too hot, but that's ok as it should melt all the pins at the about the
same time and let you get the chip off. Preheating first and then a quick
focused heat at the chip. Might remove another chip first on the same board
and see if they have pre-glued the chip when it was placed, in which case a
bit more pull will be needed.

If I only had a solder pot I would consider cutting the scrap board down to
about one chip and dunking it board first, chip up holding the chip with
tweezers with ends that hook under the chip.


Luckily there is plenty of stuff to practice on, on CL

John



I wish to replace a defective SMT linear IC (28pin), something I haven't
done before. I have experience with thru-hole analogue assembly. This is a
hobby project (fixing a CD player) and not having the professional SMT
rework tools I plan to use a solder pot to get the old chip off. Is this
method likely to prove successful? Do chips float in solder, or do I need to
improvise a "scoop" for the chip? Any recommendations for a cheap solder
pot? I only have this single project in mind, it doesn't need a long life, I
would probably sell it again after this is done.


Best
Ted NY USA


stefan_trethan
 

There is no easy way to apply a solder pot to SMDs, unless the IC is
very exposed.

If you do not want hot air for whatever reason the next best option
that is borderline OK with the manufacturer is to use a form fitting
soldering iron tip.
<http://store.curiousinventor.com/media/images/how_to_solder/desolder_soic.jpg?1248413798>
You may be able to make one from a small piece of copper sheet bent
into a U shape and attached to your iron.

Why is this on Tekscopes again and not Electronics_101?
I'll make a point from now on to only refer such questions there,
often I don't notice it's in the wrong forum before replying,
repeatedly. Tekscopes should not be a catch-all.

ST


stefan_trethan
 

Just in case you don't already know this:
Cutting the pins is not allowed in some high end applications because
there is no good way to do that without stressing the pads, possibly
leading to delamination.

I don't say that it doesn't work, it probably works just fine most of
the time and may well be appropriate here, but that's what they say,
for your consideration.

ST

On Sat, May 16, 2015 at 8:05 PM, 'John Snyder' Kochcal@...
[TekScopes] <TekScopes@...> wrote:
I would split the job in to two parts.


Save the good board:

To take the bad chip off I would cut the pins and use a soldering iron and
solder wick to clean/wipe the old pins off


Joseph Strickland
 

That is what I would recommend too. As was said, you already know the part is bad, so do not hesitate to destroy it in the removal process. A fine tip soldering iron is worth the investment if you do not already have one. Get a unit that has an adjustable temperature control. Use just enough heat to do the job without overdoing it. A wooden toothpick can be a real help in moving pieces away without conducting so much heat from the item that the solder solidifies. A Q-tip can sometimes be a help in removing the tiny pieces of the leads while the solder is molten.

Joe


chipbee40
 

Use the right tool for the job..... seriously, hot air desolder guns are very cheap and they are very useful, heat shrink, plastic welding, thermal fault finding, car repairs etc. You WILL find you need one again and I'm not a fan of this destroy the chip idea.


---In TekScopes@..., <rooknrol@...> wrote :

I wish to replace a defective SMT linear IC (28pin), something I haven't done before. I have experience with thru-hole analogue assembly. This is a hobby project (fixing a CD player) and not having the professional SMT rework tools I plan to use a solder pot to get the old chip off. Is this method likely to prove successful? Do chips float in solder, or do I need to improvise a "scoop" for the chip? Any recommendations for a cheap solder pot? I only have this single project in mind, it doesn't need a long life, I would probably sell it again after this is done.


Best
Ted NY USA


boid_twitty
 

If you look at some of the older security tags used by vendors to reduce shoplifting - in a CD or DVD case, for instance, you'll find inside the adhesive-backed package 3 lengths of crystaline-nickel steel strip.

Two of these are 1thou thickness, the third is 2thou.

The 2thou strip will fit into an xacto knife blade holder.

By slipping the strip under the body of an SMD device, you can reheat pins one at a time and slip the shim into the interface, without stressing the pin or the board. No solder will stick to the shim.

Some of the security device 2thou strips are cut at a bias, which is marginally easier to work into the heated joint, from underneath the chip, outwards.

I use this method in any instance where the part must be saved for examination or re-use, or if the board is irreplaceable.

Once the chip is removed, residual solder can be reflowed evenly to provide a clean working surface for the new part.

Try the technique on junk or scrap, first. A magnified, well-luminated visual aid is recommended for any manual smd rework.

A clean, fine tip soldering iron, with 60/40 solder is recommended.

RL


---In TekScopes@..., <rooknrol@...> wrote :

Thank you gentlemen. I am concerned about heat damage to the IC, my iron is a Curie point
thermostat type that has a minimum temperature rating of 600F


Brian Clarke <brianclarke01@...>
 

Hello Joe,
Perhaps you were asleep this week, when another list member requested
that in replying, we keep enough of the previous message that later
readers can get your message.

As it is, your message refers to nothing and has about the same value
to later readers.

73 de Brian, VK2GCE.

On 16 May 2015 12:14:58 -0700, Joe blurted:
 

That is what I would recommend too. <snip>

Joe



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