"DaveC" wrote in message
al.net...
I need to desolder (with no damage to the components) some SMD ROM chips.
Is
there a good tutorial somewhere on the 'net about how to go about this?

The absolute best and cheapest way (in my opinion) to desolder SMD chips is
to use Chip-Quik. The "solder" they use has a VERY low melting point. Even
after 30 seconds or so, it's still in a molten state which allows you to
just pick up the chip with your hands.

More info he

http://www.chipquikinc.com/

-Tim


BTW, I found a great tutorial on technique and equipment (lo-cost, some of
it
make-yourself) on the 'net about soldering SMDs:

http://www.wku.edu/~barceed/SolderPage/index.htm

Thanks,
--
DaveC

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Please reply in the news group

DaveC wrote:
I need to desolder (with no damage to the components) some SMD ROM
chips. Is there a good tutorial somewhere on the 'net about how to go
about this?

Some fairly in-depth stuff at http://www.circuittechctr.com/guides/8-0.shtml
--
Correct address is cpemma at mexbro dot co dot uk

On Sun, 4 Jan 2004 2:30:51 -0800, DaveC wrote:

I need to desolder (with no damage to the components) some SMD ROM chips. Is
there a good tutorial somewhere on the 'net about how to go about this?

BTW, I found a great tutorial on technique and equipment (lo-cost, some of it
make-yourself) on the 'net about soldering SMDs:

http://www.wku.edu/~barceed/SolderPage/index.htm

Thanks,

The following instructions will work for removing smd chips.

1.) Take an oven tray and cover with aluminum foil, place board on foil.
2.) Set oven to 300-350 degrees F. depends on solder type used.
3.) Place tray in oven for approx. 10-15 minutes
4.) Open oven door, grab a pair of tweezers and try lifting component. If
component does not lift close oven door and try again every 2-3 minutes until
successful.


That's it ...cheap too!



Remove "HeadFromButt", before replying by email.

In article et,
says...
I need to desolder (with no damage to the components) some SMD ROM chips. Is
there a good tutorial somewhere on the 'net about how to go about this?

BTW, I found a great tutorial on technique and equipment (lo-cost, some of it
make-yourself) on the 'net about soldering SMDs:

http://www.wku.edu/~barceed/SolderPage/index.htm

Thanks,


The author of that page - Eduardo Barcellos - should consider giving
proper credit to the original source of his idea
(www.usbmicro.com/odn/index.html). He presents the hot-air idea as if it
were his own.

It is an unfortunate trend that students steal ideas from the internet
and boldly present the information without due credit. A whole
generation of people without morals would be the downfall of society.

DaveC wrote:
I need to desolder (with no damage to the components) some SMD ROM chips. Is
there a good tutorial somewhere on the 'net about how to go about this?

Given your requirement is to avoid damage to the SMD components, I
assume you need to re-use them?

As Tim H. posted, Chipquik is ideal for SMD removal by hand as it allows
you to reflow solder at temperatures low enough to avoid heat damage to
the board or component - the tricky part is removing and cleaning the
component without bending any pins. Most of the SMD rework information
available assumes devices will be discarded after removal.

I use the stainless steel strips orthodontists wrap around teeth. Coat
the pins with copious amounts of paste flux and reflow the solder with
Chipquik. The lowest temperature setting on my soldering station is
~325F, hotter than required but not hot enough to cause damage. Be
generous with the Chipquik as this will make it easier to maintain
molten material on all pins simultaneously. When the device is ready to
lift, it will be floating in a puddle of flux and solder, now you can
slide the stainless strip between the board and device to pick it up.
Warming the board from the underside with a hair dryer while working
facilitates the process. Where possible, slide the stainless strip under
the device body first, then keep it parrallel to the row of pins as you
move it under them to avoid bending. QFP devices are more difficult as
there's no 'pinless' side from which to access the underside of the
body, but trimming the stainless strip to a tapered point and starting
at one corner works reasonably well - the key is to make sure the device
is floating and avoid any sideways pressure on the pins. The stainless
strip method has the advantage of leaving the site much cleaner than
simply lifting the device with tweezers, so I use it when removing dead
devices too.

The freshly removed device will be somewhat protected by a coating of
Chipquik bridging all the pins, but still must be handled carefully.
Next you need a clamp capable of holding the device body while leaving
the pins accessible - mine came from the orthodontist. Hold the clamp at
an angle to the edge of the workbench, reflow the Chipquik with the iron
and tap the clamp against the edge of the bench to flick the pins clean.
Results are best if you can flick all the material off a row of pins in
one shot, so allow time for complete reflow before tapping the clamp.
The Chipquik can be collected and re-used several times.

HTH

Sunny


BTW, I found a great tutorial on technique and equipment (lo-cost, some of it
make-yourself) on the 'net about soldering SMDs:

http://www.wku.edu/~barceed/SolderPage/index.htm

Thanks,

DaveC wrote:

On Sun, 4 Jan 2004 10:14:44 -0800, Sunny wrote
(in message ):


As Tim H. posted, Chipquik is ideal for SMD removal by hand as it allows
you to reflow solder at temperatures low enough to avoid heat damage to
the board or component - the tricky part is removing and cleaning the
component without bending any pins. Most of the SMD rework information
available assumes devices will be discarded after removal.


Is your brother-in-law a dentist? Where do you get the stainless steel
strips? Is there a supplier you use? Or do you just ask your personal
dentist?

How do you know my brother-in-law's profession? :-)

I did get some used picks from him, but there's a surplus electronics
store near me that stocks a variety of small surgical and dental tools,
including the stainless strips. I have also used automotive feeler
gauges, but it gets expensive buying full sets of those just to use the
thinnest ones.

Great ideas. Never having done this before, you have alerted me to some
issues I need to be cautious about.

If at all possible, practice on junk hardware first. Each package type
and location presents it's own challenges, and the first attempts often
result in bent pins until you get a feel for the technique. Even
slightly bent pins are almost impossible to straighten and greatly
reduce the chances of a successful re-installation. If you must
re-install a device with a small number of bent pins, IMHO it's best to
leave them alone and resolder all the good pins, then push the point of
a needle between soldered and bent pins to re-align them with their pads.

DarkMatter wrote:

Considering that 63/37 solder does not melt until it reaches nearly
500 degrees F, I'd say that you just described how to **** up a PCB.

It is not as bad as all that.
http://www.rfcafe.com/references/electrical/solder.htm

But I am still reluctant to cook boards or components that long.

--
John Popelish

In sci.electronics.repair DarkMatter wrote:


On Sun, 04 Jan 2004 15:31:10 GMT, maxfoo
Gave us:

The following instructions will work for removing smd chips.

1.) Take an oven tray and cover with aluminum foil, place board on foil.
2.) Set oven to 300-350 degrees F. depends on solder type used.
3.) Place tray in oven for approx. 10-15 minutes
4.) Open oven door, grab a pair of tweezers and try lifting component. If
component does not lift close oven door and try again every 2-3 minutes until
successful.


That's it ...cheap too!


Considering that 63/37 solder does not melt until it reaches nearly
500 degrees F, I'd say that you just described how to **** up a PCB.

http://www.kester.com/alloy_temp_chart.html

HTH

Given your requirement is to avoid damage to the SMD components, I
assume you need to re-use them?

As Tim H. posted, Chipquik is ideal for SMD removal by hand as it allows
you to reflow solder at temperatures low enough to avoid heat damage to
the board or component - the tricky part is removing and cleaning the
component without bending any pins. Most of the SMD rework information
available assumes devices will be discarded after removal.



I had to replace an FPGA on a development board once. I used a $20 heat gun
clamped in a partially-completed CNC machine I was building. It only takes a
few seconds for the solder to melt when the heat gun is on its lowest
setting. I also used the heat gun to solder on the new FPGA, then touched up
a few pins with a soldering iron. Ideally there would be a heat shield to
prevent heating up other components, but in this case it wasn't a problem.
The pins heat up so much faster than the rest of the chip; all you need to
do is keep the internal temperature of the device less than 450 degrees F.
Here's a photo of the removed chip:
http://www.macetech.com/desolder-close.jpg

DaveC wrote:
On Sun, 4 Jan 2004 12:22:52 -0800, Sunny wrote
(in message ):


If at all possible, practice on junk hardware first. Each package type
and location presents it's own challenges, and the first attempts often
result in bent pins until you get a feel for the technique.


I need to preserve one set of ROMs from a PCB. This PCB can be trashed; I
have no need for it afterward. The ROMs on another board can be trashed
(they're defective), but the PCB needs to be preserved.

In that case my approach would be to remove the defective ROMS first.

With Chipquik and a temperature controlled iron, preferably at 300F but
not more than 350F, there's virtually no possibility of damaging the
PCB, so removing and cleaning the defective parts can be treated as a
practice session prior to working on the parts you need to preserve and
re-install.

If you plan to use the continuous flow method of reinstallation,
practicing by installing one or two defective parts on the trash PCB
first would also be a good plan - the temperature and solder volume need
to be just right to avoid dry joints or bridges between pins, and
bridges can be quite difficult to wick off without increasing
temperature beyond the ideal. I wasn't aware cupped SMD flow tips were
available for my station until I followed the links posted earlier, but
I plan to order one tomorrow :-)

I have been posting to this thread under the assumption you are dealing
with fine pitch (0.5mm) gull wing lead devices, SSOP or QFP/LQFP. I have
no experience with using the techniques I've described on J-lead
devices, and after looking at a couple I expect it might be difficult to
flow Chipquik under the device to where much of the solder is.

Another post suggested cutting the leads to remove defective devices,
however that's not an approach I'd use on fine pitch leads as there is a
risk of damaging PCB pads due to mechanical stress.

One job I need to be careful with the chips; the other, with the PCB.

Feeler gauges... hmm, I have several old sets of those lying around.

The dental bands I use are .002" thick

DaveC wrote:
(snip)
Feeler gauges... hmm, I have several old sets of those lying around.

Rolls of stainless steel shim stock are not very expensive. You can
cut the thinner sizes with sharp scissors.

http://www.precisionbrand.com/produc...sp?p_catid=222

--
John Popelish

Here's a pic of the ROMs I want to desolder (the big chips in the photo).
Identical set on identical board I want to replace...

http://home.covad.net/~peninsula/ROMpic.jpg

How do these rate on the scale of difficulty? (What are these packages?)


Those would be pretty easy to remove with the hot air gun method. I've
removed hundreds of similar-sized chips from laptop motherboards. However
the tough part is the proximity of those two plastic sockets; on the PCB you
want to keep, you'll need to shield those somehow. Perhaps tape a couple
layers of aluminum foil over them, and only heat the chips until you see the
solder wet up, then quickly turn off the heat gun and flip the chips over
with a dental pick. You would probably want to practice with the board you
don't want to keep, and see if you can keep the plastic sockets from
melting. If you can't, then maybe you should use a Chipquik or hot air
pencil method.

For chips that size, and with only two side with pins, I've removed many by
simply dolloping solder on and continually wiping the tip of the soldering
iron along the row of pins, while keeping upward pressure on that side with
a dental pick. You should be able to flex one side of the chip free from the
board, then do the same thing to the other side. That always used to work
with DIP packages too, but it's actually much easier on these small
surface-mount chips.

DaveC wrote:
On Sun, 4 Jan 2004 15:39:59 -0800, Garrett Mace wrote
(in message ):


I had to replace an FPGA on a development board once. I used a $20 heat gun
clamped in a partially-completed CNC machine I was building. It only takes a
few seconds for the solder to melt when the heat gun is on its lowest
setting. I also used the heat gun to solder on the new FPGA, then touched up
a few pins with a soldering iron. Ideally there would be a heat shield to
prevent heating up other components, but in this case it wasn't a problem.
The pins heat up so much faster than the rest of the chip; all you need to
do is keep the internal temperature of the device less than 450 degrees F.


Here's a pic of the ROMs I want to desolder (the big chips in the photo).
Identical set on identical board I want to replace...

http://home.covad.net/~peninsula/ROMpic.jpg

How do these rate on the scale of difficulty? (What are these packages?)

They appear to be 44-pin SOP packages with a gull wing lead pitch of 1mm.

I would rate them as fairly easy as there is good access to the ends of
the devices for introducing the stainless strip, and 1mm pitch leads are
quite resistant to bending and easy to resolder without bridging
(compared to 0.5mm pitch SSOP leads).

I have used the Chipquik-and-stainless-strip method successfully many
times on identical parts. They might also be good candidates for the
Radio Shack desolderer/Aquarium pump hot air gun (I bought the parts
today but haven't assembled and tried it yet).

Hakko makes a 85W iron for desoldering flat packs. The iron is about $80.00
and all the tips run about 150.00 It is called the mach FP and is on hakko's
site at:
http://www.hakkousa.com/WEB1/Product...FP/mach-fp.htm
The trick is to tin the tip good and invert the item you are desoldering for
"gravity assist". Ive been using one for sevral years and after practicing
with some old PCB's for about 20 minutes have never lifted any traces or
damaged a device. You can get it form East Coast Transistor
http://www.kenwoodparts.com
--
Jammy Harbin
J & J Electronics, Inc
227 S. 4Th St.
Selmer, TN 38375
731-645-3311
"Garrett Mace" wrote in message
...

Here's a pic of the ROMs I want to desolder (the big chips in the
photo).
Identical set on identical board I want to replace...

http://home.covad.net/~peninsula/ROMpic.jpg

How do these rate on the scale of difficulty? (What are these packages?)


Those would be pretty easy to remove with the hot air gun method. I've
removed hundreds of similar-sized chips from laptop motherboards. However
the tough part is the proximity of those two plastic sockets; on the PCB
you
want to keep, you'll need to shield those somehow. Perhaps tape a couple
layers of aluminum foil over them, and only heat the chips until you see
the
solder wet up, then quickly turn off the heat gun and flip the chips over
with a dental pick. You would probably want to practice with the board you
don't want to keep, and see if you can keep the plastic sockets from
melting. If you can't, then maybe you should use a Chipquik or hot air
pencil method.

For chips that size, and with only two side with pins, I've removed many
by
simply dolloping solder on and continually wiping the tip of the soldering
iron along the row of pins, while keeping upward pressure on that side
with
a dental pick. You should be able to flex one side of the chip free from
the
board, then do the same thing to the other side. That always used to work
with DIP packages too, but it's actually much easier on these small
surface-mount chips.

DaveC wrote:
On Sun, 4 Jan 2004 15:39:59 -0800, Garrett Mace wrote
(in message ):


I had to replace an FPGA on a development board once. I used a $20 heat gun
clamped in a partially-completed CNC machine I was building. It only takes a
few seconds for the solder to melt when the heat gun is on its lowest
setting. I also used the heat gun to solder on the new FPGA, then touched up
a few pins with a soldering iron. Ideally there would be a heat shield to
prevent heating up other components, but in this case it wasn't a problem.
The pins heat up so much faster than the rest of the chip; all you need to
do is keep the internal temperature of the device less than 450 degrees F.


Here's a pic of the ROMs I want to desolder (the big chips in the photo).
Identical set on identical board I want to replace...

http://home.covad.net/~peninsula/ROMpic.jpg

How do these rate on the scale of difficulty? (What are these packages?)

They appear to be 44-pin SOP packages with a gull wing lead pitch of 1mm.

I would rate them as fairly easy as there is good access to the ends of
the devices for introducing the stainless strip, and 1mm pitch leads are
quite resistant to bending and easy to resolder without bridging
(compared to 0.5mm pitch SSOP leads).

I have used the Chipquik-and-stainless-strip method successfully many
times on identical parts. They might also be good candidates for the
Radio Shack desolderer/Aquarium pump hot air gun (I bought the parts
today but haven't assembled and tried it yet).

On Sun, 4 Jan 2004 2:30:51 -0800, DaveC wrote:

I need to desolder (with no damage to the components) some SMD ROM chips. Is
there a good tutorial somewhere on the 'net about how to go about this?

BTW, I found a great tutorial on technique and equipment (lo-cost, some of it
make-yourself) on the 'net about soldering SMDs:

http://www.wku.edu/~barceed/SolderPage/index.htm

A radioamateur which desolders SMDs a lot told me the following technique:
Take a heat-resistant, insulated wire like that used to wind transformers.
Stick it behind one row of pins until it comes out on the other side, the
wire should lay just behind the pins. Fasten it some way at one side (e.g.
solder it), preferable somewhat in front of the line of the pins. At the
other side, start heating the pins with a soldering iron, while gently
pulling the free end away from the chip so that the wire pushes against the
back of the pins. When the solder melts, the strain on the wire causes it to
lift the pin and prevent resoldering. Move along the row of pins until all
are done. Repeat as required for other sides.

Mat Nieuwenhoven

Mat Nieuwenhoven wrote:
On Sun, 4 Jan 2004 2:30:51 -0800, DaveC wrote:


I need to desolder (with no damage to the components) some SMD ROM chips. Is
there a good tutorial somewhere on the 'net about how to go about this?

BTW, I found a great tutorial on technique and equipment (lo-cost, some of it
make-yourself) on the 'net about soldering SMDs:

http://www.wku.edu/~barceed/SolderPage/index.htm


A radioamateur which desolders SMDs a lot told me the following technique:
Take a heat-resistant, insulated wire like that used to wind transformers.
Stick it behind one row of pins until it comes out on the other side, the
wire should lay just behind the pins. Fasten it some way at one side (e.g.
solder it), preferable somewhat in front of the line of the pins. At the
other side, start heating the pins with a soldering iron, while gently
pulling the free end away from the chip so that the wire pushes against the
back of the pins. When the solder melts, the strain on the wire causes it to
lift the pin and prevent resoldering. Move along the row of pins until all
are done. Repeat as required for other sides.

Mat Nieuwenhoven

I have used that technique, and it's very effective if the device is
slated for the dumpster after removal - although finding an anchor point
is sometimes challenging. This method should not be used if you intend
to re-use the device as it applies pressure at an angle to the pins and
will bend them.