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From: N_Cook on 27 May 2010 08:51
I've only used full size hot air gun and protective masking-off before. I
prefer the short sharp shock of full size rather than the "proper" pulse jet
type things, presumably for rework only really.

Couldn't resist one in a pound shop, unbelievably precisely small spot of
flame and also adjustable (upwards), amazing engineering, minimum about 1mm
diameter.
For SM salvaging rather than just removal, any other tips from actual users?
Seems necessary to hold the pcb vertical in a vice and hold the pencil
with flame upwards about 20 degrees of angle so butane liquid is not at the
outlet.
Mask off surrounding areas (including body of IC) with PTFE or woven glass
matt cut to fit the paricular situation.
Sub mm tungsten wire or something strong enough in those dimensions to
push under the IC or the pins , to loop around, and tug on while heating.
Freezer spray blast just prior to heating pins.

For DIP do one side of pins at a time, while tugging ?
Scalpel blade , perhaps bent, under pins ?
What sort of lighting is best ie to see the flame but also the work?


From: William Sommerwerck on 27 May 2010 08:55
> I've only used full size hot air gun and protective masking-off.
> I prefer the short sharp shock of full size rather than the "proper"
> pulse jet type things, presumably for rework only really.

Don't stint on the removal tool -- a cheap and chippy chopper is not a good
choice. You also need a big black block for proper support.


From: Winston on 27 May 2010 09:55
On 5/27/2010 5:51 AM, N_Cook wrote:
> I've only used full size hot air gun and protective masking-off before. I
> prefer the short sharp shock of full size rather than the "proper" pulse jet
> type things, presumably for rework only really.
>
> Couldn't resist one in a pound shop, unbelievably precisely small spot of
> flame and also adjustable (upwards), amazing engineering, minimum about 1mm
> diameter.
> For SM salvaging rather than just removal, any other tips from actual users?

That torch produces plenty of temperature but not nearly enough heat.

I use two hot air guns, one aimed at the back of the board and one
on the front. (The copper ground planes act as heat sinks, so you need
to pour a bunch of thermal energy into the area in question in order
to get sufficient heat rise to melt solder.)

I normally heat up the back of the board before I even start the
'front side' air gun. Two guns are more convenient than one.
Most of the time however, I can use the same gun for both.
Heat the back thoroughly and then concentrate on the front.

I dab a little solder paste in the area. That is my local
'thermometer'. When it melts, I know I'm only seconds away
from 'liftoff'.

Strip some 30 ga. wirewrap wire to route underneath BGAs.
You can form a cradle to gently lift the device off the board.


--Winston

From: stickyfox on 27 May 2010 10:01
On May 27, 8:51 am, "N_Cook" <dive...(a)tcp.co.uk> wrote:
> I've only used full size hot air gun and protective masking-off before. I
> prefer the short sharp shock of full size rather than the "proper" pulse jet
> type things, presumably for rework only really.
>
> Couldn't resist one in a pound shop, unbelievably precisely small spot of
> flame and also adjustable (upwards), amazing engineering, minimum about 1mm
> diameter.
> For SM salvaging rather than just removal, any other tips from actual users?
> Seems necessary to hold the pcb vertical in a vice and hold the pencil
> with flame upwards about 20 degrees of angle so butane liquid is not at the
> outlet.
> Mask off surrounding areas (including body of IC) with PTFE or woven glass
> matt cut to fit the paricular situation.
> Sub mm tungsten wire or something strong enough in those dimensions to
> push under the IC or the pins , to loop around, and tug on while heating.
> Freezer spray blast just prior to heating pins.
>
> For DIP do one side of pins at a time, while tugging ?
> Scalpel blade , perhaps bent, under pins ?
> What sort of lighting is best ie to see the flame but also the work?

Do you have a particular rationale for freeze blasting prior to
rework? I think the resulting thermal shock would increase the
likelihood of damage. Reflow ovens have temperature ramps for a
reason. As long as you aren't charring the numbers off the package
with a bernz-o-matic until it falls off the board, you are safe
heating the entire device to reflow temp. That's how it was put on in
the first place. Just do it uniformly and gradually.

If you are serious about salvaging QFP/TSOP/TSSOP devices, you might
want to look into a regular size heat gun with a nozzle designed for
these packages. An OKi is about 500 bucks but you can get a cheap
chinese knockoff for under 200. If you really want to do it quickly
and safely I'd recommend getting a solder tip for each package. But
this could run you anywhere from 200-1500 depending on what you've got
to start with.

But if you're like me and you are salvaging chips because you don't
have the cash to buy new ones, then I suggest you look into chip-quik.
It's low-temperature solder you "blob" over the leads with an ordinary
iron. It stays liquid for 10-30 seconds so you can do a few laps
around the device with your pencil iron, then grab the device with
forceps and pluck it right off the board. You can set your iron a lot
lower if you have an adjustment.

I used to use that tungsten wire trick (steel or ordinary enameled
magnet wire works great too) but chip quik is much faster and less
traumatic to the device.

I routinely use chip quik these days to upgrade 80-pin
microcontrollers. I am not salvaging them but the lower heat causes
less damage to the board, and that saves me trouble later.
From: N_Cook on 27 May 2010 10:42
Winston <Winston(a)bigbrother.net> wrote in message
news:htltjn06q1(a)news7.newsguy.com...
> On 5/27/2010 5:51 AM, N_Cook wrote:
> > I've only used full size hot air gun and protective masking-off before.
I
> > prefer the short sharp shock of full size rather than the "proper" pulse
jet
> > type things, presumably for rework only really.
> >
> > Couldn't resist one in a pound shop, unbelievably precisely small spot
of
> > flame and also adjustable (upwards), amazing engineering, minimum about
1mm
> > diameter.
> > For SM salvaging rather than just removal, any other tips from actual
users?
>
> That torch produces plenty of temperature but not nearly enough heat.
>
> I use two hot air guns, one aimed at the back of the board and one
> on the front. (The copper ground planes act as heat sinks, so you need
> to pour a bunch of thermal energy into the area in question in order
> to get sufficient heat rise to melt solder.)
>
> I normally heat up the back of the board before I even start the
> 'front side' air gun. Two guns are more convenient than one.
> Most of the time however, I can use the same gun for both.
> Heat the back thoroughly and then concentrate on the front.
>
> I dab a little solder paste in the area. That is my local
> 'thermometer'. When it melts, I know I'm only seconds away
> from 'liftoff'.
>
> Strip some 30 ga. wirewrap wire to route underneath BGAs.
> You can form a cradle to gently lift the device off the board.
>
>
> --Winston
>

Some interesting ideas there. I don't often meet ground planes but if I do ,
how do you gauge the rear heat ?
I like the solder paste indicator.


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