Prev: Microcontroller for sale
Next: Difficulty identifying SMD semis via markings
From: N_Cook on 27 May 2010 10:48
<stickyfox(a)gmail.com> wrote in message
news:c56e3798-5ae3-4a5d-b8dc-53c8ecdb2e94(a)y21g2000vba.googlegroups.com...
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.

OOOOOOOOO

I'm probably to old to change my ways now unless a proven advantage to do
so. I like to go in and out as quick as possible with hot air source having
heated up for 30 seconds before applying. No known failures in reuse from
pre-freezing. I like the way they come off in their 0.1mm tugsten wire
strops and they can be placed in the palm of the hand, IC body face down,
and be just warm , not hot.


From: mike on 27 May 2010 14:55
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?
> 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?
>
>
You're on the right track.
Get a pencil torch with a catalytic "hot air" tip.
I use a Weller PortaSol.
MUCH better ratio of temperature to heat delivered.
Works way better than I'd expected. Preheting the
board closer to solder temperature with a big hot air
gun or temperature controlled hot plate makes it even easier.
From: Winston on 27 May 2010 15:38
On 5/27/2010 7:42 AM, N_Cook wrote:

(...)

> I don't often meet ground planes but if I do ,
> how do you gauge the rear heat ?

I have not been measuring the temperature at all.
I've been relying on experience to know that I've heated up the back
side of the board 'sufficiently' but not so much as to loosen
components.

I've been eyeing these Tempilstiks to get a better idea:
http://www.use-enco.com/CGI/INPDFF?PMPAGE=1130&PARTPG=INLMK32

One could mark the board with three crayons of increasing
melting temperature and get a better idea when to start
pulling on the BGA.


> I like the solder paste indicator.

It works 'better than nothing'.
Of course the virgin solder melts at a much lower temperature
than does the used solder.

--Winston
From: N_Cook on 28 May 2010 03:50
Winston <Winston(a)bigbrother.net> wrote in message
news:htmhm6022th(a)news2.newsguy.com...
> On 5/27/2010 7:42 AM, N_Cook wrote:
>
> (...)
>
> > I don't often meet ground planes but if I do ,
> > how do you gauge the rear heat ?
>
> I have not been measuring the temperature at all.
> I've been relying on experience to know that I've heated up the back
> side of the board 'sufficiently' but not so much as to loosen
> components.
>
> I've been eyeing these Tempilstiks to get a better idea:
> http://www.use-enco.com/CGI/INPDFF?PMPAGE=1130&PARTPG=INLMK32
>
> One could mark the board with three crayons of increasing
> melting temperature and get a better idea when to start
> pulling on the BGA.
>
>
> > I like the solder paste indicator.
>
> It works 'better than nothing'.
> Of course the virgin solder melts at a much lower temperature
> than does the used solder.
>
> --Winston


Another reason to investigate these , but 1/2 deg C resolution fine for that
purpose. For general fault hotspot monitoring 0.1 deg C resolution ones
would be more useful but too expensive. Another gizmo I must get around to
trying. Using the pyrometer of a PIR unit , setting in an insulated tube
shroud for pointing and then analogue fashion monitor the output in a
relative way, absolute temp not required for that purpose.


From: N_Cook on 28 May 2010 04:03
N_Cook <diverse(a)tcp.co.uk> wrote in message
news:htnsgv$vpv$1(a)news.eternal-september.org...
> Winston <Winston(a)bigbrother.net> wrote in message
> news:htmhm6022th(a)news2.newsguy.com...
> > On 5/27/2010 7:42 AM, N_Cook wrote:
> >
> > (...)
> >
> > > I don't often meet ground planes but if I do ,
> > > how do you gauge the rear heat ?
> >
> > I have not been measuring the temperature at all.
> > I've been relying on experience to know that I've heated up the back
> > side of the board 'sufficiently' but not so much as to loosen
> > components.
> >
> > I've been eyeing these Tempilstiks to get a better idea:
> > http://www.use-enco.com/CGI/INPDFF?PMPAGE=1130&PARTPG=INLMK32
> >
> > One could mark the board with three crayons of increasing
> > melting temperature and get a better idea when to start
> > pulling on the BGA.
> >
> >
> > > I like the solder paste indicator.
> >
> > It works 'better than nothing'.
> > Of course the virgin solder melts at a much lower temperature
> > than does the used solder.
> >
> > --Winston
>
>
> Another reason to investigate these , but 1/2 deg C resolution fine for
that
> purpose. For general fault hotspot monitoring 0.1 deg C resolution ones
> would be more useful but too expensive. Another gizmo I must get around to
> trying. Using the pyrometer of a PIR unit , setting in an insulated tube
> shroud for pointing and then analogue fashion monitor the output in a
> relative way, absolute temp not required for that purpose.
>
>

In this situation would thore remote IR thermometers pick up the temp of the
board or the much higher temp of the hot air above it , but in line of
"sight" of the sensor?


First  |  Prev  |  Next  |  Last
Pages: 1 2 3 4
Prev: Microcontroller for sale
Next: Difficulty identifying SMD semis via markings