Re: Fast removal of FBT's Was: De-soldering ICs with a hot air gun.
- From: "N Cook" <diverse8@xxxxxxxxx>
- Date: Mon, 22 Oct 2007 12:32:20 +0100
Mark D. Zacharias <mzacharias@xxxxxxxxxxxx> wrote in message
news:zk%Si.119$yV6.94@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Just had to tell someone - I got a bright idea to remove a flybackit
transformer using a paint stripper gun.
AMAZING. Had that FBT out of there in about 40 seconds - no need to fight
the thing clearing eyelets, etc.
Done it twice now. Works great. Surely someone here has done this, But I
work with a couple really experienced TV techs and they hadn't thought of
before...
I would recommend watching out for any nearby SMD's, though...
Mark Z.
I've always used it for LOPT and pcb mounted mains ones and near enough
removing everything else except soft plastic enclosed components.
I very rarely use this SMD technique for more than 16 pin DIL format but it
does work for karger formats but I would not like to rely on any salvaged in
such manner.
Note the residual patterning in the solder, on the board, makes it a doddle
for replacing with a new one. Again you have to exert quite a pull on the IC
to keep IC heating time to a minimum. Another reason for making a strong IC
extractor tool for the basic DIL IC format removal.
Hint for de-soldering surface mount ICs.
Use a hot-air paint-stripper,1400W,500 degree centigrade,with 2 level heat
control to prolong element life.
Form a ring of silicone covered wire around the IC{to isolate the remaing
components on the pcb.Push a thin piece of wire
under one side of the IC and form a loop around the IC,repeat on the other
side;this is to remove the IC when the solder melts, tug on these wires
while
heating up to ensure minimum heating contact time.
Place a slab of PTFE with right size hole cut into and
clip pcb and slab together with clothes pegs/Bulldog clips etc.
If the IC is for re-use then cover body of IC with heat insulating material
or blast IC with freezer spray.Allow the hot-air gun to get up to heat{say 1
minute}
before applying to IC.
For more crowded boards make "conical" shrouds to surround the IC. I used
some PTFE strip that i had but thin paxolin or similar but drilled and wired
together would probably do. Cut 4 small trapezoids from the PTFE
or tin-plate and wire at the corners to form a
truncated pyramidal frustrum.
Fixed PTFE together with paper staples but for the smallest shroud
for 8 pin SM had to wire together the final join.
Tie to the PTFE/ tin-plate cone (to stop the blower blowing it off) with
copper wire or temporarily solder to distant points.
When practised the heated contact time should be less than
2 seconds - no board distortion or collateral damage surprisingly.
If you can't get the tugging wires under the IC then pass
under a few pins at each corner.
Because this tugging frees the IC at the earliest moment, the solder
on the board is not fully melted and leaves a profile for localising
the new IC in place and then solder pin by pin.
Even for thick board and plated-through holes
so only tips of IC leads protrude,
very thin signal traces, traces to tiny pads on both sides of boards of same
pin in some cases and plated vias under ICs as well. I know if i used
"proper " vacuum assist desolder or butcher-and-remove-single-pins , many of
those traces/pads would have dislodged.
I had to sharpen the points of my large adapted circlip pliers to get the
extra purchase on the ends of 14,16, and 28 pin ICs. Not one dislodged
track using a paint-strip hot-air gun. Next time i'll have to take some
before and after pics for the doubting thomases.
SAFETY NOTE:- ensure good ventilation, use safety goggles,and beware of very
slight risk of combustion.
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/
.
- References:
- Re: De-soldering ICs with a hot air gun.
- From: hr(bob) hofmann@xxxxxxx
- Fast removal of FBT's Was: De-soldering ICs with a hot air gun.
- From: Mark D. Zacharias
- Re: De-soldering ICs with a hot air gun.
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