Jeff Walther said:
If you want really cheap, get a heat gun with adjustable temperature and
some modeling clay.
Cover the surrounding components with modeling clay (so they don't blow
away), set the heat gun to about 600F and apply to the target component
until the solder melts and the components can be easily lifted or its pins
pushed out of their holes. I use a dental pick to test the solder every
few seconds to see if it's soft yet.
This is not the most component friendly method, but I've been using it on
home projects for several years, with very few failures.
I've removed things as simple as 32 pin DIPs and as complex as 208 pin QFPs.
For clean-up afterwards you may still need braid. But with the component
removed you can use a wider braid (higher capacity per inch) and more
powered soldering pencil and the braid's price seems to be constant per
length regardless of width. Cleaning through-holes will be easier with
the pins removed and can be done with the various air methods mentioned by
others.
I can second that, used the following today to remove a 32 pinner
but most often use it for salvaging ICs before discarding rest.
No troubles with over-heating of the salvaged ICs.
Just to emphasise practise on an old board of TTL or such
before using for repair.
I own an old Pace, i think, de-solderer but last time i used it
was perhaps 3 years ago. The great advantage of the following is
you're pulling from the other side and it is very rare to dislodge
a solder pad/trace and extremely quick and cheap.
Other tips on
http://homepages.tcp.co.uk/~diverse/
De-soldering ICs
Use a hot-air paint-stripper,1400W,500 degree centigrade,with 2 level heat
control to prolong element life. Activity may appear fearsome but it is no
worse than a flow-solder bath.Pre-heat for one minute then apply to
pcb,make
extractor tool to pull ic from component side. Make an IC extractor from an
old large pair,10 inch, of
circlip pliers,the jaws need to open out enough to clip around the ends of
up to 64 pin
ICs with enough force to overcome the mechanical force of the situation
where all
the pins are angled relative to the PCB holes.Forge around both of the
original circlip
pins,one joggle at right angle to clear the heigth of the ICs and a slight
inwards joggle
to make purchase on the underside of the IC,grinding a wedge angle to the
points
helps particularly where there is no clearance between IC and pcb.
[ Because of these joggles this tool is also useful for depressing the rear
grippers
and releasing of that type chassis mount fuseholders and switches when
internally surrounded by other
components ]
Use this technique for salvaging (working order) up to 64 pin ics ( when
practised ),other
components, sm and even repair (tracks are not dislodged).For repair work
beware of
spatter of molten solder causing solder bridges on adjascent compoents
because if you
are doing the job properly,ie not dislodging pcb tracks the IC must be
pulled out with
some force and the board tends to flex so possibility of flicking solder.
The secret is to be as quick as possible,idealy the body of the extracted ic
will
be just about handleable rather than too hot to touch.Try practising on a
board
with close packed TTL chips or similar and aim for an extraction rate of
something like one every 2 seconds.Between boards keep the hot air gun
running on
low power setting (not switching off).Don't rest the gun against the board
when heating
as vibration seems to affect the element life also don't allow the board to
flex back onto the gun for the same reason.Hold the gun so airflow is angled
to the board
as solder spat directly into the nozzle can kill the element.
About the only components that cannot be removed with this technique are
parts
moulded in soft plastic,e.g. crystal sockets,rf coils with plastic former
(IF coils usually OK)
some DIP switches. Even these are desolderable intact if the body of the
component is previously
cooled with a blast of aerosol freezer spray.
SAFETY NOTE:- ensure good ventilation, use safety goggles because trapped
water etc in the capaillary structure of glass fibre reinfiorced PCB can
super-
heat to steam and jet out molten solder,also it is possible to overlook
small
electrolytic capacitors on the solder side of the board which of coarse
explode
with the direct heat of the hot air gun and beware of very
slight risk of combustion of adjascent flammable parts especially where
components have extra (un-noticed) mechanical bonding leading to extended
duration of heating activity.
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 strip.
Fixed together with all long edges one side and short edges adjascent on the
other side. Fixed together with paper staples but for the smallest shroud
for 8 pin SM had to wire together the final join. Forms a sort of truncated
cone in shape. Tie to the PTFE 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.
SAFETY NOTE:- ensure good ventilation, use safety goggles,and beware of very
slight risk of combustion.
