N
N Cook
In response to someone who emailed me a couple of
months back saying he did not believe it
was possible to desolder , with a hot-air gun,
ICs soldered in plated through hole pcb boards,
without causing mayhem.
And anyone else who could use the technique.
The following is some before and after pics
of such a board this week, with thin tracks, through pin tracks and
a nearby via for good measure.
http://home.graffiti.net/diverse:graffiti.net/de_sol1.jpg
http://home.graffiti.net/diverse:graffiti.net/de_sol2.jpg
Masked off with the thick form of plummer's PTFE
tape to protect adjascent components from desoldering/
flicking off.
http://home.graffiti.net/diverse:graffiti.net/de_sol3.jpg
http://home.graffiti.net/diverse:graffiti.net/de_sol4.jpg
After blasting with hot-air and before cleaning
up the holes with a needle-point probe and soldering iron.
Usually the polyester of the pcb does not discolour, for
normal cheap IC soldering, but the plated-through
fixings mean more heat required than usual.
http://home.graffiti.net/diverse:graffiti.net/de_sol5.jpg
http://home.graffiti.net/diverse:graffiti.net/de_sol6.jpg
The converted circlip pliers extractor tool , with a close up
of the double joggled tips.
Lines of bending are at B-B and the red lines.
Graph paper is mm squares.
The full text for the tip
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 ] . For awkward positions lock the pliers to the IC by wrapping
a cable tie around the handles, tighten, slide down and
add a couple of notches to the tie and force back along the handles.
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.
Mask off surrounding areas with wide aluminium tape or thick plummer's PTFE
tape around both sides of board to avoid unsoldering
and flicking off nearby minor components and trap any that do.
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.
You definitely need a tool to pull the IC off the board as soon as the
solder is non-solid/breaking up ie before even fully melted quite possibly.
An old pair of long nose pliers with the ends ground down so the remnant
tips can be bent inwards to grab the ends of the IC would probably be
sufficient to show the method works.
Also definitely practise on an old/scrap board first as it needs that
confidence because otherwise pointing a glowing hot element and 300 degree C
or more blast of hot air at a pcb is not a natural thing to do.
SAFETY NOTE:- ensure good ventilation, use safety goggles because trapped
water etc in the capaillary structure of glass fibre reinforced 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.
months back saying he did not believe it
was possible to desolder , with a hot-air gun,
ICs soldered in plated through hole pcb boards,
without causing mayhem.
And anyone else who could use the technique.
The following is some before and after pics
of such a board this week, with thin tracks, through pin tracks and
a nearby via for good measure.
http://home.graffiti.net/diverse:graffiti.net/de_sol1.jpg
http://home.graffiti.net/diverse:graffiti.net/de_sol2.jpg
Masked off with the thick form of plummer's PTFE
tape to protect adjascent components from desoldering/
flicking off.
http://home.graffiti.net/diverse:graffiti.net/de_sol3.jpg
http://home.graffiti.net/diverse:graffiti.net/de_sol4.jpg
After blasting with hot-air and before cleaning
up the holes with a needle-point probe and soldering iron.
Usually the polyester of the pcb does not discolour, for
normal cheap IC soldering, but the plated-through
fixings mean more heat required than usual.
http://home.graffiti.net/diverse:graffiti.net/de_sol5.jpg
http://home.graffiti.net/diverse:graffiti.net/de_sol6.jpg
The converted circlip pliers extractor tool , with a close up
of the double joggled tips.
Lines of bending are at B-B and the red lines.
Graph paper is mm squares.
The full text for the tip
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 ] . For awkward positions lock the pliers to the IC by wrapping
a cable tie around the handles, tighten, slide down and
add a couple of notches to the tie and force back along the handles.
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.
Mask off surrounding areas with wide aluminium tape or thick plummer's PTFE
tape around both sides of board to avoid unsoldering
and flicking off nearby minor components and trap any that do.
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.
You definitely need a tool to pull the IC off the board as soon as the
solder is non-solid/breaking up ie before even fully melted quite possibly.
An old pair of long nose pliers with the ends ground down so the remnant
tips can be bent inwards to grab the ends of the IC would probably be
sufficient to show the method works.
Also definitely practise on an old/scrap board first as it needs that
confidence because otherwise pointing a glowing hot element and 300 degree C
or more blast of hot air at a pcb is not a natural thing to do.
SAFETY NOTE:- ensure good ventilation, use safety goggles because trapped
water etc in the capaillary structure of glass fibre reinforced 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.
