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.
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.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on