De-soldering is required when electronic components need to be removed from a circuit, usually because they are faulty. It may sometimes be necessary during testing or assembly, if a wrong part has been fitted or a modification has to be made. In the field, it's not uncommon for faulty electronic components to be swapped out, or poor joints (perhaps "dry" or gray joints) to need re-making properly, months or years after manufacture. Experienced engineers can often diagnose a particular faulty joint immediately, because they may have seen the same problem on similar electronic equipment before, especially if the equipment has a "reputation". A proper desoldering technique can soon be acquired with practice - all you need to do is buy some scrap boards to have a go with, and desolder to your heart's content!
The next photo sequence illustrates the basic steps for desoldering a printed circuit board, in order to remove a faulty part. Both the technique for using a desoldering suction pump as well as desolder braid are illustrated. Some real-life examples of poor soldering are shown too, in my Black Museum of Bad Soldering!
Remember - it costs just as much to get it right as it does to get it wrong! Practice makes perfect.
|(Left) The two solder joints to be desoldered, to enable a faulty electrolytic capacitor to be removed from the printed circuit board.|
|(Right) If using a suction-type desoldering pump, apply the soldering iron tip first to melt the solder joint (say for 1-2 seconds). Ensure the spring-loaded desoldering pump is 'primed' and ready to go...|
|(Left) The PTFE nozzle of the desoldering pump is applied to the molten solder and the spring-loaded plunger is then immediately released, drawing the molten solder up into the pump. Remove the soldering iron tip. Repeat the process if needed. Handy tip: sometimes it helps to add some fresh solder and then desolder the whole joint.|
|(Right) The first p.c.b. joint, now desoldered. The second joint will be desoldered using traditional desoldering braid.|
|(Left) Select a suitable width of desoldering braid, and press it down onto the COLD joint using the hot tip of the iron. A flat soldering iron bit is preferable.|
|(Right) The molten solder is drawn up by capillary action into the desoldering braid. Take care not to overheat the board (the p.c.b. copper track may lift off), nor 'drag whiskers' of solder over the board, nor let the braid solidify onto the joint! Remove the braid while the joint is still molten.|
|(Left) The faulty electrolytic capacitor dropped out of the board after desoldering. Sometimes, it may need persuading with pliers.... but don't overdo this or you risk damaging the copper tracks on the p.c.b.|
|(Right) Close-up photograph of both joints, now desoldered and ready for the replacement component to be fitted.|
|The Black Museum of Bad Soldering|
|These are all genuine examples which have not been retouched or reworked in any way.|
|(Left) A tenfold excess of solder on this hand-soldered printed circuit board, and (extreme left) an incomplete solder joint with poor coverage. There is no need to add more solder "for luck".|
|(Right) An example of a dry (or gray) solder joint found inside a commercial PSU for a computer peripheral. The wire had been fed through the hole in the brass terminal, and merely tacked on with a blob of solder. This is a fire hazard (risk of arcing and overheating).|
|(Left) Hmmmm... this joint looks somewhat suspect as well... it's the earth (ground) wire in the same PSU|
|(Right) A close-up reveals the terrible standard of soldering (and quality control), with a fracture visible on this ground/ earth joint.|
|(Left) How not to make a mains voltage soldered joint. This solder joint went "dry" and starting arcing, nearly destroying the attached equipment. It is also a fire hazard.|
|(Right) The same mains connection, the wire merely being 'tacked on' with a blob of solder.|
ICopyright notice: these photos are Copyright © Alan Winstanley 1997-2010. They may not be used in any commercial publication, mirrored on any web site site nor appended to or amended, or used or distributed for any commercial reason, without the prior permission of the writer.
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