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  components to be swapped out, or poor joints (perhaps "dry" 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 equipment before, especially if it 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 a desoldering 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.

 

 

Solder joints to be desoldered

The two solder joints to be desoldered, to enable a faulty component to be removed.

Applying the iron

If using a desoldering   pump, apply the iron first to melt the solder (1-2 seconds). Ensure  the pump is 'primed' and ready to go...

Applying the nozzle of the desoldering pump

The  nozzle of the desoldering pump is applied to the molten solder and the  spring-loaded plunger is then released, drawing the solder up into the  pump. Repeat if needed.

Desoldered joint #1

The  first joint, now desoldered. The second joint will be desoldered using braid...

Applying the braid with the hot iron

Select a suitable width of braid, and press it down onto the COLD joint using the hot tip of the iron.

Continue heating...

Molten solder is drawn up by capillary action into the braid. Care not to   overheat, or 'drag whiskers' of solder over the board, nor let the braid  solidify on the joint!

Component removed

The   component dropped out of the board after desoldering. Sometimes, it may need persuading with pliers....

Both joints desoldered

Close-up shot of both joints, now desoldered and ready for the replacement  part to be fitted.

 

The Black Museum of Bad Soldering

These are all genuine examples which have not been retouched or reworked in any way.

excess solder, incomplete joints

Tenfold excess of solder, and (extreme left) incomplete joint with  poor coverage. There is no need to add more solder "for luck".

Dry joint

  One  example of several dry joints found within a commercial PSU adaptor for a computer peripheral.

Suspect joint

  Hmmmm... this joint looks somewhat suspect as well...

Dry joint, fracture

  A close-up reveals the terrible standard of soldering (and quality control),  with a fracture visible on this ground/ earth joint.

Dry joint - mains connection arcing

How  not to make a mains voltage soldered joint. This went "dry" and starting  arcing, nearly zapping the equipment. It is also a fire hazard.

Dry, arcing, open circuit

The  same mains connection, the wire merely being 'tacked on' with a blob of solder.

 

Copyright Notice: these photos are Copyright © Alan Winstanley 1999. You may download them for personal use, or for training or  educational purposes only. They may not be used on a commercial or sponsored web  site without prior permission (conditions apply). If you wish to use these  pictures for any commercial reasons, e.g. to enhance any commercial product,  enframe in any external commercial web site or apply for any other commercial  use, you must seek my prior approval first. Very high resolution photos with  licence for reproduction are also available on CD from the author, on payment of  a royalty. The author is also happy to quote for specialist/ macro colour  photography assignments. This email address is being protected from spambots. You need JavaScript enabled to view it.

 

For the photographer: the photographs were taken by the author using a  Minolta X-700 SLR with 50mm Minolta MC manual-focus macro lens at f11-16,  coupled to a Minolta Auto 80PX macro ring flash gun. Film was 3M Colour Print  200. The prints were scanned using an HP ScanJet 6250 flatbed scanner, and  enhanced using JASC Paintshop Pro 5 with  filters, before uploading.

V1.0 Last updated 9th July 1999

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