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Inspection of solder joints

We have to inspect quality of solder joint to ensure that it provides good electrical connection. Microscope or a good magnifying lamp is required for proper and thorough inspection. Use an ohm-meter to test for continuity.
Good solder joints are:

  • smooth, shiny, volcano-shaped
  • without excess solder
  • completely covered with solder
  • without any remaining pockets of flux
  • with no pits or porosities on the surface

Bad solder joints are:

  • Cold solder joints (they have frosted appearance). They are caused by insufficient heat. Cause of cold solder joints can also be movement of component’s lead in solder joint before solder has cool down and solidified. You must re-solder this cold solder joints. First, remove solder from bad solder joints with solder wick or de-soldering pump, and then re-solder component following the proper soldering technique.
  • Solder bridges. If you apply too much solder to joint it can bridge two adjacent pads on circuit board. To repair this solder joint you should remove excess solder with solder wicks and soldering iron.
  • Solder balls.  Cause of solder balls may be impurities in the solder or improper solder cooling. Solder balls should be removed with a small brush.
  • Insufficient amount of solder.  In this case the joint is not completely covered with solder. This joint is weak. This can be easily repaired by adding more solder to solder joint.
  • Damaged or lifted pads. Too much heat applied to the solder joint can damage, brake or lift pads and conductors on printed circuit boards. This can not be repaired since pads are separated and peeled off the board. You can only partly repair this damage of pads or conductors - scrape the damaged copper foil and run a piece of wire instead. The only way to deal with this issue is preventing it from happening – avoid applying excess heat to solder joint, use proper temperature-controlled soldering iron and follow proper soldering technique.
  • Remains of flux. All flux should be removed with ethanol alcohol or other solvent once when solder has cooled and solidified.