Solder joints

An overview of solder joints and what solder joints in electronics equipment should be like if they are made correctly.

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Soldering Tutorial Includes:
Soldering basics     Manual soldering: how to solder     Soldering irons     Tools for soldering     Solder - what it is and how to use it     De-soldering - the secrets of how to do it properly     Solder joints     PCB solder resist    

See also: SMT soldering techniques for PCB assembly    

Ensuring the solder joints are made correctly is of prime importance in any electronics construction. Solder joints that are poor will either cause the equipment to not to work once it has been completed, or there is the possibility that the solder joint could fail intermittently or introduce noise into the electronics circuit. While complete failure of a joint immediately has been made is bad enough, a latent failure, or an intermittent failure can be worse as it will cause the equipment to fail once it is in service.

Good solder joints

Fortunately most solder joints are good and do not cause any problems. A good solder joint will have a shiny finish to it, and it should not have too much solder. Typically the contour of the solder around the joint should be slightly concave. To much solder on a joint may lead to poor joints, and there is always the possibility, particularly on printed circuit boards that if too much solder is used then it could spill over onto another track, causing a short circuit.

Dry joints

Dry joints are the main form of problem solder joint. These solder joints may be completely open circuit, or they may be intermittent, high resistance or noisy. It is therefore essential that no dry solder joints are present in any electronics equipment.

It is easy to identify dry joints. Unlike good solder joints that are shiny, dry joints have a dull or matt finish. Also when soldering them they appear to have a more granular appearance as the solder is melted.

When a dry joint is found, the solder on the joint should be removed and care taken when re-soldering it to ensure that a good joint is made.

How to make good solder joints

With a little practice it becomes very easy to make good solder joints. Coupled with careful inspection afterwards, virtually every solder should be good and free from problems.

It naturally helps to have the right equipment (see the page on soldering irons under the related articles title under the main menu on the left hand side of tis page). However to help a few pointers to making good solder joints can be helpful:

  • Ensure that all surfaces to be soldered are clean and free from grease.
  • Ensure that the items to be soldered are secured so that they will not move in the soldering process as this can result in a dry joint.
  • Tin the tip of the soldering iron, wipe it clean on a damp spongue and then add a small amount of solder again - this helps the heat to flow onto the joint quickly.
  • Apply the soldering iron to the joint and quickly add some solder
  • Allow the solder to flow onto the joint, and just sufficient to allow a concave meniscus to form.
  • Remove the soldering iron as soon as possible. If the iron is left on the joint for too long, the flux will become exhausted, the solder will oxidise and a dry solder joint will result. Typically a couple of seconds is sufficient more most solder joints.
  • Allow the solder on the joint to cool and solidify before allowing any movement.

These simple steps will help to enable good solder joints to be made. When constructing any electronics equipment, whether commercially or as a hobby, soldering is an essential skill. It is necessary to make good solder joints if equipment and circuits are to work properly.

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