Manufacturing - Soldering

Soldering is a manufacturing process whereby metal is joined together using molten solder to form an electrical connection. A Soldering Iron is a temperature controlled heated ceramic element encased in a plastic and metal housing with a conductive tip

Solder is a soft alloy of predominantly Tin and a range of other metals that has a melting point of 180°c - 190°c. Lead based solder has a lower melting point but has been banned from use commercially by the WEEE (2006) due to the toxicity of lead. All solder contains a flux core, typically Rosin, which removes oxidisation from the metal surface to allow the solder to form a strong conductive bond


  1. The soldering iron is heated to a temperature of 330°c at the tip after about a minute
  2. Solder is melted onto the tip of the iron to 'tin' the surface and prevent oxidisation and allow for maximum heat transfer
  3. The tip is gently cleaned into brass wool to remove any excess solder or oxidisation
  4. A through hole component is fitted to the board and placed facing up on a heat proof mat with the component legs in the air
  5. The soldering iron is used to heat the PCB copper pad for a few seconds and solder is fed onto the pad and melted (wetted) around the component leg to fully enclose the hole as a cone
  6. Solder is then removed from the joint and the soldering iron cleaned once again in the brass wool to remove excess solder
  7. Wire cutters are used to carefully remove excess component legs

Wetting is the term used to describe the molten state of solder with sufficient flux when it has made a complete electrical connection between the pad & component leg. A properly 'wetted' joint will appear shiny and smooth. Incorrect heat, little or no flux, over heating solder, over oxidised tip and contaminants on the pad surface can cause insufficient wetting


Advantages of Soldering -

  • Low cost - soldering equipment is readily available at a very low cost compared to other manufacturing processes 
  • Low Skill - soldering requires minimal skill and experience so limited training is required to manufacture PCB's
  • Easy to repair/modify - All solder joints can be reheated multiple times once cooled and components are easy to remove and replace
  • Low Temperature - compared to other metal joining methods such as welding it is very low temperature and safer to do

Disadvantages of Soldering -

  • Harmful Fumes - When soldering the flux fumes must be extracted through a HEPA filter, over exposure causes respiratory problems 
  • Dry Joints - If components are solder incorrectly without sufficient flux there may be no or little electrical connection between them
  • Weak Joints - Soldered joints are prone to cracking and fatigue if excessive stress is applied to them

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