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An Introduction to the Printed Circuit Board Soldering Process

An Introduction to the Printed Circuit Board Soldering Process


While the soldering process may seem difficult to you as a beginner, but it is rather an enjoyable process once you get the hang of it. Soldering is the process by which two or more components are joined by dissolving solder and running it between the joint. This process is used during PCB fabrication to mount SMT components onto the PCB. The soldering process should be done properly because it has a huge influence on the performance of the circuit. Here are some of the basics of PCB soldering you should have an idea about.

What is soldering?

Soldering helps to mount components onto the PCB. An iron tip is heated and used to heat the solder in return which melts and flows around the spaces between your components. The solder heats the metallic part of the component to roughly the solder’s melting point; this allows the component to stick to the PCB.

What are the uses of soldering?

Soldering has a wide range of uses in electronics. It helps in joining components in circuits and making electrical contacts. Soldering takes us of alloys whose melting point typically lies in the range below 450°C. The components are connected through their terminals with the circuit with the help of the soldering process.


The types of soldering processes: 

  1. Reflow soldering: Reflow soldering is the process in which a sticky mixture of flux and powdered solder is used to attack tiny several electrical components to contact pads. After this heat melts the solder and connects the joint permanently. Then the entire assembly is passed through a reflow oven.
  • Process: the reflow process is made up several stages. First SM Technology is used to place components on the board directly using solder paste. Then the board is baked at around 2000°C so the solder properly melts. Then the board is treated in a series of chambers.
  • Reflow Zones:
  • Preheating: The circuit is preheated slowly for uniform heating. The temperature is raised 3-50 F/ second.
  • Thermal Soak: The board is passed through the thermal soak chamber. Here the chemicals in the paste are activated which stop it from forming microbeads. It also ensures uniform distribution of heat.
  • SMT-Oven: Here the board is heated to a maximum temperature so the solder melts. Timing is integral since the solder should melt but not vaporize.
  • Cooling: The board is cooled down to around 860 F. The solder forms a crystalline structure which helps strengthening the bond.
  • Washing: The last (often missed) but essential process is washing. This helps remove all the grit and chemical residue from the board. A clean and neat board is what you want to have in the end!
  • Temperature and Curvature:When the board undergoes the process of heating and cooling, it has a tendency to The copper and multiple layers present usually cool down slower than the substrate. By using controlled cooling we can minimize the effect of warping and even out stresses (stresses cause failure in the board). We can also adjust certain parameters to allow even heating to minimize thermal shock.


Wave Soldering: This is a large scale soldering process in which components are soldered into the PCB to form an electronic assembly. This process is fast and efficient as compared to manual soldering. Machine and designated components are used which can handle both SM and TH processes.


Above: An Wave Soldering Machine. Photo Courtesy: Wikimedia


Manual Soldering: This is the oldest form of soldering in which the surface is heated to melt the solder. However, we now have far more efficient methods so this technique is not used. It is used for certain start-ups and can also be used where the soldering of very small or meticulous components is required.

Tips and Precautions:

The soldering process is a very important component of the entire process. However, this process is equally dangerous and certain precautionary measures should be adopted. Some of them are mentioned here:

  1. Do not touch the soldering iron tip as it is heated to around 400 degrees.
  2. Do not touch the main flex with the soldering iron. The flex helps provide protection since it is heatproof.
  3. Remember to put the soldering iron back to its stand and not somewhere it doesn’t belong!
  4. Remember to solder your PCB in ventilated areas. Do not inhale the fumes released from the solder. For this make sure your room has proper air circulations.
  5. Solder is made up of lead which is poisonous so remember to wash your hands thoroughly once you’re done with the entire process.

Flux and its Function:

Flux is an important part of the PCB soldering process. It is a purifying agent which helps to reduce/eliminate the toxins formed due to oxidation and. It helps remove rust from the elements being soldered. Flux also helps the solder to melt and work properly. It also helps remove the wetting bridges.


Now that you have learned the basics of the soldering process, you can now proceed to make your own PCBs. Look for a reliable manufacturer and make sure that all the necessary steps are taken in each part of the process for a well-built PCB.

This article and associated images (except the Wikimedia image) are is provided by PCB Manufacturer PCBGOGO. You can contact them even for small order.