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PCB/PCBA knowledge
What do you need to know before PCB soldering

PCB soldering refers to a process of joining electronic components to a printed circuit board. Soldering is a crucial step in the manufacturing of electronic devices and involves the use of a soldering iron or machine to melt a small amount of metal alloy, called solder, and apply it to the junction of the component lead and PCB.

PCB soldering creates a mechanical and electrical connection that ensures that the component remains fixed to the PCB and provides a reliable electrical path between the component and the circuit. PCB soldering requires the use of various tools, equipment, and techniques to ensure high-quality connections, such as soldering irons or rework stations, flux, solder wick, and solder pumps, among others. Properly soldered PCBs play a key role in the overall functionality and longevity of electronic devices.

What is PCB soldering?

PCB Soldering is an electronic components joining process by melting solder to bind components to a printed circuit board (PCB). Solder is a melted metal alloy with a low melting point to join electrical components.

PCB soldering process involves heating the component leads and PCB pads with a soldering iron or a reflow oven and then applying molten solder to create a strong electrical and mechanical connection. PCB soldering requires a high degree of precision and skill to ensure that the components are attached securely without damaging the surrounding circuitry.

What are the different types of solder?

What are the types of solder
What are the types of solder

PCB manufacturing and assembly process includes multiple steps, from design to assembly and packaging. PCB soldering palys a crutial role in PCB assembly, and there are different types of PCB solder with different characteristics, safety considerations, and disposal concerns that should be considered when used to assembly components.

The types of PCB solder can be distinguish by core material, metallic constituent.

1. core material

  • Rosin core solder: With a mild flux and flux residue cannot be removed.
  • Acid core solder: With aggressive flux and flux residue from acid core solder must be removed after soldering
  • Solid core solders: Without flux and can be used for manual soldering

2. metallic constituents
Two main include lead solder and lead-free solder, and others such as silver solder, aluminum solder, copper solder, brass solder

  • Lead solder:
    -Melting point: around 180-190°C
    -Common lead-based solder alloys:
60/40 Sn/Pb
63/37 Sn/Pb
62/36/2 Sn/Pb/Ag
  • Lead-free solde: gaining more popularity when the EU started restricting the Restriction of Hazardous Substances (RoHS) Directive in consumer electronics.
    – higher melting point

What are the steps of PCB soldering?

PCB soldering steps
PCB soldering steps

1. Gather materials: soldering iron, solder wire, flux, PCB board, and components.

2. Surface Preparation: Prepare the workspace by ensuring it is clean and free of flammable materials.

3. Place components: Place components onto the PCB board according to the circuit diagram and use a helping hand tool to hold them in place.

4. Apply flux: Apply flux to the joints where the components will be soldered.

5. Apply heat: Heat the soldering iron and apply it to the joint, allowing the heat to melt the solder wire.

6. Soldering: Touch the tip of the solder wire to the joint and allow it to melt and flow over the joint, forming a solid bond.

Move to the next solder joint and repeat the process until all components are soldered in place.

7. Clean: Clean the excess flux off the PCB board using a brush and isopropyl alcohol.

8. Inspect: Inspect the soldered joints for any signs of defects or bridges, and fix any issues as needed.

9. Test: Testing the circuit to make sure it is functioning properly.

PCB soldering processes
PCB soldering processes

What are the basic principles of PCB soldering?

The basic principles of PCB soldering PCB
The basic principles of PCB soldering PCB

Properly prepared surfaces – ensuring that the surface of both the PCB and the component is clean, free from dust or dirt, and has been properly prepared for soldering.

Appropriate solder temperature – at a suitable temperature to ensure it melts evenly and bonds firmly without causing damage to the components.

Solder placement – should always be placed in the right area and not overflow onto other parts of the board.

Correct solder quantity – using just enough solder to make an effective connection, avoiding any excess material as this could cause short circuits and heat-related issues.

Adequate support – ensuring proper mechanical support during and after soldering, such as
holding the components with tweezers or fixing them into place on a jig when possible.

Avoiding movement – preventing any unnecessary movement of the components soon after they’ve been assembled to minimize faults caused by their displacement.

Safety precautions – following standard safety protocols and wearing appropriate protective
gear while working with high temperatures materials.

What soldering equipment you need?

What soldering equipment you need
What soldering equipment you need

Soldering iron – A tool that provides heat to melt the solder.

Wire strippers – Used to remove insulation from the wire.

Safety glasses – Protect your eyes from flying debris or molten solder

What are the most common faults in PCB soldering?

Cold solder joints occur when the solder does not flow properly, resulting in an incomplete joint.

Solder bridges: This happens when excess solder connects two adjacent pins or legs of a component.

Tomb stoning: This typically occurs when one end of a surface mount component lifts off the PCB, causing the component to stand up like a tombstone.

Solder balling: This occurs when small droplets of solder form on the pad or component.

Lifted pads: This happens when the copper pad lifts off the PCB, leaving the component without a connection.

Insufficient solder: This happens when there is not enough solder applied, resulting in an incomplete joint.

Excess solder: This happens when too much solder is applied, resulting in a blob of metal on the PCB.

Common faults in PCB soldering
Common faults in PCB soldering

How to achieve perfect PCB soldering?

Adequate Lighting: Choose a well-illuminated workspace as it allows you to work freely without squinting your eyes, which could lead to a mistake.

Prepare the Surface by Cleaning It: The surface of your printed circuit board (PCB) must be cleaned with isopropyl alcohol or any other cleaning agent to get rid of oils and dirt.

Use Correct Solder Temperature: Every solder has a melting point beyond which it begins to corrode. To achieve the best results possible, heat the iron until it reaches roughly 10°C over the temperature of the surrounding material.

Don’t Keep Your Iron at One Location for Too Long: When heating your solder iron to the correct temperature, keep in mind that you do not need it constantly hot.

Holding the iron on one spot of your PCB may harm the conductor traces within the pad.

Use Flux: Adding flux increases the spreadability of liquid solders across metallic surfaces making them stick more easily and accurately.

Limitive Usage of Solder: Do not put excessive quantities of solder onto your circuit board. Instead, use the tiniest quantity required so soak into and solidify around the bare metal pins or holes.

Check Connections After Soldering: Ensure all connections affected by the solder are conductive after allowing them enough time to cool down.
By following these steps correctly, you should attain satisfactory PCB soldering results!

How to achieve perfect PCB soldering
How to achieve perfect PCB soldering


In conclusion, PCB soldering is a critical process in the fabrication of electronic devices. It requires precision and skill to ensure that the components are correctly connected to the board. Proper preparation, careful handling of parts, accurate placement, and appropriate temperature control are all essential aspects of successful PCB soldering. Ensuring these elements are done right can help prevent damage to equipment, and delays due to rework or failures, and ultimately improve the reliability and efficiency of electronic devices.
1.Gather materials: soldering iron, solder wire, flux, PCB board, and components. 2.Surface Preparation: Prepare the workspace by ensuring it is clean and free of flammable materials.

When soldering, you need to foucs on three important factors:
1. Heat: a suitable temperature to ensure it melts evenly and bonds firmly without causing damage to the components
2. Time: Appropriate soldering time to ensure its quality
3. Surface: ensuring that the surface of both the PCB and the component is clean, free from dust or dirt, and has been properly prepared for soldering.

  • Solder bridges
  • Tomb stoning
  • Solder balling
  • Lifted pads
  • Insufficient solder
  • Excess solder
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Hi, I am Ruth. Based on extensive studying and working experience in electronic, PCB and related industry, I am proficient in electronic components, PCB production process and assembly technology. It's my honer to share with you the professional knowledge of PCB, PCBA and related industry through my articles. If you have any demands about PCB such as design, manufcturing and assembly, I would like to provide you the most effective views and suggestions.

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