PCB Blog - How to solder to a PCB?

Soldering is the process of connecting two metals by melting the filler metal in the middle. The most common use of soldering is to connect electronic components to printed circuit boards (PCBs). The main purpose of soldering is to establish a solid and reliable electrical connection. There are many reasons why correct soldering is necessary. Poor soldering of joints can lead to short circuits, thermal damage, and signal interference.

PCB soldering

Main PCB soldering technology

The best way to ensure good solder joints is to use the correct tools and follow the correct soldering techniques. The most commonly used technologies are:

Wave soldering: Wave soldering is a manufacturing process in which electronic components are soldered onto printed circuit boards (PCBs) using one or more soldering waves on a wave soldering machine. Solder waves are generated by heating the solder bath to the melting point and then using PCBs and components. Wave soldering is the most popular technology for manufacturing PCBs, accounting for over 60% of all PCB components.

Reflow soldering: This is a process of coating solder paste on the surface of the printed circuit board (PCB) through a spot welder. Next, the PCB is placed in an oven, where the solder paste is melted and allowed to flow through the surface of the circuit board. Then, solder joints are manufactured by making the PCB and component leads come into contact with each other. Reflow soldering is often used to weld surface mount components in mass production.

Selective soldering: Selective soldering is the process of soldering specific components on a printed circuit board (PCB) to avoid other components. In selective welding, only specific solder joints are melted, while the rest of the circuit is not affected. This can more effectively use solder and help prevent damage to precision components.

What are the steps involved in PCB soldering process?

1. Clean the work area and ensure that all necessary tools and materials are within reach.

2. Place the PCB board on the working surface so that it can easily reach all solder joints.

Next, coat the solder joints with a thin layer of solder, as this helps ensure a secure connection.

4. Preheat PCB and soldering iron

5. Apply solder to the tip of the soldering iron

6. Contact the solder with the joint to be welded

7. Apply pressure to the soldering iron when it comes into contact with the solder and PCB

After the solder melts, fix the soldering iron for a few seconds to ensure a good connection

9. Remove the soldering iron and wire and check if the solder joints are connected correctly

10. Clean PCB

Tools and materials required for soldering PCB

1. Soldering iron

Solder iron, also known as a soldering gun, is the most important piece of equipment for soldering. The handle, core, and head of a soldering iron are the three main components of a soldering iron.

A soldering iron and an electric heater have the same heating element. When current flows through the component, heat is generated. This heats a piece of iron and then transfers the heat to the welded joint.

Use soldering and desoldering rework stations in repair workshops, factories, and laboratories instead of independent soldering irons. These systems provide higher efficiency and can perform more complex tasks than individual functional devices.

2. Solder wire

Alloys containing 60% tin and 40% lead are the most commonly used solder wires in electronic manufacturing. It has a melting point of 190 degrees Celsius and will solidify after cooling.

This alloy comes in various sizes of metal wire forms. Using a thinner gauge is better than using a thicker gauge. Specification 18 or 22 soldering wire is a suitable choice for general applications.

3. Welding flux

Another substance called flux, usually called solder paste, is used to promote the soldering process. Flux removes the oxide coating on the surface of the weldable metal and improves the wettability of the solder. The current welding wire has flux in the center core. The melting point of flux is lower than that of welding wire. It does not require a separate flux. Soldering iron, welding wire and flux are required for soldering. Other soldering accessories include soldering gun holders, cutting tools, desoldering pumps, etc.

How to solder a PCB?

The welding technology of PCB boards is generally divided into two methods: manual soldering and machine soldering.

1. Manual welding

Manual welding is usually carried out using a handheld electric soldering iron or a temperature-adjustable welding furnace.

1) It is necessary to prepare tools such as soldering wire, soldering iron/soldering furnace, PCB board, components, and materials such as heat shrink tubes.

2) Place the components in the corresponding positions on the PCB board according to the shape and arrangement of the component pins.

3) Use a handheld soldering iron or soldering furnace to heat the pins of the components and the solder pads on the PCB board, making them hot.

4) Place the solder wire on the pins and pads, and wait for some time until the solder wire melts and adheres to the pins and pads.

5) For components that require heating and sealing of the shrink tube, a welding gun or furnace can be used to heat and seal the shrink tube.

6) After soldering is completed, it is important to check the correspondence between the component pins and the solder pads on the PCB board, and also check the quality of the solder joints to ensure their firmness.

2. Machine welding

Machine welding is a method of automatically heating and soldering components, usually using an SMT machine for soldering.

1) We need to prepare an SMT machine, soldering wire, components, PCB board, and other materials.

2) Place the components at the feeding port of the SMT machine and observe whether the packaging type and pin position read by the device are correct.

3) The SMT machine will perform a series of automatic operations such as heating, welding, pressing, and bonding based on preset process parameters to complete the soldering work.

4) After soldering is completed, inspect and inspect the solder joints to ensure their integrity.

Whether it is manual soldering or machine soldering, it is necessary to pay attention to the correct soldering temperature and time, select appropriate and sufficient solder wires, and strictly follow the component data manual and PCB layout for welding operations to ensure the quality and stability of soldering.

During the PCB soldering process, the welding points are heated to combine with the copper foil on the circuit board to achieve electrical connection and mechanical fixation. PCB soldering is one of the essential processes in the manufacturing of electronic equipment and products.