A Complete Guide to PCB Soldering

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Mar 3, 2021|Manufacturing Excellence

PCB soldering is an essential skill for electrical technicians or anyone interested in the mechanics of electrical circuits. It’s also a relatively easy process to learn and can be applied to an array of soldering jobs. In this article, we will dive into the process of PCB soldering, the various techniques you can apply, and the materials needed.

What is PCB Soldering?

PCB soldering refers to the process of using solder to join two small pieces together onto the surface of an electrical circuit board. The process involves dissolving a solder and running it on the two contacts you wish to bond together.

This technique is a relatively simple and effective way of connecting two or more electrical components on a circuit board.

Soldering Techniques

You can execute the PCB soldering process using a variety of different methods. The two main techniques are soft soldering and hard soldering, both of which are equally effective when correctly performed.

What is Soft Soldering?

Soft soldering is perhaps the most common PCB bonding process. If you’re asking yourself, “what temperature should I solder PCB?”, this method involves soldering with relatively low liquifying temperatures of up to 450 °C or 842 °F. Soft soldering is best for attaching small components onto a larger PCB.

Before melting the components, you must use a tin-lead alloy as a filler metal. This alloy must have a melting point greater than 400 °C or 752 °F to successfully act as a binding agent between the component and the board. A gas torch will distribute the heat needed to break down the alloy, binding the component and the board together.

What is Hard Soldering?

Hard soldering, commonly referred to as brazing, joins two different surfaces using an alloy film, such as brass. This technique is used on metallic surfaces and creates a stronger bond than can be achieved with soft soldering as a result of atomic magnetism and diffusion.

The hard soldering process involves spreading the solder throughout the holes of the components. The holes then become unlocked once exposed to high temperatures. It’s important to note that you must carefully clean the surfaces before beginning the process, removing all grease traces.

Hard soldering can also involve silver soldering, which uses a silver alloy as the space-filling metal. This method re-creates small components on the circuit board for free-running individuality. However, it is not the most reliable option for space-filling.

What Equipment Do You Need to Solder?

Soldering tools and equipment may vary depending on the type of soldering projects you’ll be embarking on and their levels of difficulty. However, if you’re a beginner just starting out, these are some essential soldering tools you’ll need for any soldering job.

1. Soldering Iron

A soldering iron is a handheld tool that acts as the heat source used to melt the solder. They can come in a variety of sizes but are typically quite small and pencil-shaped. Each soldering iron comes with a tip, a wand, a solder wick, and a rest.

Made from copper plates, the tip is where the heat will emit from and where you place the solder to melt and manipulate its shape. The wand is the area at which the iron is held and usually has a padded grip for comfort and insulation, so you are protected from its heat. The solder wick is made of braided copper wire and is used to remove any excess solder.

Finally, the rest is a separate accessory where you can place the soldering iron when not in use to avoid damage to your table or workspace.

2. Solder Flux

Solder flux’s primary function is to act as a chemical purifying agent for the components by removing rust. It also prevents further oxidation by blocking any air from coming in contact with the material. As a result, this improves the soldering process by altering the surface tension of the solder.

3. Soldering Paste

Soldering paste is a putty-like material made up of solder particles and sticky flux. It functions as an adhesive that temporarily binds the components to the PCB.

4. The PCB

PCB stands for printed circuit board and is the surface on which all the soldering will take place. The circuit board is where all the various components and terminals will be soldered and bound. If you don’t know where to purchase PCB and you are in need of PCB manufacturing, Candor is your go-to.

Steps to Soldering a PCB

There are some basic steps to follow for any PCB soldering job to ensure you’ve done your job correctly and efficiently.

1. Prepare the Soldering Iron

The first step to PCB soldering requires the initial preparation of the soldering iron. Begin with the process of tinning, which involves coating the tip of the iron in the solder. Allow the iron to heat up thoroughly before covering the entire tip, using plenty of solder to do so. Once coated, immediately wipe off any excess flux, as it can harden quite quickly.

Pay close attention to the temperature of your soldering iron. Can soldering damage PCB? If you leave your soldering iron on for too long, the excessive temperatures can burn PCB causing irreversible damage.

2. Prepare the Surface

Next, you’ll need to prepare the surface of the PCB board. The board should be as clean as possible, free of dust, debris, and grease. Wipe clean with an industrial cleaning pad and clear off any lingering particles with a blast of compressed air if possible.

3. Place the Components

Experts recommend that you start the soldering process with smaller pieces, working your way to the bigger ones. This allows the circuit board to stay balanced and you to evenly distribute the pieces across the board. But, what side of PCB is correct for soldering? Typically, you will have a “bottom” side that is without components. This is the side that you should be working on.

Select a few small components and place them throughout the board. Bending the lead, sometimes at a 45-degree angle, will assist you in inserting the components successfully into the holes and helping keep the pieces in place.

4. Apply Some Heat

If you’re wondering how you hold the PCB when soldering, you should always use a heat-resistant pad to keep the PCB in place. Apply a small amount of solder on the tip and position the iron so that the tip touches the board and the lead. The solder will then make contact with both, heating up in preparation for the soldering. Hold the iron in place for a few seconds before releasing it.

It’s important not to hold the iron down for too long as it can result in overheating very quickly.

5. Add Solder to the Joint

Once heated, gently touch the tip of a strand of solder to the solder pad and lead. At this point, the solder should flow smoothly, and the flux will start to liquify. Continue to add the solder around the joint, forming a small mound. From here, remove the soldering iron and set it down.

To achieve a smooth finish, ensure the joint stays absolutely still while it cools. From here, you can begin trimming the lead using side cutters. Always be sure to clean up any excess flux from the board once you’ve finished with the job. If there appear to be any errors, it’s relatively easy to desolder and start again.

Conclusion

PCB soldering is a simple soldering technique that anyone with an interest in electrical mechanics can employ. It’s a fundamental skill that can save you time and money in the long run if executed correctly.