Overview of PCB Soldering Techniques

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Guide to PCB Soldering Techniques

Curious about the world of PCB soldering irons, techniques and processes? It can be a tricky topic to jump into, especially if you have no prior experience. Today, we want to provide you with a basic overview of soldering, the various soldering techniques and how you can get started with PCB soldering.

We hope this serves as an excellent jumping-off point if you're looking to head to more in-depth information after this or as a perfect refresher if you already have some background in soldering but are looking to brush up on the basics. In this guide, you'll find information regarding the following:

Read our entire guide, or jump ahead to just the section you want to brush up on.

What Is Soldering?

Soldering means joining metal components with a melted metal called solder, which has a low melting point compared to other metals. Soldering is crucial in the electronics industry and is the primary method of joining electrical components. In addition to constructing printed circuit boards (PCBs), soldering is used in roofing, making jewelry, plumbing and joining pipes.

There are different solder types, though they're typically mixed to have low melting points. The most common combination is a tin or lead metal alloy mixed with silver or brass. The soldering iron melts the metal so it can be used like glue to connect two pieces. Once the solder cools and hardens, the two pieces become a single component. Usually, the solder looks like a thin wire or tube. Inside the tube is an acidic mixture called flux, which prevents oxidation.

In the interest of reducing lead use due to safety and environmental concerns, some lead-free versions of solder are now available, though they're typically less effective. These alternatives often include copper, brass, silver or tin.

What Are Soldering Irons?

A soldering iron is a pen-shaped tool used to melt the solder and combine your two pieces. An electric soldering iron, by definition, runs on electricity. Electric soldering irons are the most common, though butane soldering irons are also available for increased portability.

A soldering iron first transfers heat to a PCB. From there, the solder is applied to connect the two metals. A soldering iron in the shape of a pen is usually the easiest to use, but all soldering irons take some practice and skill to use effectively.

What Is PCB Soldering?

PCB soldering refers to applying solder to printed circuit boards, one of the most common types of soldering. There are various PCB soldering processes, though most typically involve joining components to the PCB surface to create electrical connections. PCB soldering is a vital skill for anyone working with electrical circuits.

What Are the Different Types of Soldering Techniques?

There are several ways to solder a PCB, which largely break down into two separate techniques known as hard soldering and soft soldering. Let's compare these two techniques.

1. What Is Soft Soldering?

Soft soldering is used for attaching small components to the larger PCB. It is also the most common form of soldering. These small components will usually have a low-liquefying temperature that will begin to break down under the high temperatures of the heat source. Rather than simply melting the component, however, an additional step must be used to attach the component to the board. In this case, this extra step is a filler metal, which is typically a tin-lead alloy.

The most important element of this alloy is that its melting temperature must be greater than 752 degrees Fahrenheit. This alloy is crucial during the soldering process since it acts as a binding agent between the component and the board, holding the two together solidly. Typically, a gas torch creates the necessary heat for this project, causing the alloy to break down and bind the component to the board.

2. What Is Hard Soldering?

Hard soldering creates a stronger bond and is a process that uses a solid solder to join two different metal elements together by spreading throughout the holes of the components that become unlocked as they're exposed to high temperatures. As a process, hard soldering is made up of two smaller sub-processes known as silver soldering and brazing.

As the name suggests, silver soldering uses a silver alloy, often cadmium-silver, as a space-filling metal. This method is used to fabricate small components and perform maintenance on a circuit board. Silver offers a free-running individuality, although it is not typically an ideal choice for space filling on its own. This is why different flux is usually used to create reliable silver soldering.

Brazing is a soldering technique that connects two terminals made of base metals using liquid filler metal. This filler runs by way of the attraction of a vessel through the board's joints and, once it cools down, provides a union through atomic magnetism and diffusion. The result is a strong joint that connects the two different terminals. For brazing, brass is typically used as the filler agent.

Necessary Soldering Equipment

The various tools and materials necessary for a soldering project will vary depending on your project. You'll likely need these basic circuit board repair tools and materials regardless of the project.

1. Soldering Iron

This handheld tool provides the heat source needed to melt the solder. Soldering irons are typically pencil-like in shape and consist of several different parts that work together to form a comfortable, practical and easy-to-use tool.

While most irons are fairly small, larger solder guns are also available. These soldering guns are often used for more precise projects, such as making jewelry, where more heat is required. Soldering guns also cool much quicker. All soldering irons have the same essential components regardless of their size or shape, including:

  • Tip: Think of this as the lead at the tip of the pencil, and the part of the iron that will be touching the solder. This is the part of the tool that gets hot and that you'll use to melt and manipulate the solder. The tip is made of a copper core and is plated with iron. A clean tip is critical for effective soldering. You can clean the tip of your soldering iron with a wet sponge before the soldering process. Tips are also interchangeable and are meant to be swapped out based on the type of project you're working on.
  • Wand: This is the iron's handle and the part you'll hold onto. The wand usually features a padded grip that provides something to hold comfortably and insulates you from the heat of the iron.
  • Solder wick: If the tip of your soldering iron is the lead in the pencil, then think of the solder wick as the eraser. The solder wick is made of copper wire braided together and removes extra solder that won't be needed. You can also use solder suckers to remove excess solder.
  • Rest: While not part of the iron itself, the rest is an essential accessory that allows you to set the iron aside to free your hands. The rest prevents your table, counter or workspace from being damaged by the hot iron if you should lay the iron directly on this surface.

If you're looking to buy a soldering iron, consider factors like temperature control, size, wattage and voltage.

2. Solder Flux

Solder flux is a purifying agent. When it comes to soldering, flux serves three different purposes simultaneously, making it an essential tool to have on hand for any project. First, it purifies the components you're soldering by cleaning them of any rust. It also closes out any extra air that might come into contact with the material, thus preventing future rust. Finally, it improves the dripping individuality of the solder itself.

It is generally recommended to solder in a well-ventilated area because solder flux often has a distinct and unpleasant odor.

3. Soldering Paste

Soldering paste is a gray putty-like material. You'll use this paste to join the various leads of chip packages to connection ends on a PCB.

4. Circuit Board

The PCB is your circuit board. All the soldering you'll do will take place on the surface of this board as you use your soldering tools to connect various components and terminals to the board.

What Are the Steps to PCB Soldering?

With a bit of knowledge about what PCB soldering is, what the various techniques are and what tools are necessary for the job, let's now take a closer look at how to solder a PCB in simple, easy-to-follow steps.

1. Tin the Solder Iron

Preparing your solder iron involves a process called tinning. Tinning helps transfer heat from the iron to the surface you're soldering to and protects the tip from unnecessary wear and tear. Tinning your iron before and after each use helps to preserve the tip and extend its life.

Allow your iron to warm up until it reaches full heat. Once the iron is hot, wipe the tip on a wet sponge to ensure it's clean before starting a new project. After it's clean, dip the iron tip in the solder, ensuring it's completely coated. Thorough coverage often requires lots of solder and is likely to drip, so be prepared to prevent making a mess. Allow the solder to flow around the tip evenly, and then it's ready for soldering.

2. Prepare the PCB or Other Surface

Whether you're soldering a PCB or other surface, it's best to start with a clean surface. Clean your surface with an industrial cleaning wipe or acetone cleaner to remove any dust or other debris that may affect your soldering. Compressed air also helps remove small particles and dries the surface quickly.

3. Position Your Components

For most soldering projects, you'll likely solder a couple of components per session, completing the project over several sessions. It's best to begin with the smaller components and finish with the larger components to prevent the surface from sitting unevenly and being weighed down by a heavy piece.

Select the small components you'll start with and position them in their places on the surface. You may insert components into through holes when placing components on a PCB. If the components don't stay in place on a PCB, you can bend the leads slightly under the board so they hold still.

4. Heat the Joint

Heating the joint conducts the iron's heat to the PCB to prepare the board for soldering. With a small amount of solder on the iron's tip, touch the tip to the component lead and board. Connecting the tip with both these pieces is critical to ensure the solder sticks them together and heats them properly. Only hold the iron on the joint for a few seconds, as overheating the joint will cause bubbling. Use caution during this step to prevent overheating.

5. Solder the Joint

Now your joint is ready to solder. While you'll want to keep your iron near the joint, you shouldn't touch the solder strand to the iron. Instead, the solder should be applied directly to the heated joint. If it's been heated thoroughly and correctly, the hot joint will be enough to melt the solder and begin to flow freely. Continue touching the solder strand to the joint until a small mound has formed.

Set the solder strand and iron aside, and allow the joint to cool. While it cools, it's essential to keep the surface flat and still, as moving it will result in a grainy, dull finish.

6. Inspect the Joint and Trim the Leads

After the joint cools, visually inspect it to ensure it looks adequate. Once you're satisfied with the soldered joint, trim the lead and extra wire just above the joint. The finished solder joint should be a smooth, shiny cone. Solder the remaining components and clean any excess flux from the surface to finish the product.

Get Soldering Training From Precision PCB Services

Are you interested in advancing your skills in the world of soldering? While you can always practice and experiment with new techniques in your own time, you may want training that goes beyond what you can teach yourself. When you reach this point, you may consider professional soldering training.

At Precision PCB Services, our seminars provide the opportunity to gain hands-on training experience in the world of assembly, re-working and soldering. The training you'll gain during these seminars will set you in a position to be eligible for job advancements and openings, making you more hirable and ready to succeed in whatever job you find yourself in.

All our assessments are done by assessing practical skills and performance levels alone, with no written tests conducted for the program. English as a second language is also a special consideration of this training series, with instructors proficient in both English and Vietnamese.

Here at PCB Precision Services, we've been immersed in the world of circuit boards for over 25 years, providing quality service, distributing unbeatable products and providing you with the training you need to succeed. Our industry knowledge is in-depth and far-reaching, and we're eager to share it with you as you begin our training sessions.

Learn more about our instructional soldering seminars and how they can help you advance your career.

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