PCB Soldering Basic Techniques and Overview

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. There are different types of soldering materials based on quality and their 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.

PCB soldering involves joining electronic components to a PCB using solder, a fusible metal alloy. The solder melts when heated and forms a strong electrical and mechanical bond between the component leads and the PCB pads as it cools. Proper soldering ensures that the components are securely attached and that the electrical connections are reliable.  In this blog, we'll explore the basics of Through hole PCB soldering, covering essential techniques, tools, and tips to help you achieve clean and effective solder joints. See our detail guide on SMT components and soldering.

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. Rather than simply melting the component onto the PCB, a filler metal must be used to attach the component to the board which is typically a tin-lead alloy. This alloy is crucial during the soldering process since it acts as a binding agent between the component and 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. As a process, hard soldering is made up of two smaller sub-processes known as silver soldering and brazing. A silver alloy, often cadmium-silver used as a space-filling metal. 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.

Further this article is divided into 3 parts, which covers all the main aspect of basics soldering techniques:

1- Basics Soldering Tools required for Through hole PCB

2- Soldering Technique for Through Hole Components

Tools Required for Through Hole PCB Soldering

Before diving into soldering techniques, it's important to have the right tools on hand. Here's a list of essential soldering tools:

• Soldering Iron: The primary tool for soldering, used to heat and melt solder. Choose an adjustable-temperature soldering iron with a fine tip for precise work. See the best available soldering tools and how to choose one.

• Solder Metal: A metal alloy, typically a mixture of tin and lead or a lead-free alternative. Rosin-core solder is common for electronics due to its built-in flux.

• Flux: A chemical cleaning agent that removes oxidation and promotes the flow of solder. Some solder comes with flux built-in (rosin-core), but additional flux may be needed for certain tasks.

• Soldering Stand: A holder for the soldering iron when not in use, often with a built-in sponge for cleaning the tip.

• Desoldering Pump or Wick: Tools for removing excess solder or correcting mistakes.

• Tweezers: For handling small components and holding them in place while soldering.

• Magnifying Glass or Microscope: Helps in inspecting solder joints, especially for small components.

• Safety Equipment: Includes goggles to protect your eyes from solder splashes and a fume extractor or fan to remove harmful fumes.

How to Solder Through Hole Component on a PCB

1. Tin the Solder Iron

Preparing your solder iron involves a process called tinning. Tinning helps transfer heat from the iron to the soldering surface. Tinning your iron before and after each use helps to preserve the tip and extend its life. 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. Allow the solder to flow around the tip evenly, and then it's ready for soldering.

2. Prepare the PCB 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.

3. Position Your Components

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.

5. Solder the Joint

Now your joint is ready to solder. 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.

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.

Quick Tips and Tricks of Soldering

Here's some common-sense advice that sometimes even soldering veterans forget:

1. Soldering bits and tools: There are many different types of bits and solder materials. Choose the right tools and materials according to the requirements.

2. Good joint/Dry Joint: To ensure a good, strong joint is formed, do not move the component or touch the solder before the solder cools or blow-cool the joining. There should be an adequate amount of solder – not too little, not too much.

3. Thermal issues: Take great care when heating the connection. Overheating can cause damage to the electronic component or PCB. To reduce the probability of damaging the component, attach a metal crocodile clip to the lead of the component to reduce heat flow from the connection to the component.

4. Soldering tip cleaning: To increase the lifespan of the soldering tip and ensure optimal performance, ensure the bit is properly tinned to prevent oxidation. Melted solder flows smoothly on a tinned tip.

Common Soldering Mistakes and How to Avoid Them

Cold Joints: A cold joint occurs when the solder doesn't fully melt, resulting in a weak connection. To avoid this, ensure the joint is heated properly before applying solder.

Bridging: Bridging happens when excess solder connects two adjacent pads, causing a short circuit. Use a fine-tipped soldering iron and minimal solder to prevent this, or remove excess solder with a desoldering pump or wick.

Insufficient Solder: Using too little solder can create a weak joint. Ensure enough solder is applied to fully cover the pad and component lead.

Safety Tips for PCB Soldering

1. Handle Soldering Irons Carefully: Always place the soldering iron in its stand when not in use, and be mindful of the hot tip

2. Work in a Well-Ventilated Area: Soldering produces fumes that can be harmful if inhaled. Use a fume extractor or fan to disperse the fumes.

3. Wear Protective Gear: Safety glasses and gloves can protect against solder splashes and burns.

Conclusion

Soldering circuit boards can be a challenging yet rewarding skill to master. By understanding the basics, using the right tools, and following best practices, you can create reliable and durable solder joints that ensure the long-term performance of your circuits. Whether you're assembling a new PCB or repairing an existing one, these skills will serve you well in all your electronics projects. Remember to follow safety precautions, work in a well-ventilated area, and keep your workspace clean and organized to ensure a successful soldering experience. To experience our world class PCB assembly services quote now!