Types of soldering (Through-hole & SMD, 2023)
There are two methods of soldering: through-hole soldering and surface mount devices (SMD). Both of these methods are different in terms of soldering techniques, tools, and component types.
In through-hole soldering the component’s leads pass through the PCB and solder on the opposite side. Conversely, SMD involves direct attachment of components on the board and eliminates the need for drilling holes. The tools required for through-hole soldering are a soldering station, brass sponge, flux, solder wick, solder vacuum, solder stand, and tip tinner. For SMD, tools involve a tweezer, thin solder flux, stencil, soldering stand, desoldering pump, and hot air rework station.
In this blog, we will explore the differences between these two methods and the essential tools required for each, to help you to create solid and reliable soldering joints.
Let’s get started
Types of soldering
Through-hole and SMD soldering are the two primary types that dominate the electronics soldering world. Let’s discuss both of the methods in detail.
Type 1: Through-hole soldering
A through-hole is a soldering technique in which the components are mounted into the PCB through physical leads. The components are placed into the hole and then the leads are soldered to the opposite side of the board to keep the components in place.
The components in through-hole soldering are categorized according to the wire leads.
- Axial lead components
- Radial lead components
Axial lead components
In axial lead components, leads are terminals coming out from both sides of a component.
Axial lead components include a resistor, inductors, and diodes. The axial components are not perpendicular to a board so when they are soldered on the board it gives a flat outline.
Radial lead components
The components in which lead is extended from the same side of a component are categorized as radial lead components.
Integrated circuits, transistors, connectors, amplifiers, LDRs, and switches are some examples of radial lead components. These components occupy less horizontal space making them suitable for high-density devices.
When we use through hole type
Most of the time through hole components no matter axial or radial are designed for high power handling.
They are big in size for the same reason to handle high current and voltages. As they are big and to soldering them primly on the PCB board we go for through hole soldering type.
Through-hole technology offers a strong soldering bond between components which makes it a perfect approach for these larger components that undergo high voltage, and high power.
Other than that, we use this approach for making prototypes. Through hole soldering is relatively easy compared to SMD soldering. Also, it increases the prototyping speed as well.
Most of the modern age circuit uses both through hole and SMD components. So, it is not like a board will have only through components or SMDs. But you will use both types of soldering to make an end-finished PCB board.
Drawbacks of through hole type
The main drawback of this technology is the drilling of multiple holes through the board which is costly and also time-consuming. Due to the holes, the space and routing area for signal traces become limited.
Through hole soldering tools
When doing through-hole soldering you will need tools to create correct and strong soldering connections.
Let’s now examine all the equipment needed for through-hole soldering.
1. Soldering Station
If we call the soldering station the backbone of the soldering process it will not be wrong. Different soldering stations with different features are available.
No matter which type of circuit boards or prototypes (2 layers to 7 layers PCBs, analog or digital) or whatever voltage levels you work on, every electronics lab needs a safe and reliable best soldering iron or soldering station (Amazon link) or in most cases both.
Because if someone intentionally or unintentionally missed up with this device i.e. soldering station. It may cause him a lot of waste of time, money, and energy.
2. Solder wire
Solder wire that filler material due to which the soldering becomes possible. The solder was originally made up of tin, and lead and this was called leaded solder. Leaded solder is considered dangerous for human health due to the presence of lead in it.
Due to health issues, people went for lead free solder (Amazon link).
Lead-free solder is used now instead of leaded solder to reduce the negative impact or exposure to lead.
3. Brass sponge
Maintaining a soldering iron and cleaning its tip is an essential step to improve the performance and lifespan of the tool.
When you’re soldering the tip becomes oxidized or accumulates dirt. The brass sponge is used to clean the tip of the iron during the soldering process.
4. Flux
Flux is a chemical agent used to improve solder flow. There are different types of flux available such as water soluble flux and no clean flux.
Both types of flux are used to aid the flow of lead free solder. But when you use water soluble flux, it is recommended to clean and remove any remaining residue of flux.
Cleaning and flux removal are not required when no clean flux is used but if someone wants to remove residue they can use isopropyl alcohol (IPA).
5. Solder wick
Solder wick is used for desoldering and is called a desoldering braid. Due to the pencil-like soldering tip, it is often referred to as a rubber.
Very thin copper wire is braided to create a solder wick. The copper absorbs the solder, thus “erasing” any extra solder.
6. Solder vacuum
In through-hole soldering a solder vacuum is an essential tool. It helps suck out any extra solder that is stuck in the hold.
When you desolder the component the solder usually gets into the holes.
7. Tip tinner
Tip tinner is a chemical compound used to clean the tip of the soldering iron.
It prevents oxidation and removes any residue when the soldering iron is not in use due to the presence of mild acid in the composition.
Type 2: Surface mount devices (SMDs) soldering
Surface mount devices (SMD) or surface mount technology (SMT) is more popular and this is due to various reasons. Surface-mount technology, also known as SMT, is a process used to create PCBs by directly mounting the components on them.
Surface mount components
The word SMD soldering is actually due to the components we’re soldering during this process. We call those component surface mount components, because these components have no long leads that need to go through the PCB holes.
These components are soldered on the PCB board. They are small in size and are low power.
Why SMD soldering
The following are some reasons why we go for SMD soldering.
- The SMD is cost-efficient and requires less space as compared to through-hole components.
- The components used in SMD are relatively smaller in size and this reduces the overall size and dimension of a circuit board.
Size is an essential factor when you are designing PCBs. The components like resistors, capacitors, and diodes come in different size packaging such as 1206, 0805, 0603, etc.
When you are designing a PCB for your project and buying components for the SMD version denote the actual size of the component.
When you don’t keep the actual size of the component in mind the process becomes frustrating as a PCB and component will have different sizes. Different packages are often used for other parts, like transistors and integrated circuits.
SMD soldering techniques
SMD soldering first appears to be challenging, but with the right tools and procedures, it can be made easy. There are three most popular techniques used in SMD soldering.
Hand Soldering
The first technique is hand soldering, and it is the most traditional way for soldering SMD. This can be done by using a soldering iron with a fine tip.
In the beginning, it may be difficult for you but with some practice, you will get used to it. Hand soldering 1206 to 0603 packages is typically not too difficult.
A soldering microscope or magnifying lens may be required if you go any further smaller, due there small size.
Hot air soldering
It is a little simpler to solder using this method than using a soldering iron. The components are mounted using a hot air station (Amazon link) and solder paste in this procedure rather than a soldering iron.
You have to apply solder paste at the footprint. A stencil makes it easier but if don’t have any then use a solder pen to inject the paste on the pad.
Place the components one by one set the hot air station at the recommended temperature and expose the board to hot air.
Hot plate soldering
Hot plate soldering is the same process as hot air soldering but here instead of heating components one by one, a heating pad heats the whole PCB board.
This method is fast and clean as compared to soldering iron and hot air gun.
SMD Soldering tools
There are different tools used for SMD soldering. It’s time to look at all the equipment needed to solder SMD components.
1. Hot air rework
Hot air rework is similar to a soldering station except it blows hot air to melt the soldering wire to make connections.
It comes very handy when we just can’t solder very small devices on the board using normal soldering tips.
2. Tweezer
In SMD soldering you can not hold an SMD resistor, capacitor or any other component with bare hands.
For this, you will need a tweezer, and it is considered one of the essential tools for SMD soldering. It will also help in aligning components and reduce the risk of static charges.
3. Flux
Flux is essential for solder flow and removes oxidation. Use the right amount of flux for a clean and neat soldering finish.
Flux comes in different forms such as paste, pen and syringes. For SMD soldering flux pen is mostly used.
4. Stencil
A PCB stencil is a stainless sheet that has components’ footprints cut out of it. It is aligned over the board to match the footprint and to apply the solder paste with ease.
Sometimes stencil is not required but it becomes difficult when there are too many footprints on the PCB or you need massive production of the same board.
5. Soldering Stand
A soldering stand is essential for holding the PCB board. There are different type of soldering stand in the market. Some come with a magnifying glass which is suitable for SMD soldering.
6. Desoldering pump
The desoldering pump is also an essential tool. Sometimes we solder the wrong component or solder a component wrongly, so you will need a desoldering pump.
Both the wick and the pump function in the same way, with the wick removing the solder lead off the joints and the pump sucking it out using an air pump mechanism.
Conclusion
In the field of soldering both the through-hole and surface-mount devices are essential technologies, each with its unique advantages and applications.
As through-hole soldering has a higher power handling capacity and mechanical stability, it is appropriate for some applications and prototyping.
SMD soldering, on the other hand, is the method of choice for modern electronic manufacturing since it is efficient when it comes to space and enables automated assembly.
You will be able to work on a variety of electronic tasks with assurance and accuracy if you are aware of the differences between these two soldering processes and have the necessary tools for each.
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