Through-hole and SMD components(Basics, 2024)

In electronic components assembling, Through-Hole Technology (THT) and Surface-Mount Technology (SMT) are the two most common assembly techniques that have influenced circuit board design.

So the components used in these technologies are through-hole and SMD components. Through-hole components have leads that extend through pre-drilled holes on a PCB and are soldered on the opposite side. SMD components, being smaller, are directly mounted onto the PCB surface without the need for holes, making them easier to place and solder.

In this article, we’ll discuss both through-hole and SMD components to understand their significance in electronic circuit design.

Through-hole components

When it comes to designing electronic devices and working with PCB (printed circuit board) there are various components to use.

To design PCB, through-hole, and SMD technology are used, the components that are used in these are called through-hole and SMD components.

Let’s discuss through-hole components first.

Through-hole components are an integral part of electronic device manufacturing. It is the old concept to design PCBs but still, some industries use this technology.

Through-hole technology is the process in which the components are placed in drilled holes on the printed circuit board (PCB). To put electronic components, holes are drilled into the PCB.

Once the holes are drilled, the components are placed through them. It is important to place the components into the holes properly.

The products that require strong connection, the through-hole components are the best because they are highly reliable. The through-hole components have leads or pins that allow them to be inserted into drilled holes.

a. Types

There are two types of through-hole components based on the lead or pin orientations.

Axial Lead: The components having leads on both ends are called axial lead components. These components leads allow easy polarity identification, and mechanical stability as they are prone to movement or displacement, making them suitable for applications with vibration or mechanical stress.

Radial lead: Radial lead components have both leads on one side. These leads run into the entire PCB board, so in various layers of the board, they can be connected. These components are easily mounted, occupy less space, and due to their larger body size provide better heat dissipation. They can be affected by mechanical stress.

b. Components

Here’s an overview of some common through-hole components, including their shape and function:

1. Resistors

The through-hole resistors are cylindrical and have two leads extended at both ends. Both leads will be inserted in holes in the PCB.

They are often color-coded to indicate their resistance value and used to limit the current in the circuit.

2. Capacitors

The though-hole capacitors are cylindrical and can have leads extended from both sides or the same sides.

Capacitors store and release electrical energy in a circuit. They are used for filtering, timing, and energy storage applications.

3. Diodes

Diodes are cylindrical and rectangular with two axial leads. They are often used for rectification.

4. Transistors

The shape of the transistor can vary but typically has three radial leads extending from a small, flat, or cylindrical body.

5. Integrated circuits (ICs)

The integrated circuit has various pins and rectangular or square with multiple radial leads extending from the sides.

It consists of various electronic components like transistors and diodes on a single chip. They perform different complex functions.

c. Benefits

In certain electronic applications, the through-hole components have several advantages.

Let’s explore these benefits in detail.

1. Mechanical stability

Through-hole components provide mechanical stability. The leads or pins of through-hole components are inserted through the PCB, which creates a strong physical connection.

The strong connections make them less susceptible to mechanical stresses such as vibration, impacts, or thermal cyclings.

In applications where the device might undergo physical stress or operate in harsh environments, the sturdiness of through-hole components ensures better longevity and reliability.

2. Repairability and accessibility

The through-hole components are large which makes them more accessible for manual soldering, rework, and repairs.

The technicians can easily identify, and replace the components that are damaged which will help to maintain the proper function of the circuit.

This accessibility is especially valuable in prototyping, testing, and low-volume production where rapid modifications or repairs are common.

3. Efficient heat dissipation

Due to the larger size of through-hole components, it provides better heat dissipation capability than SMD’s components.

For applications where components can generate more heat such as power transistors and diodes, this feature is beneficial for them.

The larger leads and exposed metal surfaces facilitate better thermal management, enabling these components to handle higher power levels without overheating.

4. Suitable for prototyping

Prototyping is a process in which a team implements the idea practically. The through-hole components are very suitable for prototyping.

These are larger in size which makes it easy to remove and reinsert it. So experimenting with them refined our idea more.

These components are fragile and easy to use for prototype circuits.

5. High voltage and current application

Because of through-hole components’ stronger design and superior electrical insulation, through-hole components are recommended for high-voltage or high-current applications.

Even in the most severe circumstances, there is less chance of an electrical breakdown or short circuit due to their bigger physical dimensions, which enables higher voltage breakdown ratings and improved isolation between leads.

d. Drawbacks

Besides several advantages, through-hole components also come with certain limitations and drawbacks.

1. Size and space constraints

One of the primary disadvantages of through-hole components is their larger physical size compared to surface-mount devices (SMDs).

We have to insert the leads of a component through the holes and solder it on the opposite side, this limits the minimization of the electronic design. So the devices that have through-hole technology are larger.

This size and space limitation becomes critical in today’s electronic devices where space is a premium, leading to constraints in compact and densely populated circuit boards.

2. Time-consuming process

The assembling process of through-hole is manual most of the time.

Components are inserted and then soldered on the other side which is a time-consuming process and requires labor compared to the automated assembly methods used for SMDs.

It also required drilled holes to insert the components lead which is also a time-consuming and costly process.

3. Thermal stress and strain

Although through-hole components are mechanically strong, they may be thermally stressed during the wave soldering process that is used to assemble them.

The entire PCB is heated during soldering, which may expose through-hole components to greater temperatures and result in thermal strain or damage to sensitive components, especially those that are heat-sensitive.

Surface mount components (SMDs)

Surface mount technology is the process in which components are mounted directly onto the surface of the PCB and its components are called surface mount devices (SMDs).

Originally it was named “Planer mounting”. Nowadays all electronic devices are manufactured using surface mount technology. It has improved the quality and performance of various devices and has also reduced the cost.

The surface mount technology doesn’t require holes to be drilled through PCB, this is the key difference between surface mount and through-hole technology.

The components of this technology are also small which reduces the device size.

a. SMD components

Surface-mount devices offer miniaturization, automated assembly, and space utilization compared to through-hole components.

Let’s discuss the SMD components in detail.

1. SMD Resistors

SMD resistors are compact, rectangular components with metal end caps or markings indicating resistance values.

They come in various forms such as thin film, thick film, and chip resistors each having its special characteristics.

The purpose of using resistors in surface-mounted technology is for voltage division, current limitation, and impedance matching in various circuits due to their small size and accurate resistance values.

2. SMD capacitors

SMD capacitors are available in ceramic, tantalum, and electrolytic varieties, each with a range of voltage ratings and capacitance values.

They have flat, rectangular, or cylindrical designs with markings denoting capacitance and voltage ratings.

They are used for energy storage, filtering, decoupling, and noise reduction in electronic circuits, especially in compact designs where space is limited.

3. SMD diodes

There are various types of SMD diodes such as Schottky diodes, zener diodes, and standard diodes in compact packages.

They are used for signal modulation and demodulation, voltage regulation, and rectification in electronic circuits.

They also offer fast switching times and they are ideal for high-frequency applications.

4. SMD transistors

SMD transistors include bipolar junction transistors (BJTs), field-effect transistors (FETs), and MOSFETs in miniature packages.

These devices amplify or switch electronic signals and are vital in amplifiers, digital circuits, and power control applications.

Their compact size and compatibility with automated assembly enhance their use in high-volume manufacturing.

5. SMD Integrated circuits (ICs)

Surface-module integrated circuits (SMD ICs) include memory chips, operating amplifiers, microcontrollers, and other specialist ICs.

These components give particular functions to electrical systems by containing intricate circuitry on a single chip.

SMD’s wide variety of components makes it easier to design electrical devices that are lighter, smaller, and more sophisticated.

b. Benefits

The surface-mount devices offer numerous advantages over through-hole components.

These advantages have significantly impacted modern electronic designs and manufacturing processes.

1. Space efficiency

SMDs are sustainably smaller than through-hole components. This feature of SMD components allows to design of compact electronic devices.

Their reduced footprint and ability to be placed on both sides of a PCB enable higher circuit density, facilitating the design of smaller, lighter, and more portable devices.

This space efficiency is crucial for smartphones, laptops, and IoT devices.

2. High-frequency

The small size of SMDs enables better performance in high-speed and high-frequency applications.

Reduced capacitance, inductance, and signal degradation are all made possible by the shorter connecting routes between components, which promote better signal integrity and quicker operation.

This is crucial for telecommunication, data transmission, and fast computing.

3. Automated assembly and cost-efficiency

SMDs work very well with automated assembly techniques like reflow soldering and pick-and-place equipment.

This automation boosts industrial throughput while drastically cutting labor expenses and production time.

The fast placement of components on the PCB enhances the efficiency, making the surface-mount technology more cost-efficient for high-volume production.

5. Design flexibility

The small components of SMD allow the greatest design flexibility. This also allows engineers to design intricate and innovative circuit layouts, enabling new functionalities and features in electronic devices.

This also creates advancement in technology and innovation in electronic devices.

c. Drawbacks

There are also limitations and challenges while using surface-mount technology.

1. Repairing challenges

SMDs repairing and replacing various components can be challenging compared to through-hole components. It will require special manual soldering or rework.

Without specific tools and knowledge, it is challenging to reach individual components due to their small size and densely packed arrangement on the PCB.

This complex can make the repairing costly and time-consuming.

2. Sensitive to environmental factors

Because SMDs are smaller and more exposed on the PCB surface, they are more vulnerable to damage from handling mistakes, static discharge, and external conditions.

Accidental damage incurred during assembly, such as bending or incorrect handling, may affect the device’s overall reliability and result in component failure.

3. Thermal Issues

Although SMDs often offer improved thermal characteristics, localized heating problems may still arise due to their smaller size and compact positioning.

In some circumstances, SMDs’ heat dissipation capacity might not be adequate for specific high-power applications, necessitating the use of extra thermal management techniques.

Remember understanding through-hole and SMD components is useless until and unless you understand the basics of electronics and electronic circuits.

Conclusion

When it comes to PCB designing the two well-known technologies are through-hole and surface mount technology. Both have their importance in certain applications.

The through-hole and SMD components are used in designing the PCB.

In through-hole technology, components with leads or pins are inserted into drilled holes on the PCB and soldered on the opposite side. The leads pass through the holes for a secure connection.

Through-hole components offer mechanical stability and good heat dissipation but are time-consuming to install and can cause size and space limitations due to their larger size.

On the other side, the surface-mount technology does not require holes in the PCB, the components are directly mounted on its surface. The components of surface mount technology are compact and small in size

Surface mount technology offers space efficiency, better high-frequency performance, cost savings, and design flexibility but poses challenges in repair, environmental sensitivity, and heat dissipation.

That’s it, this article covers the basics of through-hole and SMD components, highlighting their key differences for better understanding.