Component Mounting Technology

Through Hole and Surface Mount Technology

Sun Jan 14, 2024

The first decision to be taken before laying out a PCB is choosing the mounting style and package of the components. The choice is made based on electrical requirements, size and cost. This critical selection influences the size and appearance of the finished or populated printed circuit board assembly (PCBA). There are mainly 2 types of component mounting technology. One is through hole technology (THT) and the other is surface mount technology (SMT). We give you an introduction on the topic as well as pointers to learn them. We discuss,
  • What is through hole technology?
  • Packaging types - THT
  • Pros & Cons - THT
  • What is surface mount technology?
  • Packaging types - SMT
  • Pros & Cons - SMT
  • THT vs SMT
  • Summary

What is through hole technology?

In through hole mounting, the component leads are placed into holes drilled on a bare PCB. The assembler or the person concerned with the component assembly process has to ensure proper consistency of the placement of the leads into the holes, the polarity and
orientation of the components. The assembler must inspect the components and make any necessary adjustments. Once these are perfectly done, the component leads are soldered to the pads around the holes on the opposite side. All these steps were done manually earlier. But today automated insertion mount machines are available for assistance. Through hole technology was commonly practiced up until the rise of SMT in the 1980s. However it is still used in some niche areas like industrial applications, defence applications & prototypes.

Packaging types - THT

There are two main types of through hole packaging. One of them is axial lead packaging. Axial lead components have leads on both ends. They come out of the component in a straight line. The other packaging type is radial lead. Radial lead components have both leads on one side. In through hole technology, the leads run through the entire board, so they can connect the various layers of the PCB. Axial lead occupies more space on the board whereas  radial leads occupy less space. That makes radial leaded components a better choice for high density boards. Integrated circuits come in through hole packaging such as DIP or dual inline packaging. Most connectors usually come in through hole packaging.

Pros & Cons - THT

Provides stronger mechanical bonds.
Components that undergo mechanical stress, such as connectors usually come in through hole packaging.
Requires holes for placing components.
This is expensive and time consuming.
Can withstand environmental stress. Benefits military and aerospace applications where extreme conditions are common.
The holes pass through the entire PCB layers limiting the amount of routing area.
Allows easy adjustments and replacements.
Products using through hole components can be easily serviced.
Assembly is very slow due to manual process. Automated assistance using machines are still slow and expensive.
Used in prototypes.
Wave soldering, selective soldering, and hand soldering techniques can be used to solder them. But these methods are not consistent throughout.

What is surface mount technology?

In surface mount technology the components are mounted directly onto the surface of the PCB. This method is also known as planar mounting. Today all electronic hardware is manufactured using  surface mount components. It has improved the manufacturing speed, the quality and performance of PCB and has also reduced the costs.

Packaging types - SMT

The list of various types of surface mount devices available is a very long one. Surface mount technology was developed to facilitate automated assembly. So the packaging styles were developed in such a way that it could be handled easily during storage, during shipping and also during assembly by the pick and place machines. The Joint Electron Device Engineering Council specification aka JEDEC specification is an industry standard that recommends component package dimensions. The JEDEC is a consortium of over 300 companies that manages and develops many semiconductor industry standards. This includes surface mount technology component packages too. Surface mount component sizes conform to these standards. Common examples surface mount packaging includes:

  • Flat Chips: small rectangular packages which are absolutely minute. Surface mount resistors and capacitors come in these packages such as 1206, 0805, 0603, 0402, 0201 etc. The numbers signify the dimensions of these packages.
  • Metal Electrode Lead less Face (MELF) : cylindrical body with 2 terminals. Resistors and diodes come in this package.
  • SOT packages are mainly used for Transistors and Diodes. Examples include SOT 23 , SOT 223 and so on.
  • Similarly integrated Circuits (ICs) come in a a variety of packages such as Small outline Integrated Circuit (SOIC), Thin Small Outline Package (TSOP), Quad Flat Pack (QFN), Plastic Leaded Chip Carrier (PLCC), Lead-less Chip Carrier (LCC), Pin Grid Array (PGA) Ball Grid Array (BGA) and so on.

Pros & Cons - SMT

Smaller PCB size.
Heavy mechanical stress can rupture the solder bond.
Lower cost and faster production time. There is no drilling of holes. This reduces cost and production time.
The smaller size of the components makes it hard to solder manually.
Soldering techniques are reliable and repeatable. Re-flow ovens are used for soldering.

As the number of pins in the component increases routing becomes very critical and tough. Highly experienced PCB designers will be required to do the routing.


Holes are required for component lead insertion.
Components mount to surface pads.
Components are assembled only on one side. 2-sided assembly is rare.
2-sided assembly is common.
Manual assembly.
Automated assembly.
Soldering can be manual or automated
Soldering is typically automated.
Lower component and circuit density. due to larger component sizes
as well as drill holes.
Increased component density due to smaller component sizes and absence of holes.
Larger PCB footprint.
Minimal PCB footprint.
Reworking is relatively simple.
Reworking certain components are a bit complex.
Mechanically reliable
Not as reliable as through hole in the absence of other attachments.


PCB Design is an interdisciplinary skill involving both mechanical and electrical domains. At one point you might be measuring the dimensions. At another instant you possibly could be calculating the impedance or current flow or temperature rise. Some consider PCB design to be an art. Designers try to express them by placing the components aesthetically. You should be very creative and technically sound to make the PCB aesthetically pleasing as well as highly functional. The process of transforming an idea into a PCB architecture has several stages with well defined steps. Each new PCB is an opportunity to be creative as well as improve your technical skills . Our course aims to equip you with technical knowledge on PCB design, help you build multi layer PCB and thus launch yourself to a platform from where you could explore the advanced concepts on your own. We welcome you to join our course "Learn PCB Design and Layout Techniques".

Our vision is to create a platform where anyone could upskill as well as build their knowledge on hardware & firmware development through industry relevant courses in electronics, programming & mathematics at affordable prices. Driven by our passion for technology, we aim to bring in innovative hardware products and software applications at affordable prices. We also offer firmware development and guidance services in Beaglebone, Nvidia Jetson, Raspberry Pi and Arduino.

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