Comparing Through-Hole (THT) and Surface Mount (SMT) Technologies in Electronics

As the technology evolved room size computers transformed into tablets and portable laptops, it’s a bigger picture while on a smaller scale, as electronic components shrank in size throughout time, as a result, electronic gadgets are becoming smaller and more portable.

During the 1980’s through through-hole components and through-hole technology were very popular but with the advancement of technology, most of the components transformed into SMD(surface mount devices) but the importance of through hole technology is still there according to the requirement. Surface mount technology (SMT) and through-hole technology are the two primary soldering methods used for electronic components. The decision between the two approaches ultimately comes down to the particular requirements of the project because each approach has pros and cons of its own. To understand the difference between THT and SMT lets understand them separately.

What is Through Hole Technology (THT)?

Through-hole technology involves drilling holes into the PCB and installing components through those holes. For larger components that must be firmly attached to the board, this technique is excellent. Because through-hole components can be easily desoldered and taken off the board, they are also simpler to replace. There are further two types of through hole soldering

Axial soldering technique: As axial component’s leads are extended from both ends in a straight line. When components are placed horizontally along with the surface of pcb both leads enter the through hole to the other side of pcb where they are soldered on respective through hole pad. This process of placing components mechanically which are in axial packaging and then soldering whether through wave soldering or with manual soldering is known as axial soldering. Mostly resistors, capacitors, inductors and diodes are in axial packaging.

Radial soldering technique: Radial components are those components which have their leads perpendicular to their body or just like they sprout out from the bottom surface of the component’s body. These components are placed flat with the surface of board and the leads entered in the respective through hole pad and then they are connected electrically and mechanically with their respective connections. This process of connecting and soldering components is known as radial soldering. Components with radial packages, including electrolytic capacitors, certain diodes, and transistors, are frequently used in this manner.

What is Surface Mount Technique (SMT)?

SMT is the process of attaching components directly to a printed circuit board’s (PCB) surface. Smaller components benefit greatly from this method’s tighter packing and better space utilization. Since SMT components are not subjected to the same stresses as through-hole components, they are also less prone to undergo mechanical stress. Electronic components are mounted onto printed circuit boards (PCBs) using surface mount technology (SMT). In contrast to conventional through-hole technology, where components have leads that pass-through holes and slots in the PCB, SMT parts have metallic pads on their outermost layers that connect directly to the PCB.

The main features of surface mount technology are as follows:

SMT components: SMT components are designed with small metal contacts on their surfaces. These components are typically smaller and lighter than their through-hole replacements.

PCB design: The SMT PCBs contain corresponding metal pads on their surfaces for mounting SMT components. Solder paste, a sticky concoction of flux and microscopic solder particles, is typically used to cover these pads.

Soldering technique: SMT components are soldered onto the PCB using solder paste during the soldering process. The components are precisely placed on the pads covered in solder paste using an advanced tool known as a pick-and-place machine. After that, a reflow oven is used to heat the entire assembly. The component leads and the PCB pads are connected mechanically and electrically by melting solder paste when it is heated.


Comparison of THT and SMT

Due to its effectiveness, ability to be reduced in size, and compatibility with current electronic equipment, SMT technology has established itself as the industry standard. It enables the manufacturing of better performing lighter, and smaller electrical goods. However, through-hole technology continues to be used in particular applications where mechanical strength, heat resistance, or the accessibility of specific parts are crucial considerations. In order to meet particular design needs, it’s common to combine SMT and THT components on the same PCB.

Here is a thorough comparison between Surface Mount Technology (SMT) vs Through-Hole Technology (THT) based on several of factors:

Series ProductionTHT assembly is usually time taking process and less cost-effective for series production since it requires more manual soldering.SMT assembly is fully automotive, and machine driven hence need less time for series production which saves time and money.
Size THT components cover more area due to size of through hole components, so they are less suitable for compact size.SMD components are smaller in size, so they are effective where there density of components is high while the size of pcb is small.
Mechanical StrengthThrough hole components have leads or pins which pass through the hole and soldered other side of the pcb which give them more mechanical strength and firmness hence they can bear more physical strains and mechanical robustness.SMT components are surface mounted, their leads are directly soldered on to the pads which are present on the surface of the pcb that’s why they are not mechanically firm where there are high vibrations and high pressures
Heat Sensitive ComponentsThrough hole soldering of heat sensitive components is easy and handy as you can control soldering temperature for each component.Reflow soldering technique is used in SMT. During which solder paste is reflowed and then whole assembly is heated to connect the pads and pins of components which is fatal for heat sensitive components.
High Frequency ApplicationsDue to high level of parasitic capacitance and inductance through hole components are not suggested for higher frequency applicationsSMT components are compatible to high frequencies because of their low parasitic capacitance and inductance.
Weather ConditionsThrough hole components are capable of heat resistance hence they are preferred in extreme weather conditionsSMT components are more sensitive than through hole, so they are avoided where systems face extreme weather conditions.
AvailabilityThrough hole components are not easily available due to advancement of technology and less frequent use of them.Currently SMT components are easily and frequently available


Overall, it may be said in modern era of electronics, SMT technology is used most while through hole is not only becoming history but also has less advantages over SMT technology but in some areas still THT is used. In SMT technology using pick and place machines for pcb assembly there comes best results for quick turn circuit boards which is becoming necessity to catch up the pace of the modern era of technology.