What Does SMT Means: Everything About Surface Mount Technology

Surface Mount is an electronic package technology that mounts the components on the printed circuit board’s surface rather than in holes. Surface Mount Devices (SMD) are these kinds of gadgets. Surface Mount Technology (SMT) is the process of mounting components on the PCB’s surface and soldering them in place.

But what does SMT in electronics mean? Why did the electronic components market abandon through-hole technology? In this article, let’s go over every important aspect of SMT.

What Does SMT Mean in Electronics?

Let’s quickly review the other widely used device mounting technology, known as Through-Hole Technology, before attempting to understand SMT. In this, the circuit board’s holes are filled with components that have leads or terminals. Hence, the name “through-hole”. The leads can be soldered to create a lasting connection once they have been inserted.

The primary issue with through-hole technology is that it relies heavily on manual labor during PCB assembly, with limited automation available for specific components like integrated circuit packages. The manufacturing process takes a long time and is expensive. Through-hole technology also has some drawbacks. We’ll talk about them later.

Surface Mount Technology is known as SMT. This method involves fixing electronic components to the printed circuit board’s (PCB) surface while leaving their leads or terminals on the surface of the board. Surface Mount Devices (SMD) are the parts created for use with Surface Mount Technology.

There has been the development of Surface Mount Technology for quite some time. It’s been around for more than 50 years, in fact. Since then, SMT has benefited from a number of technical advancements in components, PCB manufacturing methods, soldering, and other areas.

Integration of more functionality on the same size PCB is crucial as system designs become more complex. It would be challenging to fit more components because through-hole devices are larger in size if the components chosen are older through-hole-style devices.

This is where surface mount technology and the associated SMT are helpful. SMD components can fit more of them in a smaller space than their through-hole counterparts because they are much smaller.

PCB assembly automation is a significant advantage of SMD and SMT. Precision pick-and-place equipment can be used to automate the assembly of SMD components after the PCB has been designed and produced. The pick-and-place machine only needs to align the components and place them properly in their designated locations because all of the components sit on the surface of the PCB and don’t require any holes.

An oven called a reflow is used to solder all of the components after they have been assembled. With very little human involvement, the entire assembly process can be automated, including testing. This essentially lowers errors while also vastly increasing production output. All thanks to SMT.

SMT Devices

The electromechanical, passive, and active components are surface-mount devices, as mentioned in the section on abbreviations. But what exactly do each of these categories include? You can learn more by reading this succinct list.


Connectors and relays fall under the electromechanical category. The energy is able to flow properly through the device thanks to these parts.


When it comes to passive SMD, there are three main components. Inductors, capacitors, and resistors are examples of these. Passive SMD is typically pre-packaged, making installation simpler.


Integrated circuits are typically the active parts of surface-mount technology. Groups of chips that are housed on a single chip are known as integrated circuits.

SMT Applications

Care must be taken when mounting surface-mount components to a board. If you want to solder such tiny items, it is a laborious and delicate task, so specialized equipment is required. As was done in the past, the application can be done in various ways. However, because of the substantial cost savings brought about by the procedure, this method of production is used.

SMT Advantages

SMT has a plethora of benefits and is helpful in many facets of life. There is less room for error, and it is also much easier to manufacture and very affordable to set up and operate. Surface-mount technology is machine-automated, removing human error.

Additionally, surface-mount technology’s smaller sizes result in a much more compact final product. The external packing and size can be more minimal due to the smaller internal components.

Surface-mount technology uses less resistance and inductance at the connection point, which benefits environmental health and is a nice bonus. So there are less adverse radio frequency effects. The high-frequency performance benefits from this reduction and becomes more stable. Because the radiation loop area is smaller and the lead inductance is lower, using SMT results in lower radiated emissions.

SMT Disadvantages

Although surface-mount technology has a lot of benefits, it isn’t always the best choice.

Surface-mount technology component repair is more difficult and expensive tools are needed, as well as a high level of skill in the event of error or breakage. Due to their small sizes and close lead spacing, many SMD types require this level of detail. Tweezers are needed if you need to work with small SMT components. It differs from the through-hole component method in that through-hole components always remain in place.

Surface-mount technology components can’t typically be installed in sockets, either. When a component fails, this technique is frequently used for quick installation or repair. Usually, this is a viable option when using through-hole components.

The Growth of SMT

SMT was mainly used for military purposes in the early years of its development. But the widespread adoption of surface mount technology prompted Japan to invest in SMT to create small and lightweight electronic products.

The size of integrated circuits was a significant contributing factor in the switch to SMT. Earlier dual-in-line package integrated circuits were quite large. However, as integrated circuits become more functional, more pins or leads are required. In order to reduce the size of the IC and pack more pins, semiconductor manufacturers chose surface mount packagings such as Ball Grid Array and Quad Flat Pack over standard dual-in-line packing.

SMT became the preeminent technology in PCB manufacturing as a result of smaller IC and components in the form of SMD devices. SMT also has the advantage of allowing components to be mounted on both sides of the circuit board, allowing for even smaller and more compact PCBs.

Since the 1980s, the electronics industry has made significant investments in SMT in order to create more compact PCBs, smaller SMD devices, and better soldering methods and equipment.

The mass production of electronic goods is a significant factor in SMT’s development. The time required to complete a PCB is noticeably longer when through-hole components are used. Because it increases the overall cost of the product, this cannot be done for mass production.

Soldering and component mounting can be fully automated with the use of SMD and SMT components. Even fault detection is done automatically. This will cut down on the product’s manufacturing time and expense.

PCB Assembly Using SMT

Before, producing printed circuit boards (PCBs) required laborious and time-consuming tasks. A factory worker or operator must frequently use manual labor to correct numerous errors that occur during PCB manufacturing.

Surface-mount technology was overwhelmingly welcomed by manufacturers as it improved PCB production. SMT assembly significantly decreased the margin of error. This not only made it possible for less human intervention, but it also started to boost output. Because of the efficiency of the work, labor costs also started to decrease.

Types of SMT Assembly

A PCB may have through-hole and SMD components together, SMD components on both sides of the PCB, or neither, depending on the circuit’s design. There are three fundamental types of SMT assembly, depending on the components used.

  • Type I
  • Type II
  • Type III

Every component in Type I SMT Assembly is SMD, and it is possible to mount the components on either one or both sides of the PCB. With regards to Type III SMT assembly, discrete SMD components like transistors, resistors, and capacitors are only mounted on the bottom side of the PCB.

The final type is Type II, which combines Type I and Type III. The fact that there are no standards for this nomenclature when it comes to the classification of SMT assembly types is crucial.

SMT Assembling Procedure

SMT adoption in the electronics manufacturing sector is accelerating exponentially. This is primarily due to a number of factors, one of which is the significant advancement in SMT assembly-related machinery. The SMT has the benefit of quick production at a low cost while also fully automating the process thanks to its machine-based assembly method.

The entire SMT assembly and soldering process will now be seen in an abstract manner. Additionally, we will study the various tools employed during each stage of assembly. The steps involved in SMT assembly are listed below.

  • PCB Loading
  • Printing Solder Paste
  • Inspecting Solder Paste
  • Mounting Components
  • Reflow Soldering
  • Optical Inspection
  • Unloading PCB

PCB Loader

PCBs are initially stacked vertically in the loader machine after they have been manufactured. To move on to the next step, it merely takes each PCB and places it on a conveyer belt.

The three most popular types of PCB loader machines are the magazine loader, vacuum loader, and gate conveyor.

As the next PCB shouldn’t arrive while the current PCB is still processing, it is crucial to set the PCB flow speed. After that, the PCB is taken to a screen-printing machine.

Screen Printing

Using a screen printing technique, the solder paste is applied to the PCB in this machine. The PCB is topped with a stencil. Every area where solder paste needs to be applied has cutouts or openings. The solder paste will then be applied with a roller on top of the PCB.

Solder Paste Inspection

This stage of SMT assembly is essential because a defective PCB will result from improper solder paste application. So, after the screen printing is finished, the PCB will go to a Solder Paste Inspector machine or SPI.

During this automatic testing, the machinery checks for screen printing flaws like missing, uneven, too much, or no solder, among others. SPI machines come in two varieties: Off-line SPI, which is only used for sample checking, and In-line SPI, which is used for 100% defect detection.

Pick-and-Place Machine

Installing the components on the PCB is the following step. This is accomplished using a Pick-and-Place or a Component Mounter machine. The machine’s back is covered with reels that are attached to various components. The pick-and-place robot takes the components from the reels and places them on the PCB at their designated location after the PCB has arrived and passed inspections for solder paste.

There are various kinds of pick-and-place equipment. One-by-one mounting devices of the Gantry type, rotary mounting devices, and module mounting devices are a few of the frequently used devices. As its name implies, the one-by-one mount machine mounts each component separately. This method, which is the slowest of the three, is frequently used to mount a few large-sized components, such as LCDs and Wi-Fi Modules, among others.

The Rotary Mount machine is used in small to medium-scale PCB manufacturing for less complex assembly. The components are placed on a rotating drum while the PCB moves in the X-Y axis in response. The Module Mount Machine, the third and final machine, has the potential to be the fastest and most effective of the three. Components are provided on several reels to speed up the pick-and-place process.

Reflow Oven

It’s time to solder the components now that they have all been placed correctly on the PCB. This is accomplished by using a reflow oven, which heats the PCB to melt the solder paste and securely solder the components. Actually, the reflow oven uses multiple zones/stages of heat rather than applying the maximum heat all at once.

Pre-heat zones are the first stage, where the PCB’s temperature is gradually increased and kept at a pre-heat temperature. Then, the PCB enters a high-temperature zone, where the temperature quickly ramps to peak, and at this stage, the “reflow” of solder occurs as it melts and spreads across the component and the solder pad. Finally, the temperature is quickly lowered to seal the bonding. While the PCB is being conveyed, all of these heating stages take place.

There are various types of reflow ovens, depending on how the heat is generated. Some of the commonly used ones are:

  • Infrared Reflow Oven
  • Laser Reflow Oven
  • Heat Reflow Oven
  • Vapor Phase Reflow Oven
  • Nitrogen Atmosphere Reflow Oven

A Quartz is applied with a voltage during an infrared-type reflow, and it emits infrared energy. Soldering uses the heat produced by this infrared radiation. Laser type reflow uses either 0CO2 or To generate the heat, a Neodymium: Yttrium-Aluminum-Garnet (Nd: YAG) laser is used.

One of the simplest is a heat reflow oven, which uses a fan heater to raise the air’s temperature through convection. In vapor phase type reflow, the hot chemical vapor is blown across the PCB for soldering.

The nitrogen-based reflow uses nitrogen gas rather than oxygen in the internal atmosphere to stop materials from oxidizing. With the widespread usage of Lead-free soldering, the N2 atmosphere reflow ovens became popular.

Optical Inspection

The PCBs are sent for automatic SMT soldering inspection after they exit the reflow oven. During the inspection, a camera captures a number of images and identifies even minor flaws. Automatic optical inspection machines come in two varieties: offline and in-line. The complexity and number of settings and options of in-line inspection machines contribute to their high cost.

What is the Difference Between SMT and SMD?

Even though surface-mount devices (SMD) are the essential parts that make the final product work, surface-mount technology uses automation to apply the SMD to the appropriate board. Surface-mount technology creates parts on a much smaller scale than mechanical processes used in a car factory to build larger products.

The SMD can keep its compact size thanks to the use of surface-mount technology. Because of the complex mechanics that make up the robotic automation device, technology can support this.

Other Common Abbreviations

The components of surface-mount technology can be distinguished in a variety of ways. Inclusive of that are many acronyms for the internal makeup of the surface-mount technology, including the following:


This abbreviation refers to surface-mount electronics. The electromechanical, passive, and active parts of the SMT are all SMDs. These components make up the majority of the apparatus.


SMA is known for its long-form, surface-mount assembly. The act of creating something by applying surface-mount technology is known as a surface-mount assembly. It describes how a device is assembled using SMT.


Surface-mount components, a catch-all term for the components found inside surface-mount technology, are what this set alludes to. Similar to SMD, these components enable the device to function.


Surface-mount packages, or SMPs, contain all the components in a case or other container. A computer tower case or a cell phone’s casing is analogous to this package on a larger scale.


SME refers to the mechanical components used to assemble surface-mount technology and is the abbreviation for surface-mount equipment. These complex machines assist in connecting all required components.


New technological advancements are made available to the public daily. Everyone aims to make current procedures simpler while serving a particular purpose.

The technology used on surfaces is not an exception. With the use of this new method, popular items are leaving the production line much faster. Additionally, the costs formerly related to the manufacture of such goods are steadily declining. Production of the same item differs greatly across the board due to falling labor costs brought on by faster and more efficient technology.

Surface-mount technology is a welcome development that has brought enormous advantages to a wide range of human endeavors. The world has been able to advance in ways that were previously impractical thanks to this new technology.