What is the difference between SMT and SMD?

Overview: The electronics manufacturing industry is a highly professional industry. Those who are familiar with it, prefer to use abbreviations to express their needs, such as PCB (printed circuit board), PCBA (PCB assembly), etc. This is not friendly to novices or electronics enthusiasts. In this article, FS Technology will explain two commonly used terms in the PCBA industry-SMT and SMD from the concept, use, and combination of these three aspects.

What is SMT?

The full name of SMT is surface mount technology, which is a new method of arranging components on PCB. This technology is widely used in the PCBA industry, and almost all companies that provide PCB assembly services can provide SMT assembly services. In the early 1970s, electronic manufacturers used through-hole (THT) assembly to realize component mounting and soldering work, that is, the leads of components were placed in drilled holes on bare PCBs, and permanent component through-hole arrangements were achieved through soldering guns. But with the development of technology, people gradually found that through hole PCB assembly is not the best solution, and SMT assembly is replaced.

Unlike plug-ins, SMT technology uses leadless assembly to solder components directly to the bare PCB, which is a faster and cost-effective assembly method. For some consumer electronic devices((mobile phones, computers, etc.)), their update frequency is less than a year, which means that electronics manufacturers urgently need to fast turnaround PCB assembly to achieve production, and SMT technology just meets this requirement.

SMT Assembly Process

Printing: The SMT instrument aligns the prepared PCB template with the PCB that needs to be patched. While the squeegee is smearing the stencil, the solder paste drips onto the corresponding solder joints along the holes of the stencil.
Mounting: The SMD components are precisely placed in place by a pick-and-place machine, where the solder paste acts as a temporary adhesive.
Reflow Soldering: FS Technology uses 10-drive advanced reflow equipment to melt the solder paste that connects the board and components.
Testing and Inspection: PCB assembly inspection is performed by manual inspection and AOI inspection in the SMT placement link to ensure the quality of the circuit board, such as component alignment and checking for solder bridges.

Features and advantages of SMT assembly

It is very helpful to reduce parasitic capacitance and parasitic inductance;
Reduce the demand for components in PCBA projects;
Automated new equipment enables fast and reliable large-scale production;
Facilitating the development of tiny electronics or implantable devices.

In summary, SMT assembly is a process that refers to applying the right amount of solder paste to mount each component. SMT also lends itself to automation as machines can be programmed to mount components on the PCB. This ensures accuracy, and it also speeds up the production process and delivery quicker. So far our introduction to SMT is over. If you want to know more about SMT, please read “What does SMT stand for in electronics”. Next, we will explain the term “SMD”, which is helpful to understand the difference between SMT and SMD.

What is SMD?

SMD, short for Surface Mount Device, is an electronic component that is soldered to a printed circuit board and is designed to be mounted directly on the PCB. At present, we have a variety of methods for PCB components. According to different installation methods, they are divided into DIP components and SMD components, as well as plug-in components and patch components. Affected by the trend of miniaturization, more SMDs are used in the production of PCBA. Here we summarize its advantages:

The SMD body is on the same side as the solder joints;
SMD has no leads or only short leads;
Smaller size but better performance;
Reduce the risk of PCB manufacturing and assembly by reducing through holes.

It took only 20 years for surface mount components to become popular, and they have dominated the field of components today. Tracing the development history of components, the components of electronic equipment used by human beings range from passive components to active components and integrated circuits, and are finally ruled by SMD. Surface mount equipment can be roughly divided into two categories, transistors and integrated circuits (SOP, SOJ, PLCC, LCCC, QFP, BGA, CSP, FC, MCM). The SMD components are classified below.

Resistor

This type of resistor SMD is usually surface mounted in SMT technology and needs special attention when it is mounted. Take the SMD on the ceramic PCB as an example: when the ceramic PCB is patched, in order to prevent the metal material from overflowing by welding, it is necessary to apply a glass passivation film on the surface.

Ceramic Capacitor

Applications such as engine engines, military communication equipment and aerospace equipment are very dependent on high frequency circuits, so we need to use SMD SMT chip technology to mount SMD ceramic capacitors.

Transistor (SOT)

The three- and four-lead SOT devices are considered one of the pioneers of surface mount active devices. Three-lead SOTs are identified as SOT 23 (EIA TO 236) and SOT 89 (EIA TO 243). The four-lead device is called SOT 143 (EIA TO 253).

Integrated Circuit

An integrated circuit, or IC chip, is a collection of components such as resistors, capacitors, and transistors. Engineers integrate a “small PCB” with specific functions through IC programming and semiconductor process Small-outline SMD active integrated circuits that are common in life generally use shrink packaging. Small outline integrated circuits have lead centers of about 0.050 inches and are primarily used to accommodate larger integrated circuits than SOT packages.

Combination of SMT and SMD

Although SMD and SMT are two completely different concepts, they are complementary in the field of electronic manufacturing. Judging from the development history of PCBA, one of the main reasons for the desolation of DIP components is that manual soldering has gradually failed to achieve the ideal state, so the placement machine was born. The traditional SMD component assembly is realized by manual soldering, but the placement machine has completely eliminated this method. In today’s era, simplicity, efficiency, and cheapness are undoubtedly necessary factors for development, and the combination of SMT and SMD just meets this requirement.

The automated production mode is the focus of reducing the cost of PCB assembly, and SMD provides a cheaper alternative on this basis.
SMT equipment installs thousands of SMD components on the board in a short time;
The size of SMD determines the capacity of the circuit board and SMT technology can expand this advantage;
SMD components use leadless soldering, while SMT can avoid PCBA failures caused by human factors and is therefore more reliable.

Summarize

At this point, the content of “SMD vs SMT” is all over, I hope this article will help you understand the difference between the two more deeply. Here is a summary of FS Technology:

SMD is a component and SMT represents the assembly process;
SMD completes welding by SMT instead of manual;
PCBA manufacturers are happy to use SMD and SMT;
SMD and SMT promote each other.

As you can see, in addition to providing a wide range of PCBA services, FS Technology also provides more interesting PCB content. Whether you are an industry practitioner or an electronics enthusiast, you can find what you need in our blog.

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