What does SMT stand for in electronics

Overview: The process of making technology smaller is moving at an increasingly faster pace that never stops amazing us. The only factor that makes the gradual shrinking of electronics conceivable is using a suitable, automatic SMT (surface-mount technology) assembly process. Instead of using standard components connected by wires (through-hole), this method allows for boards to be covered with smaller components that can be mounted directly on the surface. 

The term ‘SMT’ may not be unfamiliar to electronic enthusiasts, but some may not know what it actually means. In fact, we have long been unable to leave the use of this patch technology, and you can find traces of SMT technology in various consumer electronic devices such as mobile phones, laptops, refrigerators, and TVs. In this article, FS Technology will introduce you to one of the most important parts of the PCB assembly process: SMT PCBA (PCB assembly).

What does SMT stand for in manufacturing

Surface mount technology is commonly abbreviated to SMT and this type of technology is frequently used together with THT (through-hole technology) in the assembly process of circuit boards. This high-precision electronic assembly technique is used to attach or solder surface mount components onto PCB pads. Its workflow is roughly described below.

Firstly, solder paste is coated on the PCB pads. Then the surface mount components (SMD) are placed accurately on the solder paste-coated pads by heating the printed circuit board until the solder paste melts. After cooling an electrical connection will be established between the components and the printed circuit.

Introduction to terms related to SMT technology

SMD: This stands for surface mount components, and PCB assembly companies usually use SMT technology to solder SMD components to the surface of electronic PCBA. If you want to know more about the difference between the two, you can read another article called “SMD vs SMT” in FS Technology’s PCBA blog.

THT: Known as through-hole technology, this term describes assembly technology used in the electronics industry, such as SMT. With THT, various types of components are welded on the surface of the PCBA board of electronic products where some are connected through patch elements and others are connected through plug-in components. THT enables the use of both service and plug-in components.

DIP: This term stands for dual in-line package. Its relationship with THT is similar to the relationship between SMT and SMD, but for some reason, we prefer to call it DIP assembly or through-hole assembly, rather than THT assembly.

The concept of SMT Process

In the SMT process, we often use two high-temperature welding processes to complete the welding of components:: reflow soldering and wave soldering. So, in the SMT production line, what is the role of reflow soldering and wave soldering, and what is the difference between them? This section will answer the above questions for you.

Regarding reflow soldering, soldering paste is first pre-coated on the pad and is subsequently melted by heating. This heating process will establish an electrical interconnection between the pins or solder ends of the electronic components premounted on the pad, and the PCB pad. This process essentially achieves the purpose of welding the electronic components onto the PCB board. Reflow welding is generally divided into three separate stages/zones: preheating zone, heating zone and cooling zone.

In short, the reflow soldering process can be summarized in these steps: print solder paste > mount components > reflow soldering > PCBA cleaning

Regarding wave soldering, this is a type of bulk soldering process where a special pump is first used to spray melted solder into a solder wave peak. After that, the pins of the electronic components to be welded are passed through the solder wave peak to establish an electrical interconnection between the electronic components and the PCB board. The wave soldering process can be divided into these four steps: spraying, preheating, heating (in a tin furnace) and cooling.

These are the steps to summarize the wave soldering process: plug-in > flux coating > preheating > wave soldering > edge cutting > PCB Assembly Inspection.

The main differences between wave soldering and reflow soldering are as follows:

  • With reflow soldering, the PCB boards are already coated with solder paste before they enter the machine. Welding is then performed by melting the solder paste that is applied onto the board pads. Contrastingly, with wave soldering, there is no solder paste that is coated on the PCB before it enters into a machine. Instead, welding by wave soldering is performed with a machine that creates the solder paste to paint on the PCB pads which require solder.
  • Wave soldering uses molten solder to form solder waves for welding components whereas reflow soldering requires high temperatures and hot air to form circumfluence molten solder that is used to weld components.
  • Reflow soldering is mostly suitable for patch electronic components whereas wave soldering is more suitable for pin electronic components.
 
Now that the processes of wave soldering and reflow soldering are highlighted, including the main differences between the two, it is important to consider that they both are equally important processes in SMT Assembly machining.

History of Surface Mount Technology

To get a clear idea of what a type of technology stands for, you have to understand its history. The development of SMT technology can be divided into four stages and the below section will explain each time period and any important characteristics as follows:

  • Phase 1: 1960 to 1975

This stage was a historic moment when circuit boards came out and changed the electronics manufacturing industry. In this phase, humans have changed from using primitive breadboards to PCBA boards, and have completely entered the era of miniaturization. The representative works of this stage are calculators and quartz watches.

  • Phase 2: 1976 to 1980

A stage in which SMT technology becomes mainstream. Before this period, THT technology was mainly used for circuit board assembly, but with the popularity of small-volume electronic products all over the world, SMT gradually began to replace THT. Using this PCB assembly technique allows electronics to have a smaller footprint and be more functional. The main representative works are camcorders, video recorders and digital cameras.

  • Phase 3: 1980 to 1995

PCBA boards have become an indispensable product in the electronics manufacturing industry, and enterprises have begun to vigorously develop production equipment to improve product cost performance. VLSI was the best electronic product produced during this period.

  • Phase 4: 1995-present

Micro-assembly, high-density assembly, and three-dimensional assembly technology are developing rapidly. According to reports, the global electronic products using through-hole assembly technology are declining at an annual rate of 11%, while the electronic products using SMT patches are increasing at a rate of 8%.

Technology development has always been the mainstream of the world. Therefore, FS Technology has always advocated advancing with the times, whether that is committing to creating automated, intelligent and flexible production lines, or using the latest SMT assembly technology to serve customers. As someone in the electronics manufacturing industry, it is very important to understand the development history of PCB, which can help your business find the right direction of change.

Why SMT is favored by the electronics manufacturing industry

Advantages of using SMT for electronic products

As mentioned above, SMT has gradually replaced THT, so what advantages does this technology have, and why do turnkey PCB assembly manufacturers prefer it? FS Technology will take you through the advantages of this technology.

High assembly density

Compared with traditional DIP technology, SMD components can make the assembly area and mass smaller. The PCBA product assembled using SMT is 40% of the volume of the DIP and only 35% of the mass. DIP components are mounted on a 2.54 mm grid, while SMD can perform better. In order to meet customers’ requirements for smaller electronic products, FS Technology’s SMT technology is becoming more and more mature. Our surface mount assembly component grid has grown from 1.27 mm to the current 0.63 mm grid, and some special components can even be mounted on a 0.5 mm grid.

More reliable technology

Because SMD components are small and light, their shock resistance and reliability are higher. When producing SMT assembled products, FS Technology uses 7 fully automatic production lines. Our production line has strict quality control standards, and the general bad solder joint rate is less than 10 parts per million. The wave soldering technology of through-hole components is an order of magnitude lower, and the average MTBF of electronic products assembled with SMT is 250,000 hours, which is the main reason why 90% of electronic products use the SMT process.

Good high frequency characteristics

SMD components are different from plug-ins. Generally, no leads or short leads are used for direct patch welding, which can greatly reduce the impact on circuit inductance, large-capacity capacitance and resistance. For a project, the MHz of the PCBA board is very important, and the frequency of the circuit can be increased by using the patch method. By comparing SMD and THT, FS Technology found that the maximum frequency of the circuit designed with surface mount technology can reach 3GHz, while the maximum frequency of through-hole technology is only 500MHz. Due to its high frequency characteristics, SMD can shorten the transmission time of your circuit board, which is very important for electronic products such as computers that require the most transmission time.

Reduce the cost of assembly projects

  • Reduce the number of holes drilled on the PCBA board
  • Reduced cost and time to debug circuit boards
  • Reduced packaging, shipping and storage costs
  • The price of chip resistors is comparable to that of through-hole resistors

Easy to automate production

Surface mount is a technology that makes it easier to automate mass production. Taking FS Technology as an example, we have 7 SMT lines, all of which use automated SMT equipment to pick up and mount SMD components with vacuum nozzles. Due to the smaller size of these vacuum nozzles, the assembly equipment can be assembled with higher precision. In fact, most PCBA companies are now produced by automated placement. If a turnkey PCB assembly company wants to use THT technology for large-scale automated production, it needs to expand the area of the PCB bare board to at least 140%.

If you need a comprehensive understanding of the significance of surface mount technology, then you need to know not only the advantages of SMT, but also its disadvantages.

Disadvantages of electronic SMT technology

  • The nominal value of SMD electronic components is not easy to see;
  • Difficulty repairing PCBAs assembled using SMT;
  • Difficulty replacing components on PCBA;
  • Poor Coefficient of Expansion Consistency of SMD components;
  • Component leakage, component misalignment and component damage are prone to occur during the assembly process;
 

In order to deal with these shortcomings, FS Technology recommends these solutions for you:

  • Maintain good wettability of SMD components
  • Maintain solder continuity on the surface of the solder joint. The closer to the edge of the solder joint, the thinner the solder layer will be.
  • Ensure a small edge line of the pad, so the contact angle between the SMT device and the pad is less than 30 degrees.
  • No contamination such as solder mask is allowed on the surface of the metal to be welded.
  • The solder joint solder layer should be moderately applied, avoid excessively too much or too little amounts.
  • The solder spot position must be accurate and the end/pin of the PCB component should be in the center of the pad. The width and length direction should not exceed the phenomenon.
  • The solder joint plane should be continuous and smooth, and the solder joint formed by reflow welding should have a bright appearance.

How to Choose Manufacturers for PCBA SMT Assembly?

The above covers almost everything that electronics enthusiasts may be interested in, but if you are a PCBA engineer and are urgently find PCBA factory to provide you with SMT assembly services, then the following content is what you have to see!

An engineer put much effort into the printed circuit board project before the assembly. Hence, it’s crucial to choose a better SMT vendor for the assembly. Selecting a company to work with can be challenging because there are so many options, and this choice is so important. If you need to choose a PCB assembly firm, how can you determine the ideal fit for your project? To make it easy for you, we are listing the services that should be available to the customers by the company:

  • The manufacturing facility with cutting-edge machinery and tools, making it capable of meeting the difficulties posed by constructing even the most complicated PCBs.
  • Engineers with years of experience who are ready to assist you throughout the whole procedure and ensure that everything runs efficiently.
  • Materials of the highest quality – The firm only utilizes SMT SMD components of the highest quality to ensure that the boards’ quality can match and surpass the user’s expectations.
  • Delivery within the specified time frame. It indicates that the company can feasibly fulfill mass production orders in the shortest amount of time. The completion of the manufacturing within the allotted time is something the firm assures.
  • Prices are reasonable; the clientele’s satisfaction is the organization’s primary focus. Because of this, you may anticipate reasonable costs suitable for any financial plan.

Summarize

No matter what you want to use a printed circuit board for, it would be best to fabricate one that is reliable and has a high-performance level during its lifetime. If you have a reliable SMT electronics manufacturer on your team, you should be easily able to accomplish this goal.

Even though it contains more electronic components, assembling a printed circuit board is just as important as designing and making it. As you can see from this article, SMT assembly plays a significant role in almost all contemporary forms of electronic product design. If your PCB design still uses the through-hole method, SMT assembly could help your product move forward. Therefore, make sure you work with a trustworthy and knowledgeable assembly partner to avoid any problems that might arise with SMT assembly.

The above article sums up FS Technology’s entire explanation of what SMT really represents in electronic products and the electronic field. From here, FS Technology will continue to update and produce more articles regarding SMT in our blog, so stay tuned.

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