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Surface mount technology (SMT) is widely accepted as the ideal process for electronic products that are compact, lightweight, and high speed. Both through-hole and surface mount assembly techniques have their own merits and demerits. To understand the wide usage of SMT in printed circuit board (PCB) assembly, this article discusses the SMT process, benefits of SMT assembly, major differences compared with the through-hole technology (THT) method, and suitable applications in the electronics industry.

While the THT process involves mounting electronic components by inserting their leads in the holes drilled on the PCB, the SMT process directly solders the components onto the surface of the PCB. These components are called surface mount devices (SMDs). They are smaller in size compared to through-hole devices and are suitable for high-routing density and compact designs.

SMT benefits include:

  • Supports assembly automation and helps in quicker bulk production.
  • Reduces manufacturing costs due to smaller PCBs. SMDs have smaller footprints, and a small board can offer more functionalities as well.
  • Supports high-speed design because it can produce densely packed PCBs.
  • Produces fewer assembly defects because the SMT process easily adapts to required modifications and upgrades.
  • Improves signal integrity and reduces electromagnetic interference because the traces become shorter between closely placed components.
  • Increases the reliability of SMT assembled PCBs. The application of solder paste instead of molten solder highly reduces the possibility of component failure due to false solder joints.
  • Offers flexibility because combining SMT with THT assembly methods provides greater functionality.

There are several differences between through-hole and surface-mount technologies that make each suitable for some specific applications. SMT, however, has penetrated almost all the electronics domains and will continue to add more features to the PCB assembly process.

SMT assembly eases the constraints of the board space when compared to the THT assembly method. Through-hole components require preparations such as lead bending and trimming before inserting in the holes. These steps increase the assembly cost of the PCB. SMDs do not have leads and are directly soldered on the surface of the PCB. Higher pin count packages are also available. However, SMDs do require advanced assembly skills and experienced staff to handle the production line.

SMT assembly is capable of mounting fine-pitch components, which is not possible using the THT method. In applications where space is premium, this SMT feature is surely the front-runner. With the SMT assembly process, PCBs that require a mixed build of both through-hole and surface-mount components can be attained. Although SMT reduces production costs, the capital investment required on machinery is quite high compared with the through-hole process. The THT method is best suited for applications where the final product is exposed to continuous vibration or periodic mechanical stress.

In applications where high-speed circuits are required, SMT PCBs are the best choice. Stray capacitance and inductance issues are reduced in SMT PCBs because there are fewer holes drilled on the PCB. The automation of the SMT assembly method drastically reduces the cost, and a compact design provides small, lightweight PCBs. Thus, SMT PCBs are used extensively in applications such as wearable consumer products and implantable medical devices.

SMT assembly has made it possible to choose flexible substrates for PCB fabrication. Flex and rigid-flex PCBs are introduced only because of the SMT assembly process. The improved efficiency of PCB assembly is attributable to the automation of the entire process, which eliminates the scope of manual errors. Pick-and-place equipment speeds up assembly of the PCB and reduces processing time significantly.

Although SMT assembly offers multiple advantages in the PCB manufacturing process, there are few disadvantages also. Surface mounting is not recommended for harsh environment applications. SMDs can easily get damaged in high-thermal operations. Due to the dense component placement on an SMT PCB, there may be insufficient space for a detailed silkscreen. Manual debugging and identifying components for any rework may become complex in such PCBs.

To decide which assembly technology is suitable for a given application, it is essential to consider factors such as the product usage, the environmental conditions and stress applied, power requirements with associated heat dissipation, performance based on the component’s package, assembly quality and ease of rework, price benefits, and component lead time. In most of the conditions, SMT will be the best option for PCB assembly.

SMT assembly is widely used in applications like consumer electronics, medical devices, telecom applications, automotive, etc. Rapid production, higher circuit speed, assembly automation, lower cost, higher density, design flexibility, and improved performance are the important features of the SMT assembly process that support the extensive usage of SMT PCBs in electronic applications.

SMT Assembly for Healthcare Systems

Healthcare systems have grown tremendously in the field of patient care. Monitoring devices like blood pressure monitors and pulse oximeters are compact and lightweight because SMT PCBs are used in such medical equipment. Increasing demand for consumer products like smartphones and smartwatches are driving growth in the telecom industry. Compact and flexible products are also possible because of the development of the SMT PCB assembly process.

Several growing trends in the SMT process include building fast and flexible assembly lines, efficient and easily upgradable assembly setup, etc. But assembly service providers are also focusing on developing environmentally friendly PCB manufacturing units. There are compliance requirements included in the SMT assembly process to develop a green line for PCB assembly.

SMT for PCB assembly makes miniaturization, versatility, and extended operations possible in the PCB industry. Electronic design automation tools have improved the design for manufacturability (DfM) software that helps PCB designers to build industry-standard products. The PCB assembly process of complex circuits has become faster and easier due to the automated SMT assembly lines. Customer satisfaction has been achieved by consistent and high-quality SMT PCB manufacturing, and contract manufacturers have built cutting-edge assembly units to capture the growing market of SMT PCB products.

This article was written by Ken Ghadia, Senior Sales Engineer, TechnoTronix Inc., Anaheim, CA. For more information, visit here . Contact: This email address is being protected from spambots. You need JavaScript enabled to view it..