Surface Mount Technology or SMT is a way of creating electrical circuits where the components are mounted or placed directly onto the surface of printed circuit boards. This technique has largely replaced the older through-hole technology where components were inserted into holes drilled in the printed circuit board (known as a PCB). SMT has revolutionised the manufacturing industry for electronics by making the production of smaller, lighter and more complicated electronic devices possible as the demand for handheld or portable electronic devices has become the norm in our day to day lives.
The key elements of SMT or surface mount technology are…
Components
SMT only involves certain Surface Mount Devices (SMDs). These components are usually smaller than their equivalent through-hole versions and, more importantly, have flat contacts or short leads that can be bent directly onto the surface of the printed circuit board for soldering.
PCB Design
SMT PCBs have copper pads on the surface, rather than holes. These are sometimes referred to as “lands” and the components connect to them.
Assembly Process
The SMT assembly process typically involves applying solder paste to the PCB, placing components, and then heating the board to melt the solder and form permanent connections.
Automation
SMT is highly compatible with automated assembly processes, allowing for faster production and higher consistency compared to manual through-hole assembly.
The SMT process will vary slightly for each associated device but will generally follow these main steps…
Step #1 – Solder Paste Application
A stencil is placed over the PCB, and solder paste (a mixture of tiny solder balls and flux) is applied through the stencil openings onto the copper pads.
Step #2 – Component Placement
Components are placed onto the PCB using automated pick-and-place machines. These machines use vision systems and precise mechanisms to accurately position components on the solder paste.
Step #3 – Reflow Soldering
The PCB with placed components passes through a reflow oven. The heat profile in the oven melts the solder paste, creating permanent electrical and mechanical connections between the components and the PCB.
Step #4 – Inspection and Testing
Automated optical inspection (AOI) or X-ray inspection systems check for defects. Functional tests ensure the assembled PCB works as intended.
Advantages of Surface Mount Technology
SMT allows for much smaller component sizes and higher component density on PCBs, enabling the creation of compact electronic devices while also offering…
Improved Performance – Shorter connection paths between components can lead to better electrical performance especially in high-frequency applications.
Increased Reliability – SMT components typically have better resistance to shock and vibration compared to through-hole components.
Lower Production Costs – Automated SMT assembly is faster and more efficient than manual through-hole assembly reducing labour costs and increasing throughput.
Double-Sided Assembly – SMT allows components to be placed on both sides of a PCB further increasing circuit density.
Surface Mount Technology – How Is It Used?
SMT is used in virtually every sector of the electronics industry. Some key applications include…
Consumer Electronics – SMT has become feasible in providing small form factors and increased functionality in the wide range of electronic devices that are used today, from smartphones and tablets to wearable gadgets and laptops.
Automotive Electronics – Numerous electronic control units (ECUs) are used in modern cars for various applications, such as engine management, GPS, in car entertainment, all of which use SMT.
Aerospace and Defense – SMT enables the production of lightweight, reliable electronics for aircraft, satellites, and military equipment.
Medical Devices – Implantable devices, diagnostic equipment, and portable medical devices benefit from the miniaturisation and reliability offered by SMT.
Industrial Control Systems – SMT is used in the production of programmable logic controllers (PLCs), sensors, and other industrial automation equipment.
Telecommunications – The use of Surface Mount Technology is high in network infrastructure devices such as routers, switches, and mobile base stations to package complex circuitry. SMT caters to a huge number of parts that need to be packed within a small space, which was observed in the complex circuitry found in networking equipment.
Internet of Things (IoT) Devices – Due to the smallness and energy efficiency required, SMT is often resorted to by IoT devices to make small, connected devices. SMT allows the installation of smaller electronic components onto the surface of printed circuit boards, which is vital inIoT applications.
Future Trends in Surface Mount Technology
As electronics continue to evolve, SMT is adapting to meet new challenges and the current trend or to move towards even smaller components. And as this miniaturisation continues, we are seeing components like 008004 resistors (0.25 x 0.125 mm) becoming more common. The main driver for this is the increased use of wearable and conformable worn about the person devices (think sports watches and associated monitors).
Comparisons Between SMT and Through-Hole Technology
While SMT has largely replaced through-hole technology in many applications, through-hole still has its place…
High-Power Components
Large power transistors or capacitors often still use through-hole mounting for better heat dissipation and mechanical strength.
Connectors
Some types of connectors, especially those subject to mechanical stress, may use through-hole mounting for added durability.
Prototyping
Through-hole components can be easier to work with in prototype or low-volume production scenarios.
Extreme Environments
Some military and aerospace applications still prefer through-hole technology for its perceived higher reliability in harsh conditions.
In practice many PCBs use a combination of SMT and through-hole components to leverage the advantages of both technologies. SMT has become the very foundation of modern electronics manufacturing. Its ability to produce small, high-performance electronic assemblies has helped enable a host of products we use daily and now take for granted.