What is Surface-Mount Technology?: Complete Explanation
Surface-Mount Technology, or SMT, is a method for attaching electrical components directly onto the surface of a printed circuit board, or PCB. This process allows for automated production to complete more of the required assembly to create a working board. It lowers the cost of production and increases the maximum output by eliminating bottlenecks on the assembly line.
SMT has another big advantage over the former ‘through-hole technology’ method. In the older method, electronic components were mounted to a circuit board through specifically cut holes in the board for the component. This required larger components, precise handling, and an extra solder to attach each component firmly. With SMT, electrical components, called surface-mount devices (SMD), are quickly sorted and attached to the top of the PCB with either minuscule leads or no leads at all.
SMT components are significantly smaller than through-hole components which are achieved by machine handling. While there may still be short pins, flat contacts, solder balls, or terminations on the circuit body, the components are still so much smaller than what is required by through-hole technology that the end result is much more compact as well. This often translates into sleek, attractive electric devices.
Along with SMT, there is a slew of other related terms that you may want to know. Here is a quick breakdown:
- SMD – Surface-mount devices: active, passive, and electrochemical components
- SMT – Surface-mount technology: assembling and mounting technology
- SMA – Surface-mount assembly: module assembled with SMT
- SMC – Surface-mount components: components used for SMT
- SMP – Surface-mount package: SMD case forms
- SME – Surface-mount equipment: SMT assembling machines
It is a lot of terms to associate with the technology, but it can be understood in an easier way. SMT is the method used by SMEs to place SMDs made of SMPs around SMCs onto PCBs. The finished assembly is an SMA.
Surface-Mount Technology: Pros and Cons!
|SMT allows for smaller components||SMT is not great for devices that need to be frequently attached and detached from other components|
|Machine precision can be used to organize smaller components into a much denser populated board||SMDs solder connections are smaller and can be damaged by potting compounds during thermal cycling|
|Components can be placed on both sides of the PCB||Manual assembly and repair are difficult and require expensive tools and a skilled operator|
|Small errors in placement are automatically corrected by surface tension when the solder is heated||Many SMT components are incompatible with sockets|
|Improved mechanical performance when shocked or vibrating||SMDs are not plug-and-play friendly and will likely require specialized PCBs for prototyping|
|Lower resistance and inductance at the connection||Due to the size of SMDs being smaller and PCBs being more densely populated, part ID codes must be made even smaller and often coded or shorthand|
|Better EMC performance|
|Fewer to no holes needed|
|Lower cost and less time to set up for mass production and automation|
|Less expensive components|
Surface-Mount Technology: An Exact Definition
SMT, or Surface-Mount Technology, is an assembly and production method for mounting components to a printed circuit board (PCB) directly to the surface. It was designed to replace the previous method known as ‘through-hole technology’.
The method was developed in the 1960s. It took until 1986 before surface-mounted components were able to reach 10% of the market. By 1990, SMDs were inside the majority of all high-tech printed circuit assemblies. Most of the work pioneering surface-mount technology was done by IBM. IBM presented its first demonstration of SMT in 1960 with a small-scale computer that was later used in the Launch Vehicle Digital Computer for the Instrument Unit that guided all Saturn IB and Saturn V vehicles.
Surface-mount technology components were designed to have small tabs or end caps where solder could be applied to mount SMDs to the surface of the PCB. Previously, components were mounted through lead holes that had to be drilled into PCBs. The holes were drilled to component size to hold each piece tightly. The grip was then soldered. SMT takes the hole drilling step out of the process. By designing SMDs that required less or no hole leads, the process of device assembly was dramatically cut. There was a much greater advantage.
SMT allowed for much smaller components to be designed that could still be held tightly to the PCB. With smaller components, comes greater component density. The advancement caused by using the SMT method has been noted under “Moore’s Law” which states that the density of components on a motherboard would double every year from 1965 to 1975. He then amended the statement to say that the density would double every two years after that.
Today, SMT is used in nearly every electronic device from children’s toys to coffee makers to smartphones and laptops. While there is always the possibility of another method arising and replacing SMT, it appears that surface-mount technology will continue to be in use for a very long time.
How Does SMT Work?
SMT is a method that makes use of specialized tools to manage tiny components onto a printed circuit board. While this process can be done by hand, it is incredibly time-consuming and tedious. The precision required to create a quality SMA, surface-mount assembly, makes it a skilled position. Most SMT production and assembly are done through automation.
The process starts with a pile of components and any type of printed circuit board. PCBs are typically covered in flat tin-lead, silver, or gold plated copper pads named solder pads. Specialized automatons then cover the solder pads with solder paste using a stainless steel or nickel stencil. With the solder paste in position, the PCB is sent down the assembly line to pick-and-place machines that take components from a conveyor and place them where they should be on the PCB.
Once the board is covered in components and ready to bake, they are sent through a reflow soldering oven. The temperature of the PCB and its components are gradually raised in a uniform manner to prevent thermal shock. Once the board is hot enough, the conveyor moves the assembly into a zone that can reach temperatures hot enough to melt the solder paste. The surface tension of the molten solder on the solder pads keeps the components in the correct place as long as the pads’ shapes are correctly designed.
After the PCB is completely soldered, they are usually taken to be washed. The reflow process can sometimes create solder paste residue or have stray solder balls. Any extra solder or conductive material can cause board shorts. Once the boards are cleaned, they are sent to be visually inspected for missing components or abnormalities. In some more advanced fabrication plants, an automated optical inspection (AOI) system is in place to cut back on human labor and decrease inspection times.
How do You Create Surface-Mount Technology?
To perform the process at home, you will need to get a hold of a few materials:
- Printed circuit board
- Solder Paste
- SMD and required components (this list depends entirely on what is being designed)
- Solder Gun
- Cleaning Solvent
Place solder paste on the solder pads across the board. If the PCB does not have a printed pattern, it will need to be screened with a conductive pathway according to your device’s schematics.
Organize the components across the board where they belong. This pattern relies completely on the intended use and design of the product.
Use the solder gun to heat the solder paste on the solder pad of each component. It may be useful to use tweezers to hold each component still.
Clean the board for solder residue or runs.
Inspect the design for missing components.
The process may sound simple, but the design knowledge required to design circuit boards alone is enormous. If you can manage to successfully design a circuit board, the rest is just a little bit of hard labor. With any luck, you’ll have a useable board. I would personally recommend that you order any custom needs from PCB manufacturers. As the size of components on SMT devices is minuscule, the identification markings can be one of the most difficult facts to read.
Where Did SMT Originate From?
The concept of SMT electronics was presented by IBM in the 1960s to showcase types of small form electronics for functional use. Around the same time, the European Philips company had developed a small surface-mounted button device for watches. It took some time for it to take over, but by 1986 it had reached 10% of the market. The method was originally called Planar Mounting and IBM designed the majority of the components required for the process.
The evolution from Planar Mounting to SMT occurred in three stages. The first stage was between 1970 and 1975. The adoption of IBM’s prototype in the 60s for space vehicle computer systems helped to grow interested in its development. 1970 marked the kick-off for reaching the goal of applying miniaturized electronics to printed circuit boards. One of the greatest early advancements was in the replacement of lead with leadless ceramic chip carriers (LCCC). By the end of 1975, SMT was widely used in civilian quartz electronic watches and electronic calculators.
From 1976 to 1985, SMT went through its second major stage of evolution. The size of components had been significantly reduced which allowed for the creation of multi-functional electronics. This lent SMT heavily for use in photography and headset radios.
At the same time, automation at the factory level of SMT production was advancing to a new point. As the production machinery matured, the foundation for even more rapid advancements in the development of SMT had been laid.
What are the Applications of SMT?
SMT can and is used to create device assemblies used in nearly every electronic device in the world. From digital cameras and smart TVs to laptops, desktops, and smartphones, SMT has made way for densely populated circuit boards which directly translates into better and more functionality.
Any time a product needs a circuit board for electronics function, SMT is used to make it. The density at which components can be placed is without true competition.
Here are a few products that you can find SMT processed circuit boards:
- Smart TVs
- Electronic Toys
- VR Headsets
- Smart Appliances
Examples of SMT in the Real World
As a method for production, SMT is in use by many different companies. You can find the end products in nearly any electronic device. Here is a quick list of some SMT manufacturers:
- Giltronics Associates Inc.
- Janco Electronics, Inc.
- Bennett Machine & Stamping Co.
- PGF Technology Group
- RBB Systems, Inc.
- DIGICOM Electronics, Inc.
- MME group, Inc.
- NAS Electronics
- Advanced Product Design & Mfg.
- MH MFG., a SEACOMP Company
- CSI Electronics
- NuWaves Engineering
- Kingston Technologies Inc.
- American Products, Inc.
- RPC Electronics, Inc.
- Providence Enterprise USA, Inc.
- LeeMAH Electronics, Inc.
- Electro-Prep, Inc.
- Accelerated Design and Manufacturing, Inc.
- A & M Electronics Inc.
- Pico Electronics, Inc.
- Creative Hi-Tech Limited
- Smart Sourcing, Inc.
- Galaxy Electronics, Inc.