Surface Mounted Devices and Technology: Things you need to Know

Take a closer look at any commercially made electronic device these days, and it’s filled

Take a closer look at any commercially made electronic device these days, and it’s filled with small devices. Instead of using conventional components with wire leads like what is used for kits and home constructions, these parts are mounted into the board’s surface, and most of them are pretty small in size. This thing is known as SMT or surface mount technology or surface mount technology components.

Usually, all of today’s devices that are manufactured commercially uses SMT because it offers tons of advantages during printed circuit board manufacture. Because of its size, these parts make sure that more electronics are packed into much smaller spaces. In addition to its size, SMTs allow automated printed circuit board soldering and assembly to be used, which brings a vast improvement in reliability and enormous savings in overall cost.

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What is SMT?

During the 70s and 80s, the level of automation gains a lot of traction for printed circuit board assembly for boards used in different equipment or devices. The use of conventional parts with leads didn’t prove easy for printed circuit board assembly.

Capacitors and resistors needed to have their leads pre-made so that they can fit through holes – even ICs or integrated circuits required to have their leads adequately set to the correct pitch so that they could be set through the board’s holes with ease. This method always proved pretty challenging as leads usually missed the holes.

Tolerances are required to make sure that they are fitted precisely through these holes, and these holes are very tight. Because of this, operator intervention was usually necessary to solve the problem of parts not fitting correctly and stopping devices. It slowed down the printed circuit board assembly process and increased the cost exponentially.

For PCB assembly, there’s no need for component leads to pass through the circuit board. Instead, it is enough for parts to be soldered to the board. Because of this, SMTs were born, and the use of these components rose exponentially as their benefits were realized and seen. Today, SMT is the leading tech used for PCB assembly in electronic manufacturing. These components are able to be made pretty small, and a lot of types are used in the billions, especially mounted resistors and capacitors.

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Surface-mounted technology devices

SMT components are very different from their leaded counterparts. Instead of being designed for wiring between two points, mounted components are intended to be put on the board and soldered. SMT leads don’t go through the board’s holes as expected from the conventional leaded components. There are various styles of packages for several types of components. Package styles can be placed into three classifications: integrated circuits, diodes and transistors, and passive parts. These three classifications of surface-mounted tech components are listed below.


There is a variety of different packages utilized for passive SMDs. But most passive surface mounted devices are either surface mounted tech resistors or capacitors for which sizes are reasonably standardized. Other parts include crystals, coils, and other components with more individual requirements, hence their own package. Capacitors and resistors have different package sizes.

The designations include 0201, 0402, 0603, 0805, 0805, 1206, and 1812. These numbers refer to the size in hundreds of an inch. They are not as much used now. But they may find use in apps where bigger power levels are necessary or where other considerations need bigger sizes. Connections to PCBs are made through metalized spaces at the end of the package.

Diodes and transistors

SMT transistors and diodes are usually contained in small plastic packages. Connections are made through leads that flow from the package and bend so that transistors and diodes touch the board. The three leads are usually used for these things. This way, it is very easy to identify where the round device needs to go.

IC or Integral Circuits

Various packages are used for ICs. They are used depending on the level of interconnectivity needed. A lot of chips like simple logic chips only require 16 or 14 pins, unlike other chips like Associated and Very Large-Scale Integration or VLSI processors can require at least 200 pins. In lieu of a wide variety of requirements, there are various packages readily available in the market today.

For smaller chips, a Small Outline Integrated Circuit or SOIC may be used. SMT versions of the familiar Dual in Line or DIL packages are used for 74 series logic chips. Not only that, there are smaller versions like Thin Small Outline Packages or TSOP and Shrink Small-Outline Packages or SSOP.

The Very Large-Scale Integration surface mounted devices need a different approach. These things are usually known to use a quad flat pack. It has a rectangular or square footprint and has pins flowing on all four sides. Pins are bent out of the pack in what is known as a gullwing formation so that they meet the circuit board.

The spacing of pins is dependent on the number of pins needed. For some, it may be as close as twenty-thousandths of an inch. Excellent care is needed when packing these things and handling them as they can be bent pretty easily. Other packs are also readily available, like Ball Grid Array, and it is used in various applications.

Instead of having connections on the side of the pack, they are connected underneath. Connection pads have soldered that melts during the soldering process, making an excellent connection with the circuit board and the mechanical parts attaching it. As the whole underside of the pack can be used, the connections are more comprehensive, and it is more reliable compared to its counterpart.