What is SMD? What’s different with SMT?

What is SMD?

SMD is the initial for Surface Mount Device. The main components for SMT (Surface Mount Technology) process. It’s common industry statement to mention about SMP (Surface Mount Package), SMA (Surface Mount assembly), SMC (Surface Mount Components), SME (Surface Mount Equipment).

To clarify what’s SMD / SMA / SMT / SMC / SMP / SME

▲ The explanation for the SMT releated abbreviation made by OPTO PLUS LED Corp.

SMT (Surface Mount Technology)

The SMT stand for the “Surface Mount Technology”. This technology is the most used mess production technology for modern electronic product to automatic assemble large amount of electronic component to PCB (Printed Circuit Board).

SMP (Surface Mount Package)

The package method that can be used for Surface Mount Technology.The reason SMT need SMP for electrical components is the size difference between the minimum size that SMT can assemble to electrical components size. For example, the size for Integrate Circuit can be hundreds to ten hundreds um^2. This size is too small for SMT to assembly to PCB. SMP package Integrate Circuit to a proper size that SMT can assemble. For Example, 0402 , 0603 package for passive component , SOP , QFN , BGA package for integrated circuit.

SMC (Surface Mount Components)

​SMC is the components that can be using SME to surface mount onto PCB, it can be sorted to 2 kinds:

SMA(Surface Mount Assembly)

  • Modules that includes multiple active or passive component . For example, seven segment display, blue tooth modules, and WIFI module.
▲ The Electrical modules’ SMP – Seven Segment display

SMD(Surface Mount Device)

Electronic components package with Surface Mount Package belong to this type: For example,0402 Resistor , 0630 capacitor , SOP24 integrated circuit …etc.

▲ The common electrical components SMP & dimension.(REF: Wikipedia)

▲ The commonly seen SMP for IC – 28 Pin QFN (Quad flat no leads package(REF: Wikipedia)
▲ 28 Pin QFN(Quad flat no leads package) the side view package(REF: Wikipedia)
▲ A picture of a brunch of 0402 package SMD LED.

SME (Surface Mount Equipment)

​This is the equipment to do the surface mount SMC to PCB. The major equivalents include:

  • Solder printing machine
  • Pick & Place machine
  • Reflow Oven
  • ICT & AOI​
▲OPTO Plus SMT Line, the nearest machine to the farthest machine: Solder printing machine /Pick & Place machine / Reflow Oven / offline ICT & AOI​ machine

SMT process

SMT have 3 main process:

  • Solder paste printing process
    • Use SME: Automatic solder paste screen printer
  • Pick-and-place process
    • Use SME: Pick-and-place machine / Mounter machine
  • Reflow soldering process
    • Use SME: Reflow oven

Below is the simple diagram for SMT process, for example, we are going to SMT a 0603 packaged resistor. Firstly, we need to clean the PCB, and then use the solder paste screen printer to print the solder on the solder pad. At this moment, the solder is in cream type. Then, use the pick & place machine to assemble the resistors onto the solder paste. As the solder paste is still in cream type, the resistors will be sink and fix into the solder paste. The use reflow oven process, due to heat the solder past can combine the resistor and PCB together.  In case, there are no outside tension or high heat, the resistor & PCB won’t be separate. Then, the SMT process is completed.

This is the simple diagram for SMT process, for example, we are going to SMT a 0603 packaged resistor.
Simple SMT Flow made by OPTO PLUS LED


This article is just to introduce the related technology for SMD & SMT, and do hope it can help readers to verify the difference in between simply. Opto Plus LED Corp. is the professional manufacture for SMD LED display (from simple seven segment to complicate custom LED display with IC driver).  If you have any inquiry or questions related to LED display, please send your questions via [email protected]

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