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What’s the SMT(Surface Mount Technology)?

Since PCB came out, it has been popular in many fields. In order to meet the needs of all walks of life, PCB is endowed with various functions and needs to be used with various components. Therefore SMT technology also arises at the historic moment.

  1. Basic concept

SMT is an English abbreviation of Surface Mount Technology, which is a relatively new electronic assembly technology. This technology compresses traditional electronic components into small devices with a volume of only a few tenths. It has the characteristics of high density, miniaturization, high degree of automation, high reliability and low cost.

  1. Why do we choose SMT

In the previous PCBA process, we usually passed the lead or other components through the holes in the PCB, and then adhered the components to the PCB surface. Obviously, this process is tedious and time consuming.

SMT is one of the new technologies to replace the old methods, which greatly reduces the manufacturing time and cost and makes mass production possible in a short time.

  1. Process

The basic process components of SMT include screen printing (or dispensing), mounting (curing), reflow soldering, cleaning, inspection, and repair.

Screen printing: Its function is to leak solder paste or paste onto the pads of PCB to prepare for soldering of components. The equipment used is a screen printer (silk screen printer), which is located at the front end of SMT production line.

Dispensing: It drips glue onto the fixed position of the PCB board. Its main function is to fix components to the PCB board. The equipment used is a glue dispenser, which is located at the front end of SMT production line or behind the testing equipment.

Mounting: Its function is to accurately mount surface assembly components to the fixed position of PCB. The equipment used is a mounter, which is located behind the screen printer in SMT production line.

Curing: Its function is to melt the patch adhesive, thus firmly bonding the surface assembly components with the PCB board. The equipment used is a curing oven, which is located behind the mounter in SMT production line.

Reflow soldering: its function is to melt the solder paste and firmly bond the surface assembly components and PCB board together. The equipment used is a reflow oven located behind the mounter in SMT production line.

Cleaning: Its function is to remove welding residues harmful to human body, such as flux, etc. on the assembled PCB board. The equipment used is a cleaning machine, and the position can be fixed, online or offline.

Inspection: Its function is to inspect the welding quality and assembly quality of the assembled PCB. The equipment used includes magnifying glass, microscope, on-line tester (ICT), flying needle tester, automatic optical detection (AOI), X-RAY detection system, function tester, etc. The position can be arranged at a suitable place on the production line according to the detection requirements.

Rework: Its function is to rework the PCB board that is detected to be faulty. The tools used are soldering iron, repair workstation, etc. It is arranged at any position in the production line.

  1. Advantage and Disadvantage of SMT

Advantage: Miniaturization,
High signal transmission speed
High assembly density
Good high-frequency characteristics
Favorable for automatic production
Low material cost and simplified procedures

Disadvantage: Small power
Easy damage
High requirements on welding technology
Easy parts falling or damage
Large equipment investment

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