What is SMT PCB​?

SMT PCB Meaning

SMT PCB / SMT , full name is called Surface Mounted Technology . It is a high precision electronic smt pcb assembly technology which to attach or weld surface mount components on PCB pads . Firstly , print solder paste coated on the PCB pads , and then place the surface mount component accurately on the solder paste coated pad, by heating the printed circuit board until the solder paste melts, after cooling will realize the connection between the components and printed circuit. FS Technology PCBA Blog will explain its specific process and advantages in detail for you.

The concept of SMT Process

There are two basic types of china smt pcb assembly process, one is reflow soldering process, the other is wave soldering process.
pcba smt process


So in high precision electronic pcb smt assembly, what is the role of reflow , what is the role of wave welding, what is the difference between them? Let us do a explanation :

Regarding Reflow: the soldering paste precoated on the pad is melted by heating to realize the electrical interconnection between the pins or solder ends of the electronic components premounted on the pad and the PCB pad, so as to achieve the purpose of welding the electronic components on the PCB board. Reflow welding is generally divided into preheating zone, heating zone and cooling zone.

Reflow soldering process: Printing solder paste > mount components > Reflow soldering > cleaning

Reharding Wave soldering: the pump is used to spray the melted solder into a solder wave peak, and then the pins of the electronic components to be welded pass through the solder wave peak to realize the electrical interconnection of electronic components and PCB board. A wave soldering is divided into spray, preheating, tin furnace, cooling four parts.

Wave soldering process: plug-in > Flux coating > preheat > wave soldering > edge cutting > inspection.

Difference between wave soldering and reflow welding

  • Reflow soldering, there already coated with solder paste on the PCB before into the machine , then welding by melting the solder paste . In wave soldering, there is no solder paste coated on the pcb before into machine, and it welds by wave machine creating solder paste to paint on pcb pads which need solder .
  • Wave soldering is molten solder to form solder wave for welding components; Reflow soldering is high temperature hot air form circumfluence molten solder to weld components.
  • Reflow is suitable for patch electronic components, wave soldering is suitable for pin electronic components.

Wave soldering and reflow are two important processes in china smt pcba machining.

SMT Visual Inspection Requirement

  • Good wettability
  • solder is continuous on the surface of the solder joint, and the closer it is to the edge line of the solder joint, the thinner the solder layer, the contact Angle should be less than 30 degrees, for the solder pad edge line is smaller, the concave menacing surface should be seen, the metal surface to be welded is not allowed to have solder blocking layer and other pollutants,
  • Solder joint solder layer should be moderate, avoid too much or too little
  • The solder spot position must be accurate, the end/pin of the component should be in the center of the pad, width and length direction should not exceed the phenomenon.
  • The solder joint plane should be continuous and smooth, and the solder joint formed by reflow welding should have a bright appearance.

Advantages of China SMT

  • High assembly density, SMT can reduce the volume of electronic products by 60% and reduce the weight by 75%
  • High reliability, generally poor solder spot rate is less than ten parts per million, one order of magnitude lower than through hole component wave soldering technology.
  • Good high frequency characteristics
  • Reduce costs
  • Convenient for automatic production.

The above content is the whole content of “The meaning of smt pcb”. If there is anything else you need to know about Surface Mounted Technology, or if you have a different opinion, feel free to email us.

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