SMT is a series of process technologies based on PCB processing, with high mounting accuracy, speed, and other advantageous features, from the SMT refers to a series of process technology based on PCB, which has the advantage of high mounting accuracy and speed and has been adopted and applied by many electronic manufacturers. The process mainly includes screen printing or dispensing, mounting or curing, reflow soldering, cleaning, testing, repair, etc., several processes in an orderly manner, to complete the entire SMD process. SMT process mainly includes screen printing or dispensing, mounting or curing, reflow soldering, cleaning, testing, rework, and so on.
PCB Assembly Process
(1) Circuit board on the solder paste
In a professional PCBA production line, mechanical fixtures fix the PCB and stencil in place. Then, a solder paste printer places the solder paste in precise amounts on the pre-set area on the pre-set area. The solder paste printer then applies the solder paste to the stencil, spreading it evenly over each open area. After removing the stencil, the solder paste remains on the PCB pads remain on the PCB pads.
(2) SMT Placement
After the solder paste is applied to the PCB, a conveyor belt on the SMT production line transfers the PCB to the SMT placement machine, which places the surface mount components on the prepared PCB. The mounter will place the surface-mounted components on the prepared PCB.
(3) Reflow Soldering
After the surface components are mounted, the PCB board is transferred to the reflow soldering furnace, the reflow soldering furnace has different temperature zones, through the heating and cooling processes Curing components on the PCB board.
(4) AOI Inspection
Through the AOI inspection equipment check whether there is no leakage of welding, wrong welding, or false welding problems on the PCB board. High volume pcb assembly,
(5) Through-hole component welding
According to the type of through-hole components, wave soldering, and hand soldering are used to solder the through-hole components on the PCB board. Wave soldering will use the wave soldering furnace.
(6) Final Inspection and Function Test
After all soldering steps are completed, the final inspection will test the functionality of the PCBA board. By simulating the PCBA board’s operating environment and monitoring the PCBA board’s electrical The quality of the PCBA board is evaluated by simulating the operating environment of the PCBA board and monitoring whether the electrical characteristics of the PCBA board meet the design requirements.
PCB Assembly Mounting Requirements
(1) The SMT mounting process requires that the type, model, nominal value, polarity, and other characteristics of the components of each assembly bit number be marked by the product’s assembly drawing and the BOM table.
(2) The SMT SMD process requires that the mounted components be intact.
(3) The SMT placement process requires the mounting of components solder end or pin not less than 1/2 thickness to be immersed in solder paste. For general component placement of solder paste extrusion The amount of solder paste extrusion (length) should be less than 0.2mm, for narrow-pitch components patch the amount of solder paste extrusion (length) should be less than 0.1mm.
(4) The SMT process requires that the component ends or pins are aligned with the pad pattern, and centered. As a result of reflow soldering has a self-localization effect, so the component Device mounting position allows a certain degree of deviation.
Advantages of SMT placement processing:
(1) high assembly density, small size, and light weight of electronic products.
(2) High reliability and shock resistance. Low solder joint defect rate.
(3) Good high-frequency characteristics. Reduced electromagnetic and radio frequency interference.
(4) Easy to realize automation and improve productivity. Reduce cost up to 30%~50%. Save material, energy, equipment, labor, time, etc.
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