The SMT (Surface Mount Technology) production line uses automated equipment to accurately mount electronic components onto the surface of PCBs and complete soldering. Its core working principle and process are as follows:
1、 Core process flow
1. Solder paste printing
Cover the PCB pads with laser steel mesh (opening accuracy ± 0.01mm), and the printing machine evenly applies solder paste to the pads. The material of the steel mesh affects the demolding effect (if there is no magnetic steel mesh, it can avoid solder paste adhesion).
After printing, 3D scanning is performed using SPI (solder paste detector) to check thickness, offset, and bridging defects.
2. Component mounting
After PCB positioning, the surface mount machine recognizes the reference point through the visual system, picks up the components from the feeder (Feida) with a suction nozzle, and attaches them to the solder pads with micrometer level accuracy (± 0.025mm).
High speed surface mount machines can reach 200000 points per hour (such as Yamaha YM40r), small components (0.4mm × 0.2mm) are processed by high-speed machines, and complex packaging such as BGA is completed by high-precision machines.
3. Reflow soldering
The PCB flows into the reflow soldering furnace and undergoes four stages: preheating (150 ℃), constant temperature, reflow (peak temperature of 245 ℃), and cooling. The solder paste melts to form reliable solder joints.
Some production lines use nitrogen protection to reduce oxidation.
4. Quality inspection
AOI (Automatic Optical Inspection): Multi angle scanning of solder joints to identify defects such as virtual soldering and offset (misjudgment rate<0.5%).
X-Ray inspection: Penetrating hidden solder joints such as BGA, detecting issues such as solder joints and voids.
Defective products are manually re evaluated and repaired
