Step 3: Backwing welding
After the welding balm and surface installation components are placed in place, they need to be kept there. This means that the welding paste needs to be curing and adheres to the component to the board. PCB assembly is achieved by the process of calling “backflow”.
After picking up and placing the process, the PCB board is transferred to the conveyor belt. The conveyor belt passed through a large return furnace, and the flow furnace was a bit like a commercial pizza furnace. The oven consists of a series of heater, which gradually heated the board to the temperature of about 250 degrees Celsius or 480 Hualhi. Its temperature is enough to melt the solder in the tinnum.
After welded, the PCB continued to pass through the oven. It cools and solidifies the melting welded through a series of cooler heater. This will create a permanent solder to connect SMD to PCB.
Step 4: inspection and quality control
Once the surface paste component is welded after the return process, the function of the circuit board can be tested. Generally, the movement during the return process will lead to poor or lost connection. Short circuit is also a common side effect of this movement, because components in the wrong position sometimes connect to parts that should not be connected in the circuit.
Inspection method includes: manual examination
Automatic optical test (called AOI)
X -ray inspection (most commonly used for more complex or layered PCB.)