/when choosing a PCB assembly process factors to be considered
The selection process is mainly based on the assembly density of the printed board and the equipment manufacturing conditions of their pcb. If the SMT production line has two types of welding equipment, reflow soldering and wave soldering, the following considerations can be made.
1.Reflow soldering is used as much as possible, because reflow soldering has the following advantages than wave soldering.
● Reflow soldering is not like wave soldering. The components are directly immersed in the molten solder, so the thermal shock of the components is small.
● The solder is applied to the pad quantitatively to control the amount of application and reduce soldering defects. Therefore, the welding quality is good and the reliability is high.
● Self Alignment, if there is a certain deviation in the placement position of the component, due to the surface tension of the molten solder, when all the soldering ends or pins are wetted simultaneously with the corresponding pads, Under the action of wetting force and surface tension, it is automatically pulled back to the approximate target position.
● Impurities are generally not mixed in the solder, and the solder composition can be properly ensured when solder paste is used.Local heating heat source can be used to weld on the same substrate using different welding processes
●The process is simple, the workload of repairing the circuit board is extremely less, thus saving manpower, electricity and materials.
2.General density hybrid assembly, when SMD and THC are on the same side of the PCB, using A-side printing solder paste, reflow soldering, B-side wave soldering process; when THC is on the A side of the PCB, SMD is on the B side, B-side dispensing and wave soldering processes are used.
3.Under high-density mixed assembly conditions, when there is no THC or only a small amount of THC, double-sided printing solder paste, reflow soldering process, and a small amount of THC using the attached method; if A side has more THC , using A-side printing solder paste, reflow soldering, B-side dispensing, mounting, wave soldering process.
Note: On the same side of the printed board, it is forbidden to use the reflow soldering SMD firstly and then wave soldering THC.
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