In the PCB Assembly Services, the PCB components are placed and soldered over the exact positions of elements matching pins of component and footprint.
Generally, this is performed manually, but due to advanced techniques, automatic pick-and-place machines are available that reduce human effort and automatically perform all manual steps.
The through-hole or significant components are assembled manually, whereas machines make small details like SMT. However, sometimes the automated pick and place machines are not feasible for small production volumes.
1. The Method
After inserting and fixing the details over the PCBs’ footprint position, through-hole components are forwarded for soldering.
Workers participate in components placement or fixing for larger PCBs with more than 100 components.
Each worker places their designated details within the allocated time over the PCB and forwards them to the next worker.
For PCB movement motorized conveyer belt is installed.
Finally, after a bit of inspection, the PCB with components is dipped into a hot molten solder reservoir for soldering. This method, called wave soldering, is preferred for large-scale soldering of PCBs.
After soldering, the inspection is carried out for unsoldered components and wrong-placed pieces and proceeds for power-up. A PCB becomes fault-free at the last and final stage and qualifies to be assembled in the mechanical jig. In figure 1, the PCB components fixing line is shown.
Figure 1: PCB components fixing and PCB assembly line
In figure 2, the wave soldering method for through-hole parts is depicted.
Figure 2: Wave soldering method for through-hole components soldering
2. Steps of SMT PCB Assembly
In the SMT/ SMD Bill Of Materials (BOM), a PCB gets fitted aboard. PCB assembly, at the first step, a small quantity of paste is applied using the stencil.
A stencil is a metallic/plastic sheet with holes in the components soldering. The paste applied before the components’ placement holds them during PCB movement.
After placement, the PCB is soldered by the reflow method. The mixed sort of components PCBs, i.e., DIP and SMD, are wave-soldered and reflow soldered.
The hand soldering method is extensively applied in rework, troubleshooting, and small-scale productions, but that is unsuitable for large-scale PCB productions.
In figure 3, the SMT components pick and place machine is shown. The complex components, such as BGA and QFN packages, are soldered and inspected with specialized devices and are even more costly.
Figure 3: SMT/ SMD auto pick and place machine
