PCB Assembly or PCBA is the process of soldering electronic components to a printed circuit board. There are various stages within this process which are all necessary to work together in order to establish an integrated process. These individual stages must be compatible with each other and the minute process must be monitored to ensure that the optimum quality is maintained throughout the entire course of the assembly.
Note that assembly of a board differs from manufacturing a board. Manufacturing PCBs involves prototype creation and PCB designing. Once the board is complete, electronic components are soldered onto it prior to using it in any electronic gadget or device.
The Assembly Process
The PCB assembly process includes applying solder paste to the PCB, pick and place, soldering, inspection, and testing.
Solder paste is a mixture of small granules of solder and solder flux. Before attaching the components to the board, you need to add solder paste to the areas of the PCB where soldering is necessary. These areas are usually the component pads. You can accomplish this task with the use of a solder screen. The process of depositing the paste in place is relatively similar to a printing process.
Place the solder screen directly onto the board. With the solder screen properly positioned, move a runner across it and squeeze a small amount of solder paste through its holes and onto the surface of the board. Since the solder screen had been made from the PCB files, it already has holes on the solder pads’ positions, so the solder is applied only on the pads.
Control the amount of solder that you apply to the board as to make sure that the ensuing joints have the proper amount of solder.
•Pick and Place
After adding solder paste to the board, it is then forwarded to the process of pick and place. In this stage of the PCB assembly process, a machine filled with component reels picks the components up from the reels and places them on the right position on the PCB.
The components that are placed on the board are sustained by the pressure of the solder paste. This is enough to keep the components in place, given that the PCB is not jolted.
The component information and position required to program the machine used in “pick and place” is derived from the PCB design information. This simplifies the programming of the pick and place process.
Once you have added the components to the board, the next step is to pass the board through the soldering machine. However, this process is not commonly used for surface mount components. If you are using wave soldering, then you do not need to add solder paste to the board because the wave soldering machine already provides the solder. Instead of wave soldering, you can use re-flow soldering techniques, which are more widely used these days.
After the soldering process, the boards are typically inspected for quality control. Surface mount boards that employ a huge number of components are not manually inspected. Instead, they are optically inspected by means of machines that can detect misplaced components, poor joints, and sometimes wrong components.
Testing of the electronic products is necessary before transporting them from the factory. There are many ways to test PCBs, such as electrical continuity testing, microsectioning, and shear testing.
In order to make sure that the PCB manufacturing process is operating satisfactorily, there must be feedback from the outputs. And thus, it is necessary to investigate any detected failure. Defects can be detected as early as the optical inspection stage and quickly rectified so that the subsequent boards are not built with similar problems.
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