Hey Guys! Hope you’re well. I welcome you on board. In this post today, I’ll walk you through PCBA (Printed Circuit Board Assembly) in detail. It's our 4th tutorial in the PCB learning series.
In the 1st tutorial, we studied printed circuit board(PCB) in detail and learned that PCB provides physical support and electrical connection through conductive copper layers for the electronic components placed on the board. We have seen in our previous tutorials that when we place our PCB order on some PCB fabrication house, they provide us with a PCB board without electronic components. We have to solder the electronic components on the board. But now these PCB companies also offer a service to provide finished PCB boards with electronic components attached. Such a finished PCB board with electronic components is called PCB Assembly(PCBA).
You can place these components by yourself, if you know how to solder them on the board or you can outsource it to the PCB company for the smooth insertion of these components on the boards without compromising the quality of the PCB. Curious to know more about PCBA? Keep reading.
Let's have a look at the Manufacturing process of PCBA in detail:
The PCB undergoes DFM(design for manufacturability) check before the actual PCBA process even starts. The DFM check cross-checks the final PCB structure with the initial blueprint of the design. This check identifies any missing links or potentially redundant and problematic features in the final PCB design.
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If PCB doesn’t undergo this check, the PCBA process can create trouble in properly mounting the components on the board and maintaining a flawless electrical connection between them. DFM checks not only reduce the cost of the manufacturing process but also ensure the overall functionality of the PCB.
PCBA production process comes with the following steps.
Before adding components on the board, a solder paste is added to the areas, where components rest on the finished PCB. The solder paste comes with greyish tiny balls of metals and is mixed with the flux that turns to a chemical composition and should be added in the right amount & in the right areas of the board.
To add the solder paste, a mechanical fixture is used to hold both the PCB and solder stencil in place. An applicator then takes the solder paste in precise amounts and places it on the desired PCB areas. The machine rolls the solder paste evenly on the intended PCB areas. As the stencil is removed, the solder paste sits on the desired areas.
After properly adding the solder paste on the board, the board is then passed through the pick and place process, where the robotic machine is used to pick the surface mount components from the reels and place them on the intended areas of the board.
The components added remain in the desired areas due to the sticky feature of the solder paste. The solder paste comes with enough bond strength that keeps the components in place.
Earlier this procedure was practiced manually by humans. However, the inception of advanced technology removed the need for this erratic manual process, since the automated process by machines is more accurate and efficient than the traditional manual process.
Once the electronic components have been placed in the desired locations, they remain there due to the presence of solder paste. The board then undergoes a Reflow Soldering process that solidifies the solder paste to keep the components at the required positions.
In this process, the finished board is transferred to a conveyor belt that passes through a big reflow oven having a series of heaters; the temperature of these heaters stays around 250oC which generates gradual heat to bake the board. At this stage, the temperature is high enough to make the solder melt, keeping the components tightly in place.
Once the solder has been melted down, the finished product is then passed through a series of cooler heaters that cools down the melted solder paste, giving it strength and creating a permanent solder joint to firmly connect the surface mount components with the board.
This is the reflow soldering for the one-sided PCB. Know that for two-sided PCB the stenciling and reflowing will be done separately for each side.
Once the reflow soldering has been done, the assembled board undergoes a proper inspection where the functionality of the board is tested. As the PCB passes through a reflow soldering process, it may result in poor connection quality or in worst cases, the elimination of the entire connection. To check these problematic features and common errors, the assembled board undergoes a careful inspection.
Based on the type of PCB board and the components used, the PCB assembly may go beyond the scope of SMT components insertion. In that case, Plated Through Hole(PTH) components insertion is used, where holes are drilled on the board and go completely through the board establishing a conductive path from one side of the board to another. Solder paste is not used in this case because it won’t stick and creeps into the drilled holes. In this PTH process, two types of soldering processes may be used:
In this process, the finished product undergoes the final inspection called the ‘functional test’ where simulated power signals run through the PCB to analyze the electrical characteristics of the board. If voltage, current or signal output in these characteristics show sudden fluctuation beyond the permitted range, it means the board has failed the test.
It is important to investigate any failures to guarantee the functionality of the manufacturing process. The recommended place to monitor the output and the potential errors is the optical inspection stage because errors are detected and rectified at this stage. This saves time ^ & money and avoids PCB production with similar defects.
PCBs are the backbone of electronic devices used for commercial and domestic purposes. More often big electronic companies don’t spend time in designing the PCB and then separately mounting the electrical components on the circuit boards. They purchase PCBA services, where circuit boards come ready-made installed with the components.
The common PCBA applications include:
That’s all for today. So far, we have discussed the basics of both PCB and PCBA, now we will have a look at the Top PCB Manufacturers to place your order. Hope you’ve enjoyed reading this article. If you have any questions, you can pop your comments in the section below. I’d love to help you the best way I can. Thank you for reading the article.
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