How PCB is manufactured?
If you visit the IPC Standards page and try to understand the general set of standards for PCBs, you will know that it may take several afternoons to just read through it. No level of comprehension is guaranteed. But, you should still understand how PCBs are manufactured and what constitutes a good manufacturing process.
Compare this with one of those sandwich outlets where you can customize your order. You never get to know the secret sauce, but you can still ask the person on the other side of the counter to make it a certain way. While you may have a clear idea about your taste profile, how do you translate it in a manner that gives you the exact sandwich that you need? Now imagine you have to order a few thousand such sandwiches. What would you do? You can simply try to educate yourself about the process, and you will be able to place a more intelligent order. If nothing else, you will be able to articulate what you seek and be explicitly avoided.
If you are not going for nuance, the analogy holds for PCB manufacturing as well. Printed circuit boards and sandwiches have otherwise nothing in common, but understanding the process that goes into building them can make you a more intelligent buyer.
Three Acts of PCB Manufacturing
All good stories have three acts – beginning, middle, and end. The beginning lays the foundation for the endproduct, gets perfected with execution in the middle parts, and towards the end, only corrective measures & last-minute changes are made. Using the same high-level configuration, one can slice the PCB manufacturing process into three distinct parts – Design, Post-Design, and Post-Completion.
The design focuses on creating an outline to understand the functionalities you seek and the structure required to attain them. Post-Design is where the actual manufacturing takes place. And Post-Completion process focuses entirely on quality control and shipping. So, the PCB manufacturing process has already begun when the design process unfolds. It ends when you receive the shipment of your printed circuit boards.
Part I: Designing
1. PCB Design and Review
Having a design of the PCB you seek establishes a common standard or language between you and your manufacturer. It helps you communicate your exact specifications and requirements efficiently and gives your manufacturer a benchmark to work with. Generally, engineers tend to use available blueprints of printed circuit boards to assess what type of changes are required. This entire process is conducted in a dedicated design & engineering software environment using tools like trace-width and critical information on inner and external layers as the input.
An automated assembly process will have a holder that keeps the printed circuit board in one place and another component that uniformly applies the solder paste over it. It is critical to apply the solder paste in the same spaces, or the PCB's performance will become unpredictable. Stencils mitigate this risk to a large extent.
2. Design Printing
Once the design starts shaping up, a plotted printer is issued to get a printed circuit board's tangible print. Generally, this also includes a film-like structure that gives you insights into how the different layers on the board will come out in the final product. The inside of the board is hence highlighted with two colors:
- Clear ink for non-conductive regions.
- Black ink for copper traces and circuits.
If you are going through the process for the first time, you might get confused while looking at the external layer. The outer layer essentially uses the same colors with inverted logic.
Part II: Post Designing
3. Interior Layer Copper Printing
At this stage, the printed circuit board starts becoming more tangible. An insulating material that generally uses resin and fiberglass is used to keep the components together on the printed circuit board. This insulating material is carefully semi-cured using an oven. Then, copper is added on both sides of the board such that the printed films and the underlying design are visible.
4. Copper Etching
The design is then printed onto a laminated layer. The structure hence created is covered with a photoresponsive layer using chemicals. These chemicals will later get substantiated when UV rays are projected at them and contribute to component alignment on the board. Some components will require holes on the board for a stronger hold. And hence the printed circuit board is carefully put through a drilling process.
5. Layer Alignment
UV rays are projected on the photo-resistant material to solidify it. The UV light makes sure the trails for all the copper layers are visible. In the designing process, blank ink was used to mark copper traces and circuits. The same ink will now ensure that the solidification process does not impact any eliminated elements later. All the photo-responsive material has to be then washed out with an alkaline mixture.
6. Optical Inspection
Now, each of the layers on the board will require very careful inspection to ensure the alignment is exactly the way it is required. The drilled cavities will assist in this process. A punch-machine that senses holes optically is used for installing pins in the holes. Post this, a separate device is used to inspect the board for any potential defects. This is one of the most critical steps in the manufacturing process. Any errors that go undetected from this point onward will be incorrigible.
7. Layer Lamination
The next step includes lamination, and the layers need to stay together. Manufacturers tend to use metal clamps for this. A resin layer, substrate material, and a copper file are pressed onto the plate. Resin is used between each layer.
8. Drilling and Plating
Usually, a mechanical press is ideal for pressing the layers as it can apply uniform pressure. Removable pins are then punched through the layers to make sure they are held together for further processes. At this stage, if the printed circuit board is found to be accurate, it is sent to the laminating process. Once passed through the laminating process, the layers would have unified with the epoxy resin melting between the surfaces and integrating them.
To get direct access to the substrate, computer-guided drilling is conducted through the layers to remove all excess copper. Right after this process, the plating begins. Chemical substances are generally used to keep the layers together, while separate chemical fluids are used for thorough cleaning. These chemical coating on the panel also ensures the copper is reaching through the drilled holes.
9. Outer Layer Imaging and Etching
Another layer of photo-responsive materials, quite identical to the one used earlier, is to the external layer before it is processed through the imaging stages. Similar to the earlier process, UV lights are used for solidifying the photo-responsive substance, and later all the excess material is removed. Following the earlier stated processes, copper layer plating is conducted at this stage, along with instilling a thin tin guard that makes sure the copper does not get extracted from the external process.
10. Applying the Solder Mask
Each of the layers in the panel has to be cleaned thoroughly before the solder masking process. The soldering mask generally gives the PCB its green color. A layer of resin is added to this soldering film. Generally, UV light is used for removing all the excess masking layer. And finally, the mask is baked onto the printed circuit board.
11. Applying the Silk-Screen
Some manufacturers add gold, silver, or hot air-leveled padding to provide a uniform surface finish. Post this, the printed circuit board is ready for silk-screen installation.
The PCB needs a silk-screen that carries vital information about the board. This information is usually printed with inkjet technology. After the information has been added, the PCB is almost ready and good to be delivered to the coating & curing stage.
12. Finishing Processes
This is an arbitrary stage. Any corrigible errors are fixed here, and the finishing touches are added to the printed circuit board. Now, the PCB is ready for rigorous testing.
Part III – Post Completion
13. Electrical Consistency Testing and Cutting
A dedicated technician conducts a thorough electrical test. This process can include a considerable degree of automation that ensures the printed circuit board is aligned with the initial design and performing in line with the stipulated parameters.
Once the tests have been successfully conducted, the PCBs are cut using a router or a v-groove system. Any of the two can be used based on the desired use-case for the PCB. The cutting process ensures the PCB pops out of the extra layering when installed in a device later.
14. Quality Check and Last Stage Inspection
Before the printed circuit board is packaged, another inspection is conducted by a technician or an automated process. This test is carefully conducted to ensure no external pressure is applied to the printed circuit board, hampering its future performance. Once green-lighted, it is ready for packaging and delivery.
15. Packaging, Delivery, and Shipping
While the manufacturing process is quite elaborate and necessitates finesse at every stage, not having a carefully engineered logistics process can throw all the precision in vain. Printed circuit boards have to be meticulously packaged with sufficient guards and protection to ensure they are not damaged in transit. PCB Power works only with leading industrial logistics partners like BlueDart, FedEx, Bombax, SpiceJet, and DHL.
In Conclusion
The PCB manufacturing process requires years of optimization, testing, and quality control. The manufacturing firm must have a grip on the entire value-chain for providing you an immaculately printed circuit board that does not require rework and has an industry-standard usable life. PCB Power has a comprehensive understanding of the printed circuit board manufacturing process, as the firm provides assembly, stencil fabrication, manufacturing, and component sourcing – all on one platform. Click here to access the firm’s printed circuit board layout and manufacturing services for quick prototyping and small, medium, or production volume scale manufacturing.
