Detailed overview of manufacturing PCB boards

Printed circuit board

To assure the functioning of the completed product, the printed circuit board (PCB) manufacturing process necessitates a lengthy procedure. Regardless of whether a circuit board is single, double, or multilayered, the manufacturing procedures employed only change once the first layer is completed. Some PCBs may take 20 or more stages during fabrication due to changes in construction.

How to manufacture PCB boards?

Design and verification are the first phases in the PCB design process, which continue through circuit board manufacture.

PCB designing

The design is, of course, the first stage in any PCB fabrication process. PCB manufacturing and design always begin with a plan: the designer creates a layout for the PCB that meets all of the specifications.

Extended Gerber is a great piece of software for PCB design because it can also be used as an output format. Extended Gerber encodes all of the information that the designer needs, including the number of copper layers, solder masks, and additional component nomenclature. The exposed copper is always more corrosive than for the solder.

A good DFM assessment assures that the PCB design meets, at the very least, the manufacturing tolerances.

Review and technical querries

An engineer examines every aspect of the PCB design to verify that no components are missing or structures are improper. The design advances to the printing process after receiving approval from an engineer.

Printing

The PCB design may be produced once all of the inspections have been completed. PCB designs, unlike other plans such as architectural drawings, do not print on a standard 8.5 x 11 sheet of paper. A plotter printer, a specific type of printer, is utilized instead.

Two ink colors are used to depict the PCB's inner layers:

•Copper traces and circuitry on the PCB are inked with black ink.

•Clear Ink: Indicates sections of the PCB that are not conductive, such as the fiberglass foundation.

An interior layer printing process

Step four is the commencement of the manufacturing process when the manufacturer begins to create the PCB. Following the printing of the PCB design onto a piece of laminate material, copper is pre-bonded to that same piece of laminate, which acts as the PCB's framework. After that, the copper has scratched away, revealing the blueprint from before.

Unwanted copper

Before the PCB production process can continue, superfluous unwanted copper must be removed from the core or inner layers of the printed circuit board. Etching entails coating the required copper on the board with a chemical and exposing the remainder of the board to it. Because of its high mechanical strength, copper foil is quite durable. Its main benefit is the apparent lack of resonant frequency in the thermal area. A cathodic electrolytic substance,  thin copper foil is a narrow, metal grid foil put on the base coat of a circuit board that acts as a conductor for PCBs. As thicknesses protection, epoxy resins and polyurethane were utilized in PCB laminate, Prepreg, and sometimes RCCs.

Multilayer design of PCB manufacturing process

During the manufacture of multilayer printed circuit boards, extra processes are taken to account for the extra layers of the design. Many of these procedures are similar to those used in single-layer PCBs.

• Imaging of the inner layers
• Etching on the inner layer
• Refuse to be stripped
• Punch for post-etching
• AOI of the Inner Layer
• Oxide in the inner layer
• Layup
• Lamination
• Alignment using X-Rays

Alignment of the layer

After each of the PCB's layers has been cleaned, it's time to align them and examine them optically. The inner and outer layers are aligned using the holes from before. A technician aligns the layers using an optical punch, which is a sort of punch machine. The optical punch aligns the layers of the PCB by driving a pin through the perforations.

Inspection

Another machine performs an optical check after the optical punch to ensure there are no faults. Because any faults that remain after the layers are put together cannot be remedied, this automated optical inspection is critical. The AOI machine compares the PCB to the Extended Gerber design, which serves as the manufacturer's model, to ensure that there are no flaws.

Printed circuit board Lamination

The PCB layers are all assembled and ready to be laminated at step six of the process. The layers are ready to be fused once they've been confirmed to be defect-free. The PCB laminating process is divided into two stages: lay-up and lamination.

Drilling

X-ray equipment is used to determine the drill locations before drilling. Then, before drilling the more particular holes, registration/guiding holes are bored to secure the PCB stack. When it comes to drilling these holes, a computer-guided drill is employed, with the file from the Extended Gerber design serving as a guide.

Plating of the PCB

The panel is now ready to be plated once it has been drilled. A chemical is used in the plating process to fuse all of the layers of the PCB. The PCB is immersed in a succession of solvents after it has been completely cleaned. A micron-thick coating of copper is deposited over the top-most layer and into the holes that have just been drilled as part of the bathing process.

Outer layer imaging

A photoresist was applied to the PCB panel earlier in the procedure. It's time to apply another layer of photoresist in Step Eleven. However, because the outer layer still has to be photographed, the photoresist is only applied to it this time. After the outside layers have been coated in photoresist and imaged, they are plated in the same manner as the PCB's inside layers in the previous phase.

Etching of the outer layer

The tin guard is utilized to assist protect the copper throughout the etching process when it comes time to etch the outer layer for the last time. Any undesirable copper is removed using the same copper solvent as before, with the tin safeguarding the etching area's valuable copper.

 AOI of the outer layer

The outer layer, like the inner layer, must be subjected to automated optical examination. This optical examination confirms that the layer fulfills the design's exact specifications.

Application of the solder mask

Before applying the solder mask, the panels must be thoroughly cleaned. After cleaning, each panel is covered with an ink epoxy and solder mask coating. This mask gives the copper on the board an extra layer of protection against corrosion and oxidation.

Application of silkscreen

Fabricators must print crucial data on the board's surface in a technique known as silkscreen application or legend printing because PCBs require information to be printed directly on the board. The following details are included in this data:

• Company identification numbers
• Labels with cautionary statements
• Trademarks or emblems of manufacturers
• Identification of parts
• Pin locators and other identifying markers

Finalizing the Printed Circuit Board

Plating with conductive materials, such as the following, is required to finish the PCB:

•Hard gold

• Immersion silver

•ENIG (Electroless Nickel Immersion Gold)

•Soldering using hot air (HASL)

•HASL without lead

•Tin for immersion (ISn)

•Preservative for organic solderability (OSP)

• Immersion gold electroless nickel electroless palladium (ENEPIG)

The best material for the job is determined by the design parameters as well as the customer's budget.

Electronic Test

A technician performs a battery of electrical tests on the different sections of the PCB to confirm operation after it has been coated and cured (if necessary). IPC-9252, Guidelines, and Requirements for Electrical Testing of Unpopulated Printed Boards, must be followed during electrical testing.

Profiling

Fabrication engineers must profile the individually printed circuit boards cut from the construction board to determine their form and size. This data is usually found in the design's Gerber files. By specifying where the machine should build the scores on the construction board, this profiling stage directs the routing out of the operation. Routing out, also known as scoring, allows the boards to be separated more easily.

Quality Inspection

This final inspection confirms several features of the boards' structure, including:

• The hole sizes must be consistent throughout all layers and fit the design specifications.

• The dimensions of the board must match the design parameters.

• Fabricators must ensure that the boards are clean and free of dust.

• Burrs and sharp edges are not permitted on finished boards.

• All circuit boards that failed the electrical reliability tests must be repaired and retested.

Wrapping everything

Packaging and shipping are the last stages of PCB production. Printed circuit boards are generally packaged with material that seals around them to keep dust and other extraneous elements out.

Conclusion

PCB engineering and production of high quality are key components of circuit board activities in electronics. Understanding the process' complexity and why each step is necessary to provide you a greater understanding of the expense and work that goes into each printed circuit board.