Before PCB design, circuit designers are recommended to visit PCB circuit board workshops and have face-to-face communication with manufacturers on PCB manufacturing needs. It helps prevent designers from passing any unnecessary errors during the design phase. However, this is becoming impractical as more and more companies outsource their PCB manufacturing consultancy to overseas suppliers. Therefore, we provide this article to have a proper understanding of the PCB board manufacturing process steps. Hopefully it will give circuit designers and those new to the PCB industry a clear understanding of how printed circuit boards are manufactured and avoid unnecessary mistakes.

PCB manufacturing process steps

Step 1: Design and output

The board should be strictly compatible with the PCB layout created by the designer using PCB design software. Commonly used PCB design software includes Altium Designer, OrCAD, pads, KiCad, Eagle, etc. Note: Before PCB fabrication, designers should inform their contract manufacturers about the version of PCB design software used for circuit design, as it helps to avoid problems caused by differences.

Once the PCB design is approved for production, the designer can export the design to a format supported by the manufacturer. The most commonly used procedure is called Extended Gerber. Gerber's name is also IX274X.

The PCB industry spawned Gerber as an extension of the perfect output format. Different PCB design software may require different Gerber file generation steps, and they all encode comprehensive important information, including copper trace layers, drill patterns, holes, component symbols and other options. At this point, every aspect of the PCB design is inspected. The software runs a supervisory algorithm on the design to ensure no errors are found. Designers also examine the plan for elements related to trace width, board edge spacing, trace and hole spacing, and hole size.

After a comprehensive inspection, the designer forwards the PCB file to the PC board room for production. In order to ensure that the design meets the requirements of the smallest tolerances during the manufacturing process, almost all PCB Fab Houses perform Design for Manufacturing (DFM) inspections before manufacturing circuit boards.

Step 2: From file to movie

PCB printing begins after the designer outputs the PCB schematic file and is checked by the manufacturer for DFM. Manufacturers use a special printer called a plotter to make a photographic film of the PCB to print the board. Manufacturers will use these films to image the PCB. Although it's a laser printer, it's not a standard laser printer. Plotters use incredibly precise printing techniques to provide highly detailed films of PCB designs.

The final product will get a plastic sheet of the PCB negative with black ink. For the inner layers of the PCB, the black ink represents the conductive copper portion of the PCB. The remaining clear parts of the image represent areas of non-conductive material. The outer layers follow the opposite pattern: the copper layer is cleared, but black refers to the areas that will be etched away. The plotter automatically develops the film and stores it securely to prevent unwanted contact.

Each layer of PCB and solder mask has its own transparent black film sheet. A two-layer PCB requires a total of four sheets: two for the multilayer and two for the solder mask. It is important that all films correspond perfectly to each other. When used in harmony, they create a PCB alignment map.

In order to achieve perfect alignment of all films, positioning holes should be punched in all films. The precision of the hole can be achieved by adjusting the table where the film is placed. Holes are punched when tiny calibrations of the table result in the best fit. These holes will be filled with alignment pins in the next step of the imaging process.

Step 3: Printing the inner layers: where will the copper flow?

The cinematic creation in the previous step aimed to draw a copper wire graphic. Now it's time to print the graphics from the film onto the copper foil.

This step in PCB manufacturing prepares the actual PCB for fabrication. The basic form of a PCB consists of a laminate with a core material of epoxy resin and fiberglass, also known as a substrate. A laminate is an ideal body to receive the copper that makes up a PCB. The substrate material provides a solid and dust-proof starting point for the PCB. The copper is pre-bonded on both sides. The process involves scraping away copper to reveal the design in the film.

In PCB construction, cleanliness is crucial. Clean copper facing laminate before sending it to a decontaminated environment. At this stage, it is critical that no dust particles settle on the laminate. The wrong blot could cause the circuit to short or remain open.

Next, the clean panel receives a layer of light-sensitive film called photoresist. The photoresist includes a layer of photoreactive chemicals that hardens after exposure to ultraviolet light. This ensures an exact match from photographic film to photoresist. The film is mounted on pins that hold the pins in place on the laminate.

The film and cardboard line up and receive a beam of ultraviolet light. Light passes through the transparent portion of the film, hardening the photoresist on the underlying copper. The plotter's black ink prevents light from reaching areas where hardening is not desired, so remove it.

After the board is prepared, it is washed with an alkaline solution to remove any unhardened photoresist. A final pressure wash will remove anything else left on the surface. The board is then dried.

The product will appear with a resist that properly covers the areas of copper that are to remain in the final form. A technician checks the board to make sure no errors have occurred at this stage. Any resist present at this point represents copper that will be exposed in the finished PCB.

This step only applies to boards with more than two layers. Simple two-layer boards can skip drilling. Multilayer boards require more steps.

Step 4: Remove Unwanted Copper

After removing the photoresist and covering the copper we wish to keep with hardened photoresist, the board moves on to the next stage: removing unwanted copper. Just as the alkaline solution removes the resist, stronger chemical formulations consume excess copper. A bath of copper solvent solution removes all exposed copper. At the same time, the required copper remains adequately protected beneath the hardened layer of photoresist.

Not all copper plates are created equal. Some heavier boards require large amounts of copper solvent and varying exposure times. As a side note, heavier copper boards require extra attention to track spacing. Most standard PCBs rely on similar specifications.

Now that the solvent has removed the excess copper, the hardened resist protecting the preferred copper needs to be washed off. Another solvent can do the job. Now the board is only flashed with the copper substrate required for the PCB.

Step 5: Layer Alignment and Optical Inspection

With all the layers clean and ready to go, the layers need to be aligned with punches to make sure they are all aligned. Pilot holes align the inner layer with the outer layer. Technicians put the layers into a machine called an optical punch, which makes an exact correspondence so the holes can be precisely positioned.

Once these layers are put together, it is impossible to correct any mistakes made on the inner layers. Another machine performs an automated optical inspection of the panels to confirm they are completely free of defects. The manufacturer received the original Gerber design as a model. The machine scans the layers using a laser sensor, then electronically compares the digital image to the original Gerber file.

If the machine finds inconsistencies, the comparison results are displayed on the monitor for evaluation by technicians. Once this layer passes inspection, it enters the final stage of PCB production.

Step 6: Layering and Binding

At this stage, the circuit board is formed. All individual layers await their union. Once the layers are ready and confirmed, they just need to meld together. The outer layer must be bonded to the substrate. The process is divided into two steps: layering and binding.

The outer layer material consists of glass fiber sheets pre-impregnated with epoxy resin. Referred to as prepreg. A thin copper foil also covers the top and bottom of the original substrate, which contains the copper wire etch. Now, it's time to sandwich them.

The bonding takes place on a heavy-duty steel table with metal clamps. The layers are held securely in dowels attached to the table. Everything has to fit snugly to prevent movement during alignment.

The technician first places the prepreg layer on the alignment tub. The substrate layer is placed on top of the prepreg before the copper sheet is placed. Additional sheets of prepreg sit on top of the copper layer. Finally, the stack is completed with aluminum foil and a copper press plate. It is now ready to be pressed.

The whole operation process is automatically executed by the computer of the bonding machine. A computer schedules the heating of the stack, when to apply pressure, and when to allow the stack to cool at a controlled rate.

Next, a certain amount of unpacking occurs. During the process of molding all the layers together, the PCB shines brightly, and the technician only needs to unpack the multi-layer PCB product. It's a simple matter of removing the restraint pins and discarding the top pressure plate. The PCB benign stands out from its aluminum laminate housing. The copper foil included in the process remains the outer layer of the PCB.

Step 7: Drill Holes

Finally, drill the holes in the stacked board. All components that are planned to come out later, such as copper connections in terms of vias and leads, rely on the accuracy of precision drilling. The holes are drilled to be as wide as a human hair - the diameter of the drill reaches 100um, while the average diameter of a human hair is 150um.

To find the location of the drill target, the X-ray locator can identify the appropriate drill target point. The appropriate pilot holes are then punched to secure the stack for a series of more specific holes.

Before drilling, the technician places a slab of cushioning material under the drill target to ensure a clean borehole. The outlet material prevents any unwanted tearing to the bit outlet.

A computer controls every tiny movement of the drill - products that determine the machine's performance naturally depend on computers. A computer-driven machine uses the drill files from the original design to identify appropriate drill locations.

The drill uses a pneumatic spindle at 150,000 rpm. At this speed, you might think drilling is instantaneous, but there are a lot of holes to drill. A common PCB contains more than one hundred integrity points. Each drill requires its own special moment during the drilling process, so it takes time. These holes will then accommodate the PCB's vias and mechanical mounting holes. Final fixing of these parts takes place after electroplating.

After drilling is complete, the extra copper lining the edge of the production panel is removed with a profiling tool.

Step 8: Electroplating and Copper Deposition

After the holes are drilled, the panel moves to the plating layer. The process uses chemical deposition to fuse the different layers together. After a thorough cleaning, the panels go through a series of chemical baths. In the molten pool, the chemical deposition process deposits a thin layer of copper (about 1um thick) on the panel surface. Copper goes into the most recently drilled hole.

Before this step, the inner surface of the hole only exposes the fiberglass material that makes up the interior of the panel. The copper groove completely covers or covers the hole wall. By the way, the entire panel receives a new layer of copper. Most importantly, the new holes are covered. The computer controls the entire process of impregnation, removal and processing.

Step 9: Imaging the Outer Layers

In step 3, we applied photoresist to the panel. In this step we'll do that again - except this time we use the PCB design to image the outer layers of the panel. We first place the layers in a sterile room to prevent any contaminants from adhering to the surface of the layers, and then coat the panels with a layer of photoresist. Prepared panels go into the yellow room. UV rays can affect photoresists. UV levels at yellow wavelengths are not high enough to affect photoresists.

The black ink transparencies are secured with pins to prevent alignment with the panel. When the panel comes into contact with the stencil, a generator blasts it with high-intensity ultraviolet light, which hardens the photoresist. The panel then goes into a machine that removes the unhardened resist and is opaquely protected by black ink.

This process is the reverse of that of the inner layer. Finally, the outer panel is inspected to ensure that any unwanted photoresist was removed in the previous stage.

Step 10: Plating

Let's go back to the electroplating room. As we did in step 8, we plated a thin layer of copper on the panel. The exposed portion of the panel from the outer photoresist table receives electroplated copper. After the initial copper plating bath, the panel is usually tinned, which removes any copper that the board was intended to remove. Tin protects part of the board so that it remains covered with copper during the next etch stage. Etching removes unwanted copper foil on the panel.

Step 11: Final Etching

At this stage, the tin protects the required copper. Remove unwanted exposed copper and residual copper underneath the resist layer. Again, a chemical solution is applied to remove excess copper. At the same time, the tin protects the valuable copper at this stage.

The conductive areas and connections are now correctly established.

Step 12: Solder Mask Application

Before applying solder resist to both sides of the board, clean the panel and cover with epoxy solder resist ink. The board receives a beam of ultraviolet light that passes through the solder mask photographic film. The covered part remains unhardened and will be removed.

Finally, the board goes into an oven to cure the solder resist.

Step 13: Surface shaping

To increase the solderability of the PCBs, we electroless plated them with gold or silver. Some PCBs also accept hot air flat pads during this stage. Hot air leveling produces an even pad. The process results in the creation of surface profiles, many types of surface profiles can be processed according to customer specific requirements.

Step 14: Silkscreen

Nearly completed circuit boards receive inkjet writing on their surface to indicate all important information pertaining to the PCB. The PCB finally goes to the final coating and curing stage.

Step 15: Electrical Test

As a last precautionary measure, the technician performs electrical tests on the PCB. Automated procedures can confirm the functionality of the PCB and its consistency with the original design. At PCB manufacturers, advanced electrical testing called "flying probe testing" is offered, which relies on moving probes to test the electrical performance of each net on a bare circuit board.

Step 16: Profile and V-groove

Now we come to the final step: cropping. Different boards were cut from the original panels. The methods employed either centered on the use of routing tools or on the use of v-grooves. A router leaves small protrusions along the edge of the board, while a v-groove cuts diagonal channels along the sides of the board. Both ways allow the board to pop out of the panel easily.