Step-by-Step Guide to the Printed Circuit Board Manufacturing Process

Printed circuit boards (PCBs) provide the electrical and mechanical foundation for electronic devices. The PCB manufacturing process transforms a PCB design into a finished board through a series of controlled steps, including imaging, etching, lamination, drilling, copper plating, solder mask application, surface finishing, and electrical testing. Understanding these PCB manufacturing steps helps designers create boards that are both functional and manufacturable.

PCB Fabrication Process

The PCB fabrication process converts digital design data into a physical circuit board through a sequence of controlled manufacturing operations. Depending on the board structure, the process can include material preparation, inner-layer imaging and etching, layer alignment, lamination, mechanical drilling, hole metallization, outer-layer pattern formation, solder mask and legend application, surface finishing, electrical testing, profiling, and final inspection.

Each stage is closely controlled because dimensional accuracy, layer registration, copper thickness, hole quality, and surface condition can directly affect the electrical performance and reliability of the finished PCB.

Steps Involved in PCB Fabrication Process

Step 1 – Imaging and Printing the Design

Before physical fabrication begins, the submitted Gerber files are reviewed through CAM and DFM processes. The manufacturer checks whether critical design features such as trace width and spacing, pad dimensions, drill sizes, copper clearances, solder mask openings, board outline, and layer registration are compatible with the selected manufacturing process.

For example, JLCPCB's standard multilayer PCB capability supports minimum trace width and spacing down to 0.09 mm (3.5 mil) for 4-layer and above boards, while the minimum mechanical drill diameter for multilayer PCBs is 0.15 mm. Designs approaching these limits require particular attention to manufacturability and cost.

The same colors are used for the outer layers, but their meanings are reversed. Each layer of the PCB and solder mask receives its own clear and black film sheet. In total, a two-layer PCB requires four sheets: two for the copper layers and two for the solder mask. To proceed further, all the film layers must be perfectly aligned with each other. To achieve perfect alignment of all films, registration holes should be punched through all films. These holes will align with the registration pins (a predefined structure) in the subsequent step of the imaging process.

Step 2 – Creating the Substrate

The substrate provides the insulating and mechanical foundation of the PCB. For standard FR-4 boards, the dielectric structure is primarily based on glass fiber reinforced epoxy resin. Multilayer PCBs use a combination of copper-clad cores and prepreg, with the prepreg serving as the bonding and insulating material between copper layers.

The selected material system influences important properties such as dielectric performance, thermal resistance, mechanical strength, and the final thickness of the PCB.

Step 3 – Printing the Inner Layers

This step in the PCB manufacturing process marks the beginning of creating the actual PCB. The process commences with the fundamental form of a PCB, consisting of a laminate board made from the substrate material. Simply put, it can be described as a mask layer utilized to pattern photosensitive material onto the copper. In this step:

● The PCB design is printed onto the laminate board

● Copper is pre-bonded on both sides of the laminate board

● Next, the laminate board is covered with a photosensitive film called the resist.

This photosensitive film is made from photo-reactive chemicals that harden when exposed to ultraviolet light (the resist) and covers the structure. This process ensures an exact match between the photo films and the photoresist. The films are placed onto pins that secure them in place over the laminate panel.

Step 4 – Ultraviolet Light Blasting

The film and board align and receive a blast of UV light. The light passes through the clear parts of the film, hardening the photoresist on the copper underneath. The black ink from the plotter prevents the light from reaching the areas not meant to harden. Only hardened areas are retained as copper pathways; the rest of the board will be etched away in the next step.

After this, the board is washed with an alkaline solution, which dissolves and removes the unhardened photoresist. A final pressure wash is used to remove any residue left on the surface. Subsequently, the board is dried. A technician examines the boards to ensure that no errors occur during this stage.

Step 5 – Removing the Unwanted Copper

After development, the exposed copper is chemically etched away while the protected circuit pattern remains. Etching must be carefully controlled because excessive etching can reduce trace width, while insufficient etching may leave unwanted copper between adjacent features.

For high-density PCB designs, accurate control of etching is especially important because small changes in trace width or spacing can affect manufacturability, current-carrying capability, and signal integrity.

Step 6 – Layer Alignment and Inspection

The newly cleaned layers will need to be inspected for alignment. The holes drilled earlier help align the inner and outer layers. An optical punch machine drills a pin through the holes to keep the layers lined up. After the optical punch, another machine will inspect the board to ensure there are no defects. From here on out, you will not be able to correct any missed errors. In the inspection process:

● The manufacturer uses an Automated Optical Inspection (AOI) system to inspect the inner-layer circuitry.

● The AOI machine compares the PCBs with the original design from Gerber.

● The AOI system captures high-resolution images of the circuit pattern and compares them with the reference design to  identify defects such as opens, shorts, missing copper, or unwanted copper features.

● The defective circuit boards are discarded at this stage.

● The process is repeated for the outer layers after imaging and etching them.

Step 7 – Laminating and Bonding the Layers

For a multilayer PCB, the inspected inner layers are assembled with copper foil and prepreg according to the specified stack-up. The layer-up process must maintain accurate registration so that pads, traces, and vias on different layers align correctly.

The stack is then placed into a lamination press. Under controlled temperature and pressure, the resin in the prepreg softens and flows into the spaces between the copper layers before curing. After curing, the individual layers are bonded into a mechanically stable multilayer structure.

Lamination affects several important PCB characteristics, including overall thickness, dielectric spacing, layer-to-layer registration, mechanical strength, and the electrical characteristics of controlled-impedance structures. For high-speed designs, the dielectric thickness between signal and reference layers should therefore be considered during stack-up planning.

● The operator places the stack on the laminate press with proper alignment.

● The bonding press computer controls the laminate press.

● The computer will heat press plates and apply pressure according to calibrations, fusing the PCB layers.

● The epoxy melts inside the prepreg, which, along with pressure, fuses the layers together.

● After removing the top press plate and the pins, the technician will pull out the printed circuit board. This process fuses all the layers together.

Step 8 – Drilling

Drilling is one of the most critical steps in PCB manufacturing because it creates the holes required for through-hole components and electrical interconnections between PCB layers.

Modern PCB drilling is performed using computer-controlled drilling equipment to achieve accurate hole locations and diameters. Before drilling, X-ray or other registration methods may be used to locate internal layer targets and compensate for dimensional changes caused by the manufacturing process.

JLCPCB's current PCB capability specifies a minimum mechanical drill diameter of 0.15 mm for multilayer PCBs, with a hole-position tolerance of ±0.05 mm. The average hole plating thickness is specified at 18 μm. JLCPCB currently supports through-hole structures and does not support blind or buried vias in its standard rigid PCB capability.

The drilling process typically includes:

● Locating registration targets

● Drilling tooling and component holes

● Drilling via holes

● Inspecting hole position and quality

● Preparing the drilled panel for subsequent desmear and copper metallization

Desmear and Hole Preparation

After mechanical drilling, resin residue can remain on the hole walls. A desmear process removes this resin residue and prepares the hole walls for reliable copper metallization. Proper hole-wall preparation is essential because poor adhesion or incomplete metallization can compromise the electrical connection between PCB layers.

Step 9 – PCB Plating

The board is now ready to be plated. PCB plating is the process of filling the drilled holes with copper, allowing the current to pass from one layer to another in the PCB by connecting them electrically. The process involves a series of chemical baths.

● Cleaning the PCB panel thoroughly

● A thin electroless copper layer first makes the drilled hole walls conductive. Electroplating then builds up the copper thickness on the hole walls and exposed copper surfaces.

● Controlling the PCB plating process using computers

The copper baths completely cover the walls of the holes. Additionally, the entire panel receives a new thin layer of copper. Most importantly, the new holes are covered.

Step 10 – Outer Layer Imaging

In Step 3, we applied photoresist to the inner layers of the panel. In this step, we repeat the same process for the outer layers of the panel. The process is conducted in a controlled clean environment to prevent any contamination.

● Pins secure black ink transparencies and prevent misalignment

● The PCB panel, after being coated with photoresist, enters the yellow room.

● The yellow and UV light blast hardens the photoresist

● The panel then passes into a machine that removes the unhardened resist, which is protected by the black ink opacity.

Finally, the outer plates undergo inspection to ensure that all undesired photoresist was removed during the previous stage.

Step 11 – Tin Plating

After the outer-layer copper electroplating, a layer of tin is electroplated onto the exposed copper features. The tin acts as a temporary etch-resistant layer, protecting the circuit-pattern copper that must remain on the outer layer during the subsequent final etching process.

The tin layer therefore serves as an etch resist rather than a permanent surface finish. After the unwanted copper is removed during final etching, the temporary tin layer is stripped away to expose the underlying copper and prepare the PCB for subsequent surface treatment.

Step 12 – Final Etching

The same chemical solution used previously removes any unwanted copper beneath the resist layer. The tin guard layer safeguards the necessary copper. This process readies the PCB panel for AOI (Automated Optical Inspection) and soldering.

● A layer of copper is applied using the electroplating method.

After the initial copper baths, tin electroplating is used to protect the copper in the critical area.

● The PCB board undergoes Automated Optical Inspection (AOI) to ensure the copper layer meets the desired specifications.

● After final etching, the temporary tin etch resist is stripped to expose the required copper pattern for subsequent finishing processes.

Step 13 – Solder Mask Application

Solder mask is a protective insulating layer applied to the PCB surface. It covers most exposed copper while leaving selected pads and other required conductive areas open for soldering and electrical contact.

In addition to protecting copper from oxidation and environmental contamination, solder mask helps reduce the risk of solder bridging between adjacent pads during assembly. For dense PCB layouts, the accuracy of solder mask openings and the remaining solder mask dams are particularly important.

JLCPCB uses Liquid Photo Imageable (LPI) solder mask for its standard rigid PCB production. Its current capabilities specify a solder mask ink thickness of at least 10 μm and a minimum solder mask bridge of 0.10 mm for many 1 oz copper configurations.

● The PCB panel is cleaned to remove impurities or unwanted copper.

● An ink epoxy and solder mask film mixture is applied to the surface.

● The boards are exposed to a UV blast, which penetrates through a solder mask photo film.

● The covered portions remain unhardened and will be removed.

Finally, the circuit board is placed in an oven and baked onto the board.

Step 14 – Silkscreening

Silkscreening is a vital step because this process is responsible for printing critical information onto the board. Once applied, the PCB passes through one final coating and curing stage. This stage typically includes:

● Warning labels

●  Logo or symbols

● Component ID

● Pin locators and other markings

Step 15 – Surface Finish

Surface finishing is applied to exposed copper areas such as component pads to protect the copper from oxidation and provide a suitable surface for soldering or electrical contact. The appropriate finish depends on factors such as component pitch, assembly requirements, storage conditions, and cost.

For standard JLCPCB rigid PCBs, available surface finishes include HASL, lead-free HASL, ENIG, and OSP, with availability depending on the PCB material and layer count. JLCPCB currently specifies ENIG for 6-layer-and-above multilayer FR-4 boards and RF boards.

Step 16 – Testing

PCB testing is also a critical step in the manufacturing process. We will use various testing methods to ensure that the PCBs are functional and conform to the original design specifications. Before the PCB is considered complete, a technician will perform an electrical test on the board to confirm that it functions according to the original blueprint designs.

Step 17 – Profiling

After electrical testing and other required inspections, the PCB panel is separated into individual boards according to the specified board outline.

Two common methods are CNC routing and V-scoring:

• CNC routing: A rotating cutting tool follows the programmed board outline to separate the PCB or create slots and irregular shapes.
• V-scoring: V-shaped grooves are cut along straight board boundaries, leaving a controlled amount of material that can later be broken apart.

JLCPCB currently specifies a dimensional tolerance of ±0.2 mm for regular CNC-routed board edges and ±0.4 mm for V-scoring, while high-precision routing can achieve ±0.1 mm under applicable conditions.

Step 18 – Final Quality Check

After profiling, each printed circuit board undergoes a final visual inspection and quality check. The manufacturer will package and ship error-free PCBs after the final examination.

JLCPCB Manufacturing Capability

JLCPCB supports a wide range of PCB manufacturing requirements, from standard single- and double-sided boards to high-layer-count multilayer PCBs. Its manufacturing capabilities cover key parameters such as layer count, trace and space, drill size, board thickness, impedance control, solder mask, surface finish, and board profiling.

The following table summarizes selected JLCPCB manufacturing capabilities relevant to the PCB manufacturing process. Actual capabilities may vary depending on the PCB material, layer count, copper thickness, board thickness, and specific manufacturing requirements. For the latest and most accurate specifications, refer to JLCPCB's current PCB manufacturing capabilities.

FAQ about PCB Manufacturing Process

Conclusion

The PCB manufacturing process is a coordinated sequence that transforms a digital PCB design into a reliable physical circuit board. From CAM and DFM checks to imaging, etching, lamination, drilling, copper plating, solder mask application, surface finishing, electrical testing, and final inspection, every stage contributes to the manufacturability and reliability of the finished PCB.

Understanding these manufacturing steps helps PCB designers make better decisions about trace geometry, layer stack-up, drill sizes, surface finish, board thickness, and other production parameters. Choosing a manufacturer with clearly defined manufacturing capabilities can also reduce DFM issues and improve production consistency.

With manufacturing capabilities covering standard and advanced rigid PCB requirements, JLCPCB provides PCB fabrication services for applications ranging from simple prototypes to complex multilayer designs.