What is a PCB?
A Printed Circuit Board (PCB) is a slim substrate made from fibreglass, composite epoxy, or other laminated materials. It serves as the foundation that connects all the electronic components, enabling the device to function as intended.
Basic PCB Manufacturing Process Step by Step
Step 1: Data Preparation
Upon receiving Gerber files from the customer, the CAD team reviews the data to ensure compliance with manufacturing standards. Most of these validations are automated, checking trace widths, spacing, pad sizes, smallest drill holes, and more. Engineers can also manually inspect specific areas as needed. Once approved, the necessary tool files for production and testing are generated.
Step 2: Film Plotting
Laser photoplotters inside climate-controlled darkrooms create films by converting board data into pixel images. A laser etches this data onto film, which is then automatically developed and prepared for fabrication. The operator aligns films for each PCB layer, making fine adjustments to ensure registration holes line up perfectly on imaging equipment.
Shearing:
Laminates are cut to specifications in the job cards and organized into panels. Single or double-sided boards proceed directly to drilling, whereas multilayer boards require inner layer development first.
Step 3: Inner Layer Printing for Multilayer PCBs
Using a photoresist laminator, a liquid photoresist coat is applied to multilayer boards. The first inner layer is exposed to UV light through a print with the copper pattern. Yellow lighting and controlled temperature create an optimal environment for this process.
After exposure, panels are treated with a strong alkali solution to etch away unhardened resist, then pressure-washed and dried. Samples are inspected to confirm the copper surface is clean and unwanted photoresist removed. The visible blue resist areas mark the copper pattern.
Inner Layer Etching:
Excess copper on the inner layers is etched using a controlled alkaline process to ensure the designed conductor widths. Designers should note that thicker copper requires wider track spacing. Operators verify that all unwanted copper is properly removed.
The blue photoresist is then stripped away, revealing the precise copper pattern. Multiple designs can be efficiently produced on a single panel for cost-effective small batch runs.
Inspection of Inner Layers
The multilayer core is now ready. Registration holes are punched to align inner and outer layers through an optical punch targeting copper patterns.
Because errors on inner layers cannot be corrected after assembly, a thorough automated optical inspection (AOI) is performed.
The AOI system scans the panel line-by-line comparing it to the digital design to identify any defects, which are displayed for operator review.
Lay-Up and Bonding
The outer layers of the multilayer PCB consist of glass cloth sheets pre-impregnated with uncured epoxy resin (prepreg) and thin copper foil.
The lay-up technician arranges copper foil and two prepreg sheets on a steel baseplate, then places the pre-treated core aligned with pins. Additional prepreg sheets, copper foil, and an aluminum press plate are layered on top.
This process is repeated to create stacks of 3 panels, which are then pressed under heat and pressure to bond layers through curing of epoxy resin. Complex boards may contain over 50 layers with multiple subassemblies.
Once bonding is complete, the stacks are unloaded, de-pinned, and the aluminum plates removed to reveal the now permanently bonded copper outer layers.
Drilling Printed Circuit Boards
Computer-controlled drilling machines create holes in the panels following CAD-generated programs. Plated Through Holes (PTH) provide electrical connections between layers and mounting points for connectors; Non-Plated Through Holes (NPTH) serve as mechanical mounting points or equipment attachments.
Step 4: Plating Through Holes
Copper is deposited inside the holes using an electroless plating process to establish conductivity between all copper layers.
Step 5: Photoresist Application (Yellow Room)
The panel is cleaned chemically, then coated on both sides with a light-sensitive photoresist layer that hardens upon UV exposure.
A photo-tool film containing the circuit pattern is vacuum pressed over the resist. UV light exposure hardens the resist where the film is clear, while dark areas protect other regions.
The panel is developed to wash away the unhardened resist, revealing the circuit pattern for further processing.
Step 6: Electroplating
Electroplating adds copper to increase thickness on both the holes and board circuitry.
Following copper plating, a tin layer is deposited over it to protect copper during the subsequent etching process.
Step 7: Etching & Stripping
Dry film photoresist is removed from the tin-plated panels, then exposed copper (not protected by tin) is etched away to leave the final circuit pattern. This marks the fundamental completion of the circuitry.
Step 8: Liquid Photo-Imageable Solder Mask
Liquid photo-imageable solder mask (LPI) is applied via screen printing to protect circuitry from environmental damage.
The solder mask hardens under UV light exposure. A photo-tool blocks light on solder pads, allowing mask removal from those areas during development.
After development, the solder mask is cured. The mask covers the entire board except for the solder pads, preventing solder shorts except where needed.
Step 9: Legend Printing (Nomenclature)
Legends mark component placements using a silkscreen printing process on the PCB.
Step 10: Routing
Routing uses milling cutters to shape the finished board outlines. Stacks of 1 to 4 panels are pinned as during drilling.
Finally, NC machines route the board edges. The completed boards are then shipped to customers.
Step 11: Electrical Testing
Electrical tests confirm circuit continuity and correctness by passing current through each circuit track using a test fixture with aligned pins. A detected signal indicates a proper connection.
Step 12: Final Inspection & Quality Control
A comprehensive visual inspection checks for defects not caught by electrical testing. Before packing and shipping, a 100% quality audit is conducted on the board lot to ensure customer standards are met.