Manufacturing a Printed Circuit Board (PCB) is a multi-stage process involving design, printing, etching, and assembly. Here's a detailed breakdown of the steps:
1. PCB Design and Schematic Capture
- Design: This begins with the electronic design of the circuit. Engineers use specialized software (like Eagle, Altium Designer, or KiCad) to create the PCB layout based on the circuit's schematic. This includes defining the layers, component placement, and routing of traces.
- Schematic Capture: This involves creating a schematic diagram of the circuit, which is a symbolic representation of the electronic components and their connections.
2. Design Review and Validation
- Review: The design is thoroughly reviewed by engineers to identify potential errors, optimize performance, and ensure manufacturability. This may involve simulations and thermal analysis.
- DFM (Design for Manufacturing): A DFM check ensures the design can be efficiently and reliably manufactured. Factors like minimum trace width, spacing, and drill sizes are verified.
3. Printing the PCB Design (Film Production)
- Photoplotting: The PCB design is printed onto a transparent film, creating a photo-negative. This film will be used to transfer the design onto the copper-clad boards during the imaging process. Each layer of the PCB (e.g., signal layers, ground plane, power plane, solder mask, silkscreen) requires its own film.
4. Printing the Inner Layers (for Multilayer PCBs)
- Copper Clad Laminate Preparation: Sheets of copper-clad laminate (a non-conductive substrate coated with copper) are cleaned and prepared for imaging.
- Photoresist Application: A photo-sensitive chemical called photoresist is applied to the copper surface. This can be done through various methods like lamination or coating.
- UV Exposure: The film is placed on top of the photoresist-coated board, and the board is exposed to ultraviolet (UV) light. The UV light hardens the photoresist in the areas where the film is transparent (corresponding to the traces and pads).
- Development: The unhardened photoresist is washed away, leaving the desired pattern of hardened photoresist on the copper surface.
5. Etching the Inner Layers
- Etching: The board is then immersed in a chemical etchant (such as ferric chloride or cupric chloride) that removes the exposed copper (the copper not covered by the hardened photoresist). This leaves the desired copper traces and pads on the board.
- Photoresist Removal: After etching, the remaining hardened photoresist is removed, leaving only the copper traces on the laminate.
6. Layer Alignment and Lamination
- Layer Alignment: For multilayer PCBs, the inner layers are precisely aligned using optical registration holes.
- Lamination: The inner layers are stacked together with prepreg (a partially cured epoxy resin) between them. The stack is then subjected to high temperature and pressure in a lamination press, bonding the layers together. This creates a solid, multilayer PCB core.
7. Drilling
- Drilling Holes: Holes are drilled through the PCB for component leads, vias (to connect different layers), and mounting. This is typically done using computer-controlled drilling machines with high precision.
- Deburring: After drilling, the edges of the holes are deburred to remove any sharp edges or burrs.
8. Plating
- Electroless Copper Deposition: A thin layer of copper is chemically deposited onto the entire surface of the board, including the inside of the drilled holes. This provides a conductive layer for subsequent electroplating.
- Electroplating: A thicker layer of copper is electroplated onto the board, further thickening the traces and providing a robust connection for vias.
9. Outer Layer Imaging and Etching
- Outer Layer Imaging: The outer layer patterns are created using a similar process as the inner layers, involving photoresist application, UV exposure with outer layer film, and development.
- Outer Layer Etching: The exposed copper on the outer layers is etched away, defining the traces and pads on the top and bottom surfaces of the PCB.
- Tin or Etch Resist Plating (alternative to Etch): To protect the desired copper features during etching, a thin layer of tin or an etch resist material can be plated onto them before etching. After etching, the tin or etch resist is removed.
10. Solder Mask Application
- Solder Mask Application: A solder mask (a protective coating that prevents solder from bridging between traces) is applied to the PCB. The solder mask is typically a green epoxy-based material, but other colors are also available.
- Solder Mask Curing: The solder mask is cured using UV light or heat. Openings in the solder mask expose the pads where components will be soldered.
11. Surface Finish
- Surface Finish Application: A surface finish is applied to the exposed copper pads to protect them from oxidation and improve solderability. Common surface finishes include HASL (Hot Air Solder Leveling), ENIG (Electroless Nickel Immersion Gold), and OSP (Organic Solderability Preservative).
12. Silkscreen Printing
- Silkscreen Printing: A silkscreen (a white epoxy ink) is printed onto the PCB to provide component identification, polarity markings, and other information.
13. Electrical Testing
- Electrical Testing: The PCB is tested to ensure that all circuits are working correctly and that there are no shorts or opens. This can be done using automated test equipment (ATE).
14. Profiling/Routing/Cutting
- Profiling/Routing: The individual PCBs are cut out from the larger panel. This is typically done using CNC routing machines.
15. Final Inspection
- Final Inspection: The PCBs are visually inspected to ensure that they meet all quality standards.
16. Packaging and Shipping
- Packaging and Shipping: The finished PCBs are packaged and shipped to the customer.
