PCB fabrication is the process of creating a physical printed circuit board (PCB) from a design. It's the transformation of a schematic into a tangible circuit board ready to have electronic components attached. In essence, it's the birth of the bare board itself.
Key Aspects of PCB Fabrication:
The PCB fabrication process involves multiple steps, each crucial for producing a functional and reliable board. Here's a breakdown:
-
Design and Preparation: This is where the circuit board layout is created using specialized software (e.g., Altium Designer, Eagle). The design specifies the arrangement of copper traces, pads, vias, and other features that form the electrical connections. Gerber files are generated, which are the standard file format used for manufacturing PCBs.
-
Film Plotting: Creating photo films based on the Gerber files. These films act as stencils in subsequent imaging processes.
-
Inner Layer Imaging: Applying a photosensitive resist to copper-clad laminate panels and exposing them to UV light through the photo films. This defines the copper traces on the inner layers of multilayer PCBs.
-
Etching: Removing unwanted copper from the panels, leaving only the desired circuit patterns.
-
Layer Alignment and Lamination: Aligning the inner layers precisely and bonding them together with prepreg (resin-impregnated fiberglass) under high temperature and pressure.
-
Drilling: Creating holes through the board for component leads and vias (connections between layers).
-
Plating: Applying a thin layer of copper to the drilled holes to create conductive vias. This often involves electroless copper deposition followed by electrolytic copper plating.
-
Outer Layer Imaging and Etching: Similar to inner layer processing, this defines the copper traces on the outer layers.
-
Solder Mask Application: Applying a protective coating (solder mask) to the board, except for the pads where components will be soldered. This prevents solder bridges during assembly.
-
Surface Finish: Applying a metallic finish to the pads (e.g., HASL, ENIG, OSP) to improve solderability and protect the copper from oxidation.
-
Silkscreen: Printing component designators and other information onto the board using silkscreen ink.
-
Electrical Testing: Testing the finished board to ensure that all connections are correct and there are no shorts or open circuits.
-
Profiling/Routing: Cutting the individual boards from the larger panel.
PCB Fabrication vs. PCB Assembly
It's important to distinguish PCB fabrication from PCB assembly:
| Feature | PCB Fabrication | PCB Assembly |
|---|---|---|
| Definition | Creating the bare circuit board. | Populating the board with electronic components. |
| Input | Circuit board design (Gerber files). | Fabricated PCB and component list. |
| Output | Bare PCB. | Functional circuit board. |
In summary, PCB fabrication focuses on building the physical board, while PCB assembly focuses on populating the board with components. They are sequential steps in creating a functional electronic device.
