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PCB CAM Manufacturing starts from the PCB fabrication data generated by CAD: Gerber layer images, Gerber or Excellon drill files, IPC-D-356 netlist and component information.[6] The Gerber or Excellon files in the fabrication data are never used directly on the manufacturing equipment but always read into the CAM (Computer Aided Manufacturing) software. CAM performs the following functions

  1. Input of the fabrication data.
  2. Verification of the data; optionally DFM
  3. Compensation for deviations in the manufacturing processes (e.g. scaling to compensate for distortions during lamination)
  4. Panelization
  5. Output of the digital tools (copper patterns, solder resist image, legend image, drill files, automated optical inspection data, electrical test files
Copper patterning

The first step is to replicate the pattern in the fabricator's CAM system on a protective mask on the copper foil PCB layers. Subsequent etching removes the unwanted copper. (Alternatively, a conductive ink can be ink-jetted on a blank (non-conductive) board. This technique is also used in the manufacture of hybrid circuits.)

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  • Silk screen printing uses etch-resistant inks to create the protective mask.
  • Photoengraving uses a photomask and developer to selectively remove a UV-sensitive photoresist coating and thus create a photoresist mask.
  • Direct imaging techniques are sometimes used for high-resolution requirements. Experiments were made with thermal resist.
  • PCB milling uses a two or three-axis mechanical milling system to mill away the copper foil from the substrate. A PCB milling machine (referred to as a 'PCB Prototyper') operates in a similar way to a plotter, receiving commands from the host software that control the position of the milling head in the x, y, and (if relevant) z axis.
  • Laser resist ablation Spray black paint onto copper clad laminate, place into CNC laser plotter. The laser raster-scans the PCB and ablates (vaporizes) the paint where no resist is wanted. (Note: laser copper ablation is rarely used and is considered experimental

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Circuit properties of the PCB

Each trace consists of a flat, narrow part of the copper foil that remains after etching. The resistance, determined by width and thickness, of the traces must be sufficiently low for the current the conductor will carry. Power and ground traces may need to be wider than signal traces. In a multi-layer board one entire layer may be mostly solid copper to act as a ground plane for shielding and power return. For microwave circuits, transmission lines can be laid out in the form of stripline and microstrip with carefully controlled dimensions to assure a consistent impedance. In radio-frequency and fast switching circuits the inductance and capacitance of the printed circuit board conductors become significant circuit elements, usually undesired; but they can be used as a deliberate part of the circuit design, obviating the need for additional discrete components.

source: https://en.wikipedia.org/wiki/Printed_circuit_board