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Printed circuit board artwork generation was initially a fully manual process done on clear mylar sheets at a scale of usually 2 or 4 times the desired size. The schematic diagram was first converted into a layout of components pin pads, then traces were routed to provide the required interconnections flex PCB. Pre-printed non-reproducing mylar grids assisted in layout, and rub-on dry transfers of common arrangements of circuit elements (pads, contact fingers, integrated circuit profiles, and so on) helped standardize the layout. Traces between devices were made with self-adhesive tape. The finished layout "artwork" was then photographically reproduced on the resist layers of the blank coated copper-clad boards.
Modern practice is less labor intensive since computers can automatically perform many of the layout steps. The general progression for a commercial printed circuit board design would include:
Schematic capture through an Electronic design automation tool.
Card dimensions and template are decided based on required circuitry and case of the Determine the fixed components and heat sinks if required.
Deciding stack layers of the PCB. 1 to 12 layers or more depending on design complexity. Ground plane and power plane are decided. Signal planes where signals are routed are in top layer as well as internal layers.
Line impedance determination using dielectric layer thickness, routing copper thickness and trace-width. Trace separation also taken into account in case of differential signals. Microstrip, stripline or dual stripline can be used to route signals.
Placement of the components. Thermal considerations and geometry are taken into account. Vias and lands are marked.
Routing the signal traces. For optimal EMI performance high frequency signals are routed in internal layers between power or ground planes as power planes behave as ground for AC Rigid flex PCB.
Gerber file generation for manufacturing.
Multi-Layer PWBs
Option for dedicating layers to ground
Forms reference planes for signals
EMI Control
Simpler impedance control
Option for dedicating layers to Supply Voltages
Low ESL/ESR power distribution
More routing resources for signals
Electrical Considerations in Selecting Material
Dielectric Constant (permittivity)
The more stable, the better
Lower values may be more suitable for high layer counts
Higher values may be more suitable for some RF structures
Loss Tangent
The lower, the better
Becomes more of an issue at higher frequencies
Moisture Absorption
The lower, the better
Can effect dielectric constant and loss tangent
Voltage Breakdown
The higher, the better
Typically not an issue, except in high voltage applications
Resistivity
The higher, the better
Typically not an issue, except in low leakage applications
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