searching for Quality pcb design Design
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 Rigid flex PCB Board. The schematic
diagram was first converted into a layout of components pin pads, then traces
were routed to provide the required interconnections. 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 China PCB Prototype.
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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