Digital Signal Processing Reference
In-Depth Information
Consider using serial signaling technology to eliminate wide, synchronous
buses.
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Consider using a cable or flexible circuit board assembly to jumper signals
from one end of a large circuit board to another. This can remove the need to
route critical, highly sensitive signals on the board, or it can be used to route
many low-performance signals.
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16.10
Steps to Take When a Circuit Board Must Be Cost Reduced
Send the board stackup out to several vendors to determine if it can be
simplified.
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Determine if a slight reduction in the board dimensions will significantly
reduce cost. Laminate panels come in standard sizes and cost will be lower
if the board is small enough to allow several copies to fit within one of the
standard sizes with little waste. A slightly smaller board that allows several
copies to be placed on a larger panel will cost less than a larger board that
can only fit one copy per panel.
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Understand what characteristics are increasing manufacturing costs of the
raw board. For instance, the need for advanced via technology or very fine
lines can drive up cost.
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Study the decoupling very carefully. Often decoupling is not rigorously ana-
lyzed during design, and more capacitors than necessary are used. Use simu-
lation to determine the worst-case conditions for power supply noise and
replicate that on prototype hardware. Then selectively remove decoupling
on the prototype to determine the minimum necessary for proper operation.
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Verify that all of the terminated nets actually require termination. Removing
unnecessary termination components frees up board space (possibly allowing
the board to be smaller or to use fewer layers) and, when using parallel ter-
mination, power can be reduced, and the costs related to parts and assembly
are also reduced.
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If controlled impedance traces are used, verify that they are necessary. Re-
quiring controlled impedance traces increase the bare board manufacturing
cost.
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Verify that trace impedance specifications are not overly restrictive and are
easy to manufacture. For example, many manufacturers are accustomed to
producing 50
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differential pairs. Specifying differ-
ent values than this will usually increase the number of boards scrapped and
increase cost.
Ω
single ended and 100
Ω
Verify that spacing between traces is not wider than actually necessary to
reduce crosstalk. Spacing that is too great reduces the number of available
wiring channels and may increase the number of required routing layers.
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Investigate the use of dual stripline. This can reduce the layer count and
board thickness, which can have a cascading effect on reducing board cost.
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