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April 1998

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Subject:
From:
Ralph Hersey <[log in to unmask]>
Reply To:
Date:
Sat, 18 Apr 1998 12:50:04 -0700
Content-Type:
text/plain
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This is a survey and a question for those of you who have knowledge
about printed board design practices.

The design requirements for printed board conductor width and conductor
spacing are mostly based on some regulatory requirement.  What I would
like to know is how are the specification's "minimum" design
requirements implemented in actual design practices.  Basically, are
design requirement "minimums" use as "minimums" in the actual design or
are they used as "nominals" knowing there is some tolerance "built-in"
for manufacturing.

Conductive Pattern Requirements:

The current-carrying ability of conductors is generally based on a chart
that appears as a figure in MIL-STD-275, IPC-D-275, or IPC-2221.  This
chart is based on thermal rise above ambient for a specified current.
These requirements are converted into a minimum "conductor
cross-sectional area", which is then converted into a minimum conductor
width and minimum conductor thickness.

The question is:

"In your design practices/experience, are the 'minimum conductor width'
and 'minimum conductor thickness' used as the "minimums" in the design
requirements or are they used as "nominals" in the product definition
data (or master drawing) ????

A simple response is located at the end of these writings.

Conductor Spacing Requirements:

A similar query is for conductor spacing"

"In your design practices/experience, are the "minimum conductor
spacings" used as the "minimum" or "nominal" design requirement in the
product definition data (or master drawing) ????

Responses:

We use minimum conductor thickness/width requirements as "minimum". (
)

We use minimum conductor thickness/width requirements as "nominal". (
)

We use minimum conductor spacing requirements as "minimum". (    )

We use minimum conductor spacing requirements as "nominal". (    )

Your response will be appreciated,

Ralph,

Ralph Hersey & Associates
3885 Mills Way
Livermore, CA 94550-3319
PHN/FAX: 925.454.9805
e-mail:  [log in to unmask]

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