IPC-2221, paragraph 6.3 Electrical Clearance, states: "The minimum spacing
between conductors, between conductive patterns, layer to layer conductive
spaces (z=axis), and between conductive materials (such as conductive
markings or mounting hardware) and conductors shall be in accordance with
Table 6-1, ... ."

We have a thermal plane which will see 600 volts worst case.  According to
Table 6-1, we would need roughly 20 mils of dielectric between this plane
and a routing or electrical plane layer.  Why?  The electrical strength of
polyimide from IPC-4101/42 is 29000 volts/mm (736 volts/mil).  Has anyone
had experience with this apparent disconnect between specs?

TIA,

Anthony Bundrant
Bell Helicopter Textron
Technical Resource Specialist - Electronic Packaging
817.280.8903

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