You should never do this. Solder mask is not considered to be an
insulator, no matter what its insulative properties are. Variations in
the soldermask thickness can lead to problems, even a very small burr on
the bottom of the washer or any other metal component can cut through
the soldermask and short to the 15VDC trace, or any other top or bottom
trace for that matter. I believe small skips in the soldermask coverage
are allowed per the specs. Therefore you never want to consider the SM
an insulator. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Abel, Shannon K.
Sent: Thursday, September 21, 2006 9:44 AM
To: [log in to unmask]
Subject: [TN] Mechanical Hardware Clearance...

I have a board with a 15VDC trace on the surface layer that runs under a
flat washer.  

The trace is covered by SM, which provides 500vdc isolation per .001 mil
of SM coating. 

2221 states that any electrical conduction trace per sec 6.3 lists a
minimum clearance of .00512 to any other conductive surface (.ie
mechanical hardware)

Do I violate the spec.

Any help would be greatly appreciated.

Shannon Abel





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