Tom Kavendek,

According to Norman S. Einarson (author of "Bare Board PWB Design Manual") 
the only time you should tie any hole directly to a plane would be for 
thermal reasons where there are multiple tie points (connections).  The 
reason is that there is thermal expansion and contractions with the bare 
board processing, during board assembly and during normal product 
operations.  This thermal thing puts stress on the connection points where 
they are tied to the plane and if they are tied directly to the plane then 
the more chance of resistance to movement thus more chance for breaking 
away.  When the connection points are tied to the plane with thermals there 
is less material thus less stress to the connection points allowing it to 
move and less chance for breakage.

Please respond.

Greg Kaskey
Checkmate Electronics, Inc.
770.594.6000 x228
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 ----------
From: [log in to unmask]
To: [log in to unmask]; [log in to unmask]; Kaskey Greg
Subject: Re: Design (fwd)
Date: Tuesday, September 17, 1996 9:00AM

<<File Attachment: ENVELOPE.TXT>>

This discussion brings up another point....

Does it make sense to use thermal connections on vias?
Thermals were originally used on thru hole comps to increase
solderability of the leads, but now that is not necessary for SMT.
Is there any reason to use them for vias?
I've been using direct connection to the inner planes.

Tom Kavendek
Lucent Technologies
Murray Hill, N.J.
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