On 09:37 PM 8/02/2001 +1000, Robi Bittler said:
>Hi Dwight - hope things turn out the way you want them to turn out.
>In regards to your email -
>yes you're right - by setting a negative value in the drc you will tent 
>the vias.
>In terms of ad, or - disad - vantages I assume the reason could be 
>"Radiation" .

Robbi - the effect of solder mask on the EMC performance of vias is, I 
would claim, bugger-all.  That is a technical measure of EMC radiation 
equivalent to a poofteenth.  The mask does have a higher dielectric 
constant than air and so would affect the field patterns but it is too thin 
to affect anything but really really high freq's.  On high freq RF boards 
the presence or absence of resist must be considered but I usually do not 
bother below a 1GHz unless the tracks are long and/or there are especially 
critical adjacent coupling calculations (microstrip/stripline filters etc 
or isolation requirements).

Tented vias are used for production reasons as others have stated.

Ian Wilson



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