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" .
Don't quote me on this  - I will follow up this question in the morning, 
with my engineers - why they request; tented vias.
There came a law in place that a pcb is only allowed a certain radiation.
People within the group will correct me, if I'm wrong.
Bare copper will radiate much more than covered or even enclosed in a 
metal-box.
With respect to - using vias as testpoints, or even hook on fly-wires - 
this certainly becomes a dis-advantage if the vias are tented.
To make you smile I'd say  -  a good engineer does not need things like 
that. However - to stay with 2 feet on the ground - yes , you are right -
once the vias are tented you first need to clean them before you can use them.
Also - as some emails just got in - regarding your email - yes, 
manufacturabillity increases with tented vias, due to less solderbridges.
I'll get back to you as soon I've claryfied why tented vias are used, 
amongst my customers.
Cheers
Robi





At 02:07 08/02/01 -0800, you wrote:
>I'm new at this PCB stuff.  We're just doing prototypes so far, and after 
>getting my 3rd board back, I (finally) noticed that the
>vias are not covered by solder mask.  Looking at various PC cards and 
>development kit boards, I see that they usually are.
>
>It looks like I can do this by setting a negative "solder mask expansion" 
>design rule for the vias -- these are then (apparently)
>referred to as "tented".
>
>My question -- what are advantages and disadvantages of tented vias?  I 
>thought of a couple disadvantages - they no longer serve
>(readily) as testpoints, or for attaching corrective wiring.  I noticed 
>that on our second board, which was machine (wave?)
>soldered, most or all of the vias were filled with solder.
>
>These are mixed analog-digital, the analog is audio, and the fastest 
>digital clock is 24Mhz (I imagine that if we had RF circuits,
>the electrical characteristics of the vias would be more critical).
>
>TIA for your thoughts,
>Dwight.
>
>
>
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Robi Artwork  -  PCB Design Bureau
PO-Box 199,    Lot 33 Jamaica Drive
Deception Bay  Q4508        Australia
------------------------------------------------------
C/o Robi Bittler
Ph: 07-3203 0634   Fx: 07-3203 3958



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