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.

I had some problems with wave soldering and "open" vias. They tend to short 
with solder if the gap is small enough. I had those problems with 8mil 
clearences.
I tent all my vias, exept sometime those on prototypes.


>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).

I don't think the RF characteristics changes a lot, but I'm not an expert.
There was a tread about the allowable current the via can carry. The soldes 
has a much higher restistance, so it doen't cary much current. If I 
remember correctly, about 10%.
Can we now say the same about the impedance? I don't know.

Edi



>TIA for your thoughts,
>Dwight.
>
>
>
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