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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