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Question on Via Symbols

Question asked by mthayer on Dec 1, 2009
Latest reply on Dec 7, 2009 by David Ricketts

Hi everyone,

 

I've been reviewing a board layout, and we've got some symbols in there that we're not sure about.  There seem to be different ways the vias are drawn, and we haven't been able to get a good answer as to what they represent and why they're different.  We've been told at one point that they're all the same, all vias, yet they're sometimes drawn with distinctly different symbols, so I don't buy it.

 

Excuse the crude MSPaint masterpieces (bottom of the post); I hope they get their point across.

 

1). Holes A and F... F is a through hole part, while A is a large Via... so I'm assuming that explains that difference.  Is this correct?

 

2)  A and C... Both large vias that are drawn differently.  If C connects, it should look like A... if not, it should be an empty hole.  Once we were told that they don't mean anything, and then later we were told that the vias drawn like A and D indicate an error that there were things overlapping that shouldn't - we found those before when we had a split region in a ground plane that was accidentally overlapping an identical area beneath it.  Those problems seemed to be fixed, but after the latest changes, they're back, and we need to stop and find out for sure what's going on.

 

3) Notice also in the C picture, the smaller connected vias on the right seem to have several different looks (the top one looks different from the lower two.. smaller?).  I believe this may just be due to them being different sizes and the way they render in the display.  Is that what's going on there?

 

4). B and E... these appear to be half-connected to the plane, half not.  In the case of E it looks intentional, as that other via is placed butted up overlapping, but B makes me wonder what's going on there and why.  It looks like this may be because there is a dedicated AGND plane, and then above that is a plane where the center region is isolated as a sensetive ground, and the exterior region duplicates AGND - it shows the top half connect on one of those and the bottom on the other - but other vias have full connections on both planes.  It's these inconsistencies that bother me, and lead me to believe that things may be hooked up in incorrect ways that we don't understand.

 

Anybody have any insight into what these various symbols mean, or where I can find documentation of such things?  I've been through the help file a bit, but haven't come across any symbol or via type pictures or anything that looks helpful.

 

Thanks,

 

Matt

 

 

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