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The reason why these different shapes exist is probably historical, but I'm interested whether there's any reason today to not only use a single kind of via.

The ones with round pads are the most effective in terms of area, so those are the ones I usually use.

Is there any scenario in which a via with an octagonal or square pad could be a better choice, even if it's just for routing purposes? Or are there maybe some PCB manufacturers only able to make certain shapes of pads?

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  • \$\begingroup\$ Are you referring to the shape of the PAD? or the hole? I have never seen anything but a round hole (or a larger opening like a slot which has been routed with a round bit). How do you make a square (or octagonal) hole? Do you mean a larger routed-out opening that happens to be plated-thru? \$\endgroup\$ – Richard Crowley Oct 18 '16 at 21:01
  • \$\begingroup\$ @RichardCrowley The shape of the pad. I'm not aware of non-round holes either. Clarified it in the question. \$\endgroup\$ – iFreilicht Oct 18 '16 at 21:01
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    \$\begingroup\$ For components, a square pad is often used to mark pin 1. I can't think of any reason to use a non-round pad for a normal via. \$\endgroup\$ – Peter Bennett Oct 18 '16 at 21:36
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The shape of the pad has no functional significance for a plated-through via. Indeed, on high-density boards, the pad around the via is sometimes as close to zero as they can reliably manage within the tolerance of the manufacturing process.

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  • \$\begingroup\$ Maybe, just maybe, in RF it might change something. But I would not expect the shape to matter much. \$\endgroup\$ – Vladimir Cravero Oct 18 '16 at 22:07
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The one thing I have found advantageous with using octagonal or square via ring shapes is when copper pours need to fit through via groups. square vias make it easy to ensure that the copper will join through the gaps based on your design rule set.

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Decades ago when vector photo plotters with an aperture wheel were used you could only use those pads sizes and shapes that were present on the wheel. With only about 32 different apertures you could not chose between round, square and octagons.

But nowadays raster photo plotters are used and you may programm the sizes and shapes you wish. You may also use pentagons and hexagons if you like as long as your PCB CAD system supports them. Even heptagons and nonagons are possible. Triangles are possible too but their area is too small compared to a round pad.

A round pad leaves more space for routing as a square pad. The octagon is a compromise between square and round. Routing traces not only with 0° and 90° but also with 45 ° fits better to octagon pads than to square or heaxgon pads.

You might use those different pad shapes for marking of some pins, for instance pin 1 of an IC square, all others round. For polarized capacitors you may use different pad shapes for the + and - pin, same for diodes. If you want to use those different shapes for marking use only those easily recognized without a magnifying glass.

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