Electronics > PCB/EDA/CAD

Avoid octagons? Why?

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bronson:
Quoth Dave in 2004: "Octagonal pads are seldom used, and should generally be avoided."  http://alternatezone.com/electronics/files/PCBDesignTutorialRevA.pdf

I actually like octagonal vias better than round and square.  They're the best of both worlds: like round they can be nicely skirted using 45deg lines and packed tighter, and like square they make it obvious when the grid is off and tracks aren't passing symmetrically between vias.  When the density is high, I like the way they look.

When routing around round/oval vias, a track can be pretty unbalanced before my eye will catch it.  With octagons, I find them immediately obvious.

I'm happy to use round or square of course, whatever the client wants.  I just tend towards octagon.  Am I missing something here?

EDIT: Oh, Dave's talking about PADS.  -EREADINGTOOFAST.   But my question is still this: why don't more people use octagons? I tend to leave pads oval but, if I'm running  a bunch of traces around them (like through the pins of a wide header), I'll make them octagonal and marvel at how much neater it makes it look.  Any downside?

free_electron:
some gerber importers have problems with octagon pads. they become rectangles .... without the chamfered corner... and then you get shorts.

bronson:
Nasty!  But has that been an issue since the 90s?

T3sl4co1l:
Never heard that before  :scared:  Personally, I've never use 'em... because they're ugly! :P  I do prefer rounded rectangles for "square pin 1" pads though.. just to take the edge off.

Tim

free_electron:
The problem has gone away. Some mom and pop shop still photoplotting and using outdated softwaref rom before 2000 may still have this problem. Cam350 was notorious for weirdness.
Even UCam had problems. Same for oblongs (rounded rectangles. I mean real rounded rectangles. Not a rectangle where two opposite ends are semicircles.)

The problems is the photolotters.
The apertures are made with a slit and a diaphragm. Flashing circles, rectangles squares is no problem. A rectangle with opposite semicrcles is no problem. Open aperture for a circle and move the head while it is open.

Component pads in Gerber format are defined as flashes: go to coordinate : set aperture for square or circle, light on light off.

Anything else needs approximation and that is where misery begins.
With the addition of arbitrary polygons in gerber standard this was solved. But not all cad programs could handle those.

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