Component ground pad vias larger in layout.

[wayneweeks]

Hi,

I am trying to understand why the small ground pad vias in the component footprint appear much larger in the layout. The ground pad has three small PTH vias (8mil drill) in the component symbol footprint, but in the layout those vias appear much larger causing DRC errors. I have tried changing the via size in the symbol and the annular ring parameters in the DRC tool, with no effect. Not sure what else to try. 

Thanks for any help.

[RichardHammerl]

Hi @wayneweeks ,

thanks for participating in the forum and for your great question. 

The reason for the difference in the library and in the 2D PCB most likely comes from the design rules you set for this board. The Design Rules allow to set minimum values for the annular ring in the Design Rules. The components' pads follow these rules in the current board. 

While in the library's footprint editor we see a kind of preview using default design rules. I guess you have tweaked the design rules settings for Annular Ring having more copper around the drills of the pads, right? 

Please check the settings and adjust them accordingly.

I hope this helps.

Best regards

[wayneweeks]

Hi Richard,

Thank you for the quick response. I am using the standard default design rules, no changes.

Perhaps I misunderstand how to use this part of the tool but see pictures. This is a standard layout via (square to show the issue) that is being added. This should be a 10mil (square) via with an 8mil drill. But the grid is set to 10mils which means this via is actually larger than 10mils (much larger), more like 20+ mils.

What is the difference between “Diameter”, “Outer Layer Diameter”, and “Inner Layer Diameter” for the Properties pop-up? It looks like the via that I thought would be 10mils is using the Outer/Inner Layer Diameter value instead. How are the inner and outer layer diameters set? That may be the problem.

Thanks

[dja22amador]

having the same issue. Spent a good 2 hours trying to fix with no luck.

[RichardHammerl]

Hi @dja22amador ,

there are Design Preferences that decide on the diameter of the vias (and also for pads and micro vias).

Please check in the 2D PCB editor the PREFERENCES menu, Design Preferences. --> look into the Annular Ring tab.

In the image you find the rules for vias. 

For the outer layers Top and Bottom the diameter of the via is calculated depending on the drill diameter. 

Assumed the drill diameter is 16mil, the rule says that the width of the annular ring is 25% of 16mil. Which results in 4 mil. 

So the calculated diameter of the via is 10 mil for the drill and 2 x the width of the ring.  A total of 18 mil. 

BUT...  there is set a minimum width for the annular ring width which is 8 mil. The copper rings follow this minimum setting and the total real diameter in the layout is 10 mil for the diameter plus two times 8 mil for the ring width, whihc finally gives 26 mil.

The minimum value usually represents a limitation of the manufacturing process. If you decide to reduce this value, check with your board manufacturer.
 I hope this helps.