I’m trying to make one of my current boards much smaller. I’m trying to go from 2x2 to ~1x1. I did this by reducing the size and number of components, and by just simply squeezing everything together as tight as I can.
Anyways, I’m at the point that I’m trying to make some really small vias. There seems to be some interdependency among the ‘Diameter’ and ‘Drill’ values for the vias. Does anybody know the crucial ratio and/or size limitations that I’m going to run into to. I’m trying to find out empirically, but I’d rather not do that if one of you already has a closed form solution 
If you’re just making plain vias, you can click the ‘Via’ tool and then change the “Diameter” to whatever number you want. Chances are, yours is set to “Auto” right now. If you want to change existing vias, you can go to “Change”->“Diameter”->“…” and specify what diameter you want to change existing vias to. If you’re worried about the size of the vias while you’re routing traces, the “Diameter” box I described above will be showing while you’re routing. You can change it the same way I described above. There are probably easier ways to do this via the command line, but I’m a GUI kinda guy. 
brennen:
If you want to change existing vias, you can go to “Change”->“Diameter”->“…” and specify what diameter you want to change existing vias to.
Well, there are some limitations as I described. I can tell just by placing the via by the pins on my processor that they can scale down to about the same minimums as I’ve encountered before, which is fine.
I also wonder if there is a rule of thumb about minimum hole diameter for the purposes of assured inter-layer connectivity; i.e. enough area for the trace to go through during the manufacturing process. :?:
The annular ring as it is called depends on your board manufacturer and their drilling tolerances. They should have the details in their spec.
Leon
If you open the Design Rule Check (DRC) dialog and go to the ‘Restring’ tab, you can change the minimum size for the annular ring in the ‘outer’ vias row. IMHO, the default values are good (make the annular ring too small and you’ll pay for it during assembly)