I'm looking at the techlef files, more specifically the via rules. So

Plus

/

Minus

via rules are if the metals connecting are perpendicular or parallel right ? But then I see

# Centered via rule, we really do not want to use it

What's a centered via rule and why don't we want to use it ? Posted in #sky130

@tnt: Sorry about the delay. You're right about the +/- rules. The centered via rule is the biggest one, where everything is contained in the minimum enclosing square. Since it's the biggest one and since it's preferable that all metal layers follow their preferred routing direction at the default width, the tools should not really have to use the centered via.

@Ahmed Ghazy Thanks so it's just an issue of space. but if I want to go from a

li

directly to

metal2

(with really no tracks on

metal1

for instance), is that the one I should use ? or I should consider the layers where I don't have any tracks as being "preferred direction" ?

In principle, you could use any via; each via is a template that contains shapes on the layers it connects. The centered one would look pretty uniform in the case you described, so it is probably a good idea. You could also use the plus vias. One thing to be careful with is violating the minimum area rules; the vias are not necessarily "mimimum-area-rule-clean" by themselves. In your example, you're probably not planning to follow a path from the middle layer (met1), so you might violate its minimum area rule if you don't at least patch it with a dummy piece of met1 shape. (e.g., the tech lef says that met1 shapes should have a minimum area of

AREA 0.083 ;

if you check the area of met1 on the

L1M1_PR

via, you'll find it

(0.115*2)*(0.145*2) = 0.0667

um^2 which violates the rule).

Oh yeah, I had no idea about those minimum area rule, good tip ! Tx.