Two questions about PR with Astro

[sicheng163]

Hi, all
I've got lots of questions about PR, and I use Astro.
1. which metal should I choose for power ring/strap, or some other important signals? and I have totally 8 Metals, 3thin-2thick-3rf
2. what shoul I do if I see lots of warnings when choose my .tf file, like this:

Warning: Layer 'M1' has rounded fat table thresholds '(0, 1.77, 4.01, 8.01, 25.01)'. (line 69) (TFCHK-055)
Warning: ContactCode 'via1' has an invalid minimum cut spacing 0.2 that is less than the cut layer minimum spacing 0.28. (line 1406) (TFCHK-072)
Warning: Layer 'MG' has a pitch 3.92 that does not match the recommended wire-to-via pitch 2.36. (TFCHK-049)

but I think It's unlikely to revise .tf file, then don't care that? is that will create many DRC errors?

thanks!!

 

[jlai2]

normally higher metal layers are less resistive then lower metal layer, so using high metal layers for pwr and global signals are good.

the tech file warning does not nessary mean you'll get many DRC violations at the end. best way it's to understand then.

 

[cffyh]

normally higher metal layers are less resistive then lower metal layer, so using high metal layers for pwr and global signals are good.

the tech file warning does not nessary mean you'll get many DRC violations at the end. best way it's to understand then.

According to your answer,when my design use 4 metal I should use metal4 and metal 3 for PWR,am I right?

 

[jlai2]

yes. use higher metal layers for pwr/gnd and global signals.

 

[sicheng163]

yes. use higher metal layers for pwr/gnd and global signals.

But when I have 8 meatals, I have to create a large mount of vias to connect std cells to Power Rings(M7/M8), because the power/gnd of std cell use M1

 

[cop02ia]

But when I have 8 meatals, I have to create a large mount of vias to connect std cells to Power Rings(M7/M8), because the power/gnd of std cell use M1

Hi,

That should be typically the case. The vias would mostly be at the intersection of M1 horizontal strap & M8 vertical stripes (you would want to place M8 horizontal stripes going from the top part of the ring down to the bottom part of the ring). Bear in mind that more vias would mean lower resistance on the power/ground nets at the location of the vias.

If your concern is that the routing to standard cells will be messy, this is why it is normal practice for designers to avoid having standard cells under stripes.