NDR --> Non Default Rule or Non Delay Rule ??

[charan teja]

Hi Friends,

What is NDR ?? where in the flow do we use them ? would like to know abt it in detail if anybody can explain. Thanks in advance.


Thanks,
Charan Teja

 

[subhash_chevella]

Hi,

NDR ~ Non Default Rule
after PnR stage, if you are getting timing/cross talk/noise violations, which are very difficult to fix @ ECO stage, we can try NDR option during routing stage.
Non Default Rule means: spacing between metals will be more (generally two spacing will be there, after NDR three spacing), metal width will be more etc.
Generally we won't apply NDR. If you don't have any other option & at critical situation only we will apply NDR.

thanks,
Subhash

 

[nav_vlsi]

NDR --> Non default Rule.

However i have different perspective about NDR than previous user.

NDR are mainly used in place & routing section of design flow. when they actually route the design.

The Default routing guideline for the router would be provided by tech Lef (incase of Encounter) or techfile (incase of ICC). However when we are routing special nets especially CLOCK, we would like provide more width & more spacing for them. Instead of default 1unit width & 1 unit spacing specified in tech LEF, NDR will have double width , double spacing or triple width double spacing rules coded in them. when the CLOCK net is routed using NDR , they would have better Signal Integrity, lesser cross talk, lesser Noise. but we cannot increase the width & spacing to some large value as it will affect the area of chip. hence backend designer needs to make a call on timing VS noise VS Area on finalizing about NDR rules.

In above example , i took CLOCK net as just example, there can be several more instances like this , such a using an NDR for routing secondary power pins inorder to reduce routing congestion & DRC and many more.