Dr. Stok calls for Prescriptive CAD

Design rules are rules which layout tools/editors (Routers, DRC checkers) have to adhere to so that final layout which goes to the fab can be manufactured correctly.

With 65 nm and below technologies the number of rules are too many, becoming difficult to code (run sets are becoming too big for DRC checkers!) and are unmanageable. DFM is partly responsible for more rules in < 65 nm technologies.

With so many rules there is too much of guardbanding which goes into design which might not be necessary.

In the below article, Leon Stok (Director of CAD, IBM) talks about Restricted Design Rules and how industry should embrace them.

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"IBM EDA Director Calls For 'Prescriptive CAD'"


Throwing more design for manufacturability (DFM) information at designers isn't a viable approach, said Leon Stok, IBM EDA director. Leveraging the concept of restricted design rules (RDRs), Stok called for a new "prescriptive" CAD methodology. Looking at handoff models, Stok noted that design rule manuals have gone from 100 or 200 rules to 600 to 700 rules and subsets. Design rules, he said, have become "difficult to formulate, impossible to code, unique to specific environments, and prone to error." And with all that, they're still incomplete, he noted. Restricted design rules (RDRs) help by bringing design rules back to a more manageable number, he said. And yet, Stok noted, everything that is not explicitly forbidden is allowed, and every design rule needs to be verified "in its complex and
unpredictable worst case scenario." Stok also noted that many DFM efforts focus on feeding manufacturing information back to the designer. For those who care most - full custom designers working in new processes - that information is too unreliable. And ASIC designers don't have time to deal with the DFM information, he said. When DFM information is fed forward, he said, optimizations can only work using very large guardbands.

http://www.eetimes.com/showArticle.jhtml?articleID=199000715