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To: Proud_Infidel who wrote (16933)	2/4/2000 8:01:00 PM
From: Andrew Vance	Read Replies (1) \| Respond to of 17305

AV - Ordinarily I wold say they factored in daylight savings time or came up with a an extra hour to the day. Seriously, % capacity is like a bunch of financials that accountants can make work anyway they want or statisitics being used by Enginners to prove opposing points. This is how Andrew views capacity. There is theoretical capacity - in a vacuum and a perfect world, everything boils down to the throughput of the equipment without and variable thrown into the equation like downtime, maintenance, idle time, testing, etc. This is a bogus capacity. Guardbanded capacity - this is when you factor in as many variables as possible. 24 hours per day - 7 days per week - 2% scheduled maintenance - 90% availability - 95% uptime - 2% idel time -and the list goes on. Bottom line: when we determine capacity of a wafer fab, we do capacity modelling that highlights where the throughput bottlenecks are. Since a fab can not be perfectly matched for identical throughput and capacity at every single operation and process, your output capacity is gated by the the bottleneck (called the capacity limiting tool). That does not mean that you can't ever move more wafers through the fab that what the capacity model suggests, it just makes it more likely that the bottleneck could come back to haunt you. So, a fab that is running 100% capacity is actually running at 100% of the calculated capacity based on the guardbanding. 100% capacity is somewhere between 85% to 90% of what the fab can actually do. the 10%-15% slop are all of the variables facotred in. Or sometimes a fab can run more capacity of an additional tool is purchased for the bottleneck, thereby increasing fab capacity that was forecasted earlier. However, the best way to run more than 100% of the published capacity is to find your capacity limiting tool and do everything possible to improve its throughput. This means making sure it is alays running wafers during break, Lunch, shift changes, etc. and making sure there is always a steady stream of products in front of the equipment to eliminate idle time. the capacity number is more of a planning tool such that you start the right amount of wafers in the fab and make sure your WIP (work in progress) does not create log jams all over the place. Hopefully I painted an understandable picture since capacity is like other illusions in our lives. Or as my 12 year old would tell me, Dad, when is a door not a door. Answer: when its ajar (a jar). <GGG> Many times in my career, I was called on to increase fab capacity without buying anything. As you pointed out, it can be done by increasing yields on wafer. It can also be done by improving the equipment throughput of the capacity limiting tools, but it can also be done by improving cycle time through the fab which is just moving the correct inventory. andrew