Unformatted text preview: nal tool if any tool is projected to be loaded beyond 85%. This is because there is a correlation between capacity loading and cycle time, and loading a tool too close to 100% usually incurs a big cycletime penalty. Buying sufficient tools to keep capacity loading below 85% is thus an indirect way of limiting cycle time. Defining “capacity” as a plant’s output at some fixed loading below 100% is sometimes referred to as “cycletime-constrained capacity” . Though 85% is a commonly used level for this, Grewal et. al.  have developed a method for modifying the 85% rule on a tool-by-tool basis based on cycle time analyses of individual tools. For simplicity, however, 85% is used across the board in this paper. That said, all tool groups that the capacity software shows are never loaded beyond 85% can be ignored for the remainder of this analysis—they have proven themselves not to be capacity constraints even when the fab is dedicated to the product that loads them most heavily. The remaining tool groups are mix-driven capacity constraints— tool gr...
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- Spring '11
- Semiconductor device fabrication, Headway, tool group