hw1solutions - Solutions to HW 1 IEOR 130 Prof Leachman 1...

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1 Solutions to HW 1 IEOR 130 Prof. Leachman 1. Line yield (LY) is the fraction of wafers started that become wafer outs from the wafer fabrication (wafer fab) factory. Die yield (DY) is the fraction of chips (dice) printed on wafers coming out of wafer fab that electrically work. That is, it is the ratio of good die out to total die out. Overall equipment efficiency (OEE) is a ratio A/B, where A is the theoretical time required to complete the good units of product actually processed by the equipment during an observation period, and B is the total time in the observation period. 2. The output of each factory is proportional to (DY)(OEE). The impact of LY depends upon where in the process the line yield loss occurs. We consider two extreme cases. Case 1: All LY loss happens after the last bottleneck step in the process. Then output is proportional to (LY)(DY)(OEE), in which case: Factory A: (.85)(.90)(.85) = .65025 Factory B: (.82)(.98)(.60) = .48216 So factory A produces more output. Case 2: All LY loss happens before the first bottleneck step in the process. Then wafer starts can be compensated for the LY loss to send the same number of wafers through the bottleneck, making output is proportional to (DY)(OEE), in which case: Factory A: (.90)(.85) = .765 Factory B: (.98)(.60) = .588 So factory A produces more output in any case.
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