1IEOR 130 - Methods of Manufacturing Improvement Spring, 2007 Prof. Leachman Homework Assignment 5 - Due Tuesday, March 61. When the "O" ring in a low-pressure CVD machine fails, the machine down time averages 4.5 hours. If the "O" ring is replaced as part of weekly preventive maintenance procedures, the incremental downtime is only 0.5 hours. Data on the lifetimes of "O" rings in this machine type are as follows. (The notation ptdenotes the fraction of the "O" ring population that fails during the tthweek of operation.) tpt1 .15 2 .20 3 .25 4 .25 5 .15 What policy for "O" ring replacement will maximize machine availability? 2. It is desired to schedule preventive maintenance (PM) procedures for a particular type of wafer processing machine. The expected cost to repair the machine after it goes down while in service is $200. The expected cost to perform a PM on a machine in working order is $50. Data on machine failures is as follows: Number of Probability Days of Service of Failure 1 0.08 2 0.12 3 0.16 4 0.24 5 0.18 6 0.12 70.10 (a)Determine the frequency at which the PM should be scheduled to minimize the expected costs. (b)During each PM or repair of the machine, the machine is thoroughly cleaned in order to re-qualify it for production. Immediately after such a clean, the die yield of the entire manufacturing process is 50%. With each additional day of service since the last clean, the machine becomes increasingly dirty. The increase in the number of fatal particles deposited on wafers is estimated to be 0.2 particles per sq cm per 24 hours. The fab makes only 10
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