Patent ID: 7174281

Claim:
A method of managing a product through a multi-step manufacturing process, the method comprising steps of: (a) collecting process data from product lots of clusters of product units wherein each product lot is characterized by a corresponding lot mean and each cluster is characterized by a corresponding cluster mean; (b) grouping the collected process data into groups according to source of variation wherein each group is characterized by a corresponding group mean; (c) subtracting the corresponding group mean from each group to generate zero mean group data for each group; (d) normalizing a standard deviation of the zero mean group data for each group to generate normalized process data in which group variance is removed; (e) subtracting the corresponding lot mean from each product lot in the normalized process data to generate zero lot variance data; (f) subtracting the corresponding cluster mean from each cluster and adding the corresponding lot mean to each product lot in the normalized process data to generate zero cluster variance data; (g) subtracting the cluster mean from each product lot in the normalized process data to generate zero lot variance and zero cluster variance data; and (h) comparing a standard deviation of the zero lot variance data, a standard deviation of the zero cluster variance data, and a standard deviation of the zero lot variance and zero cluster variance data to determine how much variation in the process data results from product lot-to-product lot, from cluster-to-cluster within a product lot, and from product unit-to-product unit within a cluster.