Functional capability space and optimum process adjustments for manufacturing processes with in-specs failure

Abstract

This paper introduces a methodology for functional capability analysis and optimal process adjustment for products with failures that occur when design parameters and process variables are within tolerance limits (in-specs). The proposed methodology defines a multivariate functional capability space (FC-Space) using a mathematical morphology operation, the Minkowski sum, in order to represent a unified model with (i) multidimensional design tolerance space; (ii) in-specs failure region(s); and, (iii) non-parametric, multivariate process measurements represented as Kernel Density Estimates (KDEs). The defined FC-Space allows the determination of a desired process fallout rate in the case of products with field failures that occur within design tolerances (in-specs). The outlined process adjustment approach identifies the optimum position of the process mean in order to minimize the overlap between the KDEs and in-specs failure regions, i.e., achieve the minimum possible process fallout rate for current process variation. The FC-Space-based process adjustment methodology is illustrated using a case study from the electronics industry where the in-specs failure region is identified based on warranty information analysis.

Keywords:

• Warranty analysis
• process capability assessment
• process adjustment
• quality
• statistical process control

Acknowledgements

The authors acknowledge the financial support provided by a UK STAR Award EP/E044506/1 and Motorola Corp. The authors would like to acknowledge Ashutosh Katiyar, ZS Associates, Princeton, NJ, for his initial work on the paper as well as Dr. Feng Niu and Bassam Bafaraj, Motorola for their discussions related to the warranty issues in electronic manufacturing.