SPC for visual rejects: a foundation for continuous improvement

Traditionally, a visual inspection is performed after electrical probe to sort reliability failures from good integrated circuits. The rejects found at this operation are the cumulative result of all aspects of wafer processing. In order to improve the yield in this operation at Digital, it was necessary to develop a project plan containing a vision and goals that would mobilize multi-organizational teams. The authors describe the process used to establish a yield enhancement program and to accomplish key project objectives. The foundation for improvement was statistical process control (SPC) charts for 100% reject inspection data. Since the existing methods for attribute data could not be directly applied because of the many challenges encountered, a unique strategy was developed and implemented. From the information found on the SPC charts, a cycle of challenges-interventions-improvements was used with customers and suppliers to realize positive change in the shortest possible time. The effects of this program to date have increased yield at the visual inspection by 15%