Process Yield is a criterion used in manufacturing to control process performance: it can be defined as a percentage of processed product units passing the compliance check (their key parameters fall within certain range of manufacturing tolerance), in other words these units will not be rejected as defective ones, so additional costs for repairing or scrapping the defective product units will not be incurred to the company. Process yield operates concepts of upper and lower specification limits (and a target limit between them) which are boundaries defining acceptable performance level.
All the product units suiting the range between the upper and lower specification limits or precisely meeting a target limit will make up a process yield rate (the fluctuation of characteristics can be depicted on X-bar chart). Yield loss (quality gaps) is caused by certain faults in the manufacturing process, entailing different defects in the key parameters. Yield loss rate can be classified by defect types and this will help to pinpoint the problematic areas of the process. Process yield prediction is used for estimating ROI from defect reduction.