Statistical bin limits

Statistical bin limits Since 1999 National Semiconductor has successfully improved its product quality and reliability performance. The overall product DPPM (defective parts per million) performance improved from >2000 DPPM to 10 DPPM. National’s customers have recognized the company with numerous quality and “best in class supplier” awards including the prestigious Stack Gold Award for National’s product quality and its customer satisfaction. At the current low DPPM quality levels, any product performance anomaly can have a major impact to the end users. The anomaly or maverick product can significantly impact the performance of our customer’s end product. A maverick product can occur during the entire spectrum of product manufacturing processes including, but not limited to, wafer fabrication, assembly and test. The potential problem from a maverick product may go undetected until the final application of the system manufactured using National’s component. The impact of the maverick product on user quality, functionality and field reliability is costly in terms of customer returns, additional screening and retesting, replacement costs, loss of customer satisfaction, and future customer business. National has been using on line process monitors (OLPM) during its wafer fab manufacturing processes along with statistical process control (SPC) for all critical unit process steps. The individual unit process steps are a mixture of a single wafer processing, partial lot processing or batch processing where one or more wafer lot may be processed together. Additional die level processing is required during the assembly and packaging before a product is ready. However, with the magnitude of the unit processes involved in the manufacturing of an integrated circuit, additional output monitoring at individual wafer level is required for the interactions from the individual unit processes. It is critical to protect National’s customers from quality and reliability perturbations that may have not been addressed by SPC at critical unit process steps. National identified two points in the entire manufacturing process to segregate a product that has a higher probability of adversely impacting its product quality and reliability. Based on the control levels deemed critical for product quality and reliability, statistical controls are implemented at the end of wafer fab processing, i.e. wafer sort, and at the end of assembly and test, i.e. final test (FT). At wafer sort and FT each die is tested and separated in passing bins (good die) and failing bins (bad die). Statistical bin limits (SBL) are applied to minimize value added to a defective product and to protect product quality and reliability. The primary purpose of SBL is to eliminate any maverick product being supplied to a customer. SBL prevents atypical product by using failure mechanism based monitors, manufacturing process controls, and user data. SBL methodology defines requirements to improve quality and reliability of National’s products and establish internal requirements to minimize our customer receiving a maverick product. National’s SBL program meets all of requirements defined in EIA/JEDEC Standard EIA/JESD50, “Special Requirements for Maverick Product Elimination”. National’s SBL program is governed by “Corporate Standard Procedure – Wafer sort / Final Test Clip Limit / Statistical Bin Limit Procedure”. Each wafer fab manufacturing, assembly and test site may implement additional site specific procedures to effectively manage site specific SBL program.