Test specs monitor automotive semiconductors

Jeff Bibbee, CTO of Pintail Technologies. Courtesy of Pintail Technologies.

Q Automotive test specifications on semiconductor parts have been under development for several years. What are some goals of these specifications?

A The Automotive Electronics Council (AEC; www.aecouncil.com) and semiconductor companies have developed specifications targeted at automotive parts to standardize or recommend statistical methodologies, increase overall quality and reliability, and standardize or recommend world-class procedures.

A The AEC-Q001 specification recommends a general method for using Part Average Testing (PAT) to remove abnormal parts and thus improve the quality and reliability of parts from a supplier. PAT is a methodology that prescribes finding test results that fall outside six sigma from the population mean for a given wafer, lot, or group of parts being tested. Any test result outside the six-sigma limit for a given device is considered an outlier and removed from the population—parts that fail the PAT limits do not get shipped to a customer, thereby improving quality and reliability.

Q What are the ramifications of PAT during testing for semiconductors designed for automotive applications?

A PAT actually lowers the yield by a small percentage since it removes outlier parts that would normally pass the specification limits. However, the most important metric in the automotive world, defects per million (DPM), can be dramatically reduced using PAT—the goal is zero.

Q Are there quantifiable failure rate reductions through implementation of semiconductor test specifications?

A Yes. According to the AEC, many studies have shown that the outlier parts cause most of the field failures. While devices that meet specification limits are technically "passing" devices, those fringe performers are typically where most field returns occur in subassemblies like powertrain, engine management, and infotainment systems. These parts endure extreme environmental conditions where the potential for failure increases so there is no place for marginally performing devices. As electronic content increases in modern automobiles, the potential for device failure increases liability for manufacturers.

Q Any final thoughts about automotive test specifications regarding semiconductors?

A There is intense pressure to improve reliability and bring the defect rate down, especially now that important functions like braking, traction control, dynamic or active stability control, and safety measures are being controlled by semiconductors.

Since manufacturing costs continue to drop and test costs remain relatively flat, margins on devices are getting smaller as the cost of test becomes a greater component of manufacturing cost. Without sophisticated analysis and simulation tools, suppliers will be applying these specifications without a good understanding of what it means to their supply chain—or worse yet, applying them blindly and missing critical tests.

To read the complete interview with Jeff Bibbee, go to www.tmworld.com/auto.