Reliability Requirements

A recent Consumer Reports article suggested that many reliability problems associated with current high-end cars from BMW, Mercedes, and others are due to the large number of complex electronic features in these vehicles and the increasing shift towards electronic control of mechanical systems. Indeed, there have been many recent high-profile examples of electronic system failures, such as an electronic transmission controller defect in some Jaguar models that prompted a recall of nearly 68,000 vehicles. This defect introduced the possibility of the electronic transmission controller inadvertently shifting into reverse if a major loss of transmission oil pressure was detected.

Reliability problems, whether as minor as a dashboard LED that doesn't work or as major as a malfunction of an anti-lock brake controller, can have a significant impact on consumer satisfaction and product safety. Even the most reliable vehicles have about a 10% chance of developing a problem within the first year, according to the 2003 Consumer Reports reliability survey. And according to the survey, electrical systems are one of the single largest contributors to problems in vehicles.

Naturally, auto manufacturers have a strong interest in maximizing reliability, and they place stringent reliability requirements on their suppliers. Electronic components are expected to operate reliably for the lifetime of the car—often fifteen years or more.

First and foremost, automakers specify a maximum acceptable initial defect rate for each component. This defect rate varies by application and component type, but is usually below 10 parts per million for semiconductors. In order to achieve such low defect rates, semiconductor manufacturers must focus on reliability in all aspects of their processes, from initial design to final product testing.

To create a reliable automotive-qualified component, designers must consider the harsh environment associated with automotive applications, such as wide temperature ranges and significant vibration. As illustrated in Table 1, automotive-grade chips must usually be able to withstand temperatures ranging from -40C to well over +125C. As a result, most high-speed chip fabrication processes and high-speed transistor libraries cannot be used because they will not operate at such extreme temperatures. Instead, very conservative fabrication technologies and transistor designs are usually employed. The resulting chips are, of course, slower than similar parts used for non-automotive applications.