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Improving the reliability of air cooled electronic equipment must include focusing on the life expectancy of the fans or blowers. Evaluating fan failure behavior, however, is not a trivial problem, as vendors report very little information on this subject. Even when product literature provides such data, one vendor’s results are generally impossible to compare with another’s due to different test procedures, different assumptions, and different calculation methods, not all of which are explicitly defined. This paper is designed to help thermal and component evaluation engineers who have been assigned the task of sorting through these sometimes conflicting, often incompatible, claims regarding fan quality. We start with a definition of fan failure in terms of rotational speed, running current, and acoustic noise. Some basic statistical principles, such as Weibull hazard rate, Mean Time To Failure (MTTF) and L10 life, are presented in the reliability section, leading into methods for the estimation of fan life. Booser’s equation for grease life is included and its limitations for modern greases are noted; the standard equation for bearing rating life is also covered. To verify calculated fan life estimates, a designed experiment may be performed. A basic formula for the design of a fan life experiment is given, together with a brief analysis of published failure data from such an experiment. Most fan life tests are conducted under stress conditions, such as high temperature, that accelerate fan failures. The final section discusses accelerated life testing, including potential pitfalls. Simulating a mini-textbook, the paper contains valuable everyday reference material, including sample calculations to illustrate the concepts reviewed.

Thermal test chips are specially designed and built for thermal characterization of electronic packages. These chips have heaters for powering the chip and temperature sensors for measuring the chip temperature. One type of temperature sensor in wide use is a diode. Small resistors (also known as resistance temperature detectors or RTDs) are also used for measuring the chip temperature. This paper reviews and compares the characteristics of the diodes and RTDs used for chip temperature measurement during the thermal characterization of electronic packages. Techniques for reducing the measurement errors associated with these chip temperature sensors are also discussed. It is shown that the temperature versus voltage characteristics of RTDs at constant current are much more linear than those of diodes. NomenclatureA B C coefficient defined in equations (2), (3) coefficient defined in equations (2), (3) coefficient defined in equation ( 3 )