Meaning
Mathematical model used to predict the fatigue life of solder joints in electronic components subject to thermal cycling. This norris-landzberg extension modifies the basic Coffin-Manson equation by adding factors for the frequency of the temperature cycles and the peak temperature reached. It allows reliability engineers to translate laboratory test results from accelerated aging into expected life under real-world operating conditions.
Frequency Factor
Acceleration of the testing process often involves rapid temperature swings that do not occur in normal use. The norris-landzberg extension accounts for the time-dependent nature of creep by including the ratio of the laboratory frequency to the field frequency. This adjustment recognizes that materials have more time to deform and crack when cycles are slower.
Temperature Sensitivity
Chemical and physical changes in the solder alloys happen faster at higher absolute temperatures. The model incorporates an Arrhenius term to describe the activation energy of the fatigue process. By calculating the difference between the maximum test temperature and the maximum operational temperature, the extension provides a more accurate estimate of how heat accelerates the failure of the bond.
Reliability specialists use this calculation to avoid over-designing the housing while still meeting the safety margins for different climates.
Predictive Application
Engineers use the resulting acceleration factor to determine the duration of the burn-in tests required for a new product line. If the model suggests a factor of fifty, then twenty hours of laboratory testing represents one thousand hours of use in the field. This calculation ensures that the product meets the longevity requirements specified by the customer without waiting years for actual failure data.
