The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Reliability Assessment of Telecommunications Equipment
Olli Salmela
Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical and Communications Engineering for public examination and debate in Auditorium S4 at Helsinki University of Technology (Espoo, Finland) on the 11th of March, 2005, at 12 o'clock noon.
Dissertation in PDF format (ISBN 951-22-7477-9) [1133 KB]
Dissertation is also available in print (ISBN 951-22-7476-0)
Abstract
This thesis studies the reliability of telecommunications equipment, its components, and the systems made using those components. Special attention is paid to creating stronger links between the reliability analyses performed at different hierarchy levels.
The thesis starts with a temperature derating study. It is found out that the generic handbook based procedures may not always be very attractive, as they do not take satisfactorily into account the actual lifetime requirements. An alternative approach is proposed as a remedy to the current situation.
Thermal cycling requirement handbooks are surveyed, and based on the findings some enhancements are proposed. Next, a component and product specific approach to create thermal cycling requirements is suggested. When applying the new approach several factors can be taken into account: the product's lifetime requirement, the field environment, the reliability test result, and the statistical distribution of the component population. A new method of how to predict the reliability of a component population that is addressed to several, different field environments is presented.
Ceramic, leadless components are studied by testing and by utilizing Engelmaier's analytical solder fatigue model and Finite Element (FE) simulations. A new approach to interpret the solder joint height in conjunction with solder castellations is introduced. Based on this, a very good correlation between the test results and the predictions based on Engelmaier's model can be obtained. The parameter sensitivity of both the Engelmaier's model and the FE analysis are studied and compared. Error margins based on the parameter sensitivity studies are given.
Time-averaged hazard rate functions are studied in order to be able to use component level test data in simplistic parts-count method type reliability predictions. Finally, the availability of a full 3rd generation telecommunications network is studied.
Keywords: reliability, availability, MTTF, MTBF, hazard rate, derating, solder joint, fatigue, 3rd generation telecommunications network
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© 2005 Helsinki University of Technology
Last update 2011-05-26