טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentDavidovitch Danny
SubjectLong Life Reliability Test of Cantilever Beam
DepartmentDepartment of Quality Assurance and Reliability
Supervisors Dr. Yefim Haim Michlin
Professor Dov Ingman


Abstract

This work presents, a long life test, based on poly-silicon beam bending, and a reliabilitytest methodology. The objective of the experimental part is to show that standard structures (2μ films) can withstand 2×1010 cycles without failure like fatigue or adherence to the substrate as a result of loading or local change of stiffness under normal pre-defined operating conditions. The load was initiated by 20 Volt peak-to-peak (rectangular) input with the frequency of 25 kHz, resulting the driving mechanical frequency of 50 kHz. Measurements of the damped natural frequency of the connecting yoke have been performed for 5 days, using a "Polytec" laser Doppler vibrometer mounted on the "Navitar" microscope (magnification x20 with high depth of field). The change in the damped natural frequency over 10% would indicated the fingers stick or broken state.

It was shown that, according to the Weibull distribution, over-cycling (by a factor h) relative to the specifications is equivalent to increasing the number of samples by a factor hn (ν - Weibull shape parameter). This permits a good statistical representation for the test, using a rather small number of samples.  

The fact that no failure occurred during testing of 3 samples with an over-cycling factor of 100 proves that the product reliability is higher than 0.99995 at confidence level 99%. Thus the study proved a successful combination of experimental technique and performance, reliability-test planning for Hi-tech products, and statistical data processing.