Dissertation > Industrial Technology > General industrial technology > Materials science and engineering > Special structural materials

Fatigue Characteristics and Life Prediction for MEMS Electroplated Copper Films

Author LiuHao
Tutor ShangDeGuang
School Beijing University of Technology
Course Mechanical Design and Theory
Keywords MEMS Fatigue electroplated copper films life prediction magnetostrictiveprinciple
CLC TB383.2
Type Master's thesis
Year 2008
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MEMS is not a simple geometric reduction of the traditional machinery. If thecomponentsaccess tomicro-nano-size,themechanics andphysicalpropertiesofthesematerials will significantly change. The elastic modulus, tensile strength, fracturetoughnessandfatigue strength ofmaterialsmeasuredunderthemacro-blockconditionmay not be applicable to MEMS design. Whether the existing theory and methods ofbulkmechanicalfatigue canbeusedinMEMSstillneedstobestudiedfurther.In this paper, notched and smooth specimens were produced for free-standingelectroplated copper films with LIGA-like process at micron dimension. With theobservationofthree-dimensionalvideo,thespecimensmetthetestrequirements.The tensile fatigue testswere completed by using MMT-11Nmechanical fatiguetesting machine. S-N curve, cyclic???curve and ??N curve were obtained.Basedonthemodifiedlocalstress-strainapproach,fatiguelivesofnotchedspecimenswere predicted. The results were found in good agreement with the experimentalfatiguelives,which provedthatsomeofthetraditionalfatigueresearchmethodscouldbe also used in MEMS. Fatigue fractograghy observation showed that fracture modewas intergranular fracture form. Cyclic hardening behavior was found during thefatigue process. A comparison of coarse-grained, fine-grained electroplated copperfilms andbulkcooperisalsodescribedinthepaper.Finally, according to the characteristics of micro-mechanical fatigue test, amicro-mechanical fatigue testing device based on magnetostrictive principle wasinvented. Three kinds of fatigue specimens, tension, bending and bending-torsion,were designed. Especially during the past micro-mechanical fatigue testing programs,bending-torsion fatigue tests were difficult to achieve, therefore, the methods in thispaper couldlead anewsubjectandthenare innovative.

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