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governed by electrochemistry, the sidewall morphology appears to be controlled by the PMMA mold. Factors such as molecular weight of the PMMA, residual stresses, and x-ray exposure conditions are believed to be the major factors influencing the sidewall morphology of LIGA fabricated parts. At high enough local stresses, the asperities on the sidewalls would deform plastically during the initial run-in period. However, at low contact pressures, mechanical interlocking of asperities on the sidewalls of surfaces described here would have a significant influence on the adhesion of LIGA microsystems. 6.4 LIGA Adhesion Probe Tips and Pull-Off Force Measurements The first task was to design an adhesion probe tip suitable to perform adhesive pull-off measurements with commercial nanomechanical testers. The probe tips were made by LIGA processing so that the sidewall morphology of the probe closely mimics the sidewall morphology of real LIGA parts. A tip with a radius of curvature of 500 µm is shown in Fig. 6.4. Fig. 6.4. SEM of a LIGA Ni adhesion probe tip. An x-ray mask with a two dimensional array of probe tips was first prepared. Poly methylmethacrylate was used as the mold material, and synchrotron radiation was used to expose PMMA and create the LIGA molds. Mold filling in this particular case was performed by conventional electrodepostion of nickel from sulfamate baths. Probe tips of different geometries and from other electroplatable metals or alloys can be prepared. A fixture was designed and fabricated to attaché the probe tip (Fig. 6.4) to a commercial MTS Nanoindenter XP unit in place of the standard Berkovich diamond indenter. The probe was brought into contact with planar surface of a metallographically polished Ni disk. The disk was also prepared by electroplating Ni into 10 mm x 10 mm square molds. The nanoindenter was programmed to collect data in the negative load in the negative load regime until the surfaces are completely separated during the unloading cycle. A typical load-displacement data for the contact of the Ni probe tip on metallographically polished Ni surface is given in Fig. 6.5. The negative load or pull-off force can be used to guide and validate analytical models to predict adhesion between LIGA fabricated parts. 56
Force (mN) Fig. 6.5. Typical load-displacement curves for a LIGA probe tip on a Ni LIGA disk 6.5 Summary -0.5 None of the existing analytical models can be applied to predict the effect of surface morphological features commonly found on LIGA fabricated on adhesion. In the current study we have developed a novel adhesion probe tip made by LIGA process itself. Used in conjunction with Nanoindenter XP or Micromaterials Nanotrest platform, the probe tip can be used to measure the adhesive pull-off forces between LIGA structures in micro- and millinewton load regimes. We hope the data generated by this technique can guide and validate future models on adhesion. 6.6 References 2 1.5 1 0.5 0 LIGA Ni Adhesion Edge on Lapped side -70 µN -83 µN -156 µN -175 µN -40 -20 0 20 40 60 80 100 120 Displacement (nm) 6.1 Prasad SV, Hall AC and Dugger MT, “Characterization of Sidewall and Planar Surfaces of Electroformed LIGA Parts”, SAND Report, SAND2000-1702 6.2 Prasad SV, Dugger MT and Christensen TR, “LIGA Microsystems: Surface Interactions, Tribology and Coatings’, Journal of Manufacturing Processes, In Press. 6.3 Johnson KL, Kendall K and Roberts, AD, Proc. R. Soc. London, A 324 (1971) 301-313. 6.4 Derjaguin BV, Muller VM and Toporov YP, J. Colloid Interface Sci., 53 (1975) 314-326. 6.5 Pashley MD, Pethica JB and Tabor D, Wear, 100 (1984) 7-31. 6.6 Fuller KNG and Tabor D, Proc. R. Soc. London, A345 (1975) 327-342. 6.7 Greenwood JA and Williamson JBP, Proc. R. Soc. London A 295 (1966) 300-319. 6.8 Hall AC, Christensen TR, Prasad SV, Dugger MT, and Widmer, M “Sidewall Morphology of Electroformed LIGA Parts – Implications for Friction, Adhesion, and Wear Control”, J. Micromech. Microeng., In Press. 57
Page 1 and 2:
SANDIA REPORT SAND2004-1319 Unlimit
Page 3 and 4:
SAND2004-1319 Unlimited Release Pri
Page 5 and 6: Contents ACKNOWLEDGEMENTS..........
Page 7 and 8: 6.5 Summary........................
Page 9 and 10: List of Figures Figure 1.1 SEM micr
Page 11 and 12: Figure 6.2 Contact between an elast
Page 13 and 14: Preface Our team was involved in a
Page 15 and 16: strength. The subsequent chapter di
Page 17 and 18: Fig. 1.3. SEM image of cylindrical
Page 19 and 20: Fig. 1.5. Schematic of primary feat
Page 21 and 22: Fig 1.7 Double-hinged pull-tab tens
Page 23 and 24: Fig 1.10. SEM image of optical forc
Page 25 and 26: 2 Strength Distributions in SUMMiT
Page 27 and 28: 2.2 Critical Flaw Size Evaluation T
Page 29 and 30: Fig. 2.5. SEM micrograph of pull-ta
Page 31 and 32: (1) Differences in surface roughnes
Page 33 and 34: 3 The Role Of Microstructure In SUM
Page 35 and 36: crystallographic orientation of a g
Page 37 and 38: direction. Also, maximum stress loc
Page 39 and 40: 3.4 References 3.1 Randle, V., Micr
Page 41 and 42: has the advantage of distributing t
Page 43 and 44: and servovalve at a strain rate of
Page 45 and 46: 4.6 References 4.1. TJ Garino, AM M
Page 47 and 48: microscopy studies. As a first step
Page 49 and 50: Fig. 5.2. Orientation imaging of a
Page 51 and 52: Fig. 5.5. Orientation imaging of a
Page 53 and 54: 6 Novel Techniques for Measurement
Page 55: of adhesion, and, (iv) a smaller co
Page 59 and 60: 7 Impact of Silane Degradation Due
Page 61 and 62: All samples were coated with alkyls
Page 63 and 64: the friction structure and the cali
Page 65 and 66: 7.4 RESULTS 7.4.1 Simulation of dos
Page 67 and 68: Dose (MeV/g) Fig. 7.4. Results of X
Page 69 and 70: heating on contact angle for PFTS.
Page 71 and 72: the C-C backbone of the PFTS molecu
Page 73 and 74: The increase in static friction for
Page 75 and 76: 8 Friction and Wear of Selective Tu
Page 77 and 78: During processing of microelectrome
Page 79 and 80: actuator. After unloading, the devi
Page 81 and 82: 9 Conclusions and Recommendations T
Page 83: 10 Distribution 3 MS 0889 M.T. Dugg
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