1. Microassembly – deterministic
Sequential: pick and place
Keller
Yeh
Wafer scale
On-wafer (Magnetic, triboelectric, motorized, residual stress, …)
Wafer-to-wafer (Howe, Cohn, Bright)
Micro-packaging

2. Manual assembly (tweezers) Corner-Cube Retroreflectors Based on Structure-Assisted Assembly for Free-Space Optical Communication, Zhou, Kahn, Pister

4. Micro-Tweezers (memspi.com)

5. Tweezers holding optical fiber
Design: Chris Keller
Fab: Sandia
Courtesy: MEMS Precision Instruments

6. Tweezer gripping Hexsil gear
Courtesy: MEMS Precision Instruments

7. Comparison with Commercial subretinal tweezer (Storz)
Photos courtesy Chris Keller,
MEMS Precision Instruments

8. Synthetic Insects (Smart Dust with Legs)
Goal: Make silicon walk.
Autonomous
Articulated
Size ~ 1-10 mm
Speed ~ 1mm/s

9. Actuating the Legs
1st Link
Motor
2nd Link
1mm

10. Magnetic Parallel Assembly
Parallel assembly of Hinged Microstructures Using Magnetic Actuation
Yong Yi and Chang Liu
Microelectronics Laboratory
University of Illinois at Urbana-Champaign
Urbana, IL 61801
Figure 1. (a) An SEM micrograph of a Type I structure. The flap is allowed to rotate about the Y- axis. (b) Schematic cross-sectional view of the structure at rest; (c) schematic cross-sectional view of the flap as Hext is increased.
Figure 2. (a) SEM micrograph of a Type II structure. (b) Schematic cross-sectional view of the structure at rest; (c) schematic cross-sectional view of the structure when Hext is increased.
Solid-State Sensor and Actuator Workshop
Hilton Head 1998

11. Sequential parallel assembly
Parallel assembly of Hinged Microstructures Using Magnetic Actuation
Yong Yi and Chang Liu
Microelectronics Laboratory
University of Illinois at Urbana-Champaign
Urbana, IL 61801
Figure 8. Schematic of the assembly process for the flap 3-D devices. (a) Both flaps in the resting position; (b) primary flap raised to 90º at Hext = H1; (c) full 3-D assembly is achieved at Hext = H2 (H2 > H1 ).
Figure 9. An SEM micrograph of a 3-D device using three Type I flaps. The sequence of actuation is not critical to the assembly of this device.
Solid-State Sensor and Actuator Workshop
Hilton Head 1998

12. Assembly via Residual Stress
Low Insertion Loss Packaged and Fiber-Connectorized Si
Surface-Micromachined Reflective Optical Switch
V. Aksyuk, B. Barber, C. R. Giles, R. Ruel, L. Stulz, and D. Bishop
Bell Laboratories, Lucent Technologies, 700 Mountain Ave.
Murray Hill, NJ 07974
0.8 dB loss in transmission w/ AR coated fibers
2 dB reflection loss
0-80dB attenuation
fibers mounted with UV cured adhesive
1550nm
Later included in a closed loop feedback system
actuator lands on dimples onto grounded pads.
HH p 79-
Figure 2. Self-Assembling optical shutter. High tensile residual stress metal
is deposited on a polysilicon beam anchored at one end. Upon release the
metal-poly sandwich structure deforms, moving the free end of the beam
upward. The lifting structure engages the cut in the hinged-plate shutter
causing it to rotate 90 degrees into tits operating position.

13. Parallel Assembly via Triboelectricity

14. OMM 16x16 switch
From
256 hinged mirrors!

15. Parallel Assembly via Surface Tension
Reflow
Silicon substrate
Silicon substrate
Compact, parallel process assembly
Accuracy and reliability ?
Syms, then Bright

16. Solder-assembly (Rich Syms)

17. Taxonomy of Microassembly
Parallel microassembly
Multiple parts assembled simultaneously
Deterministic: pre-determined destination for parts
Stochastic: random process determines part destinations
Serial microassembly
“Pick and place” on a microscale
Courtesy: Roger Howe, UCB

18. Parallel Microassembly Processes
K. Böhringer, et al, ICRA, Leuven, Belgium, May 1998
Courtesy: Roger Howe, UCB

19. Stochastic Parallel Microassembly
Agitated parts find minimum energy state via an annealing process
Gravitational well: J. S. Smith, UC Berkeley and Alien Technology Corp., Morgan Hill, Calif.
(video)
Patterned chemical “binding sites” G. M. Whitesides, Harvard: hydrophobic surfaces formed by self-assembled monolayers define the binding site
Courtesy: Roger Howe, UCB

20. Courtesy: Roger Howe, UCB
Biomimetic Approach
Pattern part surfaces with hydrophobic and hydrophilic regions using self-assembled monolayers (SAMs).
free energy cost of SAM-water interface is high
hydrophobic regions act as binding sites
Terfort, A. et al. Nature, 386, (1997).
Courtesy: Roger Howe, UCB

21. Application to Microassembly
Pattern complementary hydrophobic shapes onto parts and substrates using SAMs.
no shape constraints on parts
no bulk micromachining of substrate
submicron, orientational alignment
Uthara Srinivasan, Ph.D. thesis, UC Berkeley Chem.Eng., May 2001
Courtesy: Roger Howe, UCB

22. Mirrors onto Microactuators
Self-assemble mirrors onto microactuator arrays
Si (100) mirrors
Nickel-polySi bimorph actuators
We have used this self-assembly technique to place ultraflat single-crystal silicon micromirrors onto surface-micromachined microactuator arrays.
The polySi actuator platform is actuated using nickel-poly-Si bimorphs. The binding site on the platform is a hexagonal shape of evaporated gold. A matching binding site also exists on the underside of the silicon mirror to be assembled. I’ll discuss how these binding sites are made hydrophobic in a few slides.
This assembly demonstrates the process decoupling that can be achieved with microassembly.
U. Srinivasan, M. Helmbrecht, C. Rembe, R. T. Howe, and R. S. Muller, IEEE Opto-MEMS 2000 Workshop, Kawai, Hawaii, Aug , 2000
Courtesy: Roger Howe, UCB

23. Courtesy: Roger Howe, UCB
Unreleased Mirrors
oxide
Si mirror
binding site
Si(100) mirror array with binding sites, fabricated from SOI wafer
And here we have the silicon (100) mirrors with gold binding sites which have been fabricated from a silicon-on-insulator wafer of silicon thickness of 15 um. The exposed sacrificial oxide is visible between the mirrors. The oxide is etched using HF, and the mirrors are released into solution.
Courtesy: Roger Howe, UCB

24. Courtesy: Roger Howe, UCB
Mirrors in Solution
This photo shows the released mirrors floating in water. Next, the binding sites are treated to render tham hydrophobic.
Courtesy: Roger Howe, UCB

25. Mirror on Released Actuator
assembled mirror
binding site
Here is a SEM of an assembled ultraflat mirror on a released microactuator. Binding sites without mirrors are also shown.
Courtesy: Roger Howe, UCB

26. Mirrors on Microactuators
assembled mirror
Here we have 7 silicon mirrors self-assembled onto a microactuator array under water. After this picture was taken, the adhesive was heat-cured and the microactuators were released using HF and dried with carbon dioxide critical point drying. The adhesive withstood this release process.
Courtesy: Roger Howe, UCB

27. Courtesy: Roger Howe, UCB
Mirror Curvature
Heat-cured acrylate adhesive
Mirror curvature less than 30 nm
Using stroboscopic interferometry, we measured the mirror curvature as less than 30 nm with the heat cured acrylate adhesive. This is well within lambda/10 for red light.
Courtesy: Roger Howe, UCB

28. Research Challenges for Self-Assembly Processes
Assembly extensions:
multi-pass and multi-part simultaneous assembly
Reduce area consumed by binding site, in order to achieve:
“High quality” mechanical interconnects
“High density” electrical interconnects
Courtesy: Roger Howe, UCB

29. Post-Assembly Processes
Polymer adhesives are not sufficient for many MEMS applications
Good interfaces require high temperatures (> 450o C), which can damage micro-components
Potential solutions:
Local heating through laser
Local resistive heating (Prof. Liwei Lin, UC Berkeley)
Courtesy: Roger Howe, UCB

30. Chip-to-chip and wafer-wafer assembly
Flat, thin gold mirror with a thick
Copper frame transferred from source
Substrate to MUMPS die.
Maharbiz, Howe, Pister, Transducers 99
MUMPS part by M. Helmbrecht

31. Moore’s Law, take 2
Nanochips on a dime (Prof. Steve Smith, EECS)

35. Remove
substrate!

36. Could be 2-axis

38. Packaging IC Packaging extremely well developed Not well addressed
Reliability
Thermal conductivity
Cost
Size
Not well addressed
Packaging with unfilled volumes
Packaging in non-standard ambients
Vacuum
Dry N2
Moist N2
100 mTorr +/- 1%
Fiber feedthroughs
Somewhat addressed
Optical I/O
Packaging induced stresses

39. 2x2 MEMS Fiber Optic Switches
2x2 MEMS Fiber Optic Switches with Silicon Sub-Mount for Low-Cost Packaging
Shi-Sheng Lee, Long-Sun Huang, Chang-Jin “CJ” Kim and Ming C. Wu
Electrical Engineering Department, UCLA
63-128, engineering IV Building, Los Angeles, California
Mechanical and Aerospace Engineering Department
85 V actuation. Smoothly controllable to 21degrees, then snaps to 45.
Releases at 53V. Switches in less than 1 ms. Insertion loss is 10 dB!
HH pp
Substrate is 2 wafers machined on 3 sides.
Figure 3. SEM of the torsion mirror device.
Figure 1. SEM of the 2x2 MEMS fiber optic switch.

40. 2x2 MEMS Fiber Optic Switches
Introduction to MEMS
2x2 MEMS Fiber Optic Switches
2x2 MEMS Fiber Optic Switches with Silicon Sub-Mount for Low-Cost Packaging
Shi-Sheng Lee, Long-Sun Huang, Chang-Jin “CJ” Kim and Ming C. Wu
Electrical Engineering Department, UCLA
63-128, engineering IV Building, Los Angeles, California
Mechanical and Aerospace Engineering Department
Figure 4. SEM of the vertical torsion mirror.
Figure 10. SEM of the fiber and ball lens assembly.
Solid-State Sensor and Actuator Workshop
Hilton Head 1998

43. Assembly - Summary
Pick-and-place assembly is the standard of the IC industry!
Chips, passives into lead frames
Bond wires
Cost is ~1 penny/operation
Parallel assembly is coming
Wafer-wafer transfer (deterministic)
Fluidic self-assembly (stochastic)