Microassembly

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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

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Micro-Tweezers (memspi.com)
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Tweezers holding optical fiber
Design Chris Keller Fab Sandia
Courtesy MEMS Precision Instruments
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Tweezer gripping Hexsil gear
Courtesy MEMS Precision Instruments
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Comparison with Commercial subretinal tweezer
(Storz)
Photos courtesy Chris Keller, MEMS Precision
Instruments www.memspi.com
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Synthetic Insects(Smart Dust with Legs)

• Goal Make silicon walk.

• Autonomous
• Articulated
• Size 1-10 mm
• Speed 1mm/s

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Actuating the Legs
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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

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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 gt 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

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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
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.

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Parallel Assembly via Triboelectricity
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OMM 16x16 switch

• From www.omminc.com
• 256 hinged mirrors!

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Parallel Assembly via Surface Tension
Reflow
Silicon substrate
Silicon substrate

• Compact, parallel process assembly
• Accuracy and reliability ?

Syms, then Bright
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Solder-assembly (Rich Syms)
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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
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Parallel Microassembly Processes
K. Böhringer, et al, ICRA, Leuven, Belgium, May
1998
Courtesy Roger Howe, UCB
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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 sitesG. M.
  Whitesides, Harvard hydrophobic surfaces formed
  by self-assembled monolayers define the binding
  site

Courtesy Roger Howe, UCB
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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, 162-4 (1997).
Courtesy Roger Howe, UCB
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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
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Mirrors onto Microactuators

• Self-assemble mirrors onto microactuator arrays
• Si (100) mirrors
• Nickel-polySi bimorph actuators

U. Srinivasan, M. Helmbrecht, C. Rembe, R. T.
Howe, and R. S. Muller, IEEE Opto-MEMS 2000
Workshop, Kawai, Hawaii, Aug. 21-24, 2000
Courtesy Roger Howe, UCB
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Unreleased Mirrors

• Si(100) mirror array with binding sites,
  fabricated from SOI wafer

Courtesy Roger Howe, UCB
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Mirrors in Solution
Courtesy Roger Howe, UCB
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Moores Law, take 2

• Nanochips on a dime (Prof. Steve Smith, EECS)

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Mirror on Released Actuator
Courtesy Roger Howe, UCB
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Mirrors on Microactuators
Courtesy Roger Howe, UCB
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Mirror Curvature

• Heat-cured acrylate adhesive
• Mirror curvature less than 30 nm

Courtesy Roger Howe, UCB
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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
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Post-Assembly Processes

• Polymer adhesives are not sufficient for many
  MEMS applications
• Good interfaces require high temperatures (gt 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
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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
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Remove substrate!
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Could be 2-axis
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Packaging

• IC Packaging extremely well developed
• 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

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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 90095-1594 Mechanical and
Aerospace Engineering Department
Figure 3. SEM of the torsion mirror device.
Figure 1. SEM of the 2x2 MEMS fiber optic switch.
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2x2 MEMS Fiber Optic Switches
Introduction to MEMS
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 90095-1594 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

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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)