Microsystems Development and Packaging

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Microsystems Development and Packaging

• Luiz Otávio Saraiva Ferreira
• LNLS
• lotavio_at_lnls.br

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OUTLINE

• Materials and Manufacturing Process
• Choosing Substrate
• Modelling
• CAD Software
• Packaging

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Basic Steps

• Good knowledge of system requirements.
• Interview with potential users.
• Understanding of the application environment.
• GOOD VISION OF THE MARKET.

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Choosing Materials and Manufacturing Process

• MATERIALS ? PROCESS

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Choosing the substrate

• How must be the format of the packaging, and how
  the packagint interfaces to the real world?
• The package and its interfaces define the cost
  and size of the product, the nature of the device
  that goes inside it, and the answer to many of
  the questions presented bellow.
• Is it needed to integrate electronic functions on
  the substrate?
• If yes, a high impedance substrate must be
  chosen.

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Production Scale

• How many devices will be produced (production
  volume or number of units) and what is its
  complexity (number of devices per sample)?
• This number may suggest serial production (small
  quantities), hybrid production (wide quantities),
  or batch production (very wide quantities).
• High complexity may suggest batch production.

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Cost

• What is the unity cost?
• High ( gt US40.00) ? serial prod.
• Low (lt US2.00) ? batch prod.
• Very low (glicose sensor, US0.20) ? continuous
  production process.
• The substrate is only a support
• ? glass, ceramic, plastic or paper.
• The substrate has mechanical function
• ? silicon is na excelent candidate.
• The substrate has optical function
• ? GaAs and PMMA.

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Modularity

• Is modularity needed?
• It is importan on chemical sensors arrays.
• The integration is undesirable because the
  incompatability between the deposition process of
  different sensors on the array.
• What are the lateral tolerances and the aspect
  ratio of the devices?
• It is not yet possible to have very small lateral
  tolerances.
• 100µm wide lines (optic lithography) ? 1 is
  good.
• Aspect ratio more than 201
• Wet anisotropic etch of Si.
• Anisotropic plasma etch (DRIE).
• LIGA Technology (UV or X).

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Environment

• To what is the environment the system will be
  exposed (air, water or other)?
• Sensors exposed to aquous environments like blood
  have more packaging problems, and are more
  dificult to integrate with electronics.
• Which substrate makes the packaging requirements
  less stringent?
• Sensor in aqueous solution
• ?ceramic substrate requires no protection of the
  sides.
• ? silicon is difficult to insulate and package,
  because the conductive medium might short out the
  sensor signal via the Si sidewalls..
• 2D or 3D parts?
• 3D ? conventional precision engineering.
• Diamond turning..
• Molding.
• 2D ? lithographic process.

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Thermal

• Thermal requirements?
• Maximum temperature.
• Si electronic circuits T lt 150oC.
• T gt 150oC ? SOI, GaAs.
• Thermal conductivity?
• Is the thermal matching with other material
  important?
• Flatness requirements (often in connection with
  the optical properties of the substrate)?
• Average roughness, Ra?
• One or both sides polished?
• Optical requirements?
• Transparency in certain wavelength regions?
• Index of refraction?
• Reflectivity?

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Electromagnetics

• Electrical and magnetic requirements?
• Conductor X Insulator?
• Dielectric Constant?
• Magnetic properties?
• Process compatibility?
• Is the substrate part of the process?
• Chemical compatibility?
• Ease of metallization?
• Machinability?
• Strain-dependent properties?
• Piezoresistivity?
• Piezoelectricity?
• Fracture behavior?
• Youngs modulus?

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Most used substrates

• Silício.
• Quartzo.
• Vidro.
• Alumina.
• Plastic.
• Aluminum.
• Poli-Si, ZnO, NiTi, PVDF, SiC.

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Formulation and Use of Macromodels

• Lumped mechanical equivalents for complex
  structures.
• Equivalent electric circuit of a sensor.
• Feedback representation for coupled-force
  problems.

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Micromechanical Device

Mathematic Formulation
Equivalent Electromechanical Diagram
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Analog Hardware Description Language
HDL-A , Spectre-HDL , VHDL 1076.1 , VHDL-AMS
LIBRARY conserved_systems USE
conserved_systems.nature_pkg.ALL ENTITY
piezopress_equ IS GENERIC (h real
17e-6 -- plate thickness
a real 1e-3 -- plate side
length r0 real
-- nominal resistance
rs real) --
sensitivity PORT (TERMINAL fp fluid
-- fluidic pin
TERMINAL ep electrical) --
electrical pin END ENTITY piezopress_equ ARQUIT
ECTURE equ OF piezopress_que IS CONSTANT
e0 real 146.9e9 -- Si elasticity
N/m2 CONSTANT v0 real 0.1846
-- Si Poissons ratio CONSTANT df real
e0h3/(12(1-sqr(v0)) -- rigidity
QUANTITY v ACROSS i THROUGH ep TO ground
QUANTITY p ACROSS ft TO fld_gnd
QUANTITY w11 real --
deflection coefficient BEGIN (w11/h)3
0.2522w11/h 0.000133pa4/(dfh) i
v/(r0 rs2.52231.5895e9w11) END ARQUITECTURE
equ
Piezo-resistive pressure sensor
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Basic Simulation Tools

• Analysis Basic Phenomena
• Thermal Heat flow
• Mechanical and structural Deformation
• Electrostatic Capac /charge dens
• Magnetostatic Induct / flux dens
• Fluid Pressure and flow

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CAD Software for Microsystems
Coventor, Inc CoventorWare software http//www.cov
entor.com
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Conceptual Design and Simulation
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Coyote Systems http//www.coyotesystems.com
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Materials Database
IntelliSuite (IntelliSense) Corp.
(http//www.intellisense.com)
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Process Simulators
Intermediate steps in the fabrication of a
thermal actuator from the University of
California, Berkeley, developed using the MUMPs
process.
Simulator of anisotropic etch of silicon.

• IntelliSuite (IntelliSense) Corp.
  (http//www.intellisense.com)
• Foundry-ready process templates include
• Cronos MUMPs
• Sandia SUMMiT
• Standard MEMS polysilicon process
• AMI MOSIS
• LIGA
• SCREAM

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Device Analysis

• Linear and non-linear analysis
• Static, steady state, and transient analysis
• Fully 3D coupled dynamics analysis
• Parametric variation of parameters
• Takes into account fabrication process-induced
  effects
• Submodeling, symmetry, and other size reducing
  techniques
• Animation and color mapping of results
• IntelliSuite (IntelliSense) Corp.
  (http//www.intellisense.com)

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Packaging

• More than 70 of the microsystem cost.
• Much more complex than ICs.
• Must protect from and enable interaction with the
  environment.
• Communication channels.
• Remove heat.
• Handling and tests.
• Chemical protection.
• Adequate interior (vacuum).

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Packaging Levels

• 0) Elementary component of a device.
• 1) Device. Sensor or IC.
• 2) Packaged device or hybrid module.
• 3) Printed Circuit Board.
• 4) Box or chassis.
• 5) Complete System.

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Adhesion

• Direct adhesion Si-Si, Polymer-Polyímer.
• Anodic bonding Si-Glass.
• Si plus 1 to 2µm PSG ? 30 _at_ 1100oC
• Eutetic bond Si-Au/Si ? _at_ 363oC.
• Photoresist AZ4000, SU-8, Polyimide, PMMA, PDMS,
  etc.