Principles of optoelectronic packaging
Dealing with the spaghetti
of optical and electrical
wires ...
Copying and processing permitted for noncommercial purposes, on condition that
proper reference to the source is given.
© Sergiusz Patela, 2000-4
Outline
1.
Introduction
2.
Optics of optoelectronic packaging
3.
Classifications and packaging systems
4.
Optoelectronic package requirements
5.
Assembly conditions
6.
Generic optoelectronic package
7.
Design solutions
8.
Some notes about materials
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Introduction
Packaging – a sequence of technologies that involve
• connecting,
• protecting,
• and manufacturing of the devices
Wafer processing
Packaging
O-e device
Packaging
20
10
80
90
In optoelectronics the package accounts for 60 to 80 percent of current
manufacturing expenses in component assembly (in microelectronic the
proportion is reversed)
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Micro versus optoelectronic packaging - similarities,
differences, challenges
Microelectronics devices
Optoelectronic devices
• high frequency design
• high frequency design
• optimized automatic assembly
• optimized for manual assembly
• planar design
• 3D design, difficult visual inspection
• electrical connection
• electrical and optical connections
• components easily recognized (with
metal lines as the references)
• fiducial markings necessary to enable
visualization and recognition of some
elements
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Future – replacement of electrical interconnections
with optical interconnections
Sooner or later, the wire bonds will talk ...
• Limitations of classical electronic interconnections (speed,
density).
• Compatibility of optical transmission systems and
termination (switching, processing) modules
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Optoelectronic device fabrication
•
•
•
•
•
Wafer processing
Thin film processing
Device and subassembly packaging
Fiber handling and alignment
The finishing steps of tuning, adjusting and testing
Question - Why is it so challenging ?
Answer - Multiple, proprietary fabrication techniques and
processes involved, coupled with a lack of package and
material handling standards.
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Optoelectronic devices assembly process
Chip
fabrication
Cleave
facets
Facet
coatings
Package and
wire bond
Burn-in test
and bin
Mount and
subassembl
y
Align and
bond fiber
Test and
labeling
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Technologies for optoelectronic device assembly
Process
Description
Eutectic component attach In-situ pulse heat, Au-Sn preform
(for heat dissipation)
Epoxy component attach
Electrically conductive and
nonconductive adhesives
Wire bond
Au wire (25µm diameter), Au ribbon
(75µm wide)
Fiber alignment
Passive of active
Active component
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Laser, detector, lens, fiber
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Optics of optoelectronic packaging – light coupling
Optical loss factors:
1.
Efficiency of power transfer (insertion loss)
2.
Reflections reduction (back reflection)
Modeling issues: depending on device dimensions
• wave optics or
• ray optics approach has to be applied.
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Optoelectronic packaging, the history and the future
1. Early days - manual assembly
2. Contemporary - semiautomatic or automatic assembly; small or
medium scale production
3. The future - fully automatic assembly; massive scale production;
short time to market for new components
Note - nowadays optoelectronic packages are complex devices
themselves - composed of optical, microwave and thermal elements.
New diagnostic methods will be necessary optoelectronic devices/
packages
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Diagnostic methods for optoelectronic packaging
Testing
1. Operational properties
optical (power/sensitivity, coupling efficiencies, optical bandwidth)
electrical DC
electrical RF
2. Structural properties (conformity with design detail, internal cracks
and voids)
3. Thermal properties
Note: 3D visualization is required optical and optoelectrical elements of
the package
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Mode Field Diameter
Power density profile of guided light beams can be approximated by
Gaussian function:
  r  2 
p(r ) = p(0) exp− 2  
  w0  
2wo is called the mode-field diameter (MFD).
It is diameter at e-2 ~ 13.5% of Pmax
λ 
MFD
= A + B 
CD
 λc 
D
A, B, C, D = empirical parameters,
λc – mode cutoff wavelength
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Optoelectronic packaging - classification according
to the packaging system
1
Alignment type
Passive
2
Active
3
Mixed
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Notes
Possible very high adjustment accuracy.
Inexpensive equipment. Different dies are needed
for different application .
Universal equipment, can be expensive if high
precision is required. Feedback during
positioning guarantees device perfomance.
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Example of mixed optoelectronic packaging
Schematic showing the construction of the package and the principle of
the mixed packaging (note infrared die-bonding)
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Photonics devices to be packaged
1
Device
Laser diodes
types
FP, VCSEL, DFB,
DBR
6
Detectors
2
3
DWDM
multiplexers and
switches
Filters
Mainly
semidonductor
Grating, waveguide,
FBG
4
Couplers
5
Isolators
6
Optoelectronic
integrated circuits
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Intereference, FBG
Fused, integrated
optics
Magnetooptic
rotators
applications
Telecommunications,
datacom., sensors,
aoutomotive industy.
All kinds of systems
High speed fiber optic
transmission (SM)
High speed fiber optic
transmission (SM), sensors
Fiber optic systems of all
kinds. SM, MM, POF fibers.
High speed telecom. In
connection with high quality
lasers.
Advanced systems
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Design type and package requirements
1
Construction class
Free space
2
Waveguides
3
Photonics devices arrays
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Requirements
Lenses, beam co llimation,
(micro)optical beam-forming elements
But-coupled waveguides, high
adjustment accuracies
Thermal problems arise for emitting
devices. High packaging density (new
connector styles may be required – e.g.
SFF connectors).
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Application and package requirements
1
Application
Telecommunications
2
Datacom., networks
3
4
5
Automotive industry
Medicine
Sensors
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Packaging requirements
Mainly SM fibers, very high accuracy, 20+ years
working time
High accuracy and reliability, SM and MM
fibers, in the future possibly POFs in massive
market (FTTH)
Very high reliability, lower accuracy.
Special material requirements
Custom parameters, system dependent.
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Optoelectronic packaging - assembly conditions
1
2
3
4
“Optical-path”
Assembly-Conditions
Accuracy
Requirements
<1µm for SM systems,
>1µm for MM systems.
10 up to 100µm for POFs and automotive applications.
Alignment (levels of freedom) X, Y, Z with different accuracies in different directions.
Φ (angle).
Alignment method
Visual (microscope, camera, image processing) or
infrared (“see through the surface”, observation of “hot”
active transmission devices (near infrared).
Other assembly issues
Optical connection efficiency
Electrical (electronic protection, ESD)
Thermal
Hermetization
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Communication system level packaging hierarchy
Level
1. System level
Contents general
System service
functions
2. Cabinet level Functioning of the
system on the rack
3. Unit level
Interconnection
between packages
4. Board level
Board functioning.
Power supply
Contents optical
Interconnection distance
Network interconnections ≥ 100 m
5. Fiber level
6. Beam level
Cabinet level
interconnection
Interconnection between
modules
On-board device
interconnections and
signal transmission
Optical fiber placement
Beam focusing
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Placement
Stability, precision
Photonic Devices. Optoelectronic Packaging
~ 10 m
<1m
~ 10 cm
~ 1 cm
~ 1 µm
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“Generic” optoelectronic package
active element(s) with
adjustment system
electrical
connections
cover
(hermetization)
fiber holder and
adjustment
segment
fiber
support and temperature
stabilization module
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window,
flat or lens
special
optical
elements
(isolators,
filters, …)
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Fiberoptic photonics systems
• Telecommunications systems. High performance, very high reliability
and longevity (up to 30 years), very high unit price. Based on metal,
glass, ceramic
• Access network systems. High performance and reliability, medium
life times (10 years). Low unit price. Based on polymer materials
(c) Sergiusz Patela 2001
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Comparison of different LD – fiber coupling
techniques
Butt coupling
Tapered waveguide
coupling
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LD coupling with lenses
possibilities
Single lens
double lens
cylindrical lens
GRIN lens
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waveguide core
planar waveguide
singlemode waveguide
F-O to strip
waveguide coupling
substrate
Butt - coupling of fiber and strip
waveguides
polished surface
singlemode waveguide
additional block of substrate material
substrate with waveguide
Butt coupling of the waveguides
with strengthening element
block of substrate material
strip waveguide
UV-hardening glue
epoxy glue
fiber waveguide
substrate
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Waveguides connection with fiber
strengthening element (ruby
bearing)
strenghtening element
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waveguide core
singlemode waveguide
planar waveguide
Butt coupling vs.
lensed fibers
substrate
Butt - coupling of fiber and strip
waveguides
waveguide core
singlemode waveguide
planar waveguide
substrate
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Lensed coupling of fiber and strip
waveguides
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Angled waveguides coupling
Polymeric waveguide as short-distance optical interconnections.
45 mirrors applied for use as connects between MM fibers and
VCSEL’s. Waveguide: d-PMME, UV-cured epoxy resin.
Insertion coupling loss 1dB.
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Diluted waveguide (beam-shape engineering)
Elliptical field distribution,
incompatible with optical fiber
planar
waveguide
light towards
optoelectronic element
taper
strip
waveguide
Cylindrical field distribution,
compatible with optical fiber
InGaAsP
towards fiber
waveguide
InP
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Diluted waveguide optical field distribution
Fiber
waveguide 1
Fiber
1
waveguide
Planar
waveguide
Planar
waveguide
0,5
Fiber
1
waveguide
Planar
waveguide
0,5
0,5
0
-1,E-05 -5,E-06 0,E+00
5,E-06
Waveguide thickness [µm]
1,E-05
0
-1,E-05
-5,E-06
0,E+00
5,E-06
1,E-05
0
Waveguide thickness [µm]
Optical field distribution
of a planar and fiber
waveguides.
Misalignment results in
large coupling losses.
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-1,E-05
-5,E-06
0,E+00
5,E-06
1,E-05
Waveguide thickness [µm]
Optical field distribution of
fiber waveguide and
thinned (tapered) planar
waveguide.
Field widths are similar,
but distributions still differ.
Photonic Devices. Optoelectronic Packaging
Optical field distribution
shaped both by taper and
diluted (multilayer)
waveguide
28
Simple standard package
Waveguide
Standard elements
TO5 package
PIN photodetector
Telecommunications PIN photodiode
with fiber pigtail
in standard TO5 package
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Design of the laser module
baseplate
laser
isolator holder
lens cap
sleve
shuffle plate
fiber assembly
lens
isolator
Fiber assembly
laser
lens
isolator
glue
fiber
primary coating
solder
H. van Tongeren, et al., IEEE Transactions on Components, Packaging and Manufacturing Technology - Part , vol. 18, (1995) 227.
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Optoelectronic packaging of advanced
modules
Microwave package
U-grove
Conducting glue
Fiber
waveguide
Alundum substrate
Microwave SMA connect.
Optoelectronic modulator
in a microwave package.
Package contains modulator
chip, microwave preamplifier,
impedance matching circuit.
microstrip line
Laser diode package. Laser
diode on submount, thermistor
and photodiode
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Arrays packaging
Schematic structure of the 2-D VCSEL module
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Materials – selection criteria
1. Temperature properties (resistance, stability,
resistance above 100C, 200C for short time,
thermal coefficients of expansion)
2. Optical properties (attenuation, refractive index)
3. Mechanical properties
4. Manufacturability
5. Environmental resistance (weatherability)
6. Price, availability
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Package types utilized in optoelectronics
Component
Dual-mode direct
feedback laser
Tunable laser
Package
14-pin butterfly TO-56
High pin-count butterfly. Low
aspect ration custom package
Pump laser
14-pin butterfly TO-46
High aspect ratio rectangular.
External modulator
Custom package
Variable optical attenuator Coaxial cylindrical package
Receiver
TO-3, TO-18, TO-46, Butterfly.
Low aspect ratio custom package
Large square custom package.
Optical switch
Small cubic custom package
Isolator, coupler, splitter
Differing length cylindrical
packages
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