the evolution of an electronic material
DESCRIPTION
This presentation displays a development effort that took several years. The achieved goal was attained: a complete materials system that may be used to fabricate substrates for high speed and microwave single and multichip semiconductor substrates and packagesTRANSCRIPT
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The Evolution of a Ceramic Materials System for Chip Packaging
Dave Kellerman
April 27, 2006
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Acknowledgements
• Digital Equipment Corporation
• Worcester Polytechnic Institute, Worcester, MA
• Emerson and Cuming Composites, Canton, MA
• EMCA-Remex Products/Ferro
• MIT Lincoln Laboratory, Cambridge, MA
• Teledyne Corporation, Marina-Del-Ray CA
• Circuits Processing Technology (CPT) Carlsbad, CA
• Advanced Materials Laboratory, University of Massachusetts, Lowell, MA
• Damaskos, midwest
• Virginia Polytechnic Institute
• Field Flow Fractionation (Postnova)
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Materials System Requirements
• Substrates and Dielectrics for Microwave, VLSI, Wireless applications
– Signals: Low loss (Tan Delta; e’/e’’) AND Low Dielectric Constant (K or Er)
• Frequency range: .5-20+ GHz
• Signal Impedance Control (50 ohms)
• Minimized Signal Propagation Delay
• Minimized Signal Capacitive load
• Minimized Signal Crosstalk
• Minimized Power/ground noise
– Excellent Dimensional Stability (300 I/O and up)
– High Current Carrying Capability for Power and Ground Structures
– Excellent Thermal Capability for higher power dissipation
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Low Dielectric Constant (K, Er) Low Loss (tan delta, dissipation factor)
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Dielectric Properties of Ceramic Substrates and Dielectrics
Substrate Dielectric Constant Dielectric Loss(K or Er)
92% alumina 1 MHz 9.0 .0003 10 GHz 8.6 .0004
96% alumina 1 MHz 9.8 .0003 10 GHz 9.2 .0005
Glass+-Ceramic 1 MHz 5.1 .003 10 GHz 4.9 .001-.005
NTK, A.-E Riad ISHM95
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Candidate Substrate Technologies for Low K
MCM-L Laminate Substrates
Dielectric Dielectric Constant Loss (Tan Delta)
Epoxy/Glass
1 MHz 4.0-5.0 <.01
1 GHz 4.0 .02
10 GHz 4.0 >1
TCE High
Low thermal capability
source: A. E-Riad et. al.; ISHM 95
• Polyimide Thin Film– Low K~3.5– High Dielectric Loss (.0X)– High TCE – Low thermal capability
Silica: K~3.8 or Cordierite– Low K~5– Low Loss (.00X)– TCE dissimilar to 96%
alumina– Expensive Processing
• > 900oC Firing
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Thick Film Technology
– High K: 7.5-8.5– Low Loss, High Q– TCE matched to Silicon – Easy Processing– Fine line and Via resolution
• Screen Printed• Photoimagable
– High Thermal capability– Integrated Passives
Approach: Lower Dielectric Constant of Thick Film DielectricENGINEER THE MICROSTRUCTURE
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Approach
Hollow Microspheres(K=1+)
Standard Thick Film dielectric(K=8)
Composite Thick Film Dielectric (K=4)
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Porous Materials
• Porous Materials
• Porous materials are low K (K gas = 1)
• Need closed cell porosity for hermeticity:
– Hollow Microspheres added to ceramic or PWB laminates
• Digital Equipment Corporation Patented approach (D. Kellerman)
– hollow microspheres(K~1) + ceramic (K~8)
– K ~ 4
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Microstructure
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New Thick Film Dielectric Formulation
• Thick Film Glasses: From 8.5 to 3.5-4.5 (DEC/EMCA/Material Solutions/ECCM)
• Patents – 4,781,968: “Microelectronic Devices and Methods for
Manufacturing Same”, Low constant material.
– 4,865,875: Process for low dielectric constant thick film material.
– 4,994,302: Process for making low dielectric constant ceramic tape substrates.
– 5,178,934: "Microelectronic Devices", Low dielectric constant thick film devices.
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Particle Size Distribution
• Lower the Particle Size Distribution
– Average Diameter: 25 Microns– Max Diameter: 40 Microns– Dielectric Thickness: 25-35 Microns each layer
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Microsphere PSD Development
0
20
40
60
80
100
120
5 10 15 20 25 30 35 40
Diameter, microns
Les
s th
an V
olu
me
Per
cen
t, %
SDT40.32
0
20
40
60
80
100
120
Diameter, microns
Less
Tha
n Vo
lum
e%
New Process
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Microsphere Electrical Measurement• Cavity Resonator Techniques
– Perturbation:• Measure fc (resonant
frequency) and Q of empty cavity cavity
• Measure fc and Q with powder sample in cavity
• find fc and Q from net analyzer, calculate e’, Tan D
– Absolute• Characterize/model cavity• Measure fc and Q, calculate e’,
TanD– Calibrated
• Measure standard materials, compare to test material
– Damaskos
Results
• Sphere Dielectric constant air+ = 1.18-1.19 over 1-25 GHz
• Sphere Loss Tangent 3.1 x 10-3 to 4.0 x 10-3 over 1-25 GHz
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Dielectric Properties of Microspheres over Frequency
1.171.1721.1741.1761.1781.18
1.1821.1841.1861.188
4.761 7.469 10.182 12.897 15.616 18.337 21.056 23.77
Frequency, GHz
Die
lect
ric
Co
nst
ant,
e'
Er[1]
Er [3]
Er[4]
3.00E-03
3.20E-03
3.40E-03
3.60E-03
3.80E-03
4.00E-03
4.20E-03
4.761 7.469 10.182 12.897 15.616 18.337 21.056 23.77
Frequency (GHz)
Lo
ss T
ang
ent
TanD [1]
TanD [3]
TanD [4]
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Techniques Employed
– SEM
– TEM
– XRD (Xray Diffraction)
• Reflection at d=1.234Ao
• Crystalline phase: BxOx
• Increasing intensity with Lot Number
Lot d spacing Relative K or Er Tan D
amplitude 10-3
001 1.234 58 1.19-1.182 3.6-3.9
003 1.234 69 1.186-1.178 3.3-4.0
004 1.179 79 1.185-1.176 3.1-3.4
Microsphere Materials AnalysisAnalysis Conclusions
• Dielectric Constant and Loss Tangent decrease with Lot Number increase
• Materials Analysis– Presence of crystalline phase– Crystallinity Increases with
Lot Number• Dielectric Constant and Loss
Tangent decrease with increasing degree of crystallinity
• Electrical performance is dependent on materials constituents and processing
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Final Microsphere Attributes
• Resilient to multiple high fire temperatures
• Electrical
– Low K (measured 1.18 @ 2-20 GHZ)
– Low Loss (measured 10-3 @ 2-20 GHZ)
– Somewhat Lot Dependent
• Sphere Particle Size Distribution < 20 microns
• Spheres will electrically and physically meet specifications for thick film dielectric material
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Electrical Insulation Properties of the Low K Thick Film Dielectric
Dielectric and Insulation Properties
Property Gold System Silver System
Dielectric Constant 4.48 4.61
Tan @ 1 MHz 2.6 x 10-4 3.0 x 10-4
Insulation Resistance, 1.3 x 10 11 1.8 x 10 11
@ 100 Volts,
Dielectric Strength, 765- 1010 412-1100VDC/mil
Electrolytic Leakage Current, nil 18 @ 10v 9A/cm2/mil)
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High Current Carrying Capability
• Thick Film Gold or Silver
• .001-.005 ohm/square/mil
• Multilayer Approach
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Thick Film on Low Temperature Cofired Ceramic
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High Dimensional Stability, Power Dissipation, Thermal
Conduction
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Dimensional Stability
3 D Shrinkage Due to Firing Constrained Sintering
(Tolerance) Thick Film
Tape Transfer (LTCC)
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Thick Film on Alumina
Teledyne Microelectronics
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Thick Film on Cofired Ceramic on Molded Aluminum Nitride:Patent 5,158,912
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Microwave Characterization and Applications
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Microwave Characterization, T Resonator
• T Resonator standard design• Process:
– Ground Plane P/D/F– Dielectric P/D/F (2x)– Planarization layer P/D/F– Signal Conductor P/D/F
• Characterized Dielectric over 1-12 GHz Range
• Flat K response over the range• Virginia Tech
4
4.5
5
5.5
6
6.5
7
7.5
8
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00
Frequency (GHz)
Die
lect
ric
Con
stan
t Etched Gold #3Etched Gold #1 & #2Etched SilverAvg Thick Film GoldAvg Thick Film Silver
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Microwave Characterization:Stripline
• Thick Film Ag on Low K on Al2O3 (6x8”)
• Stripline Structure
– Ground Plane
– Dielectric
– Signal layer
• Characterized at 2 GHz
• Acceptable for microwave applications
• MIT Lincoln Labs
• EMCA/FerroMicrostrip Impedance of Four Thick Film Dielectric Groups
0
10
20
30
40
50
60
1 1 1 1 1 2 2 2 2 2 2 3 3 3 4 4
Group Number
Imp
ed
an
ce, o
hm
s
Ave Z, ohms
Min
Max
Derived Dielectric Constant Based on TDR Impedance
0
5
10
15
1 1 1 1 1 2 2 2 2 2 2 3 3 3 4 4
Group
Die
lect
ric
Co
nst
ant
Dielectric Constant
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Application: Re-Design Single Layer Thin Film Microwave Circuit
• MIT Lincoln Labs Amplifier Design
• Thin Film on Alumina• Redesign for Thick
Film
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Device Development Steps
•Choose Material
oLow K thick film system; gold
oResistor Material Candidates
•Design substrate Thin Film to Thick Film
•Model Designs
•Develop Materials, Process
oBuried Thick Film Resistor!
oMultilayer Thick Film
•Fab Substrates
•Electrical: Transmission Parameters (S)
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Thick Film Design
Signal Layer
Signal Layer
Ground Plane
Ground Plane
Ground Plane
Vias
New Thick Film Amplifier description
•.015 alumina, 5 metal layers
•ground plane on back side of alumina-plugged vias
-2 signal layers-resistors on buried signal layers
•asymmetric signal layer on alumina under dielectric
•symmetric signal layer on/under dielectric
•Low K thick film dielectric separates
•first signal layer from buried ground plane (above signal),
•second signal layer from top and buried ground plane
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Materials Issues
• Low K thick film dielectric • good isolation and smooth surface• Microsphere filled dielectric • EMCA fine line gold characterized to 12 GHz in prior work
• fine line gold ink• EMCA 3204D
• Via plug in substrate• EMCA 3266E, extruded through .008 laser drilled vias
• Buried Resistors
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Redesigned Thick Film Lincoln Labs Circuit
First Layer Second Layer(EMCA/Ferro)
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Buried Resistor PerformanceOn alumina, under Low K On Low K, under Low K
0
20
40
60
80
100
120
0 5 10 15 20 25 30
Number of Refires
Re
sist
an
ce (
oh
ms)
32A 32B 32C 32D
020406080
100120
0 5 10 15 20 25 30
Number of Refires
Resi
stan
ce (o
hm)
32A 32B 32C 32D
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Electrical Performance
Conclusions• HP 8510 Network Analyzer
– S Parameters: (S11, S12, S21)(SPort
output Port input)– 1-20 GHz
• Screen Printed conductors may be adequate for this application
– Performance through 13 GHz adequate
– > 13 GHz may require line length adjustment, or etched lines
• Low K Dielectric performed adequately in application
• Buried Resistors are feasible
-60
-50
-40
-30
-20
-10
0
1
2.1
3.2
4.3
5.4
6.5
7.6
8.7
9.8
10.9 12
13.1
14.2
15.3
16.4
17.5
18.6
19.7
Frequency (GHz)
Tra
nsm
issi
on
(d
B)
S21 (theory)
S21 (meas)
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Bottom Lines
• Development effort on ceramic materials system successfully developed for VLSI, microwave, wireless substrates
• Step wise approach to develop a system: materials component by materials component