The Evolution of a Ceramic Materials System for Chip Packaging

Dave Kellerman

April 27, 2006

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)

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

Low Dielectric Constant (K, Er) Low Loss (tan delta, dissipation factor)

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

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

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

Approach

Hollow Microspheres(K=1+)

Standard Thick Film dielectric(K=8)

Composite Thick Film Dielectric (K=4)

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

Microstructure

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.

Particle Size Distribution

• Lower the Particle Size Distribution

– Average Diameter: 25 Microns– Max Diameter: 40 Microns– Dielectric Thickness: 25-35 Microns each layer

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

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

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]

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

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

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) 

High Current Carrying Capability

• Thick Film Gold or Silver

• .001-.005 ohm/square/mil

• Multilayer Approach

Thick Film on Low Temperature Cofired Ceramic

High Dimensional Stability, Power Dissipation, Thermal

Conduction

Dimensional Stability

3 D Shrinkage Due to Firing Constrained Sintering

(Tolerance) Thick Film

Tape Transfer (LTCC)

Thick Film on Alumina

Teledyne Microelectronics

Thick Film on Cofired Ceramic on Molded Aluminum Nitride:Patent 5,158,912

Microwave Characterization and Applications

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

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

Application: Re-Design Single Layer Thin Film Microwave Circuit

• MIT Lincoln Labs Amplifier Design

• Thin Film on Alumina• Redesign for Thick

Film

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)

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

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

Redesigned Thick Film Lincoln Labs Circuit

First Layer Second Layer(EMCA/Ferro)

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

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)

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