Molecular Modification of PCB Substrates for Fine Line...
Transcript of Molecular Modification of PCB Substrates for Fine Line...
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Molecular Modification of PCB Substrates for Fine Line Patterning
Werner G. Kuhr, Ph.D.Founder and Vice President, Research
ZettaCore, Inc.369 Inverness Drive, Suite 350,
Englewood, CO 80112 [email protected]
Presented W
ednesday, Sept. 9, 2009
IEE
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anta Clara V
alley Chapter, C
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ociety
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ZettaCore, Inc. Confidential and Proprietary
Next Generation IC Packages
Microprocessor package
DieLaminateCopper
Solder Resist
Goal: Multilayer PCB substrate with ~10 micron L/S
Process: Semi-additive (plating and build-up lamination)
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Adhesion Issues in Substrates
• Fine line patterning (< 25 um) requires smooth surface• Semi roadmap requires ~10um line/space on substrates in 3-5 years• Mechanical adhesion insufficient for reliability of fine line traces
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1um
• Adhesion mechanism for fine lines will depend on mechanical and chemical forces
Existing Approach New approachRoughened surface “Smooth” surface
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Improving Adhesion in Substrates
• Chemical composition of surface depends on many factors• Material composition• Curing conditions• Storage history• Chemical treatments (cleans, desmear, etc.)
• Selection of adhesion chemistry• Stable chemistry (i.e., good shelf life, reproducibility)• Wide process window (time, temperature, concentration)• Broad application to many substrates
CH2OHCO2H
CH2CH2R
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ZettaCore, Inc. Confidential and Proprietary
ZettaCore Approach: Molecular Interface
Cu
Epoxy
Cu
EpoxyN
NN
NZn
HH
NN
NN
ZnH
H
NN
NN
ZnH
H
NN
NN
ZnH
H
NN
NN
ZnH
H
NN
NN
ZnH
H
NN
NN
ZnH
H
NN
NN
ZnH
H
NN
NN Zn
HH
NN
NN Zn
HH
NN
NN Zn
HH
NN
NN Zn
HH
NN
NN Zn
HH
NN
NN Zn
HH
NN
NN Zn
HH
NN
NN Zn
HH
• Molecules can attach “incompatible” materials
• Copper can be attached to epoxy
• Epoxies, resists, etc. can be attached to copper
• Chemistry engineered for specific material properties
Molecular Unit
~ 1 nm
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Summary of ZettaCore feasibility studies
• Porphyrin molecules have survived exposure to various electroplating solutions • Cu plating demonstrated on a variety of substrates• Enhanced peel strength correlates with good porphyrin
coverage• Porphyrin survives Cu metal deposition
• Porphyrin configuration does not change significantly in Cu film
• Metal structure of Cu film on top of porphyrin monolayer is as smooth as underlying Si (100) structure
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ZettaCore, Inc. Confidential and Proprietary
ZettaCore Chemistry: Initial Work
Y
X
X X
Z Z Z
Y
X
X X
X
X X
Z
X
X X
YZ YZ
X: Cu, Pd-binding component
Y: Surface reactive component
Z: Surface leaving group
Surface
Surface
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Molecule / Process Development
• Identification of reactive components• Chemical characterization of target substrates• Identification of reactive chemical species on surface
• Molecular design and synthesis• Design of reactive intermediates for attachment to selected surface• Id or synthesis of desired molecules and chemical characterization
• Molecule attachment and characterization• DOE on attachment conditions (time, temperature, concentration)• Method development for surface characterization
• Copper deposition / Lamination evaluations• Electroless plating / Electroplating
- or -• Lamination
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Overview: Molecule-enhanced Cu2+ plating
Molecule Reaction
Epoxy
Porphyrins forms a complex with Pd2+
catalyst
Pd2+.. Pd2+
..Pd2+..Pd2+
.. Pd2+.. Pd2+
..Pd2+..Pd2+
..
Catalyst Reduction
&Nucleation
Cu Plating
Pd0 Pd0Pd0 Pd0
Pd0 Pd0Pd0 Pd0
2e- 2e- 2e-2e-
Cu2+
Cu
Cu2+
Cu
Cu2+
Cu
Cu2+
Cu
Electroless Cu2+
reduction and adhesion
Pd0 Pd0Pd0 Pd0
Pd0 Pd0Pd0 Pd0
Pd0 Pd0Pd0 Pd0
Pd0 Pd0Pd0 Pd0
Lamination
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Molecule Optimization
• Utilize a stable molecular platform• Each site can perform different function
– Individually optimized for specific function – Failure analysis possible for each function
• Systematic building block approach – Isolate the chemistry needed for specific function– Each site can be optimized independently and systematically
• Allows root cause failure analysis and complete characterization– Allows rational design and optimization of each molecular component– Preserves flexible design that can be modified & optimized as conditions change
X for Cu substratesNumerous chemistries tested and available for use
R for carbon substratesNumerous C-C linkages can be formed with existing chemistries
R3
R2
R1
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ZettaCore, Inc. Confidential and Proprietary
ZettaCore MI Process for Cu Plating
Molecule Attachment
E-less CuPlating
Pre-anneal
ElectrolyticCu Plating
Post-anneal
Testing HAST Repeat Peel Test
Standard Chemistries EmployedNo need for changes in standard processes!!!
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Correlation of porphyrin and Pd distribution on surfaces
Porphyrin distribution Pd distribution
• Porphyrin molecules distribute uniformly on the epoxy surface• Pd catalyst distributes uniformly on top of porphyrin
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Cross-sectional SEM of E-less Cu deposition
10min. 20min. 40min.
Roughened surface
Porphyrin attached smooth surface
Eless-Cu: @ 30oC
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Optimization of Molecule Properties
Identify reactive components
Does an existing linker work?
Synthesize/optimize new linker/process
No
Molecule attachment and optimization
Yes
Copper deposition
Peel strength adequate?
No
Yes
Reliability testingFail
Pass
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Demonstration of Peel Strength on Planar Substrates
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Time (s)
Peel
Str
engt
h (K
g/cm
)
Smooth substrate0.62 ± 0.02 Kg/cm
Roughened control0.60 ± 0.02 Kg/cm
• Demonstration of peel strength pre-HAST testing• 0.62 ± 0.02 Kg/cm on smooth surface, better than roughened control
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Time (s)Pe
el S
tren
gth
(Kg/
cm)
Without Treatment
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Summary: Impact of Molecular Layer for Copper on Epoxy – Reliability Tests
Test Test conditions Success criteria Result /StatusPeel strength
Peel width 1.0 cm, speed 5.0 cm/min at 90 degree angle
Roughened control (~0.6 Kg/cm)
0.62 Kg/cm
Reflow and HAST
Pre-conditioning (Level 3): 125C – 25 hr, 30oC/60%RH – 192 hrReflow: 260oC 3 timesHAST: 130oC, 85%RH – 96 hr
Peel strength degradation < roughened control
10% degradation vs. 13% for roughened control
Extended Bake
165oC – 504 hr Peel strength degradation < roughened control
No degradation
ThermalCycle
Pre-conditioning (Level 3)Reflow: 260oC 3 timesTC (cond. C): -65oC to 150oC, dwell 15 min, 1000 cycles
Peel strength degradation < roughened control
No degradation
Thermal Shock
Preconditioning (Level 3)Reflow: 260oC 3 timesTS (condition C): -65oC to 150oC, dwell 5 min, 1000 cycles (in liquid)
Peel strength degradation < roughened control
4% degradation vs. 8% for roughened control
THS 85oC, 85%RH – 1000hr Peel strength degradation < roughened control
9% degradation - same as control
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Plating: Enabling Fine-line patterning
Patterning completed on ZettaCore processed substrates to L/S of 8um
L/S
Custom
er A
Custom
er B
Custom
er C
Custom
er D
50/50um Pass Pass N/A N/A
30/30um Pass Pass N/A N/A
20/20um Pass Pass Pass N/A
18/18um Pass Pass Pass N/A
14/14um Pass Pass Pass N/A
12/12um Pass TBD* Pass N/A
10/10um Pass TBD* Pass Pass
8/8um Pass TBD* TBD* Pass
Patterned structures
* Requires etch / process modification
Current
capabilityE
nabledcapability
Confirms value of ZettaCore technology in enabling advanced geometries
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Adhesion Issues in Lamination on Copper
• Fine line patterning (~10 um) requires smooth Cu surface• Mechanical adhesion insufficient for reliability of fine line traces• Conventional Cu roughening processes provide insufficient adhesion
• Adhesion mechanism for fine lines will depend on mechanical and chemical forces
Existing Approach New approach
Roughened Cu surface “Smooth” Cu surface
1um
��
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Y
X
X X
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Optimization of Molecule Properties for Adhesion in Cu Lamination Process
Identify reactive components
Does an existing molecule work?
Synthesize/optimize molecule/process
No
Molecule attachment and optimization
Yes
Epoxy Lamination
Peel strength adequate?
No
Yes
Reliability testingFail
Pass
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ZettaCore, Inc. Confidential and Proprietary
ZettaCore MI Process for Cu Lamination
Molecule Attachment
TestingHAST Repeat Peel Test
Standard Chemistries/ProcessesNo need for changes in standard processes!!!
Lamination
Surface Cleaning
Surface Conditioning
Surface Treatment
Baking Drying
Peel Test
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SEM of Smooth and MITM–treated Copper Surfaces
Surface is clean Cu suggesting that the peeled surface breaks at the Cu-resin interface.
Untreated Smooth Cu MiTM - Treated Cu Surface
Cu surface
Resin
Most areas covered by resin suggesting Cu-resin interface breaks within the resin, not at the Cu-resin interface
After HAST and Peel-back of laminated Epoxy
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Lamination: Peel Strength Data
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Solder Resist: Paste and Dry Film Processes
Solder Resist ( SR coating / baking / UV / develop / UV / post-bake)
Smooth Cu Foil
Pre-clean (NaOH / soft-etch / acid clean)MI treatment
MI treatment layer
Solder Resist
Lamination (GX-13 / backing board / curing)
ABFbacking substrate
Peel strength measurementReliability Test (Reflow / 48 and 96-hrs HAST)
Paste SR ProcessSmooth Cu Foil
Pre-clean (NaOH / soft-etch / acid clean)MI treatment
Solder Resist (SR dry-film lamination / UV / baking / UV)
MI treatment layer
Solder Resist
Lamination (3X GX-13 / backing board / curing)
ABFbacking substrate
Peel strength measurementReliability Test (Reflow / 96-hrs HAST)
Dry Film Resist Process
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Solder Resist: DFR Material Summary
ZettaCore treated smooth Cu shows superior HAST stability and No undercut or delamination after subsequent processing (soft-etch and Ni/Au plating)
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Roughened Smooth Smooth Treated
Peel
Str
engt
h (K
g/cm
)
Initial96 hr HAST
Initial 96 hr HASTRoughened 0.65 0.20 0.53Smooth 0.16 0.02 0.13Smooth w molecule 0.68 0.53 0.14
Peel Strength (Kg/cm) Roughness(Ra, µm)
Substrates
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Lamination: Results Summary
Peel strength and HAST stability:• 1.33 Kg/cm before and 1.15 Kg/cm after HAST• 14% degradation vs. 36% for roughened control
Lamination and HAST stability on patterned Cu lines:• ZettaCore process does not roughen the Cu lines• No delamination after HAST• Isolation resistance > 1012 Ω
after HAST
Laser drilling and via clean/plating compatibility:• No delamination or undercut post via-clean and plating
ZettaCore process enhances adhesion without roughening the Cu surfaceDemonstrated through HAST testing
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MI Results Summary
• ZettaCore solutions available for all 3 interfaces• e-less plating on smooth dielectric• resin lamination on smooth copper• solder resist on smooth copper
• Provides finer line dimensions and improved reliability performance