Understanding Wet Chemical Etching and Metallization of Micro Vias Fabricated Using Micro Mechanical Punching in LCP Substrate Mohammad K. Chowdhury, 1 Li Sun, 2 Shawn Cunningham, 2 and Ajay P. Malshe 1* 1 Materials and Manufacturing Research Lab University of Arkansas, Fayetteville, AR 72701 2 WiSpry Inc., Irvine, CA 92618 * Contact : [email protected]IMAPS 2010 Research Triangle, Raleigh, NC November 3 rd , 2010
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Understanding Wet Chemical Etching and Metallization of Micro Vias
Fabricated Using Micro Mechanical Punching in LCP Substrate
Mohammad K. Chowdhury,1 Li Sun,2 Shawn Cunningham,2 and Ajay P. Malshe1*
1Materials and Manufacturing Research Lab
University of Arkansas, Fayetteville, AR 727012WiSpry Inc., Irvine, CA 92618
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Dealing with the Fabrication Issues
Expansion
Warpage1. Z-axis expansion of the LCP Film
2. Warpage of the LCP sample
50 µm Via, 75 µm Pitch, 10 x 10 Array
LCP Burr
Bottom Cu Film
Bottom Cu Film
Copper Burr
3. LCP Burr
4. Copper Burr
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Via Pitch and Array Dependency of Z-axis Expansion
REF: “Mechanically Punched Micro Via Fabrication Process in LCP Substrate for RF-MEMS and Related Electronic Packaging Applications,” Mohammad K. Chowdhury, Li Sun, Shawn Cunningham, and Ajay P. Malshe, 42nd International Symposium on Microelectronics (IMAPS 2009) Proceedings, pg. 174-180, November 1 - 5, 2009
7
Addressing the Fabrication Issues
1. By Wet Chemical Etching
Anisotropic
Isotropic (For LCP & Cu Burr)Ref: http://www.emeraldinsight.com/fig/0870220101014.png
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Via Fabrication: Test Structure
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The test structure are of 75µm in diameter and 187.5µm in pitch both X & Y axis Via punching follows zigzag or spiral path during micro via fabrication
Chemical Etching Using Promoters
PROMOTER 3308A (20 – 40 % NaMnO4) @ 850C
PROMOTER 3308B (NaOH < 30%) @ 850C
3314 Neutralizer (3% H2SO4 + 3% H2O2)
Sample 1 5 Min 1 Min 5 MinSample 2 5 Min 5 Min 5 MinSample 3 5 Min 10 Min 5 Min
Experimental Matrix - 1
PROMOTER 3308A (20 – 40 % NaMnO4) @ 850C
PROMOTER 3308B (NaOH < 30%) @ 850C
3314 Neutralizer (3% H2SO4 + 3% H2O2)
Sample 4 1 Min 5 Min 5 MinSample 5 5 Min 5 Min 5 MinSample 6 10 Min 5 Min 5 Min
Experimental Matrix - 2
PROMOTER 3308A (20 – 40 % NaMnO4) @ 850C
PROMOTER 3308B (NaOH < 30%) @ 850C
3314 Neutralizer (3% H2SO4 + 3% H2O2)
Sample 7 5 Min 5 Min 1 MinSample 8 5 Min 5 Min 5 MinSample 9 5 Min 5 Min 10 Min
Experimental Matrix - 3
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Chemical Etching Using Promoters
PROMOTER 3308A (20 – 40 % NaMnO4) @ 850C5 Minutes
PROMOTER 3308B (NaOH < 30%) @ 850C5 Minutes
3314 Neutralizer (3% H2SO4
+ 3% H2O2)5 Minutes
Best recipe out of the matrices
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REF: “Investigation of Chemical De-burring and Subsequent Plasma Cleaning of Mechanically Punched Micro Via Array Fabricated in LCP Substrate,” Mohammad K. Chowdhury, Li Sun, Shawn Cunningham, and Ajay P. Malshe, 60th Electronic Component and Manufacturing Technology Conference (ECTC) proceeding, pp. 998 – 1003, June 1-4, 2010
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5 Min - A & Neutralization, 1 Min - B
5μm 5μm 5μm
Sample 1
5 Min – A, B, & Neutralization
Sample 2
5 Min - A & Neutralization, 10 Min - B
Sample 3
PROMOTER 3308A (20 – 40 % NaMnO4) @ 850C
PROMOTER 3308B (NaOH < 30%) @ 850C
3314 Neutralizer (3% H2SO4 + 3%
H2O2)
Sample 1 5 Min 1 Min 5 MinSample 2 5 Min 5 Min 5 MinSample 3 5 Min 10 Min 5 Min
Experimental Matrix - 1
Longer etching with promoter B (etching agent) gives the much rougher surface determined by qualitative visual observation
Promoter B (NaOH < 30%) EtchingBottom Copper Film
SEM View
Figure: 30 Degree Tilted SEM images
PROMOTER 3308A (20 – 40 % NaMnO4) @ 850C
PROMOTER 3308B (NaOH < 30%) @ 850C
3314 Neutralizer (3% H2SO4 + 3% H2O2)
Sample 4 1 Min 5 Min 5 Min
Sample 5 5 Min 5 Min 5 Min
Sample 6 10 Min 5 Min 5 Min
Experimental Matrix - 2
5μm 5μm 5μm
1 Min – A, 5 Min - B & Neutralization
Sample 4
5 Min – A, B, & Neutralization
Sample 5
10 Min – A, 5 Min - B & Neutralization
Sample 6
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Promoter A (20 – 40 % NaMnO4) Oxidation
1 minute of oxidization does not make an effect on the surface roughness Oxidation for more than 5 minutes does not show any extra roughness
Bottom Copper Film
SEM View
Figure: 30 Degree Tilted SEM images
PROMOTER 3308A (20 – 40 % NaMnO4) @ 850C
PROMOTER 3308B (NaOH < 30%) @ 850C
3314 Neutralizer (3% H2SO4 + 3% H2O2)
Sample 7 5 Min 5 Min 1 Min
Sample 8 5 Min 5 Min 5 Min
Sample 9 5 Min 5 Min 10 Min
Experimental Matrix - 3
5μm 5μm 5μm
Sample 7 Sample 8 Sample 9
5 Min – A, B, & Neutralization5 Min - A & B, 1 Min - Neutralization 5 Min - A & B, 10 Min - Neutralization
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Neutralization treatment time creates almost equal roughness without any variation
Neutralization (3% H2SO4 + 3% H2O2)
Bottom Copper Film
SEM View
Figure: 30 Degree Tilted SEM images
Electroplating of the Micro Vias
Direct Current Plating
1. Constant current for plating duration
Reverse Pulse Plating (RPP)
1. Periodic for forward – reverse – off state
2. Forward - 10 mA/cm2 for 100 ms
3. Reverse - 100 mA/cm2 for 1 ms
4. Off state - 10 ms
Forward: 100 ms 10 mA/cm2
Off: 10 ms
Reverse: 1 ms 100 mA/cm2
Time (sec)
Cu
rren
t D
ensi
ty (
mA
/cm
2 )
Current Density Duty Cycle for Reverse Pulse Plating
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Forward 10 mA/cm2
Time (sec)
Cu
rren
t D
ensi
ty (
mA
/cm
2 )
Current Density Duty Cycle for
Direct Current Plating
After 1 Hr After 2 Hrs
After 3 Hrs After 4.5 Hrs
DC Plating of the Micro Vias
DC plating is capable of uniform via filling without any void formation for a 75 µm via with 187.5 µm pitch
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RPP Plating of the Micro Vias
After 1 Hr After 2 Hrs
After 3 Hrs After 4.5 Hrs
RPP is not capable of via filling even after 4.5 hours of platingRPP is taking excess amount of deposited ion from forward bias plating
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Linear correlation between the via electroplating thickness and plating timeDC plating (~7.68 µm/Hr.) gives faster via electroplating than RPP (~3.18 µm/Hr.)
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Linear correlation between the surface electroplating thickness and plating timeDC plating (~11.67 µm/Hr.) gives faster via electroplating than RPP (~4.99 µm/Hr.)
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Conclusions Longer etching with promoter B (etching agent) gives the much
rougher surface observed qualitatively by visual observation 1 minute of oxidization does not make an effect on the surface
roughness Oxidation for more than 5 Minutes does not show any extra roughness Neutralization treatment time creates almost equal roughness without
any variation
DC plating is capable of uniform via metallization for 75 µm via with 187.5 µm pitch without any void formation
RPP is not capable of via metallization even after 4.5 hours of plating Linear correlation between the plating thickness and plating time DC plating gives more than twice faster electroplating than RPP
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Thank You!
Plating Fixture
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Power Supply
(+) To Cu Anode
(-) To Sam
ple Holder
From Pump
To Pump
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