Imaps 2010 Mohammad Chowdhury

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

*Contact : [email protected]

IMAPS 2010Research Triangle, Raleigh, NC

November 3rd, 2010

mailto:[email protected]

April 13, 2023 IMAPS 2010, Raleigh Convention Center, Raleigh, NC 2

Acknowledgements

The National Science Foundation

wiSpry Inc., Irvine, CA

High Density Electronics Center

(HiDEC) Staff

Rogers Corporation

Rohm and Hass

IMAPS 2010

Industry need for:

Cost effective way of micro via fabrication

High speed processing of through via fabrication with high yield

throughput

Compatible process with the conventional via fabrication tool

Elimination of thermo processing of the substrate during through

via fabrication

Fabrication of vias with uniform through via wall

Motivations of the Research:


Die Bushing

PinLCP

Copper

Copper

LCP

Copper

Copper

Before Punching

Copper

Copper

LCP

After Punching APS 8718 Automatic Punching SystemPacific Trinetics Corporation

6” x 6” Sample Holder

Punch Pin Holder & Die

Bushing

LCP

Copper

Copper

LCP

Copper

Copper

Copper

Copper

LCP

Figure: Uniform and nice via formation

µ-Via Fabrication by Mechanical Punching:


Driver Applications:

Ref:http://www.mpdigest.com/issue/Articles/2009/june/mmic/

Default.asp

MMIC (Microwave Monolithic IC)

Ref: http://www.pcdandf.com/cms/magazine/220-2009-issues

3D Packaging & MCM Module

Ref:http://www.cmst.be/projects/img9.jpg

Flexible Electronics

Ref: http://www.techwear-weblog.com

Wearable Electronics

www.smalltimes.com

RF-MEMS Devices in Cell Phone

www.ec.europa.eu – ANASTASIA Project

Satellite and Aerospace Applications


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


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

2. By Dry Etching

Reactive Ion Etching (O2 Plasma

Cleaning)

Deep Reactive Ion EtchingRef:

http://knol.google.com/k/-/-/2ufdlj2yc019u/u4nyvf/deep-reactive-ion-etching%20(1).jpg


Via Fabrication: Test Structure


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












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


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


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



3314 Neutralizer (3% H2SO4 + 3%

H2O2)



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




Sample 4 1 Min 5 Min 5 Min




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


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









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


Neutralization treatment time creates almost equal roughness without any variation

Neutralization (3% H2SO4 + 3% H2O2)

Bottom Copper Film

SEM View


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

April 13, 2023 15

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


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


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.)


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.)


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


Thank You!

Plating Fixture


Power Supply

(+) To Cu Anode

(-) To Sam

ple Holder

From Pump

To Pump


Plating Fixture

Imaps 2010 Mohammad Chowdhury

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