60th Ectc Presentation Chowdhury, Mohammad Kamruzzaman

-1-Add Author’s Name Here

Add Company Logo HereJune 1 – June 4, 2010

The 60th ECTC Paris Las Vegas, Nevada, June 1 - 4, 2010

Investigation of Chemical De-burring and Subsequent Plasma Cleaning of Mechanically Punched Micro Via Array Fabricated

in LCP Substrate

Mohammad K. Chowdhury,1 Li Sun,2 Shawn Cunningham,2 and Ajay P. Malshe1*

1Materials and Manufacturing Research Laboratories (MMRL)University of Arkansas, Fayetteville, AR 72701

2WiSpry Inc., Irvine, CA 92618

*Contact: E-mail: [email protected], Tel: (479) 575-6561, Fax: (479) 575-2669

Chowdhury, Li Sun, Shawn, and Ajay



Acknowledgements

The National Science Foundation

wiSpry Inc., Irvine, CA

High Density Electronics Center (HiDEC)

Staff

Rogers Corporation

Rohm and Hass

ECTC 2010




Need for a

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:




How The Punching System Works?

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

In MMIC (Microwave Monolithic IC)

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

In 3D Packaging & MCM Module

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

In Flexible Electronics

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

In Wearable Electronics

www.smalltimes.com

In RF-MEMS Devices in Cell Phone

www.ec.europa.eu – ANASTASIA Project

In 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



Addressing the 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 Etching

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



Chemical Etching Using Ethanolamine


20 wt% EA + 40 wt% KOH + 40 wt% Water @ 850C

3314 Neutralizer (3% H2SO4 + 3% H2O2)

1 Min5 Min5 Min

10 Min

Molecular Formula: C2H7NO Chemical Structure: HOCH2CH2NH2

Physical State: Viscous Hygroscopic Liquid

50 µm Via, 75 µm Pitch, 10 x 10 Array

Chemical Property of Ethanolamine

Chemical Property of LCP

Due to its Hygroscopic nature the Ethanolamine was not an effective etchant for low moisture absorbent ULTRALAM 3850TM LCP



Oxidation of the LCP burr by 20 – 40% NaMnO4

Etching of the LCP burr by < 30% NaOH

5 Minutes Neuratilzation by (3% H2SO4 + 3% H2O2)

Chemical Etching Using Promoters

The LCP burr need to be functionalized before it can be etched out

Permanganate solution is a strong oxidizer can help in this process


Chemical Property of LCP

Promoter A: NaMnO4 (Strong Oxidizer)

Promoter B: NaOH (Strong Etchant)





PROMOTER 3308A (20 – 40 % NaMnO4) @ 850C

PROMOTER 3308B (NaOH < 30%) @ 850C

3314 Neutralizer (3% H2SO4 + 3%

H2O2)

5 Min

1 Min

5 Min5 Min

10 Min15 Min




1 Min

5 Min 5 Min5 Min10 Min15 Min




5 Min 5 Min

1 Min5 Min

10 Min15 Min

75 µm Via, 187.5 µm Pitch, 10 x 10 Array



Chemical Etching – Process Conditions

2.5 Liter of Promoter A & B were taken in a beaker to submerge the 5” LCP wafer sample

The solutions were continuously stirred using a magnetic stirrer

A solution temperature of 850Cs was monitored continuously during the process for

Promoter A & B

Top view SEM images of the same spot of the samples were taken before and after

The cross sectional analysis was done for the same sample after taking the SEM images



Add Company Logo HereJune 1 – June 4, 2010 Chowdhury, Li Sun, Shawn, and Ajay


1. PROMOTER 3308A (20 – 40 % NaMnO4) @ 850C - 5 Minutes

2. PROMOTER 3308B (NaOH < 30%) @ 850C – 5 Minutes

3. 3314 Neutralizer (3% H2SO4 + 3% H2O2) – 5 Minutes

Best recipe out of the matrices




1. PROMOTER 3308A (20 – 40 % NaMnO4) @ 850C - 5 Minutes

2. PROMOTER 3308B (NaOH < 30%) @ 850C – 5 Minutes

3. 3314 Neutralizer (3% H2SO4 + 3% H2O2) – 5 Minutes

Best recipe out of the matrices



200 μm 50 μm


Delamination due to longer etching time of 15 minutes

Promoter A – 5 min , Promoter B – 15 min, Neutralization – 5 min




Delamination due to higher processing temperature (900C)

Promoter A – 1 min (900C) , Promoter B – 5 min, Neutralization – 5 min

After

200 μm 50 μmDelamination of the bottom Cu film



Issue to Overcome after Chemical Etching


Carbonated LCP debris leftover after chemical etching

Carbonated LCP Debris



O2 Plasma Cleaning of LCP Debris

Micro vias were cleaned by using 5 Min Promoter A (NaMnO4) – 5 Min Promoter B

(NaOH), 5 Min Acid Neutralization (3% H2SO4 + 3% H2O2)

125 watt power at 320 miliTorr pressure with 160 sccm of oxygen flow was used

Samples were treated for 5 min, 15 min, and 30 minutes

SEM images were taken for the same spot before and after of plasma cleaning

process




05 minute oxygen plasma cleaning


After After

Before Before

LCP precipitation

O2 Plasma Cleaning after Chemical Etching

Precipitation of LCP




After After

Before Before


LCP debris did not get cleaned very well due to large volume of the debris





After After

Before Before

LCP Precipitation

Copper Etching

Small Precipitation of LCP debris also copper film get etched





Very nice uniform cleaned via fabrication after 30 minutes oxygen plasma cleaning

Bottom Copper Layer



5 min

5 min 15 min

15 min

30 min

30 min

O2 Plasma Cleaning Without Chemical Etching

No improvement on the LCP and copper burr removal process due to ignoring the chemical etching process before the plasma cleaning



Summary of µ-Via fabrication

Micro via fabrication by mechanical punching

5 Minutes Oxidation of the LCP burr by 20 – 40% NaMnO4


5 Minutes Etching of the LCP burr by < 30% NaOH

5 Minutes Neuratilzation by (3% H2SO4 + 3% H2O2)

30 Minutes oxygen plasma cleaning with 125 watt power at 320 mili torr pressure with 160 sccm of oxygen flow



Conclusions

Ethanolamine with KOH is not a good chemistry to address the burr elimination

NaKMnO4 for oxidation needed to functionalize the LCP before it can be etched by

NaOH

Acid neutralization is needed after strong caustic solution etching

5 minutes oxidation, 5 minutes etching, and 5 minutes neutralization gives the best

cleaned micro vias

Oxygen plasma cleaning is needed to remove carbonated LCP burr formation during the

etching process

Therefore, a sequential treatments of wet chemical etching and oxygen plasma etching is need to make uniform micro via fabrication by mechanical punching technique




Thank You!


60th Ectc Presentation Chowdhury, Mohammad Kamruzzaman

Technology

Transcript of 60th Ectc Presentation Chowdhury, Mohammad Kamruzzaman