VII. Colloidal Processes

7.2 Tape Castingp g

Professor W. J. WeiDept. Mat. Sci. Eng.National Taiwan University

Ref.1 J R Reed Chapter 25 and 261. J. R. Reed, Chapter 25 and 262. 陶瓷技術手冊, 第 13 章

http://www.mse.nthu.edu.tw/~jhjean/http://www.mse.nthu.edu.tw/ jhjean/resource.htm

What is “Tape Casing”?What is “Tape Casing”?What is Tape Casing ?What is Tape Casing ?

The tape casting (doctor blade process) is p g ( p )-a shape forming technique, which produces thin flat sheets.-a doctor blade to conrol a moving ceramic slurry.

bi d t ff h ' t th' t th'-a binder system offer enough 'green strength'green strength'Punching and Printing on TapesLaminationLaminationBinder-burn-out (BBO) stepsSintered.

Tape Casting Equipment

http://drm.kist.re.kr/cerapedia/ process/jgl003.html

Multi-layer Assembly of MLCC(passive chips) or ceramic/metal module

Formulation of Tape Casting

Powder + solution (water or organic solvent) +bi d + di t + d f + l ti i +h ibinder + dispersant + de-foamer + plasticizer +homogenizer

Binder and Plasticizer for Tape CastingBinder and Plasticizer for Tape Casting

Effect of Binder Content

Effect of Binder: ζ-potentialEffect of Binder: ζ-potential

B. Bitterlich and J. G. Heinrich, J. Euro. Ceram. Soc. 22(2002) 2427~2434 C.A. Gutierrez and R. Moreno, J. Euro. Ceram. Soc. 20(2000) 1527~1537

Ad ti I th f P l i AdditiAdsorption Isotherms of Polymeric Additives

0,2 μm Alumna powder0,2 μm Alumna powder with BET area: 11.2 m2/gm, in MEK/toluene

Plateau coverage:

PVB = 3.46 2mmg

MFO = 2.31 2mmg

Binders: PVB(B79 and B76) M W B79 = 65000 B76 = 105000Binders: PVB(B79 and B76) M.W B79 = 65000, B76 = 105000

Dispersants: Mahatan Fish Oil (MFO) M.W=2000-3000

Tape Forming FundamentalsTape Forming Fundamentals

a combination of pressure driven flow and shear driven flowa combination of pressure-driven flow and shear-driven flow

Y. T. Chou, Fluid flow model for ceramic tape casting, J. Am. Ceram.

Soc., 70 [10] C-280-C-282 (1987)

Effect of Casting Variables (the forces)Effect of Casting Variables (the forces)

the ratio of pressure force to viscous force, Π,

Thickness vs Tape Casting VelocityThickness vs. Tape Casting Velocity

At various viscosity!

High viscosity is in-sensitive to elocity!

Critical Tape Casting Factors: CCR & Gap

• critical casting rate is 5mm/s • the thickness and density• critical casting rate is 5mm/s• below C.C.R. the shearing is very low, and the viscosity of slurry is

• the thickness and density didn’t change at constant casting speed, y y

high.

Gap Size in Tape Castingp p g

s (m

m)

Blade Gap 1.2 mmBlade Gap 0.4 mmBl d G 0 2

hick

ness Blade Gap 0.25 mm

Tape

Th

Casting Speed (mm/s)

Fig. Plot of the green tape thickness obtained at different casting speeds for three different blade gaps.

Ref: A.I.Y. Tok et al., Tape casting of high dielectric ceramic composite substrates for microelectronics application”, Journal of Materials Processing Technology 89-90 (1999) 508-512

Thickness vs. Gap and Speedp p

s (m

m) Blade Speed 5 mm/s

Blade Speed 10 mm/sBlade Speed 20 mm/s

hick

ness

Tape

Th

Blade Gap (mm)Blade Gap (mm)

Fig. Plot of the green tape thickness obtained at different blade gaps for three different casting speeds.g p

Defects in Tape: cavity on surface

Green tape

Binder burn-out

SinteredSintered tape

Defects in Tape: Non-uniform Shrinkage5 cm

(0,Y)

(X,0)

Casting Direction

• Four main stabilization treatment– Bake: 2 h at 120oC in flowing air. – Thermal cycling: -5oC for 30 min, then 120oC for 30 min, 4 times.

S l t t t d t l f 1 h t– Solvent exposure: saturated toluene vapor for 1 h at room temperature, then simple bake.

– Humidity: 24 h at 100% RH, 80oC, then 24 h at 80oC in flowing air.• Aging : 23oC, 50% RH

Directional Linear Aging Shrinkage of Green Tapes

Treatment Shrinkage %

Solvent-based Aqueous-based

Untreated X : 0.92 Y : 0.71 X : 0.40 Y : 0.31

Bake 0 30 0 27 0 28 0 32Bake 0.30 0.27 0.28 0.32

Thermal cycle

0.25 0.27 0.40 0.36y

Solvent 0.25 0.27 0.40 0.44

Humidity 0 15 0 14 0 17 0 21Humidity 0.15 0.14 0.17 0.21

*After 35 days of agingte 35 days o ag g

Organic: bottom Microstructure of

AqueousAqueoussurface vs. bottom

AqueousqBottom Surface

3 μmsurface

10 μm

Cross-Sectional MicrostructuresCross-Sectional Microstructures

Laminated Sintered

1mm

• Laminated by compression at room temperaturey p p• Green tape sintered at 1800°C/60min• No single layer can be distinguished after laminated• No single layer can be distinguished after laminated and sintered

MLCC: Engineering of Ceramic TapeMLCC: Engineering of Ceramic Tape

Ref: http://www.tactilecomponents.com/ ceramicacapacitor.htm

Properties of Cofired multilayer Ceramic Capacitor (MLCC)

Important Properties Important Properties

1. Slip viscosity (mPa·s)2. Green density (g/cm3)3. States (thickness, etc.) of the tape 4. Microstructure of green tapes4. Microstructure of green tapes5. Tensile strength (kPa), for example6 Sintered density (g/cm3)6. Sintered density (g/cm3)7. Microstructure of sintered tapes8 Di l t i ititi it d di i ti f t (%)8. Dielectric permititivity and dissipation factor (%)

Tensile Strength and Strain-to-Failure of TapeTensile Strength and Strain-to-Failure of Tape

*Effect of plasticizerfor tape properties

Summary

• Multi-layer structure and tape process are most l d i f l ipopular and important process for electronic

components (e.g. L-C-R);• Processing parameters are extremely complex;• The manufacturing has faced the competition from g p

the field of silicon industry (system on chip, SOC). • Adapt several technologies from thin filmAdapt several technologies from thin film

processes and inject-printing.