Polymer Composites for Electronics Packaging Applications

James E. Morris, Portland State University, Oregon USA

j.e.morris@ieee.org

SIITME 2014 Bucharest Supported in part by the IEEE CPMT Society Distinguished Lecturer program.

Packaging Issues Thermal 3D Integration Embedded Passives

2 & Mechanical Support

Roadmap • Polymer/metal composite example:

Isotropic Conductive Adhesive (ICA)

• Percolation

• Polymer cure

• Electrical properties

• Reliability:

• Drop test

• Galvanic corrosion

• Miscellaneous

• Magnetic alignment

• Flip chip underfill filler

• Nanoparticles

• ICAs

• Embedded components

• Carbon nanotubes (CNTs) & graphene

• Electrical & thermal

28-Oct-14

ICA: Isotropic Conductive Adhesives

ICA: Flip Chip Interconnect

Bi-modal distribution

e.g.

10μm diameter flakes (<1μm thick)

plus

1-3μm diameter powder (spheres)

28-Oct-14 5

Creep & Coffin-Manson Lifetimes: Comparisons with Solder (Rusanen)

1

10

100

1 000

10 000

0.01 0.10

Non-recoverable strain range

Nf(5

0) in

num

ber o

f cyc

les

ICA (Rusanen &Lenkkeri 1999)ICA (Rusanen 2000)

Sn63Pb37 (Doi et al.1996)Sn63Pb37 (Dudeket al. 1997)Sn5Pb95 (Darveaux& Banerji 1991)

• Polymer/metal composite example: Isotropic Conductive Adhesive (ICA)

• Percolation

• Polymer cure

• Electrical properties

• Reliability:

• Drop test

• Galvanic corrosion

• Miscellaneous

• Magnetic alignment

• Flip chip underfill filler

• Nanoparticles

• ICAs

• Embedded components

• Carbon nanotubes (CNTs) & graphene

• Electrical & thermal

28-Oct-14

ICA: Conducts by percolation

Current path Powder

Flakes (Ag) Polymer

ICA: SMT Interconnect

Insulating

conducting

Percolation threshold

Site percolation modeling in a 12x12 array

40% 50% 55% 60%

65% 70% 75% 80%

Critical percolation

65% 65%+1 65%+2 Percolating Size Effect Cluster (70%) Middle 1/3 sections: 55% conducts 75% no conduction

28-Oct-14 10

Monte Carlo Percolation Models

(Smilauer)

Percolation Threshold: Size Effects & Dispersion

Averaged simulations

Reproducibility

small sizes

incr tolerances

higher Ag

Constable et al (Adhesives’98)

• Polymer/metal composite example: Isotropic Conductive Adhesive (ICA)

• Percolation

• Polymer cure

• Electrical properties

• Reliability:

• Drop test

• Galvanic corrosion

• Miscellaneous

• Magnetic alignment

• Flip chip underfill filler

• Nanoparticles

• ICAs

• Embedded components

• Carbon nanotubes (CNTs) & graphene

• Electrical & thermal

28-Oct-14 13

Polymer Cure Process

Log Time

Tem

pera

ture

Tg0

gelTg

Tg∞

Liquid

Sol/Gel Rubber Gel Rubber

Gel Glass

Char

Sol/Gel Glass Gelation

Vitrification

Complete Cure Vitrification

Devitrification

Tc>T∞

Tc<T∞

Sol Glass

DSC: Differential Scanning Calorimetry

Directly determine degree of cure α & rate of cure dα/dt

28-Oct-14 14

Use second DSC as measure of degree of cure -

∫1HdT/(∫1HdT+∫2HdT)

Delamination & Bubbles

Thermoplastic (Perichaud/Fremont)

Thermoset (Morris/Li)

• Polymer/metal composite example: Isotropic Conductive Adhesive (ICA)

• Percolation

• Polymer cure

• Electrical properties

• Reliability:

• Drop test

• Galvanic corrosion

• Miscellaneous

• Magnetic alignment

• Flip chip underfill filler

• Nanoparticles

• ICAs

• Embedded components

• Carbon nanotubes (CNTs) & graphene

• Electrical & thermal

28-Oct-14 17

Frequency Effects: Tunnel Gaps?

Percolation curves

AC Effects: Uncured ↓

Experimental: TCR Results

TCRICATCRAg

RICA RAg

Contact R negligible

Resistivities for various

temperatures.

(a) Brass stenciled CT-5047-02

thermoset sample (TCR-

0.0039/ºC).

(b) (b) CSM-933-65-1 screen

printed thermoplastic

sample {TCR=0.0038/ºC}

28-Oct-14 19

Frequency Effects: Skin Effect

R

L

This graph shows the linear

relationship between the

resistance at high frequencies

and the square root of

frequency

This figure exhibits the linear

relationship of the inductance

at high frequencies with f^.5

f

1/f

• Polymer/metal composite example: Isotropic Conductive Adhesive (ICA)

• Percolation

• Polymer cure

• Electrical properties

• Reliability:

• Drop test

• Galvanic corrosion

• Miscellaneous

• Magnetic alignment

• Flip chip underfill filler

• Nanoparticles

• ICAs

• Embedded components

• Carbon nanotubes (CNTs) & graphene

• Electrical & thermal

28-Oct-14 21

Impact Strength/Drop Test (Tong)

Adhesion tests passed

Devices fall off PWB if dropped

Large devices fail; small OK

No correlation between drop test results and adhesion strength testing

Complex shear modulus

Storage and loss moduli

Shear Stress & Strain Complex Shear Modulus

Shear stress =S/A Charge density =Q/A

Shear strain =a/h Electric field =V/d

= G = [Q = (A/d)V]

Elastic shear modulus Dielectric constant

G = G´ + iG´´ = ´ + i´´

Loss tangents:

tan = G´´/G´ tan = ´´/ ´

2

t

t

High tan by Tamb >Tg high CTE

28-Oct-14 23

Contact R 85/85: Au & Cu contacts

A on Au

A on Cu

C on Au

C on Cu

(Li & Morris)

28-Oct-14 24

Galvanic Corrosion

Electrode Reaction Normal Potential

Au - 3e- = Au3+ 1.50 v

Pt - 2e- = Pt2+ 1.20 v

Ag - e- = Ag+ 0.80 v

Cu - e- = Cu+ 0.52 v

H2O + O2 + 4e- = 4OH- 0.40 v

Cu - 2e- = Cu2+ 0.34 v

Pb - 2e- = Pb2+ - 0.13 v

Sn - 2e- = Sn2+ - 0.14 v

Ni - 2e- = Ni2+ - 0.25 v

ICA: Lee, Cho, & Morris, Proc. EMAP 2007 Ag-ICA performance comparison on Cu and

immersion-Ag PWB contacts

A1Cu2 B1Cu1 BiCu2 A1Cu1/All Ag

A3Cu2 B3Cu1 B3Cu2 A3Cu1/All Ag

185oC cure 185oC cure

170oC cure 170oC cure

B1Cu1 B1Cu2 A1Cu2 A1Cu1/All Ag

A3Cu1 A4Ag1 B3Cu1 A3Cu2/B3Cu2 3x Ag

• Polymer/metal composite example: Isotropic Conductive Adhesive (ICA)

• Percolation

• Polymer cure

• Electrical properties

• Reliability:

• Drop test

• Galvanic corrosion

• Miscellaneous

• Magnetic alignment

• Flip chip underfill filler

• Nanoparticles

• ICAs

• Embedded components

• Carbon nanotubes (CNTs) & graphene

• Electrical & thermal

Ramkumar & Srihari, Proc. ECTC 2008, pp. 225-233 Magnetic field alignment of Ag-coated Ni particles

Dendrites form from excess paste Particle alignment and voids Sancaktar: Ni rods

Nano-Silica Flip-Chip Underfill

0

2

4

6

8

10

12

0 25 50 75 100 125 150 175 200

Temperature, T (˚C)

Elast

ic M

odulu

s, E

(GPa

)

NUF1

UF1

Sun & Wong, ECTC’04

(Lall et al)

CTE/modulus reduction with less settling

Compare CTE mis-match: Si = 4-5 ppm/°C Ag = 20 ppm/°C Epoxy = 54 ppm/°C FR4 = 36 ppm/°C

Glass Transition Temperature

TG ↓

• Polymer/metal composite example: Isotropic Conductive Adhesive (ICA)

• Percolation

• Polymer cure

• Electrical properties

• Reliability:

• Drop test

• Galvanic corrosion

• Miscellaneous

• Magnetic alignment

• Flip chip underfill filler

• Nanoparticles

• Carbon nanotubes (CNTs) & graphene

Nanoparticle Composites (High surface/volume ratio →catalysts, etc)

Nanoparticles → single grain, no defects (Mallik) Incr surface area → incr adhesion

Percolation limits of different ICA filler particles

Added Ag more effective on conductivity as flakes or powder than as nanoparticles

28-Oct-14

Surfactants: 5% diacids

Without surfactant ↓

With surfactant ↓

[Wong et al, ECTC ’04 & ’06]

Nanoparticle Sintering

Nanoparticle Sintering

47/

(Ohring) dominatesdiffusion Surface3 7 :

2 5 : radius sphere & radiusneck

).(

RRXt

mndiffusionSurface

mndiffusionBulk

RX

wheretTAR

Xm

n

Sintering by surface self-diffusion, which is thermally activated, with net diffusion away from convex surfaces of high curvature.

Particle interior retains crystallinity (not melting)

Raut, Bhagat, Fichthorn, Nanostruct. Mater. 10(5) 1998, 837-851

Das et al, ECTC 2009, 591-598

Embedded Components

Embedded capacitors: C: Shrink area → shrink thickness for same C, i.e. µm scale → nm

TCC control of nanocomposite capacitors: High-k BaTiO3- & low-k BCB

[Abothu et al, ECTC’06]

Resistors (length L, width W, thickness t): R = (L/W)(ρ/t) = Number of squares x resistance/square Decrease t → increase R decrease power

Nanoparticle Charging: the Coulomb Block (Morris)

28-Oct-14 34

x0

r r+ s

E ( x )

-q Fx

srr

q

r

qE

1144

22

Spherical nanoparticles, radius r, separation s

Electrostatic charging energy:

Electrostatic charging energy

Field assistance

Net thermal barrier →0 for qV=∆E

↓

0.5nm 1nm 2nm 4nm

The Coulomb blockade effect, which requires an external field or thermal source of electrostatic energy to charge an individual nanoparticle, and is the basis of single-electron transistor operation

I-V characteristics of Crx(SiO)1-x

S u b s t r a t e

A l A l o r W

S i O 2

C r x ( S i O ) 1 - x

S u b s t r a t e

S i O 2

A l B o t t o m E l e c t r o d e

C r x ( S i O ) 1 - xS T M t i p

( a )

( b )

-5

-4

-3

-2

-1

0

1

2

3

4

5

1 3 5 7 9 11 13 15 17 19 21

Bias (mV)

Curr

ent (

nA)

120K77K250K

Electrical characteristics typical of Coulomb Blockade devices

Coulomb effects “wash out” at room temperature (thermal charging) unless nanoparticles ~ single-nm scale

(Wu & Morris)

RT ↔ 77K

• Polymer/metal composite example: Isotropic Conductive Adhesive (ICA)

• Percolation

• Polymer cure

• Electrical properties

• Reliability:

• Drop test

• Galvanic corrosion

• Miscellaneous

• Magnetic alignment

• Flip chip underfill filler

• Nanoparticles

• ICAs

• Embedded components

• Carbon nanotubes (CNTs) & graphene

• Electrical & thermal

37

Kyoung-Sik Moon et al, ECTC’08

(Kunduru et al)

Lee et al, ECTC’05

Carbon Nanotubes (CNTs): SWNTs & MWNTs

(Kureshi & Hasan, J. Nanomaterials 2009, ID 486979)

EMC Shielding MWCNTs (Cheng et al)

28-Oct-14 38

0

0.03

0.06

0.09

0.12

0.15

0.18

0.21

0.24

0 20 40 60Weight Percentage of CNT (%)

Ele

ctr

ica

l C

on

du

cti

vit

y(S

/cm

)

ADM CNT-LCP Composite

CVD CNT-LCP Composite

CNTs in LCP

Shielding Improvement (Ionic Liquid) at low CNT content (Jin-Chen Chiu, ECTC’08)

28-Oct-14

CNT Composites Conductivity

Oh et al, Nanotechnology, 19 (2008) 495602 (7pp)

Yan et al, Nanotechnology 2007

(Metallic) SWNT thermal expansion coefficient (Jiang et al, J. Eng Materials & Technology, 126 (2004) 265-270)

TSV reliability issues (Sinha et al, NMDC 2010)

a) Cu filled via at normal temperature

b) Copper expansion can fracture the oxide layer above

c) Delamination as a result of thermal cycling

Thermal Management in Microelectronics: Graphene & CNTs

Balandin, Advancing Microelectronics, 38(4) July/August 2011, 6-10

Thermal Interface Material (TIM) thermal conductivities

Graphene flakes

Graphene flakes & CNTs in polymers

• Polymer/metal composite example: Isotropic Conductive Adhesive (ICA)

• Percolation

• Polymer cure

• Electrical properties

• Reliability:

• Drop test

• Galvanic corrosion

• Miscellaneous

• Magnetic alignment

• Flip chip underfill filler

• Nanoparticles

• ICAs

• Embedded components

• Carbon nanotubes (CNTs) & graphene

• Electrical & thermal

Questions?