Polymer Composites for Electronics Packaging...
Transcript of Polymer Composites for Electronics Packaging...
Polymer Composites for Electronics Packaging Applications
James E. Morris, Portland State University, Oregon USA
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
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ICA: Isotropic Conductive Adhesives
ICA: Flip Chip Interconnect
Bi-modal distribution
e.g.
10μm diameter flakes (<1μm thick)
plus
1-3μm diameter powder (spheres)
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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
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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
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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
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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
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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}
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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
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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
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Contact R 85/85: Au & Cu contacts
A on Au
A on Cu
C on Au
C on Cu
(Li & Morris)
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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
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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)
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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)
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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?