Polymers Hard at Work
in Your Smart Phone
Jeffrey T. Gotro, Ph.D.
President and Founder
InnoCentrix, LLC
949-635-6916
www.innocentrix.com
Dr. Jeffrey Gotro
• Over 30 years experience in
polymers in electronics (IBM,
AlliedSignal, Honeywell, Ablestik
Labs)
• Recognized expert in thermosetting
polymers
• Ph.D. in Materials Science from
Northwestern University, specialty in
polymer science/ polymer physics
• Founded InnoCentrix in 2008
– Technical and management consulting
in thermosets/electronic materials.
2
Bell Labs versus Motorola
• Inventor of the cellular phone at
Motorola
• First person to make a call on a
portable cell phone on April 3,
1973 from the corner of 56th and
Lexington in New York City
• The first call he made was to his
rival, Joel Engel, Bell Labs head
of research.
Bell Labs and Motorola were in a race to introduce the first
cellular telephone
Martin Cooper
First Cell Phone (1973)
Name: Motorola Dyna-Tac
Size: 9 x 5 x 1.75 inches
Weight: 2.5 pounds
Display: None
Number of Circuit Boards: 30
Talk time: 35 minutes
Recharge Time: 10 hours
Features: Talk, listen, dial
Smart Phones pack a powerful punch
• Phone
• Video
• MP3 music player
• Camera
• High resolution
screens
Significant processing power in a small package
Multiple Electronic “Packages”
Package Types:
• QFP
• QFN
• PBGA
• Flip Chip
HTC Evo 4G
Uses of Polymers in Packaging
• Die attach adhesives (glue computer chips to carriers)
– Conductive
– Non-conductive
– Dispensable paste and film formats
• Underfills (flow under chips)
– Capillary and wafer level (no-flow)
• Mold compounds (encapsulate chips)
• Laminate substrates (circuit connections)
– Base laminate
– Printed circuit boards
• Camera Modules
– Various types of adhesives
Polymers in Leadframe Packages
Mold Compound
Die attach adhesive
Die Pad
Die
Lead finger Lead finger
Depending on the metal leadframe used:
• Epoxy-based die attach adhesives
• BMI/acrylate die attach adhesives
Mold compounds are typically epoxy-based
QFN
Multiple Polymers Used
• Polymer film redistribution layers
•Bis-maleimide triazine epoxy (BT) laminate used in flip chip
substrates
• Epoxy/acrylate soldermask
• Silicones/thermal greases in TIM materials
• Epoxy or cyanate ester/epoxy used in capillary underfills
soldermask
Laser drilled re-
distribution layers Filled via’s
•Conductive
•non-conductive
Epoxy lid
attach
Adhesive
Thermal Interface
Material Heat Spreader
High density BT substrate Capillary Underfill
What is a Polymer?
From the Greek word poly – meaning many and meros –
meaning units
Merriam – Webster online dictionary;
“A chemical compound or mixture of compounds formed by
polymerization and consisting essentially of repeating
structural units.”
As we will see, polymers gain their unique and useful
properties by being long molecules with specific chemical
repeat units.
Polymers Can Have Many Forms
Branched
Crosslinked
or Network
Linear
Thermoplastic versus Thermoset
12
Polymer Melt
Solid
Polymer Melt
Solid
Cool
Heat
Heat
Cool
• Polymer chains not linked
• Melted by heating cycles
Polymer Melt
Crosslinked Network
Monomers and
Oligomers
Heat Chemical
Reaction
X
• Polymer chains are crosslinked
• Stable on heating
Thermoset Polymers
Epoxy
Acrylate
Cyanate Ester
Bismaleimide N
O
O
N
O
O
R
CH
O
CH3
OCN C N
R
Examples of Different Network Structures
Epoxy Cyanate Ester Bismaleimide
Modulus vs Temperature for Polymers
Temperature
Log
E, dyn
es/
cm2
Log
E, Pa
Glass Transition
Melting Point
Polymers in Semiconductor Packaging
There are some tough material requirements
• Low viscosity to flow (die attach and underfills)
• Wide range of cure profiles
– Thermal (oven, snap and spot cure) and UV cure
– Partial cure (B-stage) for printable pastes and films
• Tailored modulus depending on the application
• Low coefficient of thermal expansion
• High temperature stability for lead-free reflow profiles
• Low moisture absorption
Thermosets Offer Wide Processing Range
Monomers/Oligomers
• Low viscosity
• Good flow/dispensing
• Use various
monomers to tailor
properties
• Reactive diluents to
control viscosity
Partially cured
• B-staged
• Film-like properties
• Can still flow with
additional heat
Fully Cured Network
• No flow
• Tailored Tg depending
on chemistry
• High temp stability
• Controlled CTE
Epoxy is Most Common Thermoset
Bisphenol A epoxy; X=H, for tetrabromobisphenol A; X- Br
Epoxy reactive site
Aromatic rings give high temperature
performance and rigidity
Molecular weight
Adhesion, reactive
site, wettability
Toughness
Epoxy reactive site
Types of Epoxies
Bis Phenol Epoxy
Epoxy novolac
Cycloaliphatic epoxy
Die Attach Adhesives
• Die attach adhesives are typically needle dispensed
– Rheological (flow) properties are critical
– Shear thinning, yield point
• Base resins are typically monomers and oligomers
• Reactive diluents used to lower viscosity, but react
into the adhesive during curing
• Additives
– Adhesion promoters, conductivity promoters
– Curing agents, catalysts
• Fillers used to tailor properties
– Silver flake for electrically conductive adhesives
– Silica for non-conductive adhesives
Die Attach Resin Technologies
• Epoxies, liquid epoxies
• Acrylate monomers, oligomers
• Reactive diluents
– Acrylates and methacrylates
• Bismaleimides (aliphatic, low viscosity)
• Hybrid resins
– Dual functionality (i.e. epoxy on one end and acrylate or
bismaleimide on the other end)
– Useful for controlling dual network formation
Polymerize across
the double bond
Epoxy ring opening
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1 10 100 1000
Shear Stress, s (Pa)
Ste
ad
y-s
tate
Vis
cosity, h
(P
as)
84-1 LMISR4
Cross eqn.
Yield-stress
Resin
Flow Curve – Uncured Filled Pastes
network aggregates
discrete
particles
Resin and
filler
Yield Stress
Resin is
Newtonian
Everyday Example of a Yield Point
• With the old-style glass ketchup bottle, what happened
when you turned it upside down?
– No flow to your burger! (has yield point due to structure)
– Hit the bottom of the bottle (apply stress to overcome the yield
point)
– If that failed, use a knife to stir the ketchup (break-up the
structure and lower the yield point)
– Flows OK onto burger
New Design
• Squeeze bottle to apply stress
• Overcome the yield point and get good flow
• Shear fields in nozzle break up structure and
lower viscosity
Good Flow To
Burger!
Die Stacking Technology Progression
25
Started with paste die attach
(using standard dispense tools)
Migrated to film die attach (with
bundled dicing tape, film
thickness down to 20 µ)
Moving to wafer backside coated
(WBC) die attach for 10 µ thickness
Die Attach Film Adhesives
• Die stacking is main use for film-based
die attach
• Need precise control of bondline
thickness
• Chemistry is based on epoxies and
polyimides
Flow Over Wire (FOW)
• Rheological properties are modified
to allow the resin to flow over and
encapsulate the wires
• Same base chemistries used, but
formulations are optimized for proper
B-stage, flow and wetting around
wires
Multiple Die Stacks Use Film Adhesive
Flow Over Wire
Polymers in a Flip Chip Package
• Underfills are typically epoxy-based, but some cyanate ester
underfills are used for fast flow
• Bismaleimide/triazine/epoxy (BT-Epoxy) is typically used for
the multilayer substrates used in semiconductor packages
• Epoxy and acylates are used in the soldermask used to
define the pads and protect the substrate surface
Underfill
Laminate Substrate Solder Balls
Chip Mold Compound
Underfill Processing
• Underfill dispensed
around edge of chip
• Surface tension and
capillary action draw
resin under chip
• Need tailored rheology
to get fast flow
• Need high filler
loading for low CTE
• Leads to a design
challenge!
Video Courtesy of Asymtek, Carlsbad, CA
Polymers are Key Integration Enablers
31
Graphic: Yole Development
Thu-Via technology
- Laser friendly mold compound
Underfills
Integrated passive devices Redistribution layers (dielectrics)
Mold Compound Technology
• Epoxy cresol nolovak mold compounds (EMC) – Phenol novolak cured
– Ease of processing, flow, molding
– Good adhesion, small shrinkage
– Chemical and moisture resistance
• Biphenyl mold compounds – Low viscosity for wire sweep control
– High filler loading
– Lower moisture absorption
• Multifunctional mold compounds – Mixture of biphenyl and multifunctional resins
– High Tg
– High filler content (rounded fused silica)
Laminate Substrate Types
• Double-sided
– Typically used in wire-bonded
applications
– Largest volumes
• Multilayer
– Used for higher end packages
– Required for flip-chip
– High Density Interconnect (HDI)
substrates
Laser drilled blind via’s
BT Epoxy Core
Build-up layers
BT Laminate
ABF
ABF
33
Substrate Materials
• Primarily BT resin (Mitsubishi Gas Chemical)
– Bismaleimide/cyanate ester (triazine)/epoxy blend
• Hitachi Chemical and Mitsui
– Hitachi EN 679 (high Tg epoxy based)
– Mitsui BN 300 ( 300°C Tg, bismaleimide-based)
• Filled PTFE composite with low Dk/Df (Rogers)
– Endicott Interconnect Technologies (EIT) in volume production
• Liquid Crystal Polymers
– Under development, lower moisture absorption, low Dk/DF
BT Epoxy Chemistry
C
CH3
O CH3 CH
CH3 OH
H2
C OOCHH2C
O
H2
C
n
C
CH3
CH3
CH2CH
O
OH2
C
CH2N
O
O
N
O
O
C
CH3
O
CH3
OCN C N N N
N O
O
O
Bis maleimide
Cyclo-trimerization of
bis-cyanate forming a
triazine network
Multitude of epoxy resins enables a large formulation toolbox
Cell Phone Camera Module
Four different adhesives in a
camera module:
1. Conductive die attach adhesive
2. Bonding adhesive for protective
glass cover sheet (prevent
damage to optical sensor chip)
3. Housing adhesive
4. Lens lock adhesive (UV cured
after lens is focused during
assembly)
Summary
• Polymers are key enabler in semiconductor packaging
• Thermosets are extensively used
– Low viscosity to enable dispensing
– Fast curing with heat or light (UV)
– Can be partially cured (B-staged) to enable unique film processing
– Tailored to form crosslinked networks with a wide range of
properties
– Easy to formulate with other ingredients (silver, adhesion
promoters, silica fillers, etc)
– High temperature stability (lead-free reflow)
– Good mechanical properties (Modulus vs. Temperature)
Contact Info
Dr. Jeff Gotro
InnoCentrix, LLC
22431 Antonio Parkway
Suite B160-515
Rancho Santa Margarita, CA 92688
949-635-6916 (office)
www.innocentrix.com