1. Polymers Hard at Work
in Your Smart Phone
Jeffrey T. Gotro, Ph.D.
President and Founder
InnoCentrix, LLC
949-635-6916
www.innocentrix.com

2. 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

3. Bell Labs versus Motorola
Martin Cooper
• 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

4. 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

5. Smart Phones pack a powerful punch
• Phone
• Email
• Video
• MP3 music player
• Camera
• High resolution
screens
Significant processing power in a small package

6. Multiple Electronic “Packages”
Package Types:
HTC Evo 4G • QFP
• QFN
• PBGA
• Flip Chip

7. 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

8. Polymers in Leadframe Packages
Depending on the metal leadframe used:
• Epoxy-based die attach adhesives
• BMI/acrylate die attach adhesives
QFN
Mold Compound
Die
Die attach adhesive
Lead finger Die Pad Lead finger
Mold compounds are typically epoxy-based

9. Multiple Polymers Used
Filled via’s Thermal Interface Laser drilled re-
Heat Spreader •Conductive Material distribution layers
•non-conductive
Epoxy lid
attach
Adhesive
Capillary Underfill
High density BT substrate soldermask
• 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

10. 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.

11. Polymers Can Have Many Forms
Linear
Branched
Crosslinked
or Network

12. Thermoplastic versus Thermoset
Polymer
Melt Polymer
Heat Cool Melt
Heat Chemical
Reaction
Solid Solid
X
Monomers
Crosslinked
and
Network
Polymer Oligomers
Cool Heat
Melt
• Polymer chains not linked • Polymer chains are crosslinked
• Melted by heating cycles • Stable on heating
12

13. Thermoset Polymers
Epoxy
CH3
Cyanate Ester N C O C
H
O C N
O O
Bismaleimide N R N
O O
Acrylate R

14. Examples of Different Network Structures
Epoxy Cyanate Ester Bismaleimide

15. Modulus vs Temperature for Polymers
Glass Transition
Melting Point
Log E, dynes/cm2
Log E, Pa
Temperature

16. 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

17. Thermosets Offer Wide Processing Range
Monomers/Oligomers Partially cured Fully Cured Network
• Low viscosity • B-staged • No flow
• Good flow/dispensing • Film-like properties • Tailored Tg depending
• Use various • Can still flow with on chemistry
monomers to tailor additional heat • High temp stability
properties • Controlled CTE
• Reactive diluents to
control viscosity

18. Epoxy is Most Common Thermoset
Adhesion, reactive Aromatic rings give high temperature
site, wettability performance and rigidity
Epoxy reactive site Epoxy reactive site
Molecular weight
Toughness
Bisphenol A epoxy; X=H, for tetrabromobisphenol A; X- Br

19. Types of Epoxies
Bis Phenol Epoxy
Epoxy novolac
Cycloaliphatic epoxy

20. 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

21. Die Attach Resin Technologies
Epoxy ring opening
• Epoxies, liquid epoxies
• Acrylate monomers, oligomers
Polymerize across
• Reactive diluents the double bond
– 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

22. Flow Curve – Uncured Filled Pastes
1.E+05
Yield Stress
Steady-state Viscosity, h (Pas) 1.E+04
network aggregates
1.E+03
84-1 LMISR4
Resin and
1.E+02
filler eqn.
Cross
Yield-stress
1.E+01 Resin discrete
particles
1.E+00
Resin is
1.E-01
Newtonian
1 10 100 1000
Shear Stress, s (Pa)

23. 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

24. 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!

25. Die Stacking Technology Progression
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
25

26. 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

27. 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

28. Multiple Die Stacks Use Film Adhesive
Flow Over Wire

29. Polymers in a Flip Chip Package
Underfill Chip Mold Compound
Solder Balls Laminate Substrate
• 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

30. 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

31. Polymers are Key Integration Enablers
Underfills
Thu-Via technology
- Laser friendly mold compound
Graphic: Yole Development
Integrated passive devices Redistribution layers (dielectrics)
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32. 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)

33. 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) ABF
substrates
 Laser drilled blind via’s BT Laminate
 BT Epoxy Core
 Build-up layers
ABF
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34. 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

35. BT Epoxy Chemistry
O O
N CH2 N Bis maleimide
O O
O N O
CH3
N C O C O C N N N
Cyclo-trimerization of
CH3 O bis-cyanate forming a
triazine network
O CH3 OH CH3 O
H2 H2 H2
H2C CH C O C O CH3 C C O C O C C CH2
H H
CH3 CH3
n
Multitude of epoxy resins enables a large formulation toolbox

36. 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)

37. 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)

38. Contact Info
Dr. Jeff Gotro
InnoCentrix, LLC
22431 Antonio Parkway
Suite B160-515
Rancho Santa Margarita, CA 92688
949-635-6916 (office)
jgotro@innocentrix.com
www.innocentrix.com