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

• Email

• 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)

jgotro@innocentrix.com

www.innocentrix.com