Nano Packaging and Interconnect Lab.

Thermosetting epoxy resin film Conductive particles + ACF =

Chip or substrate 1

Substrate 2

Heat

Chip or substrate 1

Substrate 2

Pressure

ACF

ACF

Anisotropic Conductive Films (ACFs)

Chip-on-Glass (COG) Chip-on-Flex (COF) Flex-on-Glass (FOG)

Flex-on-Board (FOB) Chip-on-Board (COB)

Applications

Nano Packaging and Interconnect Lab.

Background of Ultrasonic(U/S) ACF bonding

ACF heating mechanism

substrate 1

Substrate 2

ACF

U/S vibration

ACF resin

Vibration Internal friction in polymer

Heat generation

Nano Packaging and Interconnect Lab.

Thermo-compression vs. Ultrasonic

substrate 1

Substrate 2

ACF Heat conduction

T/C ACF bonding

Heating tool

U/S ACF bonding

substrate 1

Substrate 2

U/S horn

Local heat generation

Heating tool (200℃~250℃) ACF (180℃)

Heat

T/C ACF bonding U/S ACF bonding

Process temperature 200℃~250℃ Room temperature

Bonding time 10 ~15 sec 1 ~ 5 sec

Assembly productivity 1 > 3 times

Thermal deformation ↑ ↓

Patent issued

U/S horn (R.T.) ACF (300℃)

Nano Packaging and Interconnect Lab.

0 2 4 6 8 10 12 14

0

50

100

150

200

250

300

AC

F te

mpe

ratu

re

(oC

)

Bonding time (sec)

2 um

4 um

6 um

8 um

10 um

12 um

Longitudinal vibration

Power : 800W

Frequency : 40KHz

ACF

8 μm diameter Ni particles

40 μm thickness

U/S bonder

Flex-On-Board applications

PCB 0.8mm thickness FR-4

Pitch : 200, 300, 400, and 800um

Flexible PCB Polyimide film

Pitch : 200, 300, 400, and 800um

FPCB

PCB

ACF

Cu electrodes

Test vehicles

ACF temperature Bonding pressure: 3MPa Amplitude

Nano Packaging and Interconnect Lab.

Electrical resistance Peel adhesion strength

Flex-On-Board applications

Total daisy-chain resistance

1.0 1.5 2.0 2.5 3.010

12

14

16

18

20

22

24

26

28

30

40%

50%

60%

Bonding pressure (MPa)

Dais

y-c

hain

resis

tan

ce (

Oh

m)

Electrical

Continuity

X

Total daisy-chain resistance

Thermo-compression

150oC 2MPa 6sec

Stable at above 2MPa

Bonding time ≥ 1 sec at 3 Mpa

Max. Peel adhesion strength : ~ 1300gf/cm

0 1 2 3 40

200

400

600

800

1000

1200

1400

260oC

220oC

180oC

Pee

l ad

hesio

n s

tren

gth

(g

f/cm

)

Time (sec)

Cured

Nano Packaging and Interconnect Lab.

Reliability evaluation

Flex-On-Board applications

0 2 4 6 8 10 12 14 16 18 200

20

40

60

80

100

As-bonded

200 hrs

400 hrs

600 hrs

800 hrs

1000 hrs

Resistance ()

Cu

mu

lati

ve d

istr

ibu

tio

n (

%)

0 2 4 6 8 10 12 14 16 18 200

20

40

60

80

100

As-bonded

200 cycles

400 cycles

600 cycles

800 cycles

1000 cycles

Resistance ()

Cu

mu

lati

ve d

istr

ibu

tio

n (

%)

-40oC/100oC thermal cycling

1000 cycles

0

140 failures

0 2 4 6 8 10 12 14 16 18 200

20

40

60

80

100

As-bonded

200 hrs

400 hrs

600 hrs

800 hrs

1000 hrs

Resistance ()

Cu

mu

lati

ve d

istr

ibu

tio

n (

%)

85oC/85%RH test

1000 hrs 125oC storage test

1000 hrs

0

140 failures 0

140 failures

US bonded ACF joints showed stable electrical resistances

in -40/100oC TC, 85oC/85%RH, and 125oC storage tests.

Nano Packaging and Interconnect Lab.

0.0 0.5 1.0 1.50

20

40

60

80

100

120

140

160

180

200

220

240

AC

A t

em

pera

ture

(o

C)

Time (sec)

ACA(Anisotropic conductive adhesive)

Au coated polymer particles

ACF temperature

Touch Screen Panel applications

Test vehicles

Bonding area 5.5 ㎜ X 2 ㎜

PET

PC

42 ㎜

60 ㎜ 1.1 ㎜

0.4 ㎜

FPC (0.16 ㎜ thickness)

PET substrate

PC substrate

Ag electrode

Cu electrode

FPC(polyimide)

ACA

ACA

0.0 0.5 1.0 1.50

20

40

60

80

100

120

140

160

180

200

220

240

AC

A t

em

pera

ture

(o

C)

Time (sec)

1 MPa pressure

2 MPa pressure

12 ㎛ amplitude

10 ㎛ amplitude

8 ㎛ amplitude

12 ㎛ amplitude

10 ㎛ amplitude

8 ㎛ amplitude

Nano Packaging and Interconnect Lab.

Electrical continuity Pull adhesion strength

Touch Screen Panel applications

PET substrate

PC substrate

Ag electrode

Cu electrode

FPC(polyimide)

ACA

ACA Ω

60 80 100 120 140 160 180

0

500

1000

1500

2000

2500

3000

Pu

ll a

dh

esio

n s

tren

gth

(g

f)

ACA peak temperature (oC)

1 MPa

2 MPa FPC tearing

ACA joint failure

Strong adhesion

Poor adhesion

80 100 120 140 160

0

10

20

30

40

50

60

70

80

90

100

Sta

ble

elec

tric

al c

ontin

uity

rat

io (%

)

ACA peak temperature (o

C)

1 MPa

2 MPa

Stable resistance (< 250 Ω)

Unstable resistance (> 250 Ω or open

failure) Bonding time : 1 sec

Bonding pressure : 2 Mpa

Max. Pull adhesion strength : ~ 3000gf/cm

Bonding time 1 sec

Bonding time 1 sec

Nano Packaging and Interconnect Lab.

Cross-section image Reliability evaluation

Touch Screen Panel applications

Cu electrode(FPCB) Conductive ball

Ag electrode(PET)

FPC(Polyimide)

Cu electrode(FPCB)

Ag electrode(PC) Test 1 Test 2 Test 3 Test 4 Test 50

50

100

150

200

250

Resis

tan

ce (

Oh

m)

Before reliability test

After reliability test

Test 1 :

Thermal shock test (- 40℃/30 min ~ 80℃/30 min, 50 cycles)

Test 2 :

Salt spray test (35℃, 5% NaCl, 48 hours)

Test 3 :

High temperature and high humidity test (60℃/90% RH, 240 hrs)

Test 4 :

High temperature storage test (80℃, 240 hrs)

Test 5 :

Writing test (250 g, 200,000 times)

bonding conditions : 2 MPa pressure,

50% amplitude,

1 second

bonding conditions : 2 MPa pressure,

50% amplitude,

1 second

Nano Packaging and Interconnect Lab.

Potential application of U/S ACF bonding

Side keys Display Sensors Camera High power

LED backlit

Battery

Multi-functional mobile devices Ultra-thin appliances

Source : Apple Source : NOKIA Source : Samsung

Nano Packaging and Interconnect Lab.

Conclusions

U/S ACF bonding method was successfully demonstrated

in Flex-On-Board and Touch Screen Panel applications

U/S ACF bonding showed

sufficient adhesion strengths, contact resistances, and reliability

Future work

U/S bonding process optimization for various applications

: FOF (Flex-On-Flex), Camera module interconnection

Theoretical analysis on U/S heating mechanisms

Flex-On-Board Touch Screen Panel

Bonding time ≥ 1 sec

Adhesion strength ~ 1300 gf/cm

Daisy chain resistance ~ 16 Ω

Bonding time ≥ 1 sec

Adhesion strength ~ 3000 gf

Electrical continuity ~ 100%