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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%