ELECTRONICS

Development of Anisotropic Conductive Film for Narrow
Pitch Circuits
Hideaki TOSHIOKA*, Kyoichiro NAKATSUGI, Masamichi YAMAMOTO, Katsuhiro SATO,
Naoki SHIMBARA and Yasuhiro OKUDA

Anisotropic conductive film (ACF) is a film adhesive with conductive particles dispersed in thermosetting resin, and ismainly used for circuit board connection in the field of liquid crystal displays (LCDs), mobile phones, TVs, etc. Highperformance LCDs require advanced ACF that is applicable to the connection of circuit boards with narrow pitchelectrodes. We have developed a new ACF for the connection of circuit boards using our nickel nano straight-chain-likeparticle technology. This paper describes the performance of the newly developed ACF.
Keywords: ACF, LCD, nickel, nano particle, circuit board

1. Introduction
Anisotropic conductive film (ACF) is an adhesive filmwith conductive particles dispersed uniformly in thermosetting resin. Because ACF can connect electrodes by one-shotpressing, it is widely used for circuit board connection in
the field of flat panel display (FPD) manufacturing. Conventional ACF contains sphere-shaped nickel particles orAu-plated resin balls as conducting materials; in contrast,
the new ACF we have developed is composed of original
nickel nano straight-chain-like particles oriented verticallyto the film(1). In response to the increasing demand forhigher resolution FPDs such as three-dimensional (3-D)
image panels, an advanced connection technique for narrower pitch electrodes is increasingly required for flexible
printed circuits (FPCs) with glass substrates (Film on Glass:FOG) or FPCs with PCB substrates (Film on Board: FOB).
We have developed a new ACF for the connection of narrow pitch circuit boards by using our nickel nano straightchain-like particles. The performance of this ACF isdescribed in this paper.

Furthermore, lower pressure bonding has become possible
because the new ACF does not need to crush the sphereshaped conducting ball for bonding as the conventional
ACF does.

3. ACF for FOG Connection (SFG130)
3-1 Connection reliability and pressure margin of bonding
Initial connection performance and environmental
tests were performed to evaluate the FOG connection
between an FPC and a glass substrate with 100 µm-pitchelectrodes (Table 1). The bonding condition is shown in
Table 2. Cu electrodes on the FPC and indium tin oxide(ITO) electrodes on the glass substrate formed a daisychain. We measured the total resistance of the entire circuit
including the daisy-chained FPC and ITO, and calculated
resistance per electrode by dividing the total resistancevalue by the number of electrodes. Environmental tests

Table 1. Substrates for estimation (FOG)

2. Development Concept
Our nickel nano straight-chain-like particles were manufactured using our innovative liquid phase process basedon the plating technology of Sumitomo Electric Industries,Ltd(2). An adhesive resin was also designed to be applied tothese nickel nano particles. More particularly, the resin isdesigned to have higher adhesiveness to a flat surface glass
substrate in the FOG application while offering clean
removability with the use of a general solvent in the FOB
application so as to reuse the PCBs. We also aimed toreduce the content of conductive particles to one tenth ofthat of the conventional ACF by vertically orienting
straight-chain-like particles of 3 µm in length. This simultaneously leads to higher connection and insulation
performance than ever, and therefore connection of finerpitch electrodes has become possible with our new ACF.

40 · Development of Anisotropic Conductive Film for Narrow Pitch Circuits

FPCComposition

Cu/PI = 9/25 µm (Double layer)

Pitch

L/S = 50/50 µm

Number of electrodes 124 lines
MaterialGlass
Thickness (ITO)
substrate
Thickness (Glass)Non-alkali glass
2000 Å
0.7 mmt

Table 2. Bonding condition

Condition

Temperature

185 ~ 200°C × 8s

Pressure

About 3MPa

Heat tool

2.0 mm × 22 mm

ACF width

1.5 mmCushionSilicone (200 µmt)

Connection resistance [Ω]were performed by measuring the resistance change in ahigh-temperature (85°C) and high-humidity (85%RH)
environment, and in a thermal cycle (−40°C ↔ 100°C)
environment. The results are shown in Fig. 1 and 2. Initialresistance was very low (under 0.5 Ω including circuit resistance), and the resistance remained unchanged after
being exposed to a high-temperature and high-humidity
environment for 1000 hours or 1000 thermal cycles. This
result has proven that the new ACF (SFG130) has excellent
connecting reliability at 180 − 200°C. Moreover, bonding
pressure dependence on connecting reliability was evaluated at a fixed bonding temperature of 190°C (for 8 sec.)
as shown in Fig. 3. The new ACF, which does not require
crushing conductive balls, enables low pressure bonding(at 1 MPa) and bonding of weak substrates such as thinglass. We expect that the wide pressure margin of the newACF will facilitate quality control of products.

5.085°C85%RH, 3MPa

4.03-2 Fine-pitch connection
The minimum connection area was evaluated. As mentioned above, FPDs have become increasingly functionalized, and the electrode pitch in the connection area has
become narrow. Therefore, ACF that can connect electrodes in an area as small as 5000 µm2 is required. In orderto evaluate the connection performance of the new ACF
in a narrow area, the test substrates shown in Fig. 4 were
designed. We tested the connection performance at abonding temperature of 190°C (for 8 sec.), which is thestandard condition of SFG130. The result is shown in Fig. 5.
Initial resistance remained under 1.0 Ω at the electrodearea over 2000 µm2. This shows that SFG130 can connect
electrodes in a small area like IC bumps. As the use ofSFG130 enables smaller area and narrower pitch connection, it may contribute to the downsizing of electronic devices and the cost reduction of such devices.

Glass substrate

200°C × 8s
190°C × 8s
180°C × 8s

AIelectrodes

L/S = 50/50µm

3.0Connection
area

2.0
1.00.0Cu/Auelectrodes
0200

400600800

1000

Exposure time [hour]

VFig. 1. Connection reliability at high temperature and humidity

FPCA

-40

4.0100°C, 3MPa

200°C × 8s
190°C × 8s
180°C × 8s

3.0
2.0
1.00.002004006008001000

Number of exposure cycle

Fig. 2. Connection reliability in thermal cycle test

Connection resistance [Ω]Connection resistance [Ω]Fig. 4. Substrates for estimation
5.0

5.0
4.0

190°C, 8s, 3MPa

3.0
2.0
1.0
0.0
1000

2000

3000

4000

5000

Connection area [µm ]Connection resistance [Ω]25.0

Fig. 5. Minimum connection area (FOG)
85°C85%RH, 190°C, 8s

4.0

3MPa
2MPa
1MPa

3.0
2.0
1.0
0.00200

400

600

800

Exposure time [hour]Fig. 3. Estimation of pressure dependence

1000

3-3 Evaluation for connection of large-size panel electrodes
In large-size panel bonding, multiple FPCs are bonded
simultaneously with a large press machine using a long
heating tool. However, it is difficult to ensure the flatnessof the bonding surface, and microscopic inclination of theheating tool or foreign objects in the connection area cancause failure in bonding. Expecting that a wider range ofbonding pressure margins of the new ACF can work effectively for a reliable connection, we have applied this ACF

SEI TECHNICAL REVIEW · NUMBER 73 · OCTOBER 2011 · 41to the one-shot bonding of large-size electrodes for large
panels. To evaluate the one-shot bonding process for wide
panels, we used a new glass substrate on which five FPCs
can be connected (Fig. 6). The bonding condition in thetest was shown in Table 3, and the connection resistanceof areas A ~ E was measured by the same method shown in
3-1 Furthermore, we evaluated the changes of resistance ina high-temperature (85°C) and high-humidity (85%RH)
environment. The result shown in Fig. 7 indicates that
unevenness depending on the bonding position is trivialand resistance during the environmental test is stable.
Thus, we confirmed that SFG130 has a superior connection
performance for large-size panel bonding.

the SFG130 evaluation test. A PCB substrate and an FPC,
on which 200 µm-pitch electrodes were formed, were prepared (Table 4). Initial resistance at the bonding condition(Table 5) and changes of resistance in a high-temperature(85°C) and high-humidity (85%RH) environment wereevaluated. The result shown in Fig. 8 indicates that resistance remained low throughout a wide range of bondingpressure between 1 and 5 MPa. Thus, we have confirmedthat SFB130R has a wide pressure margin in the same manner with SFG130. It is expected that SFB130R’s wide bonding margin will improve productivity by enabling low
pressure bonding in connecting thin or weak substrates.

Table 4. Substrates for estimation (FOB)
288mm

Composition

Glass substrateA

Cu/PI/ = 18/25 µmt (Double layer)

FPC Pitch
BCDPIEFPC

L/S = 100/100 µm

Number of electrodes 80 lines

Electrodes

PCBFig. 6. Substrates for estimation of large size panel

Material

Glass fiber reinforced epoxy

Composition

Cu/FR-4 = 25/600 µm

Table 3. Bonding condition

Connection resistance [Ω]Main bonding

5.075°C × 1s

Pressure

About 1MPa

Heat tool

2.0 mm × 30 mm
Condition

Pressure

1 ~ 5 MPa

Heat tool

2.0 mm × 22 mm

CushionSilicone (200 µmt)

ACF width

1.5 mmTemperature

190°C × 8s

CushionSilicone (200 µmt)

Pressure

About 3.5MPa

Heat tool

1.5 mm × 530 mm

CushionSilicone (200 µmt)

AB
CDE

3.0
2.00.1

85°C85%RH, 180°C, 10s

0.08

1MPa
2MPa
3MPa
4MPa
5MPa

0.060.040.0201.00.0

180°C × 10s

1.2 mm

85°C85%RH, 190°C, 8s

4.0

Temperature

ACF widthConnection resistance [Ω]Pre bonding

Table 5. Bonding condition

Temperature

02004006008001000

Exposure time [hour]
0200400600800

Fig. 8. Connection reliability at high temperature and humidity

1000

Exposure time [hour]Fig. 7. Result of estimation with long heat tool

4. ACF for FOB Connection (SFB130R)
4-1. Connection reliability and pressure margin of bonding
We evaluated connection reliability of the ACF for
FOB connection (SFB130R) by the same method used in4-2 Fine-pitch connection
The target connection area in FOB applications islarger than that in FOG applications. We measured theresistance of the minimum connection area by shifting theFPC intentionally. We used the same substrates describedin 4-1 in the condition of 180°C and 3 MPa for 10 sec. as
the SFB130R standard condition. Although the connection
area is limited to 27,000 µm2 due to the influence of substrate size and machine performance, connection resistance

42 · Development of Anisotropic Conductive Film for Narrow Pitch Circuits

In order to evaluate the reusability of the cleaned PCB, theFPC was bonded again by using the ACF in the same condition as shown above and its initial connection resistanceand changes in connection resistance were measured in ahigh-temperature (85°C) and high-humidity (85%RH)
environment. The result shown in Fig. 10 indicates that theresistance of the repaired ACF remained almost unchanged. Thus, we confirmed that this substrate can bereused after some simple repair work and SFB130R is environment-friendly.

Connection resistance [Ω]was maintained sufficiently low in the area over 27,000 µm2.
Therefore, we believe that SFB130R has a great potential
for pine-pitch connection, just as SFG130 does.
4-3 Insulation performance
In the use of electronic devices, short circuits mayoccur due to the isolation of metal ions from the electrodesof substrates caused by ACF impurities. With the aim ofpreventing this problem, we tested the insulation performance between the electrodes. We prepared an FPC and a
PCB on which comb-shaped electrodes were formed. Inthe condition of 180°C and 3MPa (for 10 sec), they werebonded to each other with the FPC shifted 50 µm from thePCB. Then we noted any changes in insulation resistance
while continuously applying a DC voltage of 15 V to theneighboring electrodes in a high-temperature (85°C) andhigh-humidity (85%RH) environment. The result is shownin Fig. 9. Although the condition was too harsh for the conventional ACF to clear, with the new ACF no ion-migration
occurred, and its insulation resistance remained over 1G Ωfor 500 hours. This result means that our ACF has superior
insulation reliability.

0.1

85°C85%RH, 180°C, 10s, 3MPa0.08
0.06
0.04
0.02
00100200300

400500Connection resistance [Ω]Exposure time [hour]
1.0E+12Fig. 10. Connection reliability of recycle substrates

85°C85%RH, 180°C, 10s, 3MPa

1.0E+11
1.0E+101.0E+09
1.0E+08

5. Conclusion

1.0E+07
1.0E+06

0200

400600800

1000

Exposure time [hour]Fig. 9. Insulation reliability at high temperature and humidity

4-4. Repair performance
In general, PCB substrates use expensive electronicparts, and therefore, re-usability of these parts is desired incase of bonding failure. In light of this, we evaluated therepairability of the new ACF and the connection reliabilityof substrates to be reused. After bonding the substrates (described in 4-1) in the condition of 180°C and 3MPa (for 10sec.), the FPC was peeled off by using heat from a fanheater, and then the residue of ACF resin on the substrates
was removed with a solvent-impregnated wiper (Table 6).
It took only 3 minutes to completely remove the residue.

We have developed a new ACF for substrate connection by applying our specialized techniques for manufacturing of nickel nano particles, vertical orientation andresin design. We confirmed that SFG130 can effectivelywork for small area bonding (about 2,000 µm2) and low
pressure bonding (1 MPa), and that it offers a stable connection for panels in various sizes. We also confirmed that
SFB130R can be used for bonding at a wide range of pressure and that it enables substrates to be reused after some
simple repair work.
We are currently producing fine substrates with a pitchof less than 30 µm. We are also planning to investigate theperformance limitations of SFG130 and nickel nanostraight-chain-like particles.

Technical Term

*1 FPC (Flexible printed circuit): An FPC is a flexible cirTable 6. Repair method

Peeling offResidue
removalEquipment

Fan heater

Solvent

AcetoneTool

Non-woven textile fabrics

Temperature

Room temp.

TimeAbout 3min.

cuit on which metal electrodes are formed. It can beeasily bent.
*2 PCB (Printed circuit board): In contrast to an FPC, a
PCB is a rigid circuit board on which metal electrodes
are formed. It is also called a rigid substrate.

SEI TECHNICAL REVIEW · NUMBER 73 · OCTOBER 2011 · 43

(1)(2)

References
Hideaki Toshioka, Motoo Kobayashi, Keiji Koyama, Kyoichiro
Nakatsugi, Tetsuya Kuwabara, Masamichi Yamamoto and HidekiKashihara, "Development of Anisotropic Conductive Film with
Straight-chain-like Nickel Nano Particles," SEI Technical Review,
p.58-61, No.62 (2006)
Masatoshi Majima, Keiji Koyama, Yoshie Tani, Hideaki Toshioka,
Misako Osoegawa, Hideki Kashihara and Shinji Inazawa, "Development of Conductive Material Using Metal Nano Particles," SEI Technical Review, p.6-80, No.160 (2002) (in Japanese)

Contributors (The lead author is indicated by an asterisk (*).)

H. TOSHIOKA*• Assistant Manager, Electronics & Materials
R&D Laboratories
He is engaged in the research and development of anisotropic conductive films.

K. NAKATSUGI• Assistant Manager, Electronics & Materials R&D Laboratories

M. YAMAMOTO• Assistant Manager, Electronics & Materials R&D Laboratories

K. SATO• Assistant General Manager, Electronics Components
Department, Electronics Business Unit

N. SHIMBARA• Manager, Electronics & Materials R&D Laboratories

Y. OKUDA• Ph. D
General Manager, Electronics & Materials R&D Laboratories

44 · Development of Anisotropic Conductive Film for Narrow Pitch Circuits