ThreeBond Technical News
Issued Jan. 1, 201075

Screen Printable Anisotropic Conductive Paste(ACP)
Introduction ________________________________________________
ThreeBond’s Anisotropic Conductive Paste (ACP) is a liquid material consisting ofelectroconductive particles uniformly dispersed within a highly-insulating adhesive component. A
functional material, ACP produces an anisotropic conductive film through application and drying inthe screen-printing process. It is capable of achieving all three of the following actions at a physicaljunction through a heat press process for several ten seconds: (1) forming an electric connection
between electronic components; (2) retaining insulation between adjacent electrodes; and (3) bonding
and fixing.
ThreeBond has pursued research and development related to ACP for the past 30 years, introducing
products that have drawn wide acclaim in markets for heat seal connectors, display devices, cell phonebacklights, membrane switches, and touch panels, among others. During this time, the development of
increasingly advanced high-function electronic components has significantly altered expectations for
ACP. In addition to high reliability and functionality, the market now demands increased usability,
increased storability over extended periods, and compatibility with environmental standards that
require, for example, halogen-free*1 and toluene-free products.
This issue discusses the traits that distinguish our ACP from other connector materials and argues for
ACP’s superiority. It also introduces products (the ThreeBond3373 series) developed to comply withmarket demands and environmental requirements.
*1: Chlorine < 900 ppm, bromine < 900 ppm, chlorine + bromine < 1,500 ppm
Hereafter, ThreeBond will be abbreviated to “TB.”

Contents
Introduction .................................................................1
1. The ACP concept and market trends .....................2
2. TB3373 series product lineup ................................3
2-1. Features of the TB3373 series .......................3
2-2. Properties of TB3373 series...........................3
2-3. Characteristics of TB3373 series ...................3
2-4. Special notes ..................................................3
2-5. Reliability data ................................................4
2-5-1. Electrical connection reliability....................4
2-5-2. 90 peel strength ........................................4

2-5-3. Creep test................................................... 5
2-5-4. Storability of dried film for TB3373F ........... 6
3. Points to note when designing the
manufacturing process .......................................... 6
4. How to use TB3373F ............................................. 7
4-1. Printing conditions.......................................... 7
4-2. Standard drying conditions............................. 7
4-3. Pressure bonding conditions.......................... 7
Conclusion .................................................................. 8

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1.

The ACP concept and market trends

As described before, anisotropic conductive paste
is a liquid material with electroconductive particles
uniformly dispersed in a highly-insulating adhesivecomponent. This material makes it possible toachieve connections along the Z-axis, insulation
betweenadjacent
electrodes,
andsubstrate-to-substrate adhesion, all through a simple
heat press process involving temperatures elevatedabove 120C for 10 seconds.

 Connecting membrane substrates in personal
computers
In general, anisotropic conductive connectormaterials fall into one of two basic categories: paste
or film (Anisotropic Conductive Film: ACF). The
following table compares the characteristics of ACP
and ACF.
Table 1. ACP/ACF comparison

Anisotropic conductive paste (ACP)

ACP

Item

Screen printing
machineFacility

Drier
Substrate

Fig. 1.

Electrode

Connection concept underlying
anisotropic conductive pasteDue to their high usability, ThreeBond’s ACP
products have been adopted for use across a wide
range of electronic components. One representative
application involves connecting touch panel
substrates. At the start of the 1990s, our ACP was
adopted for use in pen-based electronic notepads.
Thereafter, it was adopted for use in various mobile
devices, including portable game units, cell phones,
portable audio devices, and digital cameras. The
growing preference for touch panel systems asinterfaces for machines such as ticket-vending
machines has made ACP essential in the electronic
devices that provide the various functions
supporting our daily lives.
We are currently seeing dramatic growth indemand for ACP in the East Asia region, includingSouth Korea, China, and Taiwan, countries at theforefront of the global production of electronic
devices. In response to growing demand for
eco-friendly materials in recent years, ThreeBondhas developed and introduced products with
reduced chlorine and bromine content that meet
halogen-free standards.
 Representative applications
 Connecting touch panel substrates in mobile
devices Connecting distributed-type inorganic EL
backlight elements

Heat press machine

Separator winding unit
Heat press machine

Three-step process(1) Screen printing(2) Drying (deposition)
Number of steps(3) Final pressure
required to establish
bonding
connection

The wide temperature
range of the pressurebonding improves
manageability.
Thermoplastic
elastomer

Five-step process(1) Cutting(2) Pasting(3) Preliminarypressure bonding(4) Separator peeling(5) Final pressurebonding
RequiresManagement of heat management of bothtemperature and timepress process(complete heat curing)
Epoxy resin (heatMajor component
curing)Approx. 1/10 of ACF

Material cost-

Refrigeration

Storage condition

Refrigeration or
freezing

3 to 6 months

Storability of film

Three days at room
temperature after
application

120 to160C

Pressure bonding
temperature

150C or above

Excellent

PET adhesiveness

Adequate

Good(compliant productavailable)

Halogen-freeCompatible withnarrow pitch
0.2-mm pitch (current)

Technical issues

None(derived from epoxy
resin)
Extended shelf life ofmaterial and productImproved PET
adhesivenessHigh reliability

As Table 1 suggests, ACP offers the benefits oflow production costs, fewer steps in the
manufacturing process, reduced production times,
and low-halogen content meeting environmental
standards.

Liquid crystal

Heat seal connector
component

Connecting EL backlight elements
Anisotropic conductive
paste TB3373C

Fig. 2. Representative examples of ACP application

2

ACF
Preliminary pressurebonding unit

2.

TB3373 series product lineup

TB3373C is widely used in the electronic device
market, mainly in touch panel systems to connect
and bond FPC/touch panel substrates.
In addition to the features (1) to (5) listed to theright, TB3373C owes its wide acceptance to therecognition of its various characteristics, including
low temperature and short processing times, film
storability, low production costs (due to lower
component costs and fewer process steps), and highreliability.
Demand for halogen-free products has increased
sharply in recent years. ThreeBond has responded
swiftly to this demand, introducing the TB3373E in2009. TB3373E is free of both halogen and toluene.
Additionally, we now offer a new product, theTB3373F, which offers the higher reliability andimproved printability and storability of dried film.
2-2.

2-1. Features of the TB3373 series(1) Deposition is carried out by screen printing sothat the formed adhesive film closely follows
the contours of the adherend surface.
(2) Any number of contact points can be connected
in a single process.
(3) Allows bonding to surfaces such as transparent
conductive glass, which cannot be joined withsolder.
(4) For permanent bonding, unlike conductive
rubber or metal-wire reinforced rubber, theTB3373 series requires no pressure after initialadhesion.
(5) Compared to conventional products, the TB3373
series offers improved adhesion to film
materials and can be used with a wider range ofadherends.
(6) TB3373E and TB3373F comply withhalogen-free and toluene-free standards.

Properties of TB3373 series
Table 2. Properties of TB3373 series
Items

Unit

TB3373C

TB3373E

TB3373F

Major component-

Synthetic-rubber-based Synthetic-rubber-based Synthetic-rubber-based
resin
resin
resin
Toluene, isophorone

Isophorone

Notes

Solvent-

Conductive particle-

Aromatic solvents

External appearance-

Pale yellowish-green

Grayish white

Grayish white

3TS-201-02

Viscosity

Pas

75

95

60

3TS-210-10*1

Specific gravity

-

1.01

1.04

1.08

Gold-plated particles

3TS-213-02*1: Shear rate: 10.0 (1/s)

2-3.

Characteristics of TB3373 series
Table 3. Characteristics of TB3373 series
Items

Unit

TB3373C

TB3373E

TB3373F

Notes

Connection resistanceLess than 1

Insulation resistance

109 or greater

3TS-403-01

90 peel strength

N/m

800 or greater*2

3TS-304-42

Four-terminal
resistancemeasurement*2: ITO glass/PET film

2-4.

Special notes
Table 4. Special notes on the TB3373 series
Items

Unit

TB3373C

TB3373E

TB3373F

Solution storability-

Refrigerated for 6
monthsRefrigerated for 6
monthsRefrigerated for 6
monthsStorability after
deposition-

Left to stand at room
temperature for 6
monthsRefrigerated for 3
monthsLeft to stand at room
temperature for 6
monthsCompliance withhalogen-freestandards

-





Compliance withtoluene-free standards

-





Notes

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2-5. Reliability data
ACP is often perceived to exhibit poor heat cycle
performance. However, as the following graphs
show, any changes from initial values in various

accelerated tests are negligible. Tests confirm that
the TB3373 series provides the reliability needed.

2-5-1.

2-5-2.

Resistance []Time of test [h]Fig. 6.

Resistance []Peel strength [N/m]Time of test [h]Fig. 3. Change in resistance when left at 85C

Fig. 7.

Resistance []Time of test [h]Fig. 5.

4

Change in 90 peel strength whenleft at 60C  95%RH

Peel strength [N/m]Change in resistance when left at
60C  95%RH

Change in 90 peel strength whenleft at 85CTime of test [h]Time of test [h]Fig. 4.

90 peel strength

Peel strength [N/m]Electrical connection reliability

Change in resistance in heat cycles
consisting of 30 minutes at each of
two temperature extremes, -40Cand 85CTime of test [h]Fig. 8.

Change in 90 peel strength in heat
cycles consisting of 30 minutes at
each of two temperature extremes,-40C and 85C

Table 5. Conditions for electrical connection reliability test
Test specimen composition

FPC

25-m-thick polyimide film/35-m-thick gold-plated copper foil, 0.4-mm pitch (L/S =0.2 mm/0.2 mm)

Glass

ITO sputtering vapor deposition on soda lime glass, 60 mm  25 mm  0.7 mm, sheet
resistance 20 to 50 /cm2(1) 85C (2) 60C  95%RH (3) Heat cycle (heat cycles consisting of 30 minutes
at each of two temperature extremes, -40C and 85C)

Environmental conditions

Model 34980A multifunction switch/measure unit (Agilent Technologies International Japan, Ltd.)

Table 6. Conditions for 90 peel strength test
Test specimen composition

38-m-thick PET film/ITO-coated soda lime glass

Environmental conditions(1) 85C (2) 60C  95%RH (3) Heat cycle (heat cycles consisting of 30 minutes
at each of two temperature extremes, -40C and 85C)

Tension speed

50 mm/min

Model RTC-1210A universal tensile and compression testing machine (Orientec Co., Ltd.)

2-5-3. Creep test
Our company uses the creep test to test products
under conditions that closely approximate those of
actual use. In a creep test, the peel distance ismeasured after subjecting the sample to a constantload along the axis of the peeling at 85C (Fig. 9).
ITO-coatedglass

The TB3373F showed no signs of air bubble
formation when left under the same conditions for
1,000 hours.
Pressure-bonded interface

Pressure-bonded interface

Product by Company B after pressurebonding at 140°C and 100 hours of heat
cycle treatment

TB3373F after pressure bonding at 140°C
and 1,000 hours of heat cycle treatment

85C
Pressure-bonded
interface (max. 50 mm)

Fig. 10.

38-m-thickPET film

29.4 N/m(3 gf/mm)

Comparison of pressure-bonded
interface after heat cycle test for
TB3373F and product from Company
B

Conductive particles

Fig. 9.

ITO glass etc.

Schematic diagram showing a creep
test in a heated environment

Table 7. Peel distance in creep test at 85C[mm]

2 h later

12 h later

TB3373F002Product byCompany A

50(dropped)

50(dropped)

50(dropped)

Product byCompany B

02

8

ACP with high adhesion reliability inheated environment

FPC etc.

24 h later

As shown in Table 7, the product from Company
A peeled completely at 85C  24 hours, with lossof weight. Virtually no signs of peeling wereobserved with the TB3373F. A product from
Company B was subjected to heat cycle treatment
for 100 hours after pressure bonding; observationsof the bonded interface showed changes similar to
those presented in Fig. 10. This is believed to be
attributable to resin relaxation induced by heat andhumidity and to the formation of the air bubbles
associated with such relaxation (Fig. 11).

ACP with low adhesion reliability in heatedenvironment
Air bubbles believed

to be attributable toresin relaxation

Fig. 11. How reliability degrades
As Fig. 11 shows, the air bubbles believed to begenerated by resin relaxation will repeatedly
expand/contract in response to heat, pushing apartthe connection interface and significantly degrading
reliability.

5

3.

Storability of dried film for TB3373F
at room temperature

Points to note when designing the
manufacturing process

Given below are two points to note for process
management when using ACP.
(1) Optimal thickness and drying conditions ofanisotropic conductive film
As shown in Fig. 13, anisotropic conductive films
have an optimal range of thicknesses. If the film is
too thin, the amount of resin filling the space
between the electrodes will be insufficient toachieve the adhesive strength needed, adversely
affecting connection reliability. If the film is too
thick, adhesive strength will be adequate, but theresin relaxation induced by heat will reduce thecontact area of the conductive particles, increasing
resistance.
Any residual solvent present due to insufficientdrying will generate air bubbles during pressurebonding (Fig. 14), degrading connection reliability.
These factors must be taken into account to set
the optimal conditions for a given application.
Peel strength

Connection resistance

Optimal range of film
thickness

Thickness of anisotropic conductive film

Fig. 13.

6

Conceptual relationship between
optimal thickness of ACP andreliability

Effect of drying conditions onpressure-bonded interface(2) Pressure, temperature, and time of pressurebonding
As shown in Fig. 15, ACP does not require
management procedures as rigorous as ACF. Checkthe following if you note significant deviations frompredicted values even after confirming adequate
film thickness and drying conditions: Low adhesive strength
The set pressure of the pressure bonding process
may be too low.
The set temperature of the pressure bonding
process may be too low.
The set time of the pressure bonding process may
be too short.
The surface of the adherend may not be clean.
 High resistance
The pressure of the pressure bonding process may
have been too low for adequate breakdown ofconductive particles.
The temperature of the pressure bonding process
may be too low.
The time of the pressure bonding process may be
too short.
 Presence of voids
The pressure of the pressure bonding process may
be too high.
The temperature of the pressure bonding process
may be too high.

Peel strength [N/m]Fig. 12.

Fig. 14.

Insufficient drying conditions

Peel strength [N/m]Storage time after deposition in various
environments [months]

Ideal drying conditions

Peel strength [N/m]Peel strength[N/m]2-5-4. Storability of dried film for TB3373F
As Table 1 shows, one advantage of ACP over
ACF is the extended shelf life of anisotropic
conductive film at room temperature after formation.
Figure 12 shows the change over time in the peelstrength of the dried film formed by screen printing
and drying of TB3373F when stored at room
temperature (25C). Since TB3373F contains noreactive components, no observable change in peelstrength occurs, even after storage at room
temperature for six months.

Pressure[MPa]

Temperature
[C]

Time
[s]

Pressuredependency

Temperaturedependency

Timedependency

Fig. 15.

Dependency of peel strength of
TB3373F on pressure bonding
conditions

4.

How to use TB3373F

Below is an example of an application of TB3373F. Since the conditions for printing, drying, and pressurebonding will depend on the instruments used, we recommend performing thorough validations with the
instruments used in the actual manufacturing processes. Also, note that the values for the physical properties andcharacteristic values given in this issue are examples of measurement results from studies performed to company
standards. They are not guaranteed values.
4-1.

Printing conditions
Table 8. Standard ThreeBond printing conditions

Mesh

Material

Stainless steel

TetronMesh aperture size

80 to 10080 to 100

Wire diameter

80 to 100

50 to 75

Mesh thickness/emulsion
thickness

225 m/15 m

86 m/50 m

Printing plate dimensions

Inner dimension: 280 mm  280 mm
Frame dimension: 320 mm  320 mm

Material

Urethane rubber

Shape

Flat

Hardness

A80

Indentation

1.0 mmClearance

0.38 mm

Printing speed

20 to 60 mm/s

Squeegee angle

60

SqueegeeSettings

Fig. 16.

Model SC-150-3 semi-automatic screen printing machine (Neotechno Japan Corporation)

4-2.

ThreeBond’s
standard printing
machineStandard drying conditions
Table 9. ThreeBond’s standard drying conditions
TB3373C

TB3373E

TB3373F

100C  10 to 20 min
120C  5 to 10 min

60C  20 to 30 min
80C  15 to 20 min

100C  15 to 20 min
120C  10 to 15 min

Hot-air oven: Model ETAC-HISPEC High Temperature Chamber HT220S environmental test chamber (Kusumoto Chemicals, Ltd.)

4-3.

Pressure bonding conditions
Table 10. ThreeBond’s standard pressure bonding conditions
Temperature

120 to 160C

Pressure

3.0 MPaTime

10 sec. retention

Press chip

Flat chip L: 65 mm, W: 3 mm

Model H800-V1S automatic heat press machine with precision pressure adjustment function(Emtec Co., Ltd.)

Fig. 17.

ThreeBond’s standard
pressure bonding
machine7

Conclusion
ThreeBond developed its ACP to help customers who own printing technologies and machines in their pursuit of
new products with added value. Our ACP provides the capabilities needed to form anisotropic conductive films onvarious component surfaces. Requiring only a screen printing machine and a drier unit, it will undoubtedly
contribute to improved productivity and lower production costs.
The TB3373F introduced in the present issue was developed based on the concepts of high reliability, usability
and manageability, and environmental compliance. Special areas of emphasis during product development
included relaxed drying conditions and storability after film formation to increase user friendliness. Other goals
included halogen-free characteristics for regulatory compliance and the absence of toluene to meet demands inthis age of enhanced environmental awareness.
We plan to continue developing high-value-added products that meet market demands, based on our key
strategy: ever-higher reliability to meet the demands of products with ever finer pitches.
Example of manufacturing process
Liquid material

Screen printing + drying

Original print fabric

Die cutting andheat pressing

Die cutting andheat pressing

LCD

Die cutting andheat pressing

Touch panel
Heat seal connector

Manabu Inoue
Toshifumi Kuboyama
Makoto Kato
Okayama Development Department
Product Development Division
R&D Group
ThreeBond Co., Ltd.
Masayuki Osada
Technical Division
R&D Group
ThreeBond Co., Ltd.

1456 Hazama-cho, Hachioji-shi, Tokyo 193-8533, Japan
Tel: 81-426-61-1333

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