ThreeBond Technical News
Issued July 1, 201993

Electrically Conductive Adhesive MarketTrends and Low Temperature Curing
Electrically Conductive Adhesives
ThreeBond 3331DIntroduction
Conductive adhesives both bond materials and conduct electricity, so they are utilized across amultitude of electrical and electronic applications. These adhesives generate conductivity at
curing temperatures that are lower than other conductive bonding methods and materials, suchas soldering or welding, and changing binder components enables them to conductively bond avariety of metals.
Furthermore, because a variety of binder components are available, conductive adhesives canbe matched to ensure application and curing in any conditions for enormous workability andproductivity.
In this article, we will introduce ThreeBond 3331D, a conductive adhesive with properties thatmake it well suited to the requirements of today’s market, such as low-temperature curing, highreliability and precise applicability.
Hereafter, ThreeBond is abbreviated as TB.

Table of Contents
Introduction.................................................1
1. Conductive Adhesives that
Fulfill Market Needs................................2
2. ThreeBond’s Conductive AdhesiveLineup ....................................................23. Product Comparison...............................34. TB3331D Characteristics........................34-1. Properties and Characteristics........34-2. Low Temperature Curing.................44-3. High Reliability.................................4

4-3-1. High Heat and Humidity
Testing..................................44-3-2. Heat Cycle Testing................44-3-3. Heat Resistance Testing.......54-3-4. Strength of Bond toVariety of Metals...................54-3-5. Connection Resistivity..........64-4. Workability.......................................7Closing........................................................811.

Conductive Adhesives that Fulfill
Market Needs

Conventionally, Sn-Pb solder had been used to bond electronic
components. However, the use of lead in electronics wasrestricted by the EU’s RoHS directive in 2006, so looking at
such a societal perspective and the corporate responsibility
associated with it, lead-free electronics development wasrequired. Accordingly, conductive adhesives have been
gaining attention as lead-free alternative. In the electronics
market of recent years, the following characteristics arerequired for conductive adhesives.
Required Characteristics

adhesive is needed to replace Pb solder.
(3) Precise applicability
With electronic components becoming smaller inrecent years, so too has the need for thin wires andfilms, leading to further diversification in what isrequired of adhesive application. In many cases,
dispensers are used to apply small quantities in small
diameters, but rheological control is required to preventthe conductive filler from separation and precipitationthat such applications require.
(4) Solvent free
In recent years, solvent free conductive adhesives havebeen in demand considering the working environment
in which such adhesives are used. By the use of solvent
free adhesive it possible to reduce or eliminate issues
such as the formation of voids inside the cured productthat occur due to solvent evaporation.

Beside the required lead-free materials there are four main
aspects that a suitable product should feature on.
(1) Low temperature curing
In recent years, smartphones, computers and otherelectronic devices have become lighter and thinner andthe use of resin and other non-heat-resistant materials
is increasing. Therefore, in order to reduce impact onthese materials, curing at low temperatures of 100°C orless is required in conductive bonding with conductive
adhesives.

2.

(2) Highly reliable
Lead-free solder is used for mounting generalequipment, but Pb solder is more reliable, therefore,
it is more commonly used for vehicle electricalcomponents. Further considering the RoHS directive
stance on eliminating Pb, a highly reliable conductive

Conductive
adhesivesThreeBond developed the new TB3331D to meet theseand future market needs. In this article, we will discuss
TB3331D, our new electrically conductive adhesive thatmeets modern requirments in the electronics market.

Singlecomponent

Thermosetting
resin

ThreeBond’s Conductive Adhesive
LineupThreeBond’s current lineup consists of the following
conductive adhesives, which handle various applications(Fig. 1)

Solventless(1) Epoxy
TB3301W, TB3331D(2) Epoxy
TB3301F

Solvent(3) Urethane
TB3302B(4) Silicone
TB3303B, TB3303R, TB3333C

Thermoplastic
resin

Twocomponent

Thermosetting
resin

Solvent

SolventlessFig. 1 ThreeBond’s Conductive Adhesive Lineup

2(5) Coating
TB3315E, TB3350B, TB3351C(6) Epoxy
TB3380(7) Acrylic
TB33813.

Product Comparison

excellent low-temperature curability that is extremelyreliable. It perfectly combines the low-temperature curability
with the high reliability. So, it fulfills the demands of themodern electronics market. In addition, in order to make iteasy to applying, we packaged TB3331D in a syringe.

We show the comparison TB3331D with other representative
ThreeBond products in terms of electrically conductive
adhesive characteristics needed on the market (Table 1).
TB3350B, a solvent-type acrylic conductive coating, has
excellent workability due to low-temperature curabilityand low viscosity. On the other hand epoxy resins are morereliable. TB3301W and TB3301F are both epoxy based andshow very good reliability and workability. Their standard
curing temperature is quite high from 120 to 150°C, so they
are difficult to use with sensitive applications.

4.

TB3331D Characteristics

4-1. Properties and Characteristics
The charts below show TB3331D’s properties (Table 2) andphysical characteristics (Table 3).

As a result, we developed TB3331D, an epoxy resin withTable 1. Conductive Adhesives for Electronics Market
Item

TB3331DTB3350B

TB3301W

TB3301F

Binder resin

Epoxy

AcrylicEpoxy

Epoxy(1) Low temperature curing(standard curing condition)◎(80°C×60min.)◎(25°C×24hrs. or
60°C×60min.)

×(120°C×60min.)×(150°C×30min.)

◎△

◎

◎

○(25Pa・s)◎(2.5Pa・s)○(37Pa・s)○(23Pa・s)

◎×

◎

×

(2) High reliability(3) Precision application(viscosity)(4) Solventless

Table 2. Properties of TB3331D
Test items

Unit

ThreeBond 3331D

Testing method

Remark(s)Appearance-

Silver3TS-2100-020-Viscosity

Pa・s253TS-2F00-007

Shear velocity 10.0 s-1

Structural Viscosity Rate-

4.03TS-2F10-007-Table 3. Characteristics of TB3331D
Test items

Unit

ThreeBond 3331D

Testing method

Remark(s)Chip bond strength test

MPa

153TS-4180-002

Ni plated board/2Φ
ceramic chip

Volume Resistivity

Ω・m

0.5×10-5

3TS-5100-002

-Tg°C

90

3TS-4730-001

DMA tensile mode(tanδ peak: 1 Hz)

Standard curing conditions-80°C×60min.

-

Hot air oven

Recommended nozzle
diameter

mm0.29 or more (inner)-25G needle

Pot lifeh48-25°C3

Low temperature curing (100°C or lower) is required in theelectronics market. TB3331D designed as can be cured at80°C, reducing risk of damage to materials that are not heat
resistant, such as electronics and plastic parts.

2.0

4-3. High Reliability
4-3-1. High Heat and Humidity Testing
We show changing of volume resistivity and bond strengthin 85°C, 85% RH environment (Fig. 4). In both cases,
performance does not deteriorate after 1,000 hours.
4-3-2. Heat Cycle Testing
We show changing of volume resistivity and bond strength
in a -40°C ⇔ 85°C heat cycle (30 min. ea.) (Fig. 5).
Performance does not deteriorate after 2,000 cycles.

5

Volume resistivity (10-5Ω•m)

Volume resistivity (10-5Ω•m)

41.515
Volume resistivity
Chip bond strength

20.5103060901200

Curing time (min)

50250

500

75001000Time (hrs)Fig. 2. Volume Resistivity in an 80°C Environment

20Fig. 4. Volume Resistivity and Chip Bond Strength
in an 85°C, 85% RH Environment

5

Volume resistivity (10-5Ω•m)

2541520310

Volume resistivity
Chip bond strength250103060

1090120

Curing time (min)Fig. 3. Chip Bond Strength in an 80°C Environment
Ni plated board/2φ ceramic chip

0151050500

1000

1500

Chip bond strength (MPa)0.0Chip bond strength (MPa)

203

1.0

425

Chip bond strength (MPa)4-2. Low Temperature Curing
We show the volume resistivity (Fig. 2) and change in bondstrength (Fig. 3) in the 80°C environment. We can see fromthe result, volume resistivity become stable in approximately
30 min. and bond strength become stable in approximately
60 min. Accordingly, TB3331D’s standard curing condition
has been set at 80°C x 60 min. to ensure stable volumeresistivity and bond strength.

02000

Time (hrs)Fig. 5. Volume Resistivity and Chip Bond Strength
in a Heat Cycle Test (-40°C 85% ⇔ 85°)

4-3-3. Heat Resistance Testing
We shows changing of volume resistivity (Fig. 6) and bondstrength (Fig. 7) in 100°C, 120°C and 150°C environments.
In both cases, performance does not deteriorate, andcharacteristics are stable.
Conductive adhesives are required a high reliability canreplace lead solder. Above durability tests results show thegood stability in terms of conductivity and bond strengthof TB3331D under various conditions. We recommend as agood alternative of lead solder with confidence.

25100°C120°C150°C

4Chip bond strength (MPa)Volume resistivity (10-5Ω•m)

532

100250500

750

4-3-4. Strength of Bond to Variety of Metals
TB3331D have good bond strength to variety of metals in
addition to curing at low temperature. We show changingof bond strength to a variety of metals in an 85°C, 85% RH
environment (Fig. 8). For all metals, it shows stable bondstrength in reliability tests.

10002015Cu
Electroless Ni
Electrolytic Ni
Au

10500250

500

750

1000

Time (hrs)Time (hrs)Fig. 6. Volume Resistivity in 100°C, 120°C, 150°C
Environments

Fig. 8. Bond Strength to Adherends and 85°C, 85%
RH Environment Test

Chip bond strength (MPa)40100℃
120℃
150℃

353025201510500250

5007501000

Time (hrs)Fig. 7. Chip Bond Strength in 100°C, 120°C, 150°C
Environments

54-3-5. Connection Resistivity
When conductive adhesive is used to connect electrodes,
the resistance measured through the electrodes (Fig. 9) is acombination of two resistances:and our reliability data of TB3331D.

the resistance of the conductive adhesive itself (volumeresistivity) andMasking tape with a 2mm hole is attached to a conductive
adherend (metal, etc.) and a squeegee is used to uniformly
apply the resin. After the conductive adhesive is apply
with the squeegee, the tape is peeled off to form a thinlayer of conductive adhesive with the hight of the thin filmon the adherend. Next, it is cured in standard conditions.
A measurement instrument is connected to the adjacentconductive adhesive to measure connection resistivity(Fig. 10). This method ensures a sufficiently thin layer ofresin, ignores volume resistivity and enables a simulated
evaluation of the connection resistivity.

the resistance generated at the point of connection between
the adherend (electrode) and the adhesive (connectionresistivity).
In recent years, in the electronics market, with components
becoming smaller and thinner, the volume of conductive
adhesive applied is decreasing. This means that the influenceof volume resistivity, once dominant, has decreased, while
the influence of connection resistivity has increased.
Accordingly, it is increasingly necessary to measurereliability, both for the volume resistivity of the resin itself
as well as the connection resistivity generated at the point ofconnection to the adherend.
We show our measurement method of connection resistivity<Measurement method of connection resistivity>
test conditions: 3TS-5110-004

A test piece is created in the above way and left in an 85°C,
85% RH environment, then taken out at specified intervals
and measured. The results are as indicated below (Fig. 11).
As it is shown the connection resistivity to the adherends isalso extremely stable over time.

ΩVolume resistivity (Rv)

Electrode

Conductive
adhesive
Connection resistivity (Rc)

Connection resistivity (Rc)

ΩConnection resistivity (mΩ)

100806040

200・・・（Formula 1）

0250

500

7501000

Time (hrs)Fig. 9. Volume (Rv) and Connection Resistivity (Rc)

ΩAdherend
Conductive
adhesive・・・（Formula 2）

From formula 1, we can see that Rv ≒ 0by reducing the thickness of the conductive adhesiveFig. 10. Connection Resistivity Measurement
Method6Cu
Au
Electrolytic Ni
Electroless Ni

Fig. 11. Change in Connection Resistivity in an85°C, 85% RH Environment

4-4. Workability
In many applications of the electronics market, dispensers
are used to apply conductive adhesives in lines and dots.
Many conventional conductive adhesives are housed in glassor plastic containers, so stirring and transfer to a separate
container for application (such as a syringe) is required
prior to use. To further improve workability TB3331D isavailable in syringes which greatly improve work efficiency
by eliminating stirring and transfer before use.
Conductive adhesive is composed of a combinationof adhesive components with low specific gravity andconductive filler with high specific gravity. In conventional
conductive adhesives, it was possible for the filler to separate
and settle, requiring stirring to return it to a uniform andwell dispersed state before application. However, it is notpossible to stir and fix separation issues due to the syringe

container, so rheology control is necessary to suppress
separation and settling during the shelf life of the product.
We used proprietary rheology control to suppress separationand settlement in TB3331D and ensure stability within thesyringe. Below we show changes in viscosity (Fig. 12) aswell as changes in volume resistivity and chip bond strength(Fig. 13) after storage in a room temperature environment(25°C). When TB3331D is poured in a syringe, viscosity
does not change within 48 hours at room temperature (25°C),
and both volume resistivity and chip bond strength remain
stable during that time. We also checked change in volume ofdispensing after 48 hours at room temperature (25°C) (Fig.
14). Discharge rate did not change, and TB3331D contains
no solvent by design, so there is no danger of solvent drying
making the product difficult to apply when there is a breakduring applications, indicating stable workability whenapplying.

16403512Discharge (mg)Viscosity (Pa•s)

302520151084500244872

Time (hrs)201614312
Volume resistivity
Chip bond strength

2108614Chip bond strength (MPa)Volume resistivity (10-5Ω•m)

184012243648

Time (hrs)Fig. 12. Change in Viscosity at Room Temperature(25°C)
50Fig. 14. Change in Discharge at Room Temperature(25°C)<Test conditions>Nozzle 25G, inner diameter 0.29 mm
0.3 MPa, 5 sec. (air dispenser)

2002448072

Time (hrs)Fig. 13. Volume Resistivity and Chip Bond Strengthat Room Temperature (25°C)

7Closing

The characteristics required of conductive adhesives increase year by year with the heightened performance and complexityof electronics. To handle these changes, it is necessary to design a resin that can correspond increasingly smaller and thinnerelectronic components. Here, we introduced our method for measuring connection resistivity. With further performanceincreases in future electronic components, other measurement method may be needed to develop. We are already designingresins that match even more to the advancing in electronic components whilst optimizing test methods in order to obtain datathat closer correlate to actual usage.
Moving forward, we expect use of these adhesives to expand into automobiles, so more reliable conductive adhesives will beindispensable. Furthermore, it will be necessary to address future issues by developing conductive adhesives outside those withtypical characteristics that are suitable for every expanding application in this evolving range.
<References>
1) Nishikawa, Hiroshi. Relation Between Metal Filler and Electrical Conductivity for Electrically Conductive Adhesives,
Journal of Smart Processing 139 (2012)
2) Kohinata, Shigeru. Fundamentals of Isotropic Conductive Adhesive Paste (Part 3), Vol. 10, No. 1, 88 (2007)
3) Fuji Keizai Co., Ltd. Overview of the Special Adhesive and Sealant Market and Application Development 2014, p. 183(2013)
4) Technical Information Institute Co., Ltd. Improvement of Dispersal, Evaluation and Application of Conductive Fillersand Aids, p3 (2015)
5) Nakaya, Manabu and Suzuki, Hironori. ThreeBond Technical News: Technological Trends in Modern Conductive
Adhesives (1999)
6) The Adhesion Society of Japan. Journal of The Adhesion Society of Japan: Adhesion Technology, Vol. 37, No. 2, pg. 26(2017)

ThreeBond Co., Ltd. R&D Headquarters
Development Division 2, Functional Materials Department
Satoru Endo
Makoto Kato
Takashi Nemoto
Technology Marketing Division, Intellectual Property Department
Kanako Morii

ThreeBond Co., Ltd.
84-3-3 Minamiosawa, Hachioji,Tokyo 192-0398
Tel: +81-42-670-5333