December 2023

Functionality and benefits of the CLS system: Rapid curing

electrically conductive adhesive.
Keisuke Ota, Ryo Ogawa,Introduction

Conventionally, solder has been used as a conductive joining material for electronic components,

etc., and in many cases Sn-Pb alloys have been used. However, there have been concerns about

adverse effects on the human body and the environment due to the lead content, and there havealso been issues such as the need for high temperatures for joining. Therefore, electricallyconductive adhesives have been applied as an alternative to solder, which are formed byelectrically conductive fillers in polymer materials. Electrically conductive adhesives have theadvantages of low environmental impact, low-temperature joining and the ability to maintainadhesive strength even at high temperatures.

Many technologies have been proposed for compounding polymers with conductive fillers. For

example, it has been proposed to blend conductive particles, such as metal particles, into adhesivecompositions obtained by containing cyanate ester resins, epoxy resins and latent curing
hardeners 1. A core-shell type curing agent with an imidazole-modified structural component as

the core is used in this reference, but it was not satisfactory in terms of conductivity and curing
properties.

Now, ADEKA has proposed new possibilities such as ultra-fast curing adhesives by applying theCLS system, which is a new formulation technology using epoxy resins, latent curing agents for

one component systems and highly reactive compounds such as cyanate ester resins. This paper

reports the functionality of electrically conductive adhesive formulations based on the CLS system.

Application to conductive adhesives

The CLS system enables phase-separated structures to be formed during curing while

maintaining rapid curing properties by optimizing the formulation. Observing the cross section of
the cured material, it can be confirmed that the CLS system cured system (1a) has a distribution

in resin density and forms a phase-separated structure in the system compared to the general

epoxy resin cured system (1b) (Figure 1).

1a: CLS system

1b: Conventional system

図 1 SEM cross section of cured material.
©2023 ADEKA Corporation1

December 2023
Ag filler, which is widely used in conductive adhesive materials, was formulated into the above

formulation, and cured. It gives a cured material with a three-dimensional mesh structure in which

Ag filler is aggregated (Figure 2, 2a). In the system using the CLS system, conductivity was achieved

with as little as 18.5 vol% Ag filler, indicating that the formation of a three-dimensional meshstructure by agglomeration is an efficient conductive path (Table 1).

2a: CLS system

2b: Conventional system

図 2 SEM cross section of cured material containing Ag filler.
Table 1 Volume Resistivity of Cured Materialsample

2a2bAg filler (vol%)

18.5

18.5

Volume resistance (Ω cm)

8.0 × 10-3

> 106This formulation also has the fast-curing properties that are characteristic of the CLS system, andcan provide high adhesive strength in a short time of only 10 seconds, which was not possible
with conventional compositions. Furthermore, high final adhesive strength can be achieved due
to lower Ag filler content, which provides the same electrical conductivity (Figure 4).

Share strength（MPa）

12.0
10.0

CLS system (Ag 18.5 vol%)Conventional system (Ag 31.0 vol%)
7.2

8.0
6.0
4.0
2.0
0.0

6.9

5.5

3.8

3.2010 sec.

10 minHeating time at 150 ºC

30 minFigure 4 Adhesive strength on Cu©2023 ADEKA Corporation2December 2023
Currently, we are developing laser-curable conductive adhesives featuring ultra-fast curing andefficient conductive path formation, and have developed the lineup shown in Table 2. The
development of high conductivity with a small amount of Ag filler is expected to reduce the weightof materials and improve adhesion.

Table 2 Typical Properties of Conductive Adhesives

Near-infrared laser curing
Viscosity / 25 ºCPa⋅s / 10rpm
Glass transition temperature(DMA) ºCCoefficient of linear expansion(<Tg) ppm

Volume resistivity
ΩcmStandard grade
ADEKA REMYLOP FL-387

High Heat-Resistant Grade
ADEKA REMYLOP FL-388

Possible

Possible

2327

140

170

4343

2 × 10-3

3 × 10-3Conclusion

As an example of application of the CLS system, which has a new and unconventional curing

behavior, electrical conductivity has been successfully achieved using Ag filler. This electricallyconductive formulation shows high electrical conductivity with a smaller amount of Ag filler bylocalising the Ag filler through the formation of a phase-separated structure during curing.

As the CLS system features ultra-fast curing, it can be successfully adapted to short-time curing

processes, such as near-infrared laser heating systems 2-4, etc., which enables joining in a shorttime as with conventional solder.

©2023 ADEKA Corporation3

December 2023

Bibliography

1. JP-A-H9-279121
2. ADEKA corporation home page

( Japanese : https://www.adeka.co.jp/develop/laboratory/polymer/laser/ )( English : https://www.adeka.co.jp/en/develop/laboratory/polymer/laser/ )3. Satoshi Matsumoto, Ph.（2017）Plastic Age，63，51
4. Sugiura, A., Suzuki, K., Ina, O., Kato, K., (2009) Denso Technical Review 14

https://www.denso.com/jp/ja/-/media/global/business/innovation/review/14/14-doc-13ja.pdf?la=ja-jp&rev=049d4dac9d8a456593a9a67bc06c03d0&hash=BD6D55993B87A631CFCD0D3075495
29E©2023 ADEKA Corporation4