Low temp. thermo-compression bonded conductive sheet

Introduction

New green technologies are being created every day to save energy and utilize renewable energy for the realization of a sustainable society. One such technology is the development of film devices.

Demand for lightweight, thin, and flexible transparent film devices is expected to continue to grow.

What are the challenges of developing transparent film devices?

Transparent conductive films are vulnerable to heat

Transparent conductive films used in film devices are generally made by adding conductivity to the surface of PET film, but while they are thin and light, they are extremely weak against heat.

"Soldering" is used for conductive connections in electronic circuits, but solder, which requires high temperatures, cannot be used to connect to film devices on which solar cells and heaters are formed. Anisotropic conductive films (ACF) and conductive adhesives are sometimes used in place of soldering, but each has its own disadvantages and technical challenges that prevent the film device from fully functioning.

Problem Solving! Flexible conductive adhesion at low temperatures

Low-temperature thermo-compression bonding conductive technology TKS-030

To solve this problem, KAKEN TECH has developed TKS-030, a conductive paste that can be bonded at low temperatures, using specially shaped silver powder.
☝ Flexible and stretchable, it is ideal for thin film devices and can be molded into 3D shapes.
☝ Enables direct wiring from ITO film and other materials, resulting in thinner devices and reduced man-hours.
☝ Good adhesion to PET, PEN, PI, polycarbonate, etc.
With TKS-030, conductive adhesion to films can be achieved in a simple process.

Comparison of electrode removal method from transparent film devices

A comparison of the new adhesive TKS-030 developed by KAKEN TECH and the conventional method is shown below.

TK PASTE
Thermo-compression type		Conductive adhesive
(Thermosetting)
Anisotropic conductive
Film (ACF)		SolderingGrommet
Deformation
by heat		○△～○××○
Flexibility○×△××
Condctivity○○△-△
Thinness○○○××
Number of
Processes		○×△～○△△
FeaturesIdeal for electrode
take-out of conductive films		Inflexible, causing
cracking and warping		Requires high temp. heating
High resistance		Cannot be used for films
due to high temperatures		No flexibility
Cannot be made thin

Conventional methods all have their challenges and do not bring out the best of film devices. TKS-030, which can be bonded by low-temperature thermo-compression, is the best method to take out electrodes from thin and flexible transparent conductive films.

Development of silver powder in optimum shape

The deciding factor is the shape of the silver!
KAKEN TECH develops unique conductive adhesives using silver powder of various shapes.

TKS-030 developed this time also uses silver powder of the most suitable shape for film devices.

【Conventional conductive adhesives】
Conductive adhesives applied to films are stretched to the left and right when they are bent. Inside the conductive adhesive, silver powders become separated from each other, resulting in increased resistance and reduced conductivity.
　　　
【TKS-030】
KAKEN TECH has developed a special silver powder that is large and thin in order to achieve both flexibility and stable conductivity. By blending this powder, we were able to develop a conductive adhesive that does not easily lose conductivity even when bent.

Possible Applications

Conductive connection of transparent film devices
・For energy field: Organic thin-film solar cells (e.g. Pebroscite)
・For automatic driving: Transparent heaters (to prevent fogging of cameras), transparent antennas (for vehicle-to-vehicle and road-to-vehicle communications)
・For electric vehicles: light control film (electronic light control window)

Product Specifications and Usage

Product Specifications and General Properties

Available in screen-printable paste type and pre-printed sheet type

　Low temp. thermo-compression bonding conductive adhesive
TK PASTE TKS-030
PropertiesPaste typeSheet type
Main componentsSilver, thermoplastic resin
Base layer-Rolled copper foil
(C1020 50um)
Printed area size-75mm×75mm
(Precut：5mm or 3mm width)
Paste application methodScreen printing-
Paste drying conditions60℃×40min~100℃×20min-
Pressure bonding conditions100~120℃/60~120sec/0.5~2.0MPa
Specific resistivity2×10-4Ω・cm
Storage conditionFreezing (-10°C or below)Room temperature

How to use

  1. Screen print on the substrate to be thermo-compressed and dry at the specified temperature and time. (Paste type)
  2. Align the conductive surface to be bonded with the thermo-compression silver paste layer and thermo-compress.
    If the conductive surface is uneven or not evenly thermo-compressed, sufficient strength may not be obtained.
    If sufficient bonding strength cannot be obtained, adjust the temperature, time, and pressure.
  3. Connect wiring, etc. to the bonded electrode.

Application Examples

Used for take-out electrode of liquid crystal dimmer film

Problem：In the conventional method, the resistance of the copper tape and ITO surface for soldering is high, so silver paste is used together. Also, the wiring part became thicker due to the use of solder.
　　
　　
Using TKS-030：Electrode terminals for wiring can be thermo-compression bonded directly to ITO. The thickness has been smartly reduced to less than half, and the process has been significantly shortened.
　　

Used for wiring and electrodes of transparent heaters

Problem：Wiring is formed on transparent conductive film with silver paste, etc., and bonded to electrodes with ACF. Stable conductivity could not be obtained due to high resistance and localized heat generation.
Using TKS-030：TKS-030 thermo-compression bonding sheet (copper foil type) is thermo-compressed directly onto transparent conductive film. When DC current is applied, heat is generated, and it was confirmed that there is no localized heat generation.

Directly thermo-compress the TKS-030
thermo-compression bonding sheet.
When electric current is applied, heat is generated.
No localized heat generation.

Used for electrodes of film solar cells (under development)

Problem：Conductive adhesion to electrodes formed on film substrates using ACF or conductive tape. The resistance of the bonded area is high, and lowering the resistance is an issue.
Using TKS-030：Investigated the use of TKS-030 thermo-compression bonding sheet (copper foil type) for bonding electrodes of organic thin-film solar cells formed on film substrates. Low resistance and stable characteristics have been obtained and are under development for practical use.

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