Anisotropic Conductive Films (ACFs) Applicable at Low Temperatures: Characteristics and Applications

Low-temperature application of Anisotropic Conductive Films (ACFs)

Dexerials’ Anisotropic Conductive Film (ACF) bonding solutions are versatile, enabling the bonding of integrated circuits (ICs) and flexible printed circuits (FPCs) onto various display types such as liquid crystal, organic light-emitting diode, and micro light-emitting diode, as well as the assembly of components such as camera modules, touch panels, and smart cards. This versatility is due to their ability to meet low-temperature bonding needs.

Some printed circuit boards and electronic components are not able to withstand high temperatures exceeding 150°C, nor maintain their performance at such high temperatures, because of their material characteristics. These include cyclo olefin polymer (COP) boards with indium tin oxide (ITO) films—a type of transparent conductive film—as circuit layers, used for capacitive touch sensors; piezoelectric sensors used in haptic modules; polycarbonate or other plastic lenses for small camera modules; and polyethylene terephthalate (PET) film materials used in smart cards, which melt below 150°C. As these materials and components can alter their characteristics when exposed to high temperatures, they must be bonded or fixed at low temperatures.

Additionally, printed electronics technology, which involves printing traces on base films, is gaining traction. This technology offers a promising approach to the printing and forming of electric circuits that contain traces, sensors, and other components directly on films or other materials.

Popular conventional methods to produce circuit boards typically involve etching or other subtraction processes that remove unwanted areas. It should be noted that these methods consume significant energy and resources, including electricity for lighting (exposure), chemicals for etching, and water for removal. It is also important to acknowledge that the majority of the removed substances are discarded. By contrast, printed electronics print circuit materials only where needed, which has the potential to produce less waste and reduce environmental impact and CO2 emissions. Furthermore, given that many base film materials have problems with heat resistance, ACFs that can be applied at low temperatures are well-suited for printed electronics.

Reworking or repairing after pressure-bonding ACF

If a flexible printed circuit (FPC) or a circuit board (printed or glass) is to be reworked or repaired after bonding with ACF, using an acrylic ACF is advisable. Note that rework or repair is not recommended. It is recommended that the reliability of a reworked or repaired product be evaluated and that any quality-related issues be confirmed before incorporating such processes into component production.

After bonding an FPC using our ACF, a heat gun or industrial iron is typically used to locally heat the bonded area and facilitate the removal of the FPC. The subsequent step involves removing any remaining cured resin from between the board’s patterns using a cotton swab soaked in a suitable solvent such as methyl ethyl ketone (MKE) or N-Methyl-2-pyrrolidone (NMP). During this stage, the FPC tends to curl, which complicates the removal of these resin residues. As such, reusing the FPC is not recommended. Although rework or repair with an acrylic ACF is possible, not doing so is preferable to maintain a high product quality.

Thermoplastic ACFs with low temperature cure and room-temperature storage properties

In addition to common epoxy and acrylic thermosetting resins, some ACF products are composed of thermoplastic resins.

For applications requiring high reliability (maintenance of functionality) in warm, humid environments (accelerated testing conditions: 85°C and 85% RH for 500 hours), thermosetting ACFs are recommended solution. However, for less demanding environments, easy-to-use thermoplastic ACFs, which can bond at around 110°C, represent a viable options.
Anisotropic Conductive Film (ACF) for Film On Board / Film as an alternative to connectors and solder connections CP850CG-35AJ

Generally, thermosetting ACFs require refrigerated storage at 5°C or below and have a shelf life of five to seven months after production. By contrast, thermoplastic ACFs can be stored at room temperature for two years after production. In addition, they can be bonded using simple thermocompression bonding equipment, such as that used for soldering, which has a potential to eliminate the need for introducing special ACF bonding equipment and could reduce investment costs. These thermoplastic ACFs are utilized in smart cards and other applications intended for use under normal conditions.
Features and Benefits of Using Anisotropic Conductive Film (ACF) for Smart Cards

As IoT and printed electronics technologies develop, there are increasing opportunities for the adoption of ACFs in various fields such as the automotive, health care, and industrial equipment industries. Dexerials proposes products that ideally meet the requirements for low-temperature bonding across a diverse range of industries. Please feel free to contact us, if you are interested in low temperature bonding with our ACF.