Thermal Bonding

Thermal bonding is a generic term for processes such as “Hot Bar Soldering” or “ACF bonding” (ACF = Anisotropic Conductive Film).

It is increasingly being used in a wide variety of applications to connect electrical components, such as FPCs (Flexible PCBs), displays and PCBAs as an alternative to conventional electromechanical connector technology.

For example, individual functional units of modern driver assistance systems, such as blind spot assistants installed in the wing mirrors, complex sensors, cameras or displays and control units, are often electrically connected using the thermal bonding process.

So-called FPCs (Flexible Printed Circuits) or FFCs (Flat Flexible Cables) are often used as connecting elements.

(Reflow) Hot Bar Soldering

“(Reflow) Hot Bar Soldering” is a thermal bonding process that belongs to the selective soldering processes. In this process, the two components are placed on top of each other on the pre-tinned and pre-wetted contact surfaces to be electrically connected. They are then heated to the melting point of the solder using a heating element (also known as a “hot bar” or “thermode”) applied under controlled pressure and then cooled in a controlled manner until the solder solidifies.

In this way, electromechanically highly stable and reliable soldered connections can be achieved in a single process step, even for large-area multi-pole fine-pitch connections such as Flex on Board (FOB) or Flex on Flex (FOF).

ACF Bonding

ACF (Anisotropic Conductive Film) bonding is an alternative thermal bonding process that can be realized on the basis of the hot bar soldering technology described above. Typical areas of application are electrical connections between chip on glass (COG), chip on flex (COF) and flex on glass (FOG).

ACF Bonding is always devided into two processes:

The first process is the so called ACF Pre-Attachment. Here, the ACF supplied on a roll is cut to size and applied to the display or substrate.

The second process is the ACF Bonding, the production of the actual connection between the FPC (Flexible Printed Circuit) and the display or substrate.

Also in this process, fine adjustability, high control accuracy and the reproducibility of the process parameters “pressure”, ‘temperature’ and “time” are crucial for high-quality electromechanical connections.