Hot sealing (AFC- and HSC-Bonding)

Heat sealing produces electrically conductive adhesive joints between flexible and rigid printed circuit boards, or glass displays and flex foils. The essential features of this process are the heating and cooling of the adhesive film under pressure. The adhesive film (ACF = Anisotropic Conductive Film) contains small conductive particles which, when compressed and heated, create an electrical connection between the parts. Electrically conductive particles are typically 3 to 12 um in size and are usually made of metal, carbon (graphite), metal-coated plastic, metal-coated glass or a combination of the above. combination of the above. An ACF three-layer film has a protective paper layer that is removed before bonding. The tape is then glued to the board. glued. The flex PCB is then placed and aligned so that the trace structures of the PCB and the flex PCB are in register. Then the heat-sealing process takes place with the thermode. The thermode presses forcefully onto the flex PCB and heats the joint to between 150°C to 230°C, depending on the adhesive. Temperature, time and pressure cause plastic deformation of the adhesive and compression of the particles. The particles that form between The particles enclosed between the conductive paths of rigid and flexible PCBs electrically connect the respective conductive paths to each other. Between the tracks the particles remain embedded in the adhesive film without conducting.

In contrast to AFC bonding, where the particles are distributed over the entire surface, in HSC bonding (HSC = HeatSealConnector) the conductor structure is printed with silver ink on a polyester film. is printed with silver ink on a polyester film. Consequently, not only the two joining partners but also the adhesive film must be precisely aligned. Otherwise the Otherwise, the process is similar.