The Tech Blog

Recently, while working on a project involving LCD screens, I came across Anisotropic Conductive Films (ACF). Though they’ve been around for decades, with patents dating back to the 80s and 90s, many aren’t aware of how vital they are in miniaturized devices. Some of you may have wondered how you bond, say, metallic flex cables to glass. In LED displays, the row and column wires are extremely thin. The challenge arises when you need to connect these delicate wires to larger driver boards, especially when the connections are on glass. You can’t solder on glass, and alignment at such small scales can be a nightmare.

Enter ACF. It’s a thin adhesive strip filled with tiny conductive particles (typically metal-coated polymer balls). These films allow you to make electrical connections between two layers, like a flex cable and a glass substrate, while ensuring the electrical flow happens only in one direction. This selective conductivity is what makes ACF “anisotropic” – it conducts electricity vertically (through the thickness of the material) but not laterally (across the surface), preventing shorts between adjacent wires.

So how does it do it? Those tiny balls in the adhesive become sandwiched between the 2 layers that you want to electrically connect(Check Images). Now the balls since they are relatively sparse, don’t form a bridge(by balls lining up) between consecutive wires shorting them. Now to bond it, usually, it’s heated/pressed together the conductive particles become trapped between the surfaces, creating electrical pathways only where they’re needed, typically on pads or traces. This allows ACF to be used in applications with very tight spacing, where conventional soldering or connectors would be impractical.

These are useful in display tech like LCDs, OLEDs, Flex PCBs, and Chip on Glass Assemblies where ICs are mounted on glass substrates(These are the small black rectangles you see on flex cables on OLED modules). ACF may not get as much attention as other electronic materials, but they’ve quietly revolutionized how we connect components. Worth learning about!