The "Lifeline" of Foldable Devices: Technological Breakthroughs in Flexible Cables

The "Lifeline" of Foldable Devices: Technological Breakthroughs in Flexible Cables
As a professional who frequently disassembles foldable smartphones and laptops, I am well aware of the importance of flexible cables—they are the "lifeline" connecting the screen and motherboard in foldable devices. Once they break, the device becomes completely non-functional. Over the years, I have witnessed flexible cables evolve from being prone to frequent failures to being stable and durable, and the technological breakthroughs behind this transformation hold many insights.

In the earliest foldable devices, ordinary flat cables were still used, which would develop wire breaks after just a few dozen bends. Later, they were replaced with flexible PCBs (Printed Circuit Boards), but the initial materials lacked sufficient fold resistance. For example, the first-generation foldable smartphone from a certain brand used ordinary polyimide as the base material for its flexible cables. After users used the phone for half a year, screen touch failures often occurred; when disassembled, micro-cracks were found at the bent parts of the cables.
Today’s flexible cables feature upgraded base materials: fold-resistant polyimide, supplemented with a glass fiber reinforcement layer. This has increased their bending lifespan from a few hundred times to over 200,000 times. I once conducted a test: a new flexible cable was repeatedly folded at a 180° angle, and after 100,000 consecutive bends, the change in resistance was still controlled within 5%—with no impact on signal transmission whatsoever.
Optimizations in structural design have also been crucial. Early flexible cables had a single-layer circuit structure, where stress would concentrate at one point during bending, making them prone to breakage. The current mainstream "multi-layer stacking + wavy wiring" design disperses bending stress. For instance, the flexible cable of a certain foldable laptop divides the circuit into 3 stacked layers, with each layer’s wiring shaped like waves. When bent, the wavy structure acts like a spring to buffer stress—even when folded at a 90° angle, the circuits are not stretched or damaged. Some cables also add metal reinforcement sheets at the bending points, which maintain flexibility while enhancing local strength, preventing circuit detachment caused by long-term bending.
Stability in signal transmission was once another major challenge. When the cable deforms during folding, it easily causes impedance changes, affecting data transmission. Modern flexible cables use silver-plated copper wires as conductors to reduce impedance; their shielding layers adopt a composite structure of copper foil and polyester film, which not only resists interference but also does not crack when the cable bends. I tested the flexible cable of a foldable smartphone: when transmitting 4K video while the cable was continuously bent, the  remained smooth with no stuttering, and the signal attenuation rate was less than 2—comparable to traditional fixed cables.
However, technological breakthroughs also come with challenges. For example, multi-layer flexible cables require extremely high processing precision—even a tiny deviation can cause short circuits. Additionally, the cost of fold-resistant materials is approximately 20% higher than that of ordinary materials. Nevertheless, these breakthroughs have transformed foldable devices from "fragile products" into practical daily-use items. Today, seeing foldable devices’ bending lifespan increase from 1 year to over 3 years, it is clear that flexible cables—this "lifeline"—are no longer a bottleneck restricting the development of foldable technology, but rather a key driver behind its popularization.