Hinge

The core technical challenge of foldable phones lies in the co-design of flexible OLED displays and precision hinge systems.

Display abnormalities near a foldable's hinge are often hard to distinguish visually as to whether they are caused by structural stress or by external compression.

Near the hinge, the foldable screen is repeatedly bent at a very small radius, with the outer layer stretched and the inner layer compressed, generating shear stress between layers.

When the bending radius is too small, hinge tolerances are too large, or the bonding between layers is uneven, stress concentrates at specific locations, which may lead to interlayer delamination, microcrack propagation, or display circuit breakage.

Leading manufacturers have begun to focus foldable screen competition on finer structural levels, such as maintaining heat dissipation in the folded form, the hinge taking on more functions, and doing thermal design within millimeter-scale space, and running a graphite tube through the hinge is a typical "structural-level optimization."

The graphite tube solution is thinner and more flexible than a VC plate and can be routed along the hinge's bending path, but its heat transfer flux per unit cross-section is inferior to that of a VC plate.

The hinge is composed of multiple metal parts and a rotating shaft, with gaps between the contact surfaces, and air is a poor conductor of heat, so without special treatment the two sides of the hinge are essentially thermally isolated, making it the worst thermal resistance segment in the entire device.

Over the past few years, competition in foldable screen hinges has mainly focused on two metrics, crease depth and open-close feel, while heat dissipation is usually categorized under the mainboard and VC vapor chamber, and few people treat the hinge as a thermal management component.

The core components of foldable screen devices, the hinge and the flexible display, involve complex processes, and yield ramp-up typically takes several months.

Foldable screen hinges need to maintain structural stability through hundreds of thousands of open-and-close cycles, and their precision mechanical structures involve hundreds of micro parts with extremely high tolerance requirements.

The core difficulty of horizontal inward folding lies in the hinge, which needs to maintain screen flatness and damping consistency after hundreds of thousands of open-close cycles, while also balancing water and dust resistance.

Apple's long absence from foldable screens is widely believed to be a wait for hinge durability, UTG (ultra-thin flexible glass) yield, and system-level large-screen adaptation to mature simultaneously.

The hinge is made up of hundreds of tiny parts and is responsible for keeping the screen flat through tens of thousands of folds.

2350MPa super-strong rocket steel refers to the yield strength level of the steel used in the hinge's key load-bearing components; the higher the value, the less prone it is to plastic deformation.