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Heat Dissipation, A Challenge for Foldables
 
Xiaomi explains that one of the issues with foldable devices is that the capacity to dissipate heat is dependent on whether its folding or not. The other) issue is that the imbalance depends on the side of the device that contains the SoC. 
 
Figure 1: Xiaomi Mi Mix Fold Heat Dissipation Design

With the Mi Mix Fold, Xiaomi has developed a “Butterfly” heat dissipation mechanism that can dissipate heat from one side of the phone to the other, across the hinge mechanism. This means that the total cooling area is much larger than that of a non-folding smartphone. The Mix Fold “has been equipped with  cutting-edge multi-dimensional heat dissipation technology in the industry”. The Mix Fold uses a combination of liquid cooling, thermal gel, multilayer graphite sheets, bend-resistant graphite sheets, and a copper foil piece. This gives the Mi Mix Fold a total of 22,583.7 sq mm (35 sq in) of heat dissipation surface area.
 
Figure 2: Xiaomi Mi Mix Fold Hinge

To ‘bridge’ the two sides of the phone together for heat dissipation, Xiaomi developed the “heat transfer tunnel”. This was achieved by the bend-resistant graphite material. This resistance to bending was achieved thanks to a “micro airbag bionic knuckle” skin along the graphite that still lets heat flow through while its bent. Xiaomi says this material only lost 3-5% of its ability to transfer heat after bending 180-degrees 200,000 times.
 
Figure 3: Xiaomi Mi Mix Fold Heat Dissipation Components

​The image above shows the process needed to make the graphite bendable, which involves several manufacturing processes. The Xiaomi Mi Mix Fold went on slae in China on Friday April 16. The smartphone is powered by the Snapdragon 888 chipset, it has a 6.52-inch external display, 8.01-inch internal folding display, a 5,020 mAh battery with 67W fast charging, 108MP main camera with liquid lens + 13MP ultrawide + 8MP telephoto camera. The 12GB/256GB model will retail for CNY 10,000 (~$1,533). a 12GB/512GB storage option will be retail for CNY 11,000 (~$1,686), and the 16GB/512GB variant will go for CNY 13,000 ($1,993).