The Xiaomi MIX Fold was released at the end of March. This is Xiaomi’s first foldable screen phone. Recently, Xiaomi officially explained some technologies of heat dissipation.
The Xiaomi MIX Fold uses a “micro airbag” structure to bend-resistant graphite sheets to open up the parallel three-dimensional heat dissipation system on both sides. This solves the problem of difficult heat dissipation of the folding screen.
Main Problems Of Folding Screen Phones In Terms Of Heat Dissipation
According to the company, at present, folding screen smartphones will mainly face two heat dissipation problems:
- The heat dissipation capacity will change when folding and unfolding.
- The internal distribution of components is not balanced, and the heat dissipation environment on the motherboard and SoC side will be even worse.
In response to these two problems, Xiaomi has developed a parallel dual three-dimensional heat dissipation system and an innovative “micro airbag” heat dissipation mechanism. Not only is there a powerful heat dissipation system on the left and right sides of the phone, but also the two are connected to achieve a brand new “Butterfly” heat dissipation.
The MIX Fold comes with Qualcomm’s flagship chip, the Snapdragon 888 platform, which brings huge heat dissipation pressure for the MIX Fold. The engineers had to extract heat from one side of the SoC, balance the temperature rise on both sides, and reduce temperature unevenness.
The MIX Fold comes with VC liquid cooling solution + thermal gel + multilayer graphite sheet + material-grade bending resistant graphite sheet. There is a whole piece of copper foil under the screen for heat dissipation, and the total heat dissipation area has reached 22583.7mm².
Even if the heat dissipation capacity is disadvantageous in the folding form, it has a larger internal space. So it has a great advantage in the total heat dissipation area compared to non-folding screen smartphones. In comparison, the total heat dissipation area of the Mi 11 is 12677mm2. As for the MIX Fold, it is almost twice that of the Mi 11, thus exerting a stronger heat dissipation capacity.
However, in actual situations, it is not easy to compare the heat dissipation area with the heat dissipation capacity. Due to the design of the folding screen of MIX Fold, the part of the shaft is beyond the reach of conventional heat dissipation materials. So the heat dissipation system of the MIX Fold will generally be based on the folding screen. The screen is divided into left and right parts, which we vividly call the parallel dual three-dimensional cooling system.
What Other Problems Are There?
But this faces the second problem. The internal components on the left and right sides are not balanced, and the side where the motherboard and SoC are located will definitely face greater heat dissipation pressure.
In order to solve the problem of unbalanced heat dissipation, Xiaomi’s R&D engineers conceived a “heat transfer tunnel” in the case of limited stacking space to connect the parallel heat dissipation systems on both sides of the shaft.
This is similar to building a bridge across the river. The heat is like a flow of traffic, which can quickly reach the other side through the bridge, thus revitalizing the mobility of the entire city.
But the key is how to build this tunnel? If you want to get through the left and right sides, you need a kind of thermal conductive material to connect the two. And this thermal conductive material also has the ability to resist bending, in order to deal with the situation that MIX Fold may be unfolded or folded at any time.
The answer given by Xiaomi’s thermal design engineer is “flexible graphite”.
Traditional graphite flakes will break or drop slag after 200,000 times of bending, while the thermal performance of bending resistant graphite flakes is even better. After 200,000 times of 180-degree bending, the thermal performance of the material will only drop by 3 %-5%, less than 9-15% of the sector structure.
However, it is not easy to realize the bending-resistant graphite sheet of the “micro airbag” structure. It requires several different process innovations in details. The company summarized it into two points:
- Folding fatigue resistant single-sided tape: thick PI substrate, compared with PET substrate products, minimizes displacement stress, and its bending resistance is greatly improved
- Bend-resistant synthetic graphite: By optimizing graphitized foaming and precision calendering technology, the micro-folding of the product is controlled, and the product is highly flexible and achieves bendable performance.
At the same time, the MIX Fold has also been upgraded on the temperature control design side:
- Dual-form shell temperature recognition model: the engineers have inserted 8 temperature sensors into the fuselage. Plus, they carried out an AI modeling to the user scene data under expansion and folding. At last, they used the neural network for continuous learning and optimization. In the very end, they obtained a concise and accurate surface temperature to accurately perceive the surface temperature of smartphones in dual modes.
- Two-form dual temperature control system: It identifies the smartphone form through the front-end app interface, and on the basis of the fine division of the original user’s use scene, in-depth customized control of the temperature control gear under expansion and folding.