iPhone X, as Apple's new product to commemorate the 10th anniversary of the iPhone, is innovative and attracts the attention of the world. In the past "Black Friday" weekend promotion, iPhone X sold 6 million units in the United States, and the market was extremely hot. As a thermal design engineer, the author conducted actual disassembly and temperature testing, and this paper interprets its hardware thermal design .
Machine architecture
The iPhone X's overall architecture is similar to that of the iPhone 8 and iPhone 8 plus. It is a two-piece structure, in which the motherboard and battery are sandwiched between the screen and the back cover, just like a sandwich. As shown below.
Two heat transfer paths: screen and back cover
Graphite sheet is attached to the inside of the screen for the purpose of soaking, large area and thickness of 0.1mm, which is double-layer graphite, as shown in the following figure. The screen acts as one of the heat transfer paths, and its thin-wall heat transfer capacity is 0.06 W/k (the definition and calculation method of thin-wall heat transfer capability is shown in the previous article, "iPhone 8 Cooling Solution Analysis").
The structure of the back cover is exactly the same as that of the iPhone 8: the back cover is a glass layer + lining steel plate, and there is a large hole in the center of the steel plate due to the presence of the wireless charging coil. A copper foil graphite layer is attached to the coil, and the copper foil and the aluminum plate are overlapped by 2 mm to compensate for the uniform heat capacity of the large hole.
The main function of the lining steel plate is to install and fix the main board and the battery. Because the thickness of the steel plate is only 0.15mm, the thin-wall heat transfer capability is very weak, and the copper foil graphite layer on the wireless coil and the thin-wall heat transfer capacity of the back cover are provided. About 0.02W / k, compared with the back cover of other mobile phones, iPhone X's back cover heat transfer capacity is weak, about 1 / 9 of the heat transfer capacity of the rear cover of the Mai Mang 5.
Motherboard
A small area of ​​graphite is attached to the shield cover on the top surface of the main board (near the screen side) as shown below. The purpose of this piece of graphite is to allow heat from the CPU to conduct to the SIM card holder. However, because this graphite sheet has a small area (about 40 mm in length) and the narrowest joint in the middle is only 4 mm, the heat conductivity of this graphite is very limited.
The bottom surface of the main board (near the back cover side) has no device, and the entire bottom surface is affixed with a large area of ​​graphite sheet. The size is the same as the main board size: 45mm*25mm*0.07mm, which is a single layer of graphite, as shown below. The graphite has a certain soaking effect, and the hot spots at the CPU of the main board are opened, which eliminates the concentration of hot spots to some extent.
The Iphone X motherboard is a major innovation. The footprint of the motherboard is 70% of the Iphone 8 plus, and the area used is 135% of the latter. This high area usage is achieved through a two-layer motherboard. As shown in the figure below.
This approach is innovative because it solves more device placement with a smaller footprint. But this solution is not good from the thermal design, because the CPU does not have a conventional thermal solution. In general, the conventional thermal conduction scheme of the CPU is that the top of the CPU is connected through one of the TIM (interface material) and one of the heat conduction paths (the middle plate or the back cover), so that the heat of the CPU can be smoothly conducted. Do not worry that the CPU is floating, because this will cause the CPU itself to be too hot.
But Iphone X's practice of sacrificing CPU temperature also has some truth. Because in the thermal design of mobile phones, the temperature of the CPU is not a bottleneck (see "The second part of the factors that determine the surface temperature of the mobile phone? "), so the temperature of the CPU has some room to make concessions, here the concession gives the floor space.
The author guesses that in the game scene, the CPU temperature of the iPhone X will be higher, which will exceed the usual 60 ° C, and may reach 85 ° C. However, because the IOS system of Apple's mobile phone is closed, it can't monitor its internal temperature like the Android phone. However, as a user, we don't have to worry about the internal temperature, just pay attention to the surface temperature of the phone.
Cooling capacity comparison
At this point, the heat transfer capability of the two heat transfer paths inside the iPhone X phone can be compared with the two mobile phones Samsung C7 and Maimang 5 with better heat dissipation design. The comparison data is as follows.
Test verification
The ambient temperature is 25 ° C, running the king glory high frame mode for 1 hour, the maximum temperature point of the iPhone X's back cover is 44 ° C, and the cold and hot spot temperature difference of the back cover surface is 7 ° C. In the competitive machine test that I conducted, this temperature performance is not good, and the surface temperature uniformity is also weak. This also basically confirms the analysis conclusion that the above hardware cooling ability is weak.
King's glory for 1 hour
to sum up
The iPhone X's hardware cooling solution is moderately weak and has room for improvement. The surface temperature of the mobile phone is high and the surface temperature is not uniform. But the author has to say again that the cooling solution of the mobile phone is not independent, but the result of balancing with the overall architecture, cost, operating system and software optimization. The iPhone X's cooling solution is so, there should be a reason. In any case, the iPhone X is by far the best smartphone and deserves careful study by practitioners. This article only analyzes from the perspective of heat dissipation design for readers' reference.
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