Actual disassemble and temperature test iPhone X, revealing hidden technology highlights!

The iPhone X, Apple's groundbreaking device celebrating the 10th anniversary of the iPhone, has captured global attention with its innovative design and advanced features. During the recent Black Friday weekend, it sold an impressive 6 million units in the U.S., showcasing its massive market appeal. As a thermal design engineer, the author conducted a hands-on disassembly and temperature testing to analyze the hardware cooling system of this flagship model. **Machine Architecture** The overall structure of the iPhone X is similar to that of the iPhone 8 and iPhone 8 Plus. It follows a two-piece design where the motherboard and battery are sandwiched between the display and the back cover, much like a layered cake. This configuration is shown in the image below. **Two Heat Transfer Paths: Screen and Back Cover** A graphite sheet is placed on the inside of the screen, designed to spread heat over a large area with a thickness of 0.1mm, consisting of two layers of graphite. The screen acts as one of the primary heat transfer paths, with a thin-wall heat transfer capability of 0.06 W/K (for more details, refer to the previous article “iPhone 8 Cooling Solution Analysis”). The back cover follows a similar design to the iPhone 8, featuring a glass layer combined with a steel plate. A central hole is present due to the wireless charging coil, and a copper foil graphite layer is attached to the coil. The copper foil overlaps the aluminum plate by 2 mm to ensure even heat distribution around the hole. While the steel plate serves to mount and secure the motherboard and battery, its thinness (only 0.15mm) limits its heat transfer capability. The copper foil graphite layer and the thin-wall heat transfer capacity of the back cover provide about 0.02 W/K, which is significantly lower than that of other smartphones, such as the Maimang 5, being roughly 1/9th as effective. **Motherboard Design** On the top surface of the motherboard, near the screen, a small graphite sheet is attached to the shield cover. Its purpose is to conduct heat from the CPU to the SIM card slot. However, due to its limited size (approximately 40mm long) and a narrow section of only 4mm, the heat conductivity is quite restricted. On the bottom side of the motherboard, there are no components, and instead, a large graphite sheet covers the entire area. Measuring 45mm x 25mm x 0.07mm, this single-layer graphite sheet helps to spread out hot spots on the CPU, reducing their concentration. One of the major innovations of the iPhone X is its motherboard, which occupies 70% of the space of the iPhone 8 Plus but uses 135% of the area. This high utilization is achieved through a dual-layer motherboard design, as shown in the image below. This design allows for more components to be placed in a smaller footprint, but from a thermal perspective, it lacks a traditional thermal solution for the CPU. Normally, the CPU is connected via TIM (thermal interface material) to a heat conduction path, such as a middle plate or back cover, to efficiently dissipate heat. Without this, the CPU could potentially overheat. However, the iPhone X’s approach may have some merit. In mobile phone thermal design, CPU temperature is not typically the main bottleneck (as discussed in the second part of “Factors That Determine the Surface Temperature of a Mobile Phone”). Therefore, some trade-off in CPU temperature is acceptable to gain more internal space. The author estimates that during intensive gaming scenarios, the CPU temperature of the iPhone X could exceed 60°C, possibly reaching up to 85°C. However, since iOS is closed-source, users cannot monitor internal temperatures like Android users can. Still, users don’t need to worry about internal temperatures; they should focus on the surface temperature instead. **Cooling Capacity Comparison** To evaluate the cooling performance of the iPhone X, we compared its heat transfer capabilities with those of two well-designed smartphones, the Samsung C7 and the Maimang 5. The results are shown in the table below. **Test Verification** In a controlled test environment at 25°C, the iPhone X was run in high frame mode for one hour using the game "King of Glory." The maximum temperature on the back cover reached 44°C, with a temperature difference of 7°C between the hottest and coldest spots. This performance is considered subpar, and the uneven surface temperature further confirms the earlier analysis that the cooling system is relatively weak. **Conclusion** Overall, the iPhone X's thermal design is moderately weak and has room for improvement. The surface temperature is relatively high and uneven. However, it's important to note that thermal solutions in smartphones are not isolated; they result from a balance between the overall design, cost, operating system, and software optimization. The iPhone X’s cooling system likely has its own rationale. Despite its limitations, the iPhone X remains one of the best smartphones on the market and deserves careful study by engineers and enthusiasts alike. This article provides a thermal design perspective for reference only.

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