In AI smart motherboard design, optimized electromagnetic interference (EMI) layout is crucial for ensuring stable system operation and compliance with electromagnetic compatibility (EMC) standards. AI smart motherboards integrate high-speed processors, large-capacity memory, and various interfaces; their high-frequency signal transmission and complex circuit layout can easily lead to excessive EMI, requiring a systematic layout strategy to suppress interference.
Isolation design of critical signal layers is fundamental to reducing EMI. In AI smart motherboards, high-speed differential signals (such as PCIe and USB 3.0) and low-speed control signals need to be layered to avoid high-frequency signals and sensitive signals being transmitted on the same plane. For example, placing the PCIe signal layer between the GPU and CPU in the middle layer of the motherboard, with complete ground layers on both sides, can form a natural shielding cavity, reducing signal radiation. Simultaneously, differential pair traces must strictly maintain equal length and spacing to avoid common-mode radiation caused by impedance discontinuities. One AI server motherboard, through optimized signal layer isolation, reduced radiation intensity in the 10GHz band, meeting FCC Part 15 requirements.
Proper allocation of power and ground is essential for suppressing EMI. The power network of an AI smart motherboard design requires a layered design, distributing core voltages (e.g., 1.8V, 0.8V) and auxiliary voltages (3.3V, 5V) to different power layers, and achieving local decoupling through decoupling capacitor arrays. The ground layer must adhere to the "single-point grounding" principle to avoid ground loops. For example, placing small-capacity (0.1μF) 0402 packaged capacitors around the processor and large-capacity tantalum capacitors (100μF) at the power input can effectively filter high-frequency noise. One AI accelerator card reduced power noise amplitude from 50mV to 15mV by optimizing the power layout, significantly reducing radiated emissions.
Shielding and filtering of interface circuits are crucial for controlling electromagnetic radiation. High-speed interfaces such as Ethernet and HDMI in an AI smart motherboard design require a combination of common-mode chokes (CMChokes) and ferrite beads for filtering to suppress common-mode current radiation. Metallized via arrays should be arranged around the interface connectors to form a Faraday cage structure. For example, after adding a ferrite bead filter to the gigabit Ethernet interface, the radiation intensity in the 100MHz-1GHz frequency band of a certain AI edge computing device decreased, passing CE certification testing. Simultaneously, interface signal lines require grounding treatment, i.e., dense vias connecting to the ground plane on both sides of the signal lines to reduce antenna effects.
Optimizing the layout of the clock circuit can significantly reduce periodic radiation. The clock source (such as crystal oscillator, PLL) of the AI intelligent motherboard needs to be kept away from high-speed signal traces, and the clock line length should be shortened. Using differential clock transmission can reduce common-mode radiation; for example, changing the processor clock signal to LVDS differential form reduces radiation intensity. A certain AI training cluster motherboard, by moving the clock source to the edge of the motherboard and adding a shielding cover, ensured that the harmonic radiation of the clock frequency (24MHz) met the CISPR 32 standard.
The coordinated design of heat dissipation structure and electromagnetic shielding must consider both thermal management and radiation control. Components such as heat sinks and fans of the AI intelligent motherboard may become "secondary antennas" for electromagnetic radiation; conductive foam or conductive adhesive should be used to achieve electrical connection between the heat dissipation components and the motherboard. For example, attaching conductive foam to the edge of a GPU heatsink can form a continuous shielding layer, reducing radiation leakage. An AI workstation motherboard, through optimized heat dissipation shielding design, reduced radiation intensity in the 30MHz-1GHz frequency band while improving heat dissipation efficiency.
Symmetrical layout and redundant design enhance electromagnetic compatibility (EMC). A symmetrical layout of the AI motherboard reduces radiation differences caused by uneven component distribution; for example, decoupling capacitors can be symmetrically placed on both sides of the processor power pins. Redundant design, such as adding backup signal paths, can prevent sudden radiation spikes caused by single-point failures. An autonomous driving computing platform significantly improved electromagnetic radiation stability by adopting a symmetrical layout and redundant power supply design.
Electromagnetic radiation optimization for AI motherboards requires a multi-dimensional approach, including signal layer isolation, power distribution, interface filtering, clock layout, heat dissipation shielding, and symmetrical design. Through the comprehensive application of these layout strategies, electromagnetic interference can be effectively reduced, ensuring stable operation of the AI motherboard in complex electromagnetic environments and meeting stringent EMC standards.
