Ensuring the signal integrity (SI) of the connecting line can be summarized as a closed-loop process of "one line, two grounds, three matching, four shielding, and five verification":

1. One line: impedance line

Control the differential impedance deviation within ± 10% according to standards (USB 90 Ω, HDMI 100 Ω, car CAN 120 Ω, etc.)

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Use a continuous reference plane (ground/power layer) and closely adhere to the signal layer to maintain uniform thickness and reduce impedance transients

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2. Two plots of land: reflux and isolation

Provide adjacent 'mirror' return paths (ground or plane) for each signal line, with a width of ≥ 3 times the line width

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Insert Guard Trace or ground copper between key signals, following the 3W rule (line spacing ≥ 3 x line width) to suppress crosstalk.

3. Three matching: source line load

Source end: Connect in series with 22-33 Ω; Load end: use parallel or Thevenin end connection to eliminate reflection

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Differential pair: equal length (≤ 5 mil error), tight coupling, same layer and same impedance

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4. Four shielding: material+structure+grounding

Material: Copper foil/aluminum foil+woven mesh, shielding effectiveness ≥ 60 dB@1  GHz。

• Structure: 360 degree surround, seamless overlap; The connector end uses a metal shell or finger spring to ensure 360 degree grounding continuity.

Grounding: Single ended shielding with single point grounding, differential shielding with both ends grounded; Multiple grounding points with RC grounding rings.

5. Five verifications: simulation+testing

• Design phase: Use SI/PI tools to run eye diagrams, S-parameters TDR， Margin ≥ 0.3 UI

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• Sample stage: TDR impedance curve measurement, oscilloscope eye diagram, network analyzer measurement of return loss>15 dB target frequency band

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Production stage: Sampling for 1000 hours of high-temperature aging, vibration, and shielding effectiveness retesting to ensure long-term stability.