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Why Impedance Control Determines 5G Module Performance

As 5G modules move into Sub-6GHz and mmWave (26GHz+) bands, their signal transmission speed easily exceeds 10Gbps. At such high frequencies, HDI PCB impedance control becomes the decisive factor affecting signal integrity.

Industry data shows:

• When impedance deviation exceeds ±10%, the Bit Error Rate (BER) of 5G signals can increase by 50%.

• One well-known module manufacturer experienced impedance drifting between 58Ω–65Ω (standard: 50Ω ±5%), resulting in:

• 22% connection drop rate

• Failure to pass carrier certification

According to IPC-2141 (High-Frequency PCB Standard), Chapter 6, the impedance deviation for 3.5GHz and 26GHz 5G bands must be ≤±5%.

PCBGOGO has focused on 5G HDI manufacturing for 7+ years, consistently achieving ±3% impedance stability for mass-produced 5G module PCBs.
This article explains the core principles, simulation workflow, and mass-production controls that guarantee 5G signal integrity.

Core Technical Analysis: Multi-Parameter Coordinated Impedance Matching

Effective impedance control for a 5G module HDI PCB requires multi-parameter coordinated matching, combining IPC-2226 HDI design rules with high-frequency signal behaviors.

2.1 Dielectric Constant (εr) Stability

The mmWave 26GHz band is extremely sensitive to εr fluctuations:

• Every 0.1 change in εr increases impedance deviation by ≈3%.

• Standard FR-4 (εr fluctuation ±0.3) may cause ±9% impedance deviation, failing 5G requirements.

Recommended Material:
? Rogers RO4350B — εr = 4.4 ±0.05@10GHz
? Loss tangent: 0.0037
? Ideal for 26GHz+ 5G modules

2.2 Trace Width & Spacing Precision

For 5G HDI differential routing:

• Trace width: 0.12–0.15mm

• Trace spacing: 0.12–0.15mm

• Tolerance: ≤±0.01mm

Every 0.02mm deviation in trace width results in ≈5% impedance error, consistent with GB/T 4677 Clause 4.1.

2.3 Layer Thickness Uniformity

HDI stack-up thickness variation must be:

• ≤±0.005mm

• A 0.01mm deviation increases impedance error by ≈2%

• Based on IPC-A-600G Class 3 requirements

Common Target Impedances

Using the classical microstrip formula:

Z=60?rln?(5.98hW)Z = \frac{60}{\sqrt{\epsilon_r}} \ln\left(\frac{5.98h}{W}\right)Z=?r60ln(W5.98h)

PCBGOGO HyperLynx simulation confirms that:

• Rogers RO4350B (εr=4.4)

• Line width W=0.15mm

• Dielectric thickness h=0.1mm

→ Achieves 50Ω ±2% impedance accuracy.

3. Implementation Guide: Four-Step HDI Impedance Control Flow

3.1 Step 1 — Material Selection

3.2 Step 2 — HDI Stack-Up Simulation (HyperLynx)

Example HDI stack-up: 6-layer 2+2 structure
Signal – Ground – Power – Power – Ground – Signal

Simulation requirements:

• Layer thickness: 0.1mm ±0.005mm

• Input measured εr (e.g., 4.42)

• 50Ω microstrip: W=0.15mm, h=0.1mm

• 90Ω diff-pair: W=0.12mm, spacing=0.12mm

Simulation pass criteria:
? Impedance deviation ≤±2%

If deviation exceeds ±3%, adjust:

• h by ±0.005mm

• W by ±0.005mm

PCBGOGO provides optimized stack-up within 48 hours.

3.3 Step 3 — Routing Execution

• Enable “trace width lock” in Altium Designer

• 50Ω single-end: 0.15mm ±0.005mm

• 90Ω differential:

• Width: 0.12mm ±0.005mm

• Spacing: 0.12mm ±0.005mm

• Differential pair length matching ≤3mm

• Add clear impedance markers (e.g., “50Ω RF”, “90Ω PCIe”)

3.4 Step 4 — Mass-Production Control

Yield rate: ≥99.5%

3.5 High-Frequency Interference Control (26GHz+ mmWave)

1. Shielding Design

• Copper pour width ≥0.2mm on both sides of the RF trace

• Keep ≥0.15mm spacing from signal line

• Shielding effectiveness ≥40dB @26GHz

• Tested via IPC-TM-650 2.8.1

2. Via Optimization

• RF via drill: 0.2mm

• Via spacing ≥0.5mm

• Ground-stitch vias around signal via (0.3mm pitch)

• Via impedance deviation ≤±5%

3. Absorbing Materials

• mmWave absorber thickness: 0.1mm

• Absorption rate ≥80% @26GHz

• PCBGOGO supports automated absorber placement

Conclusion: Reliable 5G Performance Requires End-to-End Impedance Control

5G module HDI PCB impedance control depends on:

1. Material stability

2. Accurate simulation

3. Strict production control

For 26GHz+ mmWave scenarios, shielding and absorber design are essential.

PCBGOGO’s Full-Process 5G HDI Impedance Service includes:

? Material εr measurement report
? HyperLynx precision simulation (≤±2%)
? HDI process control (trace/layer tolerance ±0.005mm)
? 100% impedance testing (yield ≥99.5%)

Future Optimization Trends

1. 5G HDI + LTCC integration

• Impedance variation ≤±2%

• Enhanced stability for mmWave

2. Impedance-attenuation coupled simulation

• Predict total transmission performance during the design stage

5G module companies are advised to establish a High-Frequency Impedance Assurance Agreement with PCBGOGO to ensure stable certification performance.