How to Identify a High-Quality PCB: Full Inspection Guide

I. Design Phase Inspection (DFM/DFA)

Core Objective: Identify design flaws in advance to minimize production rework risks.

1. Electrical Performance Design Verification

• impedance Matching: Characteristic impedance of high-speed signal transmission lines (e.g., USB, HDMI, RF lines) must meet design requirements (e.g., single-ended 50Ω, differential 90Ω). SI simulation tools (e.g., HyperLynx) are used to avoid signal reflection and attenuation.
• Signal Integrity: Check for cross-talk, delay, and power integrity (PI) to ensure high-frequency signals are interference-free. Maintain good power/ground plane coupling to reduce EMI radiation.
• Layer Stackup Design:Confirm Insulation layer thickness, copper layer count, and stackup order to balance heat dissipation and impedance control, meeting EMC requirements.

2. Manufacturability Rule Check (DFM)

• Trace Parameters:Minimum trace width/spacing ≥3mil (1mil for HDI), Solder Mask bridge ≥4mil.
• Hole Diameter and Pad: Recommended via 0.3mm, pad 0.6mm to prevent drill deviation or pad detachment.
• Copper Thickness Design: Power traces use 1oz–2oz (35–70μm) to meet current load and prevent overheating.

3. Mechanical Structure Adaptability

• Outline, holes, and slots match enclosure tolerance (±0.1mm).
• Thermal-sensitive components spaced from heat-generating parts with ventilation paths.
• Polarity markings must be clear for capacitors and ICs.

II. In-Production Quality Monitoring

Core Objective: Real-time control of process deviations to ensure process compliance.

1. Substrate and Material Inspection

• Check material type (FR-4, Rogers, PI), thickness (±5%), and copper roughness.
• Surface should be scratch-free, oxidation-free, no delamination.

2. Drilling and Vias Process

• Hole Diameter Accuracy: Tolerance ±5%, clean hole walls, no burrs or smear.
• Hole Metallization: Electroless copper ≥0.5μm, plated copper ≥20μm (IPC-6012 Class 3).

3. Imaging and Etching

• Registration deviation ≤5mil, trace width uniform, residual copper ≤1%.
• Silkscreen clear, offset ≤10mil, good adhesion.

4. Surface Finish Inspection

• ENIG: Nickel 3–5μm, gold 0.05–0.1μm, no black pad.
• OSP: Coating 0.2–0.5μm, ion contamination ≤1.56μg/cm².
• HASL: Thickness ≥2.5μm, smooth surface, ≥95% solder wetting.

5. Lamination and Impedance Control

• Registration deviation ≤10mil, even dielectric thickness, no bubbles or delamination.
• Critical signal impedance within ±10%, verified by TDR.

III. Finished Product Functional and Reliability Testing

Core Objective: Ensure PCB electrical performance and long-term stability.

1. Electrical Performance Testing

• Continuity ≤5mΩ, insulation ≥10⁹Ω @500V DC.
• Test insertion loss (≤3dB @5GHz) and return loss for high-speed designs.

2. Reliability Testing

• Thermal Shock: 260°C, 10s immersion, no delamination or blistering.
• Dielectric Withstand: 500V DC for 1 min, no breakdown.
• Solderability: 245°C for 3–5s, ≥95% wetting.

3. Visual and Dimensional Inspection

• AOI for short/open circuits, solder mask, oxidation.
• Outline ±0.1mm, hole ±0.05mm, lamination thickness ≤±10%.

4. Advanced Structural Testing

• Plating Thickness: XRF to check copper and gold/nickel layers.
• Cross-Section: Optical check for layer thickness, adhesion, and hole wall metallization.

IV. Special Scenario Additional Inspections

1. High-Frequency/High-Speed PCBs

• Network analyzer for S-parameters: signal loss ≤3dB @≥5GHz, impedance error ≤±8%.

2. Flexible/Rigid-Flex PCBs

• Bending Test: 100,000 cycles @R≤2mm, no cracks.
• Mechanical Strength: No delamination in stiffened areas.

3. Automotive/Medical/Aerospace-Grade PCBs

• Meet IPC-A-600 Class 3, UL, RoHS/REACH, V-0 flame resistance.

V. Inspection Tools and Industry Standards