X-Ray Inspection in PCB Manufacturing

Not all PCB defects are visible from the surface.

As PCB designs become:

• Thicker
• More complex
• Higher density

Many critical defects occur inside vias, plated holes, and internal layers—areas invisible to optical inspection.

X-ray inspection enables manufacturers to examine these hidden structures and identify defects that AOI cannot detect.

Previous inspection method:
AOI Inspection in PCB Manufacturing

What Is X-Ray Inspection?

X-ray inspection utilizes controlled X-ray radiation to visualize the internal structures of PCBs.

Unlike optical inspection, X-ray imaging:

• Penetrates materials
• Reveals internal geometry
• Shows density variations

This makes it ideal for evaluating vias, plated through holes, and internal features.

What Is X-Ray Inspection?

X-ray inspection utilizes controlled X-ray radiation to visualize the internal structures of PCBs.

Unlike optical inspection, X-ray imaging:

• Penetrates materials
• Reveals internal geometry
• Shows density variations

This makes it ideal for evaluating vias, plated through holes, and internal features.

Defects Commonly Detected by X-Ray Inspection

X-ray inspection is especially effective at identifying internal and volumetric defects.

Via and Hole Defects

• Voids in copper plating
• Incomplete hole fill
• Thin barrel copper
• Offset or misaligned vias

Internal Structure Issues

• Layer misregistration
• Internal shorts
• Resin voids
• Delamination pockets

Failure mechanisms:
PCB Reliability Testing Explained

X-Ray Inspection vs AOI

X-ray inspection and AOI address different types of defects.

They are complementary, not interchangeable.

When X-Ray Inspection Is Applied

X-ray inspection is typically used:

• For high-density or multilayer PCBs
• On high-aspect-ratio vias
• During process validation
• For failure analysis

It is less common for low-complexity, high-volume products due to cost.

X-Ray Inspection in HDI and High-Reliability PCBs

HDI designs increase reliance on:

• Microvias
• Stacked or staggered vias
• Thin dielectrics

X-ray inspection helps verify:

• Microvia fill quality
• Stacked via alignment
• Copper continuity across layers

Process complexity:
PCB Manufacturing Process Explained

Limitations of X-Ray Inspection

Despite its strengths, X-ray inspection has limitations.

Key Limitations

• Limited resolution for very thin features
• Interpretation requires skilled engineers
• Cannot fully evaluate electrical performance
• Sampling-based, not always 100%

X-ray inspection identifies potential issues but often requires correlation with electrical or reliability testing.

X-Ray Inspection and Reliability Risk Reduction

X-ray inspection plays a key role in reducing:

• Latent via failures
• Thermal fatigue issues
• Intermittent electrical faults

By identifying internal plating defects early, manufacturers can adjust:

• Drilling parameters
• Plating chemistry
• Aspect ratio limits

Cost-quality balance:
PCB Manufacturing Cost vs Quality Trade-offs

How X-Ray Fits into a Complete Inspection Strategy

A robust PCB inspection strategy typically includes:

• AOI for surface defects
• X-ray for internal structures
• Electrical testing for continuity
• Reliability testing for long-term performance

At TOPFAST, X-ray inspection is selectively applied based on design complexity and reliability requirements, ensuring efficiency without unnecessary cost.

Conclusion

X-ray inspection provides visibility into the hidden structures of PCBs that optical methods cannot reach.

While it is not required for every design, X-ray inspection is essential for:

• HDI PCBs
• High-reliability applications
• Process validation and failure analysis

This article forms the second technical pillar of the PCB Inspection & Testing cluster.

X-Ray Inspection FAQ