PCB & PCBA X-Ray Inspection Services

What Is PCB X-Ray Inspection?

PCBA is made up of mechanical and electrical components; together, these create a complete electronic package. An X-Ray can be used as a PCB inspection method to non-destructively inspect the assembled PCBA for hidden structural defects. The X-Ray images are captured by sending radiation through the PCBA and using the X-Ray detector to record the amount of radiation received on the opposite side.

The X-Ray shows attenuation differences associated with different materials used on the PCBA; for example, thick solder joints and metal attenuate more radiation than thin laminate, while air and low-density voids create measurable grayscale differences in internal connections that cannot be seen with optical cameras.

The X-Ray allows an inspector to view internal connections and component features while maintaining the integrity of the assembled PCBA. Common features that cannot be viewed with standard optical cameras include BGAs, QFNs, PTH barrels, vias, and connections hidden by shields.

Non-Destructive Internal Imaging

The X-Ray image is created by positioning the target component so that it has the appropriate penetration, contrast, and geometric magnification to produce a clear X-Ray image. When X-Ray imaging is performed, material-density differences among solder masses, voids, gaps, laminate, and adjacent materials appear as various shades of gray. Projection angles produce different images; in some cases, a feature may appear clear at one projection angle but be obscured by another component at another projection angle.

Since X-Ray does not destructively alter the PCBA, it allows the same assembly to be reimaged at different projection angles, measured, electrically tested, and reworked before shipment.

Structural Evidence From X-Ray Inspection

Engineers can identify an area, establish a measurement region, and evaluate the visible condition against an accepted criterion. Electrical testing verifies continuity or functionality, while cross-section studies clarify selected interface, plating, and metallurgical details. X-Ray is responsible for locating and measuring the concealed structural condition.

Hidden PCB Connections Requiring X-Ray Inspection

When a connection is inside a plated barrel, behind a shield, beneath a package, under overlapping material, or otherwise inaccessible to common inspection methods, X-Ray provides the primary imaging method for confirming its structural condition.

Bottom-Terminated Packages

BGA, LGA, and CSP packages hide their connection arrays under the component body. X-Ray visualizes ball-to-pad alignment, solder distribution, potential hidden bridges, missing connections, and solder collapse consistency.

For devices that use a QFN layout with a central thermal pad and perimeter terminations, the joints cannot be viewed optically after mounting. X-Ray delineates the pad region, indicates void distribution and solder coverage, and compares alignment with the placement footprint. Package guidance and the accepted measurement rule control acceptance.

FC and other fine-pitch connections have smaller bumps located beneath the die or package. X-Ray may assess bump placement, bump geometry, bridging, and density variation. Separating bump views from surrounding materials generally requires angled X-Ray projections or CT imaging.

Structures Beyond Optical Access

Although the PTH may appear acceptable from the surface, there could be internal voids or insufficient fill in the barrel. X-Ray identifies how solder flows through the barrel and distinguishes low fill from voided areas using a defined view and barrel reference. When an acceptance criterion is based on interface, plating features, or metallurgical information, a cross-section through the selected area determines acceptance.

Shields, tall components, and other supports can create an additional line-of-sight obstruction. Therefore, inspecting through the material stack to expose hidden terminations and connector regions requires more than simply increasing magnification. An angled beam, laminography, or CT imaging may be needed to achieve the separation required for acceptance.

AOI vs. X-Ray by Joint Visibility

AOI is generally used to view exposed leads, markings, and placement features. PCB X-Ray is used when the joint or barrel is hidden or when solder distribution through a barrel or thermal area must be measured. Electrical testing verifies continuity and operation. Cross-sectioning is used when interface, plating, or metallurgical evidence is required.

2D vs. 2.5D vs. 3D X-Ray Inspection

The correct inspection method depends on the ability to separate and measure the target features. The largest magnification number printed on a system specification is not the determining factor when choosing between these methods.

Inspection engineers begin with the least complex method that produces a stable result. Factors that affect the choice of method include target size, material density, thickness, field of view, required measurements, and production demand.

AXI is an automated system that implements an inspection process; it is not a separate type of X-Ray imaging geometry. A programmed AXI system can repeat supported 2D, oblique, or laminographic views at specific locations to screen production items, monitor trends, and give immediate process feedback.

2D X-Ray Inspection

2D X-Ray inspections have limitations because they provide only a two-dimensional projection, allowing no separation between different depths in the same projection. Unrelated features can make the 2D void percentage inaccurate when they enter the denominator or segmentation region. Either a different viewing direction or a method of separating features by depth must be used to provide the correct measurement.

2.5D Laminography

Oblique imaging causes the beam to pass through the sample at a different angle and therefore causes the interfering feature to move away from the target feature. SUGA configurations allow up to 82° of oblique viewing angle. The usable angle is determined by the size of the board, height of components, fixture clearance, and location of the target. Laminography can also use multiple angled images to focus on a specific depth band without reconstructing a full CT volume.

Laminography has a limited imaging angle range. Sample height limitations, sample motion during inspection, and interference from high-density material can create blurring in the target image even after the layers have been separated. Laminography is suitable for dense assemblies when the required feature remains repeatable under these constraints.

3D CT Inspection

CT requires more scanning, reconstruction, and data evaluation than 2D or laminography. The volume to be scanned, the size of the features, and the area being evaluated determine how the CT is set up. The larger the reconstructed volume, the less detail is available in the area of interest. When scanning high-density metals, the material can create streak artifacts or beam-hardening effects. Feature recognition, voxel size, and the ability to guarantee defect detection are not interchangeable terms; therefore, the feature of concern needs to be defined before scanning.

X-Ray System Capability and Usable Limits

The focal spot and detector response characteristics, together with object-to-detector and source-to-object distances, field of view, material stack, and contrast, create the geometric magnification trade-off between field of view, penetration, and visible detail. The established SUGA capabilities include a 160 kV source and an oblique viewing angle of up to 82°; the remaining functions are platform-dependent based on the inspection system selected and how the job is configured.

Double-Sided PCB Overlap

Double-sided PCBs may have components placed both above and below the target beam path. That means a top-side joint could overlap a component, shield, or internal copper region on the bottom side. The combined density of both areas could hide a void, merge a bridge, or distort the defined measurement region.

The engineer determines the target measurement and whether the 2D projection produces repeatable results. When structures cross the beam path, oblique imaging or laminography precedes full CT analysis. Source energy, projection geometry, field of view, and exposure follow the required penetration and feature recognition, while production quantity determines whether to use AXI or deeper offline analysis.

X-Ray Inspection Deliverables

The deliverables associated with X-Ray inspection include a package that identifies the inspected PCB, panel, or lot; target locations; imaging method and configuration; original and marked images; measured values, units, regions, and calculation basis; the controlling customer, standard, or package requirement; and the final result or action. The program version, equipment used, and calibration records maintained as part of the completed inspection preserve traceability for future inspections.

How Is Inspection Coverage Set?

How Are X-Ray Results Traced?

Each result links those identifiers to the board or lot, inspected location, program version, equipment record, view, measurement region, and calculation basis. Repeat inspection reuses the same identifiers and settings; if the original projection is unstable, the report records the added oblique, laminographic, or CT method instead of comparing unlike measurements.

How Do X-Ray Findings Guide Process Changes?

BGA separation, alignment, or collapse patterns can indicate issues with placement, package warpage, paste transfer, or reflow. The pattern of voids formed beneath QFN or BTC thermal pads can indicate process-related issues with the stencil, paste, pad design, or thermal profile. PTH fill trends can indicate wave- or selective-solder parameters and local thermal mass.

Teams categorize defect patterns by location, panel position, lot number, reflow lane, or assembly line. Following a process adjustment, teams re-inspect using the same method and measurement region used before the adjustment. The data collected from X-Ray inspection is correlated with the corresponding print, placement, reflow, material, and electrical data to establish the root cause.