X-ray Inspection of PCBAs - 2D or 3D-CT?
Hidden solder joints under BGA, QFN or bottom-termination parts cannot be checked optically. This guide explains when X-ray inspection is required and how 2D radiography and 3D-CT differ for finding defects on assembled boards.
View soldering guidesWhen is X-ray inspection needed?
X-ray inspection becomes necessary whenever the solder joint is no longer optically accessible. On BGA, LGA, QFN and bottom-termination components the terminals sit under the package, so automated optical inspection (AOI) cannot see them. Only radiography reveals voids, bridges, open joints and head-in-pillow defects.
It also delivers reliable results on selective or wave-soldered through-hole joints, on press-fit contacts and when checking solder-paste coverage after reflow. In series production X-ray serves process control; in the lab it supports failure analysis on field returns.
- BGA / LGA / CSP: voids, bridges, missing balls, head-in-pillow.
- QFN / bottom termination: wetting and solder volume under the pad.
- Selective / wave THT: solder rise through the barrel.
- Press-fit pins and hidden connectors.
- Process control: void ratio and alignment after reflow.
2D radiography or 3D-CT - what does each show?
2D X-ray penetrates the assembly in one plane and produces a summed image of all overlapping structures. An oblique view (45‑70 degrees) lets you estimate joints in three dimensions. 2D is fast, affordable and sufficient for most production defects.
3D computed tomography (CT) captures hundreds of projections from many angles and reconstructs a volume model. Every slice plane can then be viewed on its own - free of superposition. CT reveals fine cracks, the exact void distribution over height and inner defects that 2D cannot separate. The cost: much longer scan time and higher system price.
What matters when choosing a system?
The key factors are tube type, detail detectability and magnification. An open microfocus or nanofocus tube reaches detail detectability below 1 µm and fine resolution on modern package terminals. Sealed tubes need less maintenance but resolve more coarsely.
- Tube power and focal spot: define detail detectability.
- Magnification: geometric (distance) plus digital at the detector.
- Detector: flat-panel detector for dynamic range and low noise.
- Tilt axis / oblique view for a 3D impression without full CT.
- Software: automatic void measurement and IPC grading.
Frequently asked questions
Is X-ray inspection dangerous for the operator?
Modern systems are fully radiation-shielded enclosed cabinets and safe below legal limits in operation. They fall under radiation-protection rules but require no personal protective equipment in normal use.
When is 2D enough and when do I need 3D-CT?
For voiding, bridges and open joints in series production 2D is enough, often with oblique views. 3D-CT pays off for fine cracks, exact void distribution over height and root-cause analysis of individual failures.
Does X-ray damage the components?
At usual inspection doses electronic parts stay undamaged. Only very high doses and very long CT scans can stress sensitive devices - mainly a concern with repeated CT analysis.
What void limit should I set?
As a guide, IPC references often cite around 25 percent void area per BGA ball. Critical power or thermal applications set tighter limits. The criterion should be fixed per project in the inspection plan.
X-ray inspection for your assemblies?
From 2D radiography for the line to 3D-CT for failure analysis - we advise on method, resolution and IPC-based void grading.
IPC-graded
Void and joint grading to IPC-A-610 and IPC-7095.
Fine resolution
Microfocus systems with detail detectability below 1 µm.
2D and 3D-CT
The right method for series and failure analysis.
Expert advice
Specialists support system choice and inspection plan.