Heat Expansion
Localized heating of the x-ray anode by the electron beam causes a physical change in the position and shape of the focal spot. As the tungsten or diamond surface absorbs energy, target thermal expansion shifts the point where x-rays are generated relative to the optical axis of the system. This movement occurs on a microscopic scale but is enough to impact the accuracy of high-magnification images.
Source Shift
Positional drift in the x-ray source introduces geometric errors into the projection data used for 3d reconstruction. If the source moves during a scan, the software sees the sample as having shifted, leading to blurring or artifacts in the final volume. Engineers measure target thermal expansion to determine the warm-up time required for the x-ray tube to reach a stable equilibrium.
Stable source geometry is essential for the automated measurement of small features like solder balls or internal copper traces.
Focal Stability
Advanced x-ray tubes use liquid cooling or specialized mounting techniques to dissipate heat and minimize the movement of the anode. Software algorithms can also detect the shift in the source position by tracking a fixed reference marker within the field of view. When target thermal expansion is properly managed, the system maintains a constant magnification and a sharp focus throughout the entire inspection cycle.
Failure to account for this physical phenomenon results in measurement variances that lead to false rejects.
