Geometric Calibration Targets for Surface Mount X-Ray Inspection
Geometric calibration targets establish spatial scale and correct optical distortion, guaranteeing valid void and dimensional measurements in SMT X-ray inspection.
Spatial Magnification Factor
Scaling Ratio
X-ray inspection systems rely on geometric projection to enlarge small internal features of printed circuit boards onto a larger digital sensor. The ratio of the distance from the x-ray source to the detector over the distance from the source to the object is the spatial magnification factor. This value determines the size of the projected image of a solder joint relative to its physical size.
It is a key variable in determining the sub-micron resolution of the system.
Geometric Influence
Machine kinematics adjust the positions of the x-ray tube, the board and the detector to alter the image size. Increasing the spatial magnification factor requires moving the object closer to the x-ray source or moving the detector further away. This shift reduces the field of view, meaning that more images must be captured to inspect a given area of the board.
The system must calculate the required magnification for each component type, balancing the need for fine-detail inspection against total scan time.
Resolution Threshold
Blur limits the effective magnification when the focal spot is larger than the required feature size. The spatial magnification factor must be matched to the spot size to avoid empty magnification where the image is larger but contains no additional detail.