Geometric Parameter
Measurement of the total space between the X-ray tube and the imaging sensor determines the magnification and intensity of the resulting inspection image. Adjusting the source-to-detector distance allows the operator to balance the field of view against the level of detail required for a specific component. This distance is a fixed constraint in many automated inspection systems.
Changing Geometry
Changing the source-to-detector distance follows the inverse square law where the intensity of the X-ray beam decreases as the distance increases. A shorter distance provides a brighter image and faster acquisition times but limits the size of the board that can be inspected at once. Conversely, increasing the gap allows for a wider field of view but requires a higher tube current or longer exposure to maintain the same image quality.
The geometry also affects the penumbra or blurring at the edges of the features. Precise control of this parameter is necessary for the software to calculate the correct magnification and perform accurate measurements of solder volume or void size.
Maintaining Consistency
Maintaining a constant source-to-detector distance is essential for the repeatability of automated inspection routines. If the sensor moves unexpectedly the system must be recalibrated to ensure the pixel-to-micron ratio remains correct.
