Geometric Distortion
X-ray image degradation occurs when the finite size of the radiation source creates a region of partial shadow around the edges of an object. This effect, known as penumbral blur, increases as the source size grows or as the distance between the printed circuit board and the detector decreases. The resulting image lacks sharp transitions, which complicates the accurate measurement of tiny assembly features.
Geometric Factors
Controlling the geometry of the inspection setup is the primary method for minimizing this unwanted edge unsharpness. A smaller focal spot in the x-ray tube reduces penumbral blur, whereas a larger focal spot increases it, causing the boundaries of solder joints to appear fuzzy. The spatial relationship between the x-ray source, the circuit board assembly and the digital sensor determines the magnification and the resulting edge transition zone.
When inspecting fine-pitch components like micro-BGAs, minimizing the distance between the board and the detector helps reduce this blur, allowing clearer visualization of internal solder voids.
Resolution Limit
Excessive edge unsharpness prevents automated analysis software from calculating the volume or diameter of solder fillets. When penumbral blur exceeds the size of the defect being sought, the defect remains invisible to the automated inspection algorithm. Maintaining a tight focus and optimal board placement is necessary to ensure consistent defect detection during production.
