Imaging Error
Apparent shifts in the position of features on a non-planar surface when viewed from different angles can lead to errors in automated optical inspection. The effect of surface topography parallax occurs when high components or warped boards are captured by cameras positioned at an offset. Measurement reliability depends on compensating for these spatial distortions.
Inspection Geometry
Light reflecting from the sides of a tall capacitor or a bent pin enters the lens at an angle that does not represent the true footprint of the part. Because surface topography parallax distorts the spatial relationship between the component and the pads, the software might report a misalignment where none exists. Telecentric lenses are often employed to mitigate this issue by ensuring that the chief rays are parallel to the optical axis.
Advanced systems use multiple cameras and structured light to reconstruct a three dimensional model of the board surface. Geometric data allows the algorithm to compensate for the height of the features.
Measurement Accuracy
Reliable defect detection requires a clear distinction between a physical shift and an optical distortion. If surface topography parallax is not managed, the inspection threshold must be widened to avoid false rejections. High density boards with many tall components are particularly susceptible to these viewing angle discrepancies.
Precise calibration of the imaging system ensures that the measured coordinates match the actual physical layout.
