Optical Triangulation Error Models under Dynamic Printed Circuit Board Warpage
Dynamic substrate distortion induces height shifts in optical triangulation systems, requiring real-time surface mesh interpolation to prevent false deposit rejects.
Optical Spatial Frequency
Periodic Resolution
Quantitative measure of the number of line pairs per unit distance defines the ability of an imaging system to resolve fine details. Within automated inspection, optical spatial frequency determines the smallest solder bridges or pad features that a camera can reliably detect. Higher frequencies represent finer details while lower frequencies correspond to the larger structures of the board.
Detail Capture
Modulation transfer function of the lens assembly limits the maximum optical spatial frequency that the sensor can capture. If the spacing of the PCB features exceeds this limit, the resulting image appears blurred or loses contrast. Designers select camera and lens combinations that maintain high contrast at the frequency required for the smallest component pads.
Small passives require a system capable of resolving very high spatial frequencies to ensure accurate edge detection.
System Bandwidth
Optimization of the lighting and sensor resolution ensures that the optical spatial frequency of the target matches the system capabilities. Aliasing occurs when the pattern on the circuit board is finer than the pixel pitch of the detector. To prevent aliasing, the inspection system must oversample the image or use optical filters.
The balance between the field of view and the resolvable frequency dictates the total inspection time per board.