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.
Height Offset Equation
Vertical Reference
Mathematical relationship used to normalize the measured elevation of a solder deposit against the local PCB surface provides the basis for volumetric accuracy. Every height offset equation must account for the difference between the zero plane and the peak of the printed material. Without this subtraction, the thickness of the copper traces or the solder mask would be incorrectly included in the paste volume.
Inspection Adjustment
Integration of the height offset equation into the inspection algorithm allows the machine to ignore board warpage. By sampling the bare substrate height at multiple points around a pad, the system calculates a localized average. The average then provides the subtracted value for every pixel within the aperture area.
Fluctuations in solder mask thickness can introduce small errors into the final result.
Differential Measurement
Precision of the calculation relies on the stability of the optical sensors and the resolution of the height map. A typical height offset equation subtracts the mean substrate height from the raw sensor data to isolate the deposit. This step is critical when inspecting small components like 01005 passives where the paste height is very low.
Software implementations of the formula often include filtering to remove noise from the PCB surface texture.