Pattern Projection
Illumination method involves projecting a known geometric pattern onto a surface to measure its three dimensional properties. Structured light is used in SMT inspection to capture the height profile of solder paste and components without physical contact. The distortion of the pattern as it hits the board surface provides the raw data needed for volumetric calculations.
Geometric Analysis
Variations in the height of the object cause the straight lines of the projected pattern to appear bent when viewed from a different angle. The system uses a camera offset from the projector to record these distortions and convert them into a 3D point cloud. This process allows for the detection of defects such as insufficient solder and component tilt that are difficult to see in two dimensions.
Multiple patterns or different colors of light are often used to improve the accuracy of the scan and reduce the impact of shadows. The software compares the captured height map against the CAD data for the board to identify any deviations from the design.
Surface Limitation
Highly specular or transparent surfaces can cause the projected light to scatter or reflect away from the camera sensor. This loss of signal results in data gaps that must be filled by interpolation or through the use of diffused lighting.
