How the Stratus Vision Technology works

The substrate is put into the system (automatically or manually), underneath the imaging head. The image head consists of a line scan camera or a field (area) camera. Directly mounted to the camera is always the optics that define the size of the pixels. Mounted close to, or with, the camera, are the different light or illumination scenarios. Wherever possible we will use backlight, because it allows better contrast and inspection quality.

Back light (from underneath the substrate) and top lighting, that are programmable and can be triggered independently, make the structures visible for the digital matrix pixel camera, that has 4 or more Megapixels. In some applications we use line scan cameras with 8k or 12k pixels. The imaging head with cameras and lighting is moved across the substrate in a precise and well defined way by fast linear motors with exactly defined positioning feedback. In some applications the camera is not moving, but the parts under test are moved through the field of view.

The images are taken with sufficient overlapping, to ensure that no area remains uninspected. When CAD data is downloaded onto the STRATUS system, a bit map is created and automatic tolerances (up to 256) are applied to all structures (conductors, pads, resistors, dielectrict, etc) and to all areas between those structures.

The system is then comparing all images against the CAD data and against the default tolerances or against the tolerances the operator has modified, according to his requirements. The illumination with strobed LEDs is automatically applied under software control, with different lighting (for maximum contrast) for different materials. The defect sizes on installed systems, that must be detected, range from 5 µm up to 50 µm, depending on pixel size and the customer’s requirements. The AOI system model STRATUS can make even glass or wet adhesive (transparent) visible with sufficient contrast to make fast, safe and accurate decisions. The illumination colors used are often outside the capability of the human eye. All defects found are stored and, if required, downloaded to the factory network, for later evaluation and documentation.

Review stations are available for later repair or decision about true or false defects.

The system is very capable to inspect gold, silver and other shiny surfaces. All defects are measured in X and Y direction and their area is calculated. Then all these values are compared to the tolerance table. Whenever they exceed the values in this tolerance table, a defect is found. Then the type of defect is identified and the data is used for statistical calculations and histograms.