Once you have determined the right camera parameters that provide the necessary image information for your measurement, there are a few more considerations that can affect the overall performance of the system. The cameras also needs to meet incoming supplier inspection requirements such as cleanliness, not require extended set-up time, enable tool matching and easy replacement in the field, and not impact the system up time. These extra factors will help with some of those intangibles that come with critical component selection and as a bonus make your coworkers a little happier.
Some of the things to investigate that can influence the ease of use of the camera and the function of the system are consistent sensor alignment, correct operation of the right embedded functions, well documented and reliable manufacturing procedures, and additional final test and sign-off procedures.
The sensor alignment procedure and its consistency are a concern because if there is any tilt in the mounting and positioning of the sensor, one edge of the image could be sharp while the other edge is blurry impacting yield immediately. If the alignment is not precisely centered, part of the image could be unusable impacting the number of false negatives in the inspection. Accurate sensor alignment needs done in all 6 positioning degrees of freedom (DoFs; translations x, y, z and rotations around x, y, z axis). As a note, it is the sensor, and not the sensor package, that should be positioned for optimal performance.
With no tilting of the sensor and a tight tolerance for the depth of focus, there is minimal calibrations and set-up required. There are also functions that can be embedded in the camera for automatic calibrations in the system. This allows for corrections of the image acquisition set-up process, such as non-uniformity of lighting source(s) and optics used in set-up. Because the sensor always in precisely the same position in every camera and there are automatic calibrations in the camera, one camera is easily replaced by another in production or in the field without additional manual tuning. This leads to faster new product introductions or better customer in-field support.
Sensor alignment must be part of the camera design and manufacturing process to ensure camera-to-camera consistency. There is also sensor grading, non-linearity verification, configuration control and more to ensure “copy exact” for the OEM who relies on the camera. Camera-to-camera consistency is critical when there are multiple cameras used for the measurement in a system or when each system must meet tool-matching requirements. This opens the path to easier system software support and saving costly on-sight field engineering support at the end-customers.
When a camera is such a critical component in inspection and metrology equipment, starting with a robust camera design for extended performance even in increased temperatures and vibration, and careful component selection can impact the lifetime of the camera and reduced system maintenance at your customers. Thorough qualification and extensive final testing verifies camera performance and increases the system up time. The care for the camera in its manufacturing process can also reduce your incoming inspection saving time-to-customer. Unlike many mainstream cameras, high-performance metrology cameras are manufactured in a clean room like environment (low dust levels) to minimize any added particles as any dirt on the sensor can impact the performance. Additional cleaning process can often be included in the outgoing inspection if necessary to save time on the receiving processes. In some cases we have even added the customer’s incoming inspection to our outgoing qualification procedures at our facilities including remote monitoring by the customer.
While the core camera specifications satisfy many of the measurement requirements, the design and handling of the camera during its manufacturing can support the other needs of the system. These are some things to consider to avoid a lot of workarounds later and hopefully reduce some of yours and your colleagues frustrations.