Sensor manufacturer deploys Mikrotron cameras for high-speed 3D measurements

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Located in Erlangen, Germany, 3D-Shape GmbH develops and markets optical 3D sensors and software for non-contact three-dimensional shape measurement. This quality-control technology is widely used in processing, analyzing, and editing three-dimensional measurement data.

Considered best-of-breed, the company's popular KORAD3D Sensor Measuring System has been successfully deployed in such applications as determining the flatness or roughness of sealing surfaces, providing 3D imaging of milling and drilling tools, giving information on wear on cutting inserts, and checking the period length and step height of the smallest contacts in electronic devices. To ensure the highest standards, the company selected the Mikrotron EoSens® 3CL three-megapixel camera for the KORAD3D.

The KORAD3D and other 3D-Shape GmbH technologies are becoming more important for quality control of complicated components. They are now superior to tactile measurement systems in speed, flexibility, precision and analytical possibilities. In keeping with the adage "a picture is worth a thousand words," this 3D image analysis allows the discovery of complex connections and many object parameters at a single glance.

A few years ago, high precision measurements on an industrial production line were unimaginable. Today, reliable quality control with measurement uncertainties of only a few nanometers are possible even with short cycle times. This is true for applications in the electronics, aircraft and automotive industries, and even in the restoration of historical artwork.

Through rapid innovation cycles in processor and camera technology, as well as in precision optics and image processing software, interferometry is increasingly coming into focus. With white light interferometry, the topographies of both rough and smooth objects can be measured and captured in a very precise way. Simply put, the measurement subject and a reference mirror are illuminated by a light source. This is separated into two parts by a semi-transparent mirror or beam splitter.

As the process continues, it results in brightness variations, which are recorded on the image sensor of the camera. These are analyzed by special software and each pixel is assigned a height value. This then creates a highly differentiated profile height in the nanometer range. If the process is carried out at various layers, complex structures are recorded in their full height.

The KORAD3D can measure fields of 0.24 × 0.18 mm at minimum, and 50 × 50 mm at maximum, meaning it can be integrated into a wide range of 3D applications. Its achievable accuracy is directly dependent on the required measurement field size, the optics, and the camera.

The most important factor influencing the measurement accuracy and measurement speed of a KORAD3D system is the performance of the built-in camera. Larger measurement fields are advantageous in ensuring the system can be used for a variety of applications. However, the greater the measurement field, the more inaccurate the measurement. A key requirement for the camera is therefore a megapixel resolution. This is, of course, in addition to other important aspects of image quality such as contrast and noise behavior and the sensitivity. At the same time, the camera must be able to deliver a high frame rate.

In many applications, the entire structure is recorded layer-by-layer, and at very short cycle times within the production line. Doubling the measuring depth, however, also causes twice the measuring time. The resulting large amounts of data need to be addressed. This can only be achieved by a camera that captures and transfers images in real time.

A ball grid array is a common surface mount package derived from pin grid array technology. It uses a grid of solder balls or leads to conduct electrical signals from the integrated circuit board.

In order to manufacture ball-grid arrays without errors, it is important to ensure that they are all placed with their top ends inside one area. The bumps in the arrays, arranged like a nail board, can be checked with the KORAD3D for different characteristics up to the µm range.

Every single contact pin in the ball-grid array is precisely checked in size and shape to the µm range. In just about one second, the topography of the entire group is captured.

3D-Shape GmbH operates along the frontier of the physically possible and therefore needed a megapixel camera with the very latest technology. Ultimately the Mikrotron EoSens® 3CL was the only camera that met all their requirements for the KORAD3D.

At a full-screen resolution of 1,280 × 1,024 pixels, the Mikrotron EoSens delivers up to 500 images per second via the high performance base/full-camera link interface.

Another important argument for the Mikrotron EoSens was its outstanding light sensitivity of 2,500 ASA, based on large 14 × 14 µm pixels and a pixel fill factor of 40%. The camera's sensitivity directly translated into saving money for lighting systems since a higher range of brightness and contrast for image processing could be set.

In addition, the camera's switchable exposure optimization adapts the usually linear image dynamics of the CMOS sensors to the nonlinear dynamics of the human eye at two freely selectable levels. The bright areas are thereby suppressed and details can be extrapolated even with extreme light-dark differences in all areas.

Given the cycle times the KORAD3D system has to maintain, each contribution to the acceleration of the data processing is important. This includes the camera's ROI function, which can be defined and customized freely to fit the size and location of individual tasks or the receptive field to be evaluated. Data loads are thus reduced and analysis is accelerated, simultaneously allowing for extremely increased frame rates. The built-in multiple ROI function allows the user to define up to three different image fields in the overall picture.

To keep the measurement accuracy of the topographies created by the KORAD3D system in a narrow range, a number of features of the imaging quality must work together to form a performance-boosting whole. The global shutter of the Mikrotron EoSens 3CL completely freezes the captured frame and stores it in real time, while the next image is already being exposed. Images are therefore free of distortion and smear effects.

Along with the C-Mount lens mount there is also an F-Mount option. The latter allows the operator to connect the camera and lens to a fixed calibrated unit, increasing the precision of the analysis.

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