Anton Schick

An endoscopic 3D scanner based on structured light

We present a new endoscopic 3D scanning system based on Single Shot Structured Light. The proposed design makes it possible to build an extremely small scanner. The sensor head contains a catadioptric camera and a pattern projection unit. The paper describes the working principle and calibration procedure of the sensor. The prototype sensor head has a diameter of only 3.6mm and a length of 14mm. It is mounted on a flexible shaft. The scanner is designed for tubular cavities and has a cylindrical working volume of about 30mm length and 30mm diameter. It acquires 3D video at 30 frames per second and typically generates approximately 5000 3D points per frame. By design, the resolution varies over the working volume, but is generally better than 200μm. A prototype scanner has been built and is evaluated in experiments with phantoms and biological samples. The recorded average error on a known test object was 92μm.

Automated solder joint inspection system using optical 3-D image detection

An automated system has been developed for visually inspecting the solder joints of SMDs (Surface Mounted Devices). The system is capable of inspecting fine pitch components down to 0.3 mm pitch QFPs (Quad Flat Packages). A unique image detection method was also developed to obtain precise 3-D images of solder joints. The principle of a confocal microscope is employed but plural sensors are used to detect reflected light at different focusing positions simultaneously. The system is unaffected by secondary reflection and dead angles. The warp in a PC (Printed Circuit) board surface is calculated in real time using the detected 3-D images, and board height to be detected in successive areas is predicted based on this calculation. Real-time automatic focusing control is then performed using newly developed defect detection algorithms, the system can recognize leads, pads and solder fillets from the detected images. Because 3-D shape features are extracted and used for defect judgment, user-defined parameters have been made easy to understand and/or to modify. Operational evaluation of the system confirms a 100% defect detection rate and a very low false alarm rate (0.16%).

Contactless Inspection of Flat-Panel Displays and Detector Panels by Capacitive Coupling

As the variety and application areas of planar electronic devices such as flat-panel displays (FPDs) and detector panels increase, flexible inspection methods are becoming more and more important. In this paper, a contactless inspection technique exploiting the capacitive coupling between probe electrodes and the conductive parts of the devices is presented. Measuring principle and setup, as well as sensor chip design, are illustrated and discussed in detail. To evaluate the performance of the system, inspection results of FPD backplanes and X-ray detector panels are compared with the optical images of the inspected areas. Various typical panel defects and defect conglomerations are resolved and can be unambiguously distinguished. Moreover, a precise classification of the detected defects is obtained. Finally, the detectability of device defects beyond the shown examples and the application to thin-film-transistor parameter extraction is discussed.

Fast scanning confocal sensor provides high-fidelity surface profiles on a microscopic scale

For a long time the confocal imaging technique was known to be a high precision imaging method in the field of microscopy providing unique depth discrimination properties, but suffering from slow response in connection with pointwise height detecting sensors. At the same time, it is obvious for triangulation systems to be unable to cope with the huge variety of shapes and specular surfaces in the continuous trend towards miniaturisation in electronics and micro machining. It is commonly understood that confocal height profiling usually requires a time consuming readjustment of the distance between the object and the sensor whilst scanning across a surface. Moreover, height steps on surfaces give rise to artefacts at the edges in many cases. In order to overcome these drawbacks we developed a high speed confocal sensor head, featuring a pixel data rate of 8000 Hz independent of surface steps and surface reflectivity. An essential feature is a fast focus scan in Z direction perpendicular to the object at a preset height measuring range. The focus adjustment is realised by scanning an image with a punctiform light source in conjunction with a punctiform detector utilizing a mirror which is attached to a high frequency mechanic oscillator. Both, the light source and the detector coincide at the end of a fibre. By moving the small sensor head relative to a surface a profile scan is taken. The time needed to determine the height value of one pixel and to measure its brightness is less than 125 microseconds. This high speed true confocal height detection technology opens up a new range of applications, e.g. in-line roughness, profile, displacement and coating thickness measurement as well as the profiling of holes where shading effects inhibit the use of triangulation based sensors.

Contactless Functionality Inspection of Flat-Panel-Display Pixels and Thin-Film Transistors by Capacitive Coupling

A fast and thorough detection of structural and functional defects of flat-panel displays, large-area image detectors, and printed electronics requires a contactless and flexible inspection technique. Moreover, to accelerate the development of new products and to increase yields, efficient device characterization including the analysis of single component functionality and testing under operating conditions is essential. In this contribution, a contactless inspection method solely based on capacitive coupling is used to analyze pixel and thin-film transistor (TFT) functionality of active-matrix liquid crystal and electrophoretic display backplanes. Employing a capacitively coupled sensor, the measurement of the evolution of the pixel electrode voltage during TFT operation (switching) yields display flicker and TFT parameters, such as TFT on- and off-currents, TFT threshold, and intrinsic capacitance. To confirm the measurement results, the pixel voltage was also measured with an active voltage probe brought into contact with the pixel electrodes under test.