Dr. Joerg Schambach Profile

Dr. Joerg Schambach

at GOEPEL Electronic GmbH

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Publications (3)

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Proceedings Article | 17 September 2019 Open Access

Three-dimensional THT solder joint reconstruction for inline inspection systems

Johannes Richter, Jörg Schambach

Proceedings Volume 11144, 111440F (2019) https://doi.org/10.1117/12.2530888

KEYWORDS: Inspection, Optical inspection, Cameras, Light sources, Reflection, Tin, Reflectivity, Specular reflections, 3D image processing, Light emitting diodes

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Automatic Optical Inspection (AOI) is an important part of modern electronics manufacturing. While profilometric technologies are very present in inspection systems specialized on surface mounted technologies (SMT), through hole technology (THT) oriented inspection still mostly relies on two-dimensional data. Solder joints of THT connections have highly reflective metallic surfaces and thus are a very challenging object for typical light based profilometric measurement systems. A new approach is presented, which uses specular reflections of angled illuminations to reconstruct the surface of THT solder joints for inline inspection. The observed reflections depend on the position of the angled light sources, as well as the surface angle of the inspected object and its relative position to the observing camera. The reflections of each angled illumination are observed separately and processed as a stack of images. To reduce the complexity the image stack is transformed into a polar coordinate system leveraging the rotation symmetry of THT solder connections. The surface angle of every observed pixel is estimated based on the observation stack and corrected for its position relative to the camera and illumination. The surface angle then gets integrated along the transformed coordinate axis. This results in the estimation of the surface profile of the solder connection. After retransformation into the source coordinate system, this can be used to classify the solder joint for defects and insufficient solder volume.

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Proceedings Article | 21 June 2019 Paper

Optical inspection of noncooperative copper surface structures using multi- and hyperspectral acquisition systems

Markus Wrieden, Andreas Breitbarth, Manuel Zimmermann, Jörg Schambach, Maik Rosenberger, Gunther Notni

Proceedings Volume 11061, 1106106 (2019) https://doi.org/10.1117/12.2525734

KEYWORDS: Optical filters, Cameras, Imaging systems, Inspection, Image filtering, Copper, Sensors, Bandpass filters, 3D metrology

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In order to enhance the efficiency of quality inspection of Direct Copper Bonded (DCB) structures an optical inspection using a 3D measuring system is conceivable. However, it is a challenging task to use 3D optical measurement techniques for diffuse reflective copper surfaces. This work deals with the optical detection of defects of the copper surface, using multi- and hyperspectral acquisition devices. Over a broad spectral range from the visual spectrum to the short-wave infrared (400 nm - 1700 nm) it is analysed which wavelengths provide good contrast ratios for the detection of flaws. For the inspection of the sample back side, the push-broom imager, operating in the VIS and NIR range (400 nm - 1000 nm), provides the best contrast ratio. An outstanding contrast is reached around 400 nm. Deposited particles on the front side of the DCB substrates are best detected by the filter wheel camera, which is sensitive in the visual and near infrared range. Outstanding contrast is reached with wavelengths around 640 nm. After evaluating the standard deviations of the gray values, it can be shown that defects differ clearly from flawless substrate areas under investigation with light of wavelengths 577 nm, 640 nm and 950 nm. Furthermore, the comparison between certain pixel spectra confirms that significant differences appear at the same three wavelengths. Regarding an automated inspection of defects, it is advisable to shift the pattern projection for the 3D correspondence analysis to the spectral ranges mentioned.

Proceedings Article | 26 June 2017 Paper

Verification of real sensor motion for a high-dynamic 3D measurement inspection system

Andreas Breitbarth, Martin Correns, Manuel Zimmermann, Chen Zhang, Maik Rosenberger, Jörg Schambach, Gunther Notni

Proceedings Volume 10329, 103290O (2017) https://doi.org/10.1117/12.2270288

KEYWORDS: 3D metrology, Motion measurement, Sensors, Inspection, Motion estimation, Optical inspection, Imaging systems, 3D image processing, Solids

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Inline three-dimensional measurements are a growing part of optical inspection. Considering increasing production capacities and economic aspects, dynamic measurements under motion are inescapable. Using a sequence of different pattern, like it is generally done in fringe projection systems, relative movements of the measurement object with respect to the 3d sensor between the images of one pattern sequence have to be compensated.

Based on the application of fully automated optical inspection of circuit boards at an assembly line, the knowledge of the relative speed of movement between the measurement object and the 3d sensor system should be used inside the algorithms of motion compensation. Optimally, this relative speed is constant over the whole measurement process and consists of only one motion direction to avoid sensor vibrations. The quantified evaluation of this two assumptions and the error impact on the 3d accuracy are content of the research project described by this paper.

For our experiments we use a glass etalon with non-transparent circles and transmitted light. Focused on the circle borders, this is one of the most reliable methods to determine subpixel positions using a couple of searching rays. The intersection point of all rays characterize the center of each circle. Based on these circle centers determined with a precision of approximately 1=50 pixel, the motion vector between two images could be calculated and compared with the input motion vector. Overall, the results are used to optimize the weight distribution of the 3d sensor head and reduce non-uniformly vibrations. Finally, there exists a dynamic 3d measurement system with an error of motion vectors about 4 micrometer. Based on this outcome, simulations result in a 3d standard deviation at planar object regions of 6 micrometers. The same system yields a 3d standard deviation of 9 µm without the optimization of weight distribution.

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