Automatic surface defect quantification in 3D

Three-dimensional (3D) non-contact optical methods for surface inspection are of significant interest to many industrial sectors. Many aspects of manufacturing processes have become fully automated resulting in high production volumes. However, this is not necessarily the case for surface defect inspection. Existing human visual analysis of surface defects is qualitative and subject to varying interpretation. Automated 3D non-contact analysis should provide a robust and systematic quantitative approach. However, different 3D optical measurement technologies use different physical principles, interact with surfaces and defects in diverse ways, leading to variation in measurement data. Instrument s native software processing of the data may be non-traceable in nature, leading to significant uncertainty about data quantisation. Sub-millimetric level surface defect artefacts have been created using Rockwell and Vickers hardness testing equipment on various substrates. Four different non-contact surface measurement instruments (Alicona InfiniteFocus G4, Zygo NewView 5000, GFM MikroCAD Lite and Heliotis H3) have been utilized to measure different defect artefacts. The four different 3D optical instruments are evaluated by calibrated step-height created using slipgauges and reference defect artefacts. The experimental results are compared to select the most suitable instrument capable of measuring surface defects in robust manner. This research has identified a need for an automatic tool to quantify surface defect and thus a mathematical solution has been implemented for automatic defect detection and quantification (depth, area and volume) in 3D. A simulated defect softgauge with a known geometry has been developed in order to verify the implemented algorithm and provide mathematical traceability. The implemented algorithm has been identified as a traceable, highly repeatable, and high speed solution to quantify surface defect in 3D. Various industrial components with suspicious features and solder joints on PCB are measured and quantified in order to demonstrate applicability

Amorphous silicon e 3D sensors applied to object detection

Nowadays, existing 3D scanning cameras and microscopes in the market use digital or discrete sensors, such as CCDs or CMOS for object detection applications. However, these combined systems are not fast enough for some application scenarios since they require large data processing resources and can be cumbersome. Thereby, there is a clear interest in exploring the possibilities and performances of analogue sensors such as arrays of position sensitive detectors with the final goal of integrating them in 3D scanning cameras or microscopes for object detection purposes. The work performed in this thesis deals with the implementation of prototype systems in order to explore the application of object detection using amorphous silicon position sensors of 32 and 128 lines which were produced in the clean room at CENIMAT-CEMOP. During the first phase of this work, the fabrication and the study of the static and dynamic specifications of the sensors as well as their conditioning in relation to the existing scientific and technological knowledge became a starting point. Subsequently, relevant data acquisition and suitable signal processing electronics were assembled. Various prototypes were developed for the 32 and 128 array PSD sensors. Appropriate optical solutions were integrated to work together with the constructed prototypes, allowing the required experiments to be carried out and allowing the achievement of the results presented in this thesis. All control, data acquisition and 3D rendering platform software was implemented for the existing systems. All these components were combined together to form several integrated systems for the 32 and 128 line PSD 3D sensors. The performance of the 32 PSD array sensor and system was evaluated for machine vision applications such as for example 3D object rendering as well as for microscopy applications such as for example micro object movement detection. Trials were also performed involving the 128 array PSD sensor systems. Sensor channel non-linearities of approximately 4 to 7% were obtained. Overall results obtained show the possibility of using a linear array of 32/128 1D line sensors based on the amorphous silicon technology to render 3D profiles of objects. The system and setup presented allows 3D rendering at high speeds and at high frame rates. The minimum detail or gap that can be detected by the sensor system is approximately 350 μm when using this current setup. It is also possible to render an object in 3D within a scanning angle range of 15º to 85º and identify its real height as a function of the scanning angle and the image displacement distance on the sensor. Simple and not so simple objects, such as a rubber and a plastic fork, can be rendered in 3D properly and accurately also at high resolution, using this sensor and system platform. The nip structure sensor system can detect primary and even derived colors of objects by a proper adjustment of the integration time of the system and by combining white, red, green and blue (RGB) light sources. A mean colorimetric error of 25.7 was obtained. It is also possible to detect the movement of micrometer objects using the 32 PSD sensor system. This kind of setup offers the possibility to detect if a micro object is moving, what are its dimensions and what is its position in two dimensions, even at high speeds. Results show a non-linearity of about 3% and a spatial resolution of < 2µm

Visible and Mid-Infrared Supercontinuum Generation and Their Respective Application to 3D imaging and Stand-off Reflection Spectroscopy.

The thesis describes broadband supercontinuum (SC) generation in optical fibers for both the visible and mid-infrared regions of the spectrum, and their respective application to 3D imaging and stand-off reflection spectroscopy. Both SC sources leverage mature telecom technology, and are based on a common all-fiber integrated platform comprising a ~1.55 micron distributed feedback seed laser diode amplified to high peak powers in two stages of cladding pumped Erbium or Erbium-Ytterbium fiber amplifiers. A visible SC extending from 0.45-1.20 microns with 0.74 W of time-averaged power is demonstrated using a two step process. The output of the Er-Yb power amplifier is frequency doubled to ~0.78 micron using a periodically poled lithium niobate crystal, followed by non-linear spectral broadening in 2m of high nonlinearity photonic crystal fiber. Numerical simulations based on solving the generalized non-linear Schrödinger equation are also presented to verify the underlying SC generation mechanisms and predict further improvements. The above SC source is used in a Fourier domain line scan interferometer to measure the height and identify shape defects of ~300 micron high solder balls in a ball grid array. The 3D imaging system has an axial resolution of ~125 nm, transverse resolution of ~15 microns, and an angular measurement range between 20 to 60 degrees depending on the sample surface roughness. The mid-infrared SC source is generated by pumping a 9m long ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber to obtain a spectrum spanning 0.8-4.3 microns with 3.9 W time-averaged power. The output power is linearly scalable with pump power, but requires optimization of the critical splices and thermal management of the gain fiber and pump diodes to ensure stable high power operation. Finally, an application of the mid-IR SC is demonstrated by measuring the diffuse reflection spectra of solid samples at a stand-off distance of 5 m and 100 ms integration time. The samples can be distinguished using a correlation algorithm based on distinct spectral features in the reflection spectrum. Signal to noise ratio calculations show that the distance is limited by space constraints in our lab and can be extended to ~150 m.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/89708/1/malayk_1.pd

Design and Development of an Optical Chip Interferometer For High Precision On-Line Surface Measurement

Advances in manufacturing and with the demand of achieving faster throughput at a lower cost in any industrial setting have put forward the need for embedded metrology. Embedded metrology is the provision of metrology on the manufacturing platform, enabling measurement without the removal of the workpiece. Providing closer integration of metrology upon the manufacturing platform will improve material processing and reliability of manufacture for high added value products in ultra-high-precision engineering. Currently, almost all available metrology instrumentation is either too bulky, slow, destructive in terms of damaging the surfaces with a contacting stylus or is carried out off-line. One technology that holds promise for improving the current state-of-the-art in the online measurement of surfaces is hybrid photonic integration. This technique provides for the integration of individual optoelectronic components onto silicon daughter boards which are then incorporated on a silica motherboard containing waveguides to produce a complete photonic circuit. This thesis presents first of its kind a novel chip interferometer sensor based on hybrid integration technology for online surface and dimensional metrology applications. The complete metrology sensor system is structured into two parts; hybrid photonic chip and optical probe. The hybrid photonic chip interferometer is based on a silica-on-silicon etched integrated-optic motherboard containing waveguide structures and evanescent couplers. Upon the motherboard, electro-optic components such as photodiodes and a semiconductor gain block are mounted and bonded to provide the required functionality. Optical probe is a separate entity attached to the integrated optic module which serves as optical stylus for surface scanning in two measurement modes a) A single-point for measuring distance and thus form/surface topography through movement of the device or workpiece, b) Profiling (lateral scanning where assessment of 2D surface parameters may be determined in a single shot. Wavelength scanning and phase shifting inteferometry implemented for the retrival of phase information eventually providing the surface height measurement. The signal analysis methodology for the two measurement modes is described as well as a theoretical and experimental appraisal of the metrology capabilities in terms of range and resolution. The incremetal development of various hybrid photonic modules such as wavelength encoder unit, signal detection unit etc. of the chip interferometer are presented. Initial measurement results from various componets of metrology sensor and the surface measurement results in two measurement modes validate the applicability of the described sensor system as a potential metrology tool for online surface measurement applications

High Speed Instrumentation for Inspection of transparent parts

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 281-286).In micro manufacturing (MEMS, polymer hot-embossing, polymer roll-to-roll imprint, etc.) precise micro and nano-sized features are distributed over large areas. In order to inspect for defects or employ statistical process control on micromanufactured parts, metrological instruments must collect data with submicron resolution at a rate fast enough to keep up with the pace of production. Commercial inspection instruments fall short on meeting these challenging demands. This doctoral thesis details the design, implementation, and results of an optical system built to provide real-time inspection for transparent polymer microfluidic devices. Our instrument utilizes a high speed camera (500 fps) in conjunction with submicron precision positioning stages (20 nm resolution) to rapidly collect topological data on the microfluidic devices. The stream of images are processed using a depth from focus technique to provide surface inspection with 0.5 micron lateral resolution and 1 micron vertical resolution at an inspection speed of 640,000 voxels per second. The instrument also demonstrates the ability to measure vertical sidewalls as a result of the tilted orientation of the camera system providing access to these typically hidden or eclipsed areas. The 3D contour plots generated by the instrument are used to characterize a manufacturing process demonstrating automatic defect detection, repeatability analysis, and run charts that can be used in process control. This thesis also explores the design and experimentation of a novel sensor that can simultaneously measure the thickness and lateral position of a transparent object. This capability is especially useful to control the lateral position of a transparent web with a feedback system during a manufacturing roll to roll process. The sensor measurement has demonstrated submicron repeatability over millimeters of range in both thickness and position.by Dean Ljubicic.Ph.D

Ultrafast laser microwelding of glass-to-glass and glass-to-opaque materials

Techniques for joining materials, especially glass to dissimilar materials, while maintaining their surface and optical properties are essential for a wide range of industrial applications. Current techniques rely on adhesives or interlayers which can exhibit issues with creep, out-gassing or aging. Ultrafast laser welding based on nonlinear absorption in transparent material offers an attractive solution to this problem. Bringing two material surfaces into close (optical) contact and focusing the ultrafast laser onto the interface allows for localised melting and rapid resolidification, forming strong bond and welding the two surfaces together. The highly localised nature of this absorption means that welds can be created whilst avoiding significant heating of the surrounding material―important for joining materials with significantly different thermal expansion coefficients. Using a picosecond laser system (Trumpf TruMicro), a range of welds between similar material (borosilicate glass to borosilicate glass, fused silica to fused silica, borosilicate glass to fused silica) and highly dissimilar materials (sapphire to stainless steel, fused silica/borosilicate glass to silicon/aluminium/copper/stainless steel) have been demonstrated. Theoretical simulations were carried out to investigate the aberrations that occur to a laser beam focused inside material and to describe the behaviour of the generated plasma. With the guidance of theoretical work and developed experiment setup, a large range of parameters related to welding were investigated both in bulk material and welding for different materials and surface conditions. Shear strength tests on welds shows a maximum value could be obtained between parameters resulting in barely welded seams, for low power, and obvious cracking, for higher power. Optimised welding for borosilicate to borosilicate glass creates stronger bonds (108.8 N/mm2) than traditional joining methods (adhesive, typically 15~25 N/mm2). Parameter maps were made for different surface separation and surface conditions to determine a successful weld. In order to weld highly dissimilar materials, different welding patterns were designed to relax residual stress and eliminate cracks. Welding with galvo-scanner was also introduced as an alternative method for industrial applications which provides a high scan speed and flexible patterns. To increase welding strength and expand the parameter tolerance for a successful welding, focus vibration methods were proposed to reduce the residual stress. Finally, welding of example industrial parts was demonstrated for different application requirements

Index to 1986 NASA Tech Briefs, volume 11, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1986 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Understanding, Modeling and Predicting Hidden Solder Joint Shape Using Active Thermography

Characterizing hidden solder joint shapes is essential for electronics reliability. Active thermography is a methodology to identify hidden defects inside an object by means of surface abnormal thermal response after applying a heat flux. This research focused on understanding, modeling, and predicting hidden solder joint shapes. An experimental model based on active thermography was used to understand how the solder joint shapes affect the surface thermal response (grand average cooling rate or GACR) of electronic multi cover PCB assemblies. Next, a numerical model simulated the active thermography technique, investigated technique limitations and extended technique applicability to characterize hidden solder joint shapes. Finally, a prediction model determined the optimum active thermography conditions to achieve an adequate hidden solder joint shape characterization. The experimental model determined that solder joint shape plays a higher role for visible than for hidden solder joints in the GACR; however, a MANOVA analysis proved that hidden solder joint shapes are significantly different when describe by the GACR. An artificial neural networks classifier proved that the distances between experimental solder joint shapes GACR must be larger than 0.12 to achieve 85% of accuracy classifying. The numerical model achieved minimum agreements of 95.27% and 86.64%, with the experimental temperatures and GACRs at the center of the PCB assembly top cover, respectively. The parametric analysis proved that solder joint shape discriminability is directly proportional to heat flux, but inversely proportional to covers number and heating time. In addition, the parametric analysis determined that active thermography is limited to five covers to discriminate among hidden solder joint shapes. A prediction model was developed based on the parametric numerical data to determine the appropriate amount of energy to discriminate among solder joint shapes for up to five covers. The degree of agreement between the prediction model and the experimental model was determined to be within a 90.6% for one and two covers. The prediction model is limited to only three solder joints, but these research principles can be applied to generate more realistic prediction models for large scale electronic assemblies like ball grid array assemblies having as much as 600 solder joints