To have ideal wetting, bond line thickness, and flanks surrounding a die after bonding the dispense quality is crucial. Depending on the used epoxy material, dispensed volume, and substrate the contrast to properly detect the dispensed pattern can be challenging. There are different approaches to mitigate this issue with obvious ones like different angles of illumination, wavelength, polarization, or improved vision algorithm. However, using conventional contrast based or gradient dependent detection routines are depending on contrast value, which can fail and do not generalize the solution to quality assessment. In this article we first go through the low contrast solution used in our conventional pipeline to improve the results and then present an artificial intelligence (AI) approach to overcome the limitations of current epoxy pattern inspection methodologies in a die bonder at production throughput. Evaluated on 3 verification datasets the detection precision for both methods shows promising results being higher than 90 percent.

During mechanical wafer dicing, chipping can occur, and this potentially leads to catastrophic failure in the application. Sorting-out these defective dice increases reliability. An all-optical detection approach with 5.5 μm resolution, a conventional algorithm, and an artificial intelligence-based (AI) detection routine are discussed. Step-cut mechanical diced wafers are assessed at high throughput in a die attach machine at high detection accuracy combined with an overkill rate smaller 0.2% for 30pm big defects.

A full optical inspection of dice for electronic components with high reliability needs is proposed. All sides are assessed checking for defects possibly trashing bad dice to mitigate fatal error in operation. The inspection sequence is optimized using an adjustable lens for focusing, thus allowing more than 5'000 units per hour output at high optical resolution better than 6µm/pixel. This study presents detected defects originating from the dicing process using cutting, laser full ablation, and stealth dicing. Distinct features at the sides captured with the up-looking 6 side module are correlated with micrographs proving the capability of this inspection routine.

MgO is a promising solid oxide-based sorbent to capture anthropogenic CO 2 emissions due to its high theoretical gravimetric CO 2 uptake and its abundance. When MgO is coated with alkali metal salts such as LiNO 3 , NaNO 3 , KNO 3 , or their mixtures, the kinetics of the CO 2 uptake reaction is signi fi cantly faster resulting in a 15 times higher CO 2 uptake compared to bare MgO. However, the underlying mechanism that leads to this dramatic increase in the carbonation rate is still unclear. This study aims to determine the most favourable location for the nucleation and growth of MgCO 3 and more speci fi cally, whether the carbonation occurs preferentially at the buried interface, the triple phase boundary (TPB), and/or inside the molten salt of the NaNO 3 – MgO system. For this purpose, a model system consisting of a MgO single crystal that is structured by ultra-short pulse laser ablation and coated with NaNO 3 as the promoter is used. To identify the location of nucleation and growth of MgCO 3 , micro X-ray computed tomography, scanning electron microscopy, Raman microspectroscopy and optical pro fi lometry were applied. We found that MgCO 3 forms at the NaNO 3 /MgO interface and not inside the melt. Moreover, there was no preferential nucleation of MgCO 3 at the TPB when compared to the buried interface. Furthermore, it is found that there is no observable CO 2 di ff usion limitation in the nucleation step. However, it was observed that CO 2 di ff usion limits MgCO 3 crystal growth, i.e. the growth rate of MgCO 3 is approximately an order of magnitude faster in shallow grooves compared to that in deep grooves.

MgO is a promising solid oxide-based sorbent to capture anthropogenic CO2 emissions due to its high theoretical gravimetric CO2 uptake and its abundance. When MgO is coated with alkali metal salts such as LiNO3, NaNO3, KNO3, or their mixtures, the kinetics of the CO2 uptake reaction is significantly faster resulting in a 15 times higher CO2 uptake compared to bare MgO. However, the underlying mechanism that leads to this dramatic increase in the carbonation rate is still unclear. This study aims to determine the most favourable location for the nucleation and growth of MgCO3 and more specifically, whether the carbonation occurs preferentially at the buried interface, the triple phase boundary (TPB), and/or inside the molten salt of the NaNO3-MgO system. For this purpose, a model system consisting of a MgO single crystal that is structured by ultra-short pulse laser ablation and coated with NaNO3 as the promoter is used. To identify the location of nucleation and growth of MgCO3, micro X-ray computed tomography, scanning electron microscopy, Raman microspectroscopy and optical profilometry were applied. We found that MgCO3 forms at the NaNO3/MgO interface and not inside the melt. Moreover, there was no preferential nucleation of MgCO3 at the TPB when compared to the buried interface. Furthermore, it is found that there is no observable CO2 diffusion limitation in the nucleation step. However, it was observed that CO2 diffusion limits MgCO3 crystal growth, i.e. the growth rate of MgCO3 is approximately an order of magnitude faster in shallow grooves compared to that in deep grooves.

A Correction to this paper has been published: https://doi.org/10.1007/s00170-020-06546-6

A Correction to this paper has been published:

Ceramic composite materials are increasingly used in dental restoration procedures, but current ceramic surface designs do not yet achieve the osseointegration potential of state-of-the-art titanium implants. Rapid bone tissue integration of an implant is greatly dependent on its surface characteristics, but the material properties of ceramic composite materials interfere with classical surface modification techniques. Here, ultra-short pulsed laser machining, which offers a defined energy input mitigating a heat-affected zone, is explored for surface modification of ceramic composites. Inspired by surface textures of clinically relevant titanium implants, dual roughness surfaces are laser patterned. Raman mapping reveals a negligible effect of ultra-short pulsed laser ablation on material properties, but a laser-induced change in the wetting state is revealed by static contact angle measurements. Laser patterning of surfaces also influences blood coagulation, but not the attachment and spreading of osteoblastic cells. The presented laser machining approach thus allows the introduction of a rational surface design on ceramic composites, holding great promise for the manufacturing of ceramic implants.

Ultra-short pulsed laser ablation enables a defined generation of micro-holes. A parameter study on the ablation characteristics of copper clearly reveals a benefit for green wavelength with lower threshold fluence, simultaneously increasing the Rayleigh length. The use of a circular drilling method allows a defined manufacturing of micro boreholes and micro through-holes with 35 μm diameter of up to 165 μm and 300 μm length. Introducing high-resolution micro-computed X-ray tomography studying the micro-hole evolution and adjacent geometrical transformations reveals micrometer resolution and high usability. The conical geometry evolving up to an aspect ratio of 5:1 fits well to established models known for percussion drilling. However, increasing the number of pulses leads to non-conical geometry evolution, and this resulting geometry is studied for the first time. Henceforth, the exact geometrical evolution from conical to cylindrical shape upon laser drilling can be resolved revealing the impact of multiple reflections at the generated steep flanks.

Ultra-short pulsed laser ablation of stainless steel is accompanied by the evolution of different microstructures. Depending on the fuence, accumulated energy and number of laser passes cones from impurities, laser induced periodic surface structures and conelike protrusion (CLP) evolve at the surface. These often unwanted morphologies can be inhibited by carefully choosing the strategy and laser parameters. Here, the identifed region shows a small processing window fordesigned 515nm sub 1 ps ablation leading to low surface roughness. CLP are still not well understood and here a pre-cursor structure is reported. Subsequently, the CLP growth is grain orientation and polarization dependent and studied in more depth. Preferentially, CLP start to evolve at the (101) grain orientations with linear polarized laser radiation. Moreover, a nanoindentation study reveals robust mechanical properties, which could be beneficial for tribology applications in the hydrodynamic regime.

The formation of self-assembled laser induced periodic surface structures (LIPSSs) after ultrashort pulsed laser ablation is still a matter of controversy in the literature. There is agreement that at least two different physical driving forces lead to ripples with distinguishable spatial periodicity. High spatial frequency LIPSSs with periodicity well below the incident wavelength are discriminated from low spatial frequency LIPSSs (LSFLs) revealing longer periodic structures. In general, both types of LIPSS appear after multipulse irradiation with the linear polarization direction on all material classes from metals to dielectrics. However, single-pulse induced LSFLs at 540 ± 35 nm periodicity with subpicosecond pulse are observed at linelike surface defects, e.g., scratches and grain boundaries. Depending on the difference in orientation between the electric field vector and the scratch direction, LIPSSs evolve upon ablation with 515 nm and 1 ps pulses near the threshold. This corroborates the theory proposed by Sipe et al. [Phys. Rev. B 27, 1141–1154 (1983)], where the impinging electromagnetic wave interacts with a collectively excited surface electron wave of the respective material at a surface defect. The observations on oxygenfree pure copper, zirconia, and a stainless steel substrate are discussed. Moreover, LSFLs generated with circular polarization at defects after single pulse ablation of wide bandgap zirconia ceramic are presented. In application, this phenomena affects the attainable surface quality, where LSFLs appear at defects such as scratches, grain boundaries, and, generally, material inhomogeneity. The absorptivity and ablation characteristic change leading to an altered material-laser interaction at the surface. This could be the root cause of conelike protrusion structures observed on stainless steel.

A routine for color marking using oxide layers and laser-induced periodic surface structures is presented. Titanium and alloys thereof are marked with pixelated graphics at a high resolution with tempering colors. A computational approach for the laser path calculation enables a fast-forward marking of complex designs. The color map attained from a laser parameter studies enables vivid coloration. The minimal color pixel size is given by the optical setup and laser wavelength at near-infrared and green radiation to the focal spot size. A pixel size of 35 and 20 μ m was reached within this study, and no cross talk and distinctness between adjacent colors were observed. The oxide layer growth is sensitive on the applied laser strategy and parameter setting; however, a set of stable coloration conditions is conceived. Hitherto, fine color nuances in blue unravel the unique potential of this approach by oxidizing the substrate leading to a defined oxide layer thickness at a high repetition rate below the threshold fluence. Additionally, ultrashort pulsed laser pulses below 10 ps enable the generation of laser-induced periodic surface structures. In the low spatial frequency regime, these structures are correlated with the polarization direction of the laser light. Afterward, diffraction gratings with rotated spatial periodicity are manufactured using a half-wave plate. This allows forgery-proof marking strategies, where both mechanisms could be superimposed to increase the information density and complicating counterfeit product labeling.

Liquid transport (continuous or segmented) in microfluidic platforms typically requires pumping devices or external fields working collaboratively with special fluid properties to enable fluid motion. Natural liquid adhesion on surfaces deters motion and promotes the possibility of liquid or surface contamination. Despite progress, significant advancements are needed before devices for passive liquid propulsion, without the input of external energy and unwanted contamination, become a reality in applications. Here we present an unexplored and facile approach based on the Laplace pressure imbalance, manifesting itself through targeted track texturing, driving passively droplet motion, while maintaining the limited contact of the Cassie-Baxter state on superhydrophobic surfaces. The track topography resembles out-of-plane, backgammon-board, slowly converging microridges decorated with nanotexturing. This design naturally deforms asymmetrically the menisci formed at the bottom of a droplet contacting such tracks and causes a Laplace pressure imbalance that drives droplet motion. We investigate this effect over a range of opening track angles and develop a model to explain and quantify the underlying mechanism of droplet self-propulsion. We further implement the developed topography for applications relevant to microfluidic platform functionalities. We demonstrate control of the rebound angle of vertically impacting droplets, achieve horizontal self-transport to distances up to 65 times the droplet diameter, show significant uphill motion against gravity, and illustrate a self-driven droplet-merging process.

The strategy of engineering the local chemical environment to direct selectivity in the electroreduction of CO2 toward value-added products is only qualitatively understood. The unfeasibility of local concentration measurements and the limited applicability of simulations to practical systems hinder more precise guidelines. Here, we quantify the impact of the (electro)chemical environment on the selectivity pattern by using microstructured copper (Cu) electrodes prepared by ultra-short pulse laser ablation. We created regularly distributed micro-probes and assessed their product distributions at distinct overpotentials. The regular geometry enabled the accurate simulation of the local pH and CO2 concentration. Selectivity maps useful for mechanistic and applied studies emerged. They revealed clear patterns for C1–C3 products, suggesting novel insights, such as the presence of two reaction mechanisms for propanol. The effect on the selectivity pattern of operating parameters, such as enhanced mass transport and electrolyte composition, was also predicted by the maps.

A novel approach for machining of cylindrical ultra-hard materials with a highly defined contour is presented. Diamond grinding tools with complex geometry are manufactured with picosecond orthogonal and quasi-tangential laser ablation. Hitherto, laser manufacturing required a special axis configuration and optical beam deflection devices are utilized. Here, strategies and processes on a scanhead-free configuration using ultra-short pulsed laser are discussed enabling straight-forward implementation in industry. This rapid and flexible approach for the production of master tools for industrial grinding processes reveals benefits compared to conventional techniques. The manufacturing time is comparable to standard processes, however, increased grain protrusion is attained with the presented laser sharpening strategy. An ablation study for maximal material-removal rate reveals the impact of wavelength, strategy, and repetition rate at high average power up to 100 W. A combined laser manufacturing routine enables an ablation rate of 35 mm(3) min(-1) and a maximal geometric deviation of 3 mu m after finishing. The final grinding tools are sharpened by a radial laser process preferentially removing the metal-based binding material. Hence, high-precision diamond grinding wheels with a mean error of smaller 1 mu m over millimeter-sized contours can be manufactured. The meta-stable diamond structure persists and is assessed via Raman spectroscopy studies at laser cut grains. (C) 2020 Published by Elsevier Ltd.

Ultra-short pulsed laser modification points to novel coloration possibilities on a broad range of materials using laser induced periodic surface structures, plasmonic nanoparticles, and thermal oxidation as principles. Here, a general parameter-dependent laser path calculation routine for marking and coloration of complex images is presented. The original image is imported, dependent on size and resolution, down sampled and dithering applied. The color map attained from a laser parameter study is registered and the computer-aided manufacturing routine maps the color space to nearest neighbors of the original image. Thereafter, the laser paths with the adjacent parameters are computed and the numerical code generated. A complex colored pixel graphic is transformed and high-contrast marked in black and grey-scale on a stainless steel plate. Moreover, to demonstrate the capabilities, a titanium alloy is ultra-short pulsed laser colored. A colorful image proves this approach with a pixel size of below 40 μm and no observable cross talk between the colors.

A tenfold increase in the mean ablation depth of burst mode ablation with 1030 nm, 1 ps and 25 ns time spacing is reported. The threshold fluence decreases and this finding is supported by a multi-pulse ablation study.

Quasi-tangential laser processing, also called laser turning, is increasingly applied for various applications. Specifically, its ability to generate complex geometries with small feature sizes at high precision and surface quality in hard, brittle, and electrically non-conductive materials is a key benefit. Due to the geometric flexibility, the process is well suited for prototyping in hard-to-machine materials such as ceramics, carbides, and super-abrasives. However, the lack of advanced software solutions for this novel process hitherto limited the exploitation of the potential. Here, we discuss a unique computer-aided manufacturing approach for synchronous 7-axes laser manufacturing with quasi-tangential strategies. This gives the peerless possibility to process arbitrary geometries, which cannot be manufactured with conventional techniques. A detailed description of the path calculation with derivation and procedures is given. The generated machine code is tested on a laser manufacturing setup consisting of five mechanical and two optical axes. Following, a processed cylindrical ceramic specimen with a continuously varying profile along a helical path is presented. The profile is constituted by a rectangular over half-spherical to a triangular groove with defined pitch on the helix. This demonstrator provides the validation of the presented CAM solution. Measurements of the produced specimen show high adherence with the target geometry and an average deviation below 10 μm.

Diamond is a wide bandgap material, which exhibits an abrupt increase of its free-electron density, when excited by an ultrashort laser pulse. The generation of free electrons transforms the insulator diamond to a conducting material with metallic optical behavior. This transformation process can be described by the multiple rate equation (MRE) model. The introduced MRE model considers strong-field excitation in the Keldysh picture as well as collisional excitation. The light attenuation results from the strong-field absorption and free-carrier absorption described in the Drude picture. Thus, the electron density and intensity distribution as functions of time, penetration depth, and laser beam radius are calculated. Furthermore, the model predicts the evolution of optical properties and estimates the ablation threshold value by the diameter and depth regression method. The calculated ablation threshold is compared to experimental results on a single crystalline chemical vapor deposited diamond by applying the diameter and depth regression method. Experimental and theoretical results are discussed with regard to the pulse duration. The discussion focuses on single pulse ablation but also addresses the multishot domain, which is essential for laser machining. At 1030 nm, the experimental single pulse ablation threshold fluence is determined to be 8.2 and 12.9 J/cm(2) for pulse durations of 400 and 700 fs, respectively. This is in compliance with the simulation results.