A key limitation of scaling electrochemical jet machining (ECJM) to multi-nozzle configurations is the loss of localized machining due to electrolyte interactions and electric-field overlap. This work establishes a quantitative design criterion for maintaining localization in dual-jet ECJM through a combined numerical-experimental approach. A two-dimensional multiphysics model is developed to analyze the coupled behavior of electrolyte flow, electric field distribution, and resulting material removal. The results reveal that nozzle pitch governs both hydraulic-jump interaction and current-density confinement. For a nozzle with inner and outer diameters of 220 mu m and 450 mu m, respectively, a minimum pitch of 2 mm is identified as the critical threshold to suppress electrolyte overlap and stray corrosion, which is validated experimentally with a prediction error below 6%. In micro-grooving, increasing the traverse speed significantly improves surface finish, reducing RMS roughness (Sq) from 648 nm to 242 nm, but at the cost of reduced depth per pass. To address this trade-off, a feed-assisted multi-pass strategy is introduced, enabling deeper machining while preserving surface quality. Using the optimized conditions, uniform micro-groove arrays with a width of 360 mu m, depth of 200 mu m, and pitch of 666 mu m are fabricated in tungsten with high repeatability and minimal stray corrosion. Dual-headed ECJM is investigated to improve machining efficiency in tungstenA 2D model captures jet-to-jet interaction and electric field overlap effectsFeed-assisted multi-pass ECJM at high traverse speed enables deep, smoother groovesUniform micro-groove arrays are fabricated with minimal stray corrosion

Through-glass vias (TGVs) are gaining importance in 2.5D/3D packaging due to their low electrical loss, dimensional stability, and panel-level manufacturability. However, the large mismatch in coefficient of thermal expansion (CTE) between copper(Cu) and glass induces significant thermo-mechanical stresses during temperature variations, leading to crack initiation, energy release, and electrical degradation. In this work, a coupled finite element method (FEM) and fracture mechanics framework is developed to analyze the reliability of Cufilled TGVs. The study evaluates stress distribution, deformation, and current density in the presence of cracks positioned at different locations within the via and along the Cu-glass interface. The fracture driving force is quantified using the Energy Release Rate (ERR), with analytical formulations validated against FEM-based Jintegral calculations. Results show that ERR scales linearly with via diameter and quadratically with temperature change magnitude, with peak values occurring when the crack length is approximately one-fourth of the via diameter. Substrate material strongly influences reliability, as fused silica produces the highest stresses and ERR, while ceramic glass gives better reliability. The introduction of polymer buffer layers significantly reduces stress in the TGV, demonstrating their effectiveness in mitigating mismatch-induced failures. Altogether, the combined FEM-ERR framework provides a unified basis for linking stress, fracture, and electrical degradation, and offers practical design guidelines for optimizing TGV-based interposers.

Electroless copper seed layer uniformity is a critical requirement for reliable through-glass via (TGV) metallization. In this work, electroless Cu deposition in tapered vias with an aspect ratio of similar to 4 is investigated using a combined numerical and experimental approach. A two-dimensional axisymmetric finite-element model incorporating species diffusion, surface reaction kinetics, and moving-boundary mesh deformation was used to simulate Cu thickness evolution along via sidewalls during electroless deposition at 30 degrees C for 1200 s. The simulated Cu thickness varies from similar to 450 nm near the via entrance and exit regions to similar to 250 nm at intermediate depths. Cross-sectional scanning electron microscopy analysis of electroless Cu deposited in silicon through-holes processed under identical conditions shows corresponding thickness values of similar to 400 nm near the top and bottom regions and similar to 200 nm at the mid-depth. Electroless Cu films deposited for 20 min exhibit continuous coverage with a sheet resistance of similar to 0.24 Omega/square, a peel adhesion strength of similar to 2.65 N cm-1, and a tensile residual stress of similar to 33.5 MPa for an average thickness of similar to 200 nm. Electrical continuity of glass-based redistribution lines (RDL) test vehicles was shown by fabricating a test vehicle using electroless Cu followed by Cu electrodeposition. A linear current-voltage behavior across the TGV-RDL network was demonstrated with measured electrical resistance of similar to 1.09 Omega.

This work presents a combined numerical and experimental investigation to evaluate the influence of ultrasonic tool vibration on the heat transfer and material removal characteristics during the deep hole formation by the ECDM. A transient 2D heat transfer model was developed, incorporating pulsed Gaussian heat flux and sinusoidal tool-workpiece gap (TWG) variation induced by ultrasonic vibration. The model predicts periodic concentration of discharge energy, resulting in deeper thermal penetration compared to conventional ECDM. Simulation results showed that ultrasonic assistance increased the predicted machining depth by approximately 96% compared to conventional ECDM. Experimental results demonstrated a corresponding improvement, with machining depth enhanced by 49% under ultrasonic assistance. High-speed imaging and current waveform analysis showed an increased occurrence of discharge events under ultrasonic vibration. SEM and EDS analyses revealed reduced peripheral damage and lower debris deposition, indicating improved electrolyte flushing and enhanced debris removal. Multiple through-holes were successfully created in 1.1 mm-thick glass.

This investigation presents a comparative analysis of two surface modification strategies: graphene oxide (GO) and silver-doped zinc oxide (ZnO + Ag), for enhancing the adhesion of electroless seed layers on glass. To address the inherently poor metal-glass interfacial adhesion in through-glass via (TGV) metallization, both chemical functionalization and topographical roughening via ultrasonic machining (USM) were examined. GO was introduced on silanized glass to enable covalent bonding, while ZnO + Ag was deposited via dip-coating to increase nanoparticle density and promote strong interfacial interaction with the glass surface. GO-modified roughened surfaces demonstrated the highest adhesion (2.75 N/cm), attributed to covalent bonding (N=C and C-O peaks) and improved nanoscale roughness. Although ZnO + Ag coatings with three dip cycles also showed high adhesion, micro-cracks raised long-term reliability concerns; therefore, a single-cycle ZnO + Ag coating was identified as the most practical configuration (2.5 N/cm on roughened glass). To assess practical applicability, the modified surfaces were implemented in TGV metallization. TGVs with an opening of nearly 280 mu m and a depth of 1100 mu m (aspect ratio, AR of nearly 4) were fabricated using USM and subsequently metallized. GO-modified vias exhibited continuous Cu coverage (similar to 20 mu m thick) along the sidewalls with strong adhesion, confirming the effectiveness of the electroless Ni seed layer. Kelvin test structures fabricated on GO-modified glass exhibited low via resistance (similar to 15 m Omega), demonstrating stable electrical conduction across the metallized sidewalls. While GO provided the most reliable metallization, accelerated reliability testing remains necessary for industrial deployment.

This study systematically investigates the influence of cavitation-driven bubble dynamics on the material removal characteristics in ultrasonic-assisted electrochemical discharge machining (UA-ECDM). A single-bubble dynamics model is developed to analyze the effect of ultrasonic vibration on bubble oscillation, collapse velocity, and transient pressure generation within the electrolyte. The model predicts that at higher vibration amplitudes, i.e. 9 & micro;m, bubble collapse pressures approach similar to 200 MPa, with collapse velocities exceeding 800 m s-1, indicating intense cavitation activity. However, the resulting stresses are lower than the fracture strength of the glass, suggesting that cavitation does not directly contribute to material removal but significantly enhances debris evacuation from the machining zone. The experimental results reveal a twofold increase in machining depth under ultrasonic-assisted conditions compared to conventional ECDM. High-speed imaging confirms intensified cavitation activity, along with earlier bubble detachment and the formation of a thinner and more stable gas film. Furthermore, discharge waveform analysis demonstrates a transition from irregular and unstable discharges to more uniform and consistent discharge events with increasing ultrasonic amplitude. The effectiveness of ultrasonic-assisted ECDM is further demonstrated by creating through-holes in 1 mm thick alumina substrates, highlighting its potential for applications in semiconductor packaging. Developed a single-bubble dynamics model to quantify cavitation in UA-ECDMUltrasonic vibration promotes thin gas film formation and stable discharge behaviorMachining depth improved by two times at 9 & micro;m ultrasonic vibration amplitudeHigh-speed imaging reveals cavitation activity and early bubble detachment

The demand for microfeatures in glass substrates has recently increased in radio frequency and microsystems packaging applications. It is primarily due to its favourable properties, including good electrical resistivity, low dielectric losses, and dimensional stability at high temperatures. However, the fabrication of intricate microfeatures on a glass substrate poses challenges due to its hard and brittle nature. Electrochemical discharge machining (ECDM) has been used as a cost-effective solution to overcome these challenges. ECDM is a non-traditional machining technique that utilises electro-discharges resulting from the breakdown of an electrochemically formed gas film enveloping a miniaturised tool electrode. The assistance of ultrasonic vibration was employed to augment the performance of the ECDM method. Herein, the experiments were performed to assess the influence of process parameters (ultrasonic power rating and applied voltage) on the machining performance. The responses evaluated included hole depth and overcut. The results demonstrated the feasibility of UA-ECDM for fabricating diverse microfeatures on glass substrates, making it suitable for high-value manufacturing applications in aerospace, microfluidics, and MEMS.

This article presents a 2D axisymmetric numerical model to predict the geometric profiles of micro-features in tungsten created by electrochemical jet drilling (EJD). The model incorporates nozzle feeding and simultaneously solves fluid dynamics, electric field, and material deformation. Without feeding, the model predicted a depth of 280 mu m after 25 s of drilling at 50 V and 500 mu m SOD. Introducing a 10 mu m/s feed rate increased the depth to 320 mu m. Numerical predictions showed strong agreement with experiments, within a +/- 5 % error. Increasing jet velocity from 9.6 m/s to 11.4 m/s improved depth by 13 % and reduced hole entrance diameter by 30 % after 8 min of drilling at 50 V and 400 mu m SOD. The mechanism of improved material removal at higher jet velocity is explained. Using the optimized jet velocity, micro-through holes were successfully drilled in 2.1 mm thick tungsten, achieving a maximum aspect ratio (AR) of 3.4.

This investigation presents a synergistic approach combining mechanical roughening via ultrasonic machining (USM) and chemical modification using (3-aminopropyl)triethoxysilane (APTES) and graphene-oxide (GO) to enhance the adhesion of electroless nickel films. The GO layer, rich in oxygen-containing functional groups, promotes metal ion coordination and catalytic activity while offering a wrinkled morphology for mechanical interlocking. Surface characterization using SEM and XPS confirmed successful functionalization and increased surface energy. Peel adhesion tests demonstrated that GO significantly improves film adhesion, increasing peel strength from 0.82 N/cm on untreated glass to 2.35 N/cm on GO-treated planar glass. The highest adhesion strength (2.75 N/cm) was achieved on roughened glass treated with GO, highlighting the synergistic effect of topographical and chemical enhancements. GO enhanced interfacial adhesion via hydrogen bonding and possible covalent linkage between its oxygenated groups and surface-bound amines.

This paper addresses challenges in debris removal and electrolyte replenishment during the electrochemical discharge micromachining (ECDM) of glass. The study presents a comprehensive numerical and experimental study of glass micromachining using ultrasonic-assisted electrochemical discharge machining (UA-ECDM). A finite element method (FEM)-based numerical model was developed to simulate the effects of ultrasonic vibrations on electrolyte flow and debris movement. The simulation results reveal that increasing ultrasonic amplitudes from 5 mu m to 10 mu m improves the electrolyte flow velocity two times at the microhole bottom. Additionally, ultrasonic vibration enhances debris distribution, shifting it towards the periphery of the microhole, thus improving the electrochemical discharge conditions. Experimentally, glass micromachining was performed at different ultrasonic amplitudes (0, 5, 8, and 10 mu m). The results demonstrate that ultrasonic vibrations increase machining depth, reducing hole taper as a result of improving electrolyte circulation, correlating with the simulation result. A 3x3 array of holes was successfully fabricated on a glass substrate with a depth of 835 mu m, confirming the feasibility of UA-ECDM for microhole drilling. This study confirms that UA-ECDM improves electrolyte circulation, enhancing electrochemical reactions at the tool-workpiece interface and increasing machining depth. (c) 2025 The Authors. Published by ELSEVIER Ltd. This is an open access article under the CC BY-NC-ND license

In electropolishing, the material removal rate is frequently neglected, as this process is primarily focused on surface finish, and yet, it is crucial for manufacturing metallic sheets. Solutions are required to enhance the material removal rate while maintaining surface quality. This work introduces an electropolishing technique that involves suspending ethanol in an electrolyte solution and employing a magnetic field during machining processes. The Taguchi approach is utilized to determine the ideal process parameters for enhancing the material removal rate of SS 316L electropolishing through a L9 orthogonal array. Pareto analysis of variance (ANOVA) is utilized to examine the four parameters of the machining process: applied voltage, ethanol concentration, machining gap variation, and the magnetic field of the electrolyte. The results demonstrate that the applied voltage, the incorporation of ethanol in electropolishing, and a reduced machining gap significantly increase the material removal rate; however, the introduction of a magnetic field did not notably increase the material removal rate.

Reliable adhesion between electroless deposited metal films and glass substrates is essential for the mechanical stability and long-term reliability of advanced microelectronic devices. In this work, graphene oxide (GO) and zinc oxide (ZnO) were evaluated as chemical adhesion promoters for electroless metallization. Glass substrates were first hydroxylated and silanized, followed by functionalization with GO or deposition of a thin ZnO layer. Surface chemistry was analyzed using X-ray photoelectron spectroscopy (XPS) survey spectra, confirming the incorporation of functional groups and oxide phases. Peel strength tests revealed substantial adhesion enhancement: GO-modified surfaces exhibited the highest adhesion strength (2.38 N/cm), followed by ZnO-modified (2.03 N/cm) and unmodified (0.85 N/cm) glass. The superior performance of GO was attributed to covalent bonding with silane linkers and nanoscale roughness, while ZnO improvement was linked to increased surface polarity and reactivity. These findings establish GO as a highly effective route for improving adhesion in glass metallization, with potential applicability in advanced electronic packaging.

Electrochemical discharge machining (ECDM) is widely used for fabricating microfeatures on brittle and non-conducting materials such as glass; however, inadequate electrolyte replenishment and debris accumulation in deep microhole drilling (>300 mu m) hinder its machining performance. Ultrasonic-assisted electrochemical discharge machining (UA-ECDM) has emerged to improve electrolyte circulation and debris evacuation, thereby enhancing the machining depth. This investigation explores the influence of ultrasonic tool vibration on electrolyte flow dynamics, debris removal, and machining performance through a combined numerical and experimental approach. A 3D numerical simulation was performed to analyze electrolyte flow velocity distribution and debris movement at various vibration amplitudes. The results indicate that ultrasonic vibration doubled the electrolyte velocity and increased the debris removal efficiency by 50%. The experimental observations confirmed that ultrasonic vibration increases hole depth by 33% and improves the aspect ratio by 16% compared to conventional ECDM. High-speed imaging, current-time signals, and EDS analysis revealed that UA-ECDM minimizes debris deposition and ensures uniform discharge distribution, reducing tool wear and improving process stability. Additionally, multiple high- aspect ratio (2.5) through-holes were fabricated in a 1.1 mm thick glass substrate using a multi-tip tool electrode in UA-ECDM.

This review article presents the current status of various micromachining techniques used to create microfeatures in alumina ceramic. Alumina has emerged as an advanced substrate in various radio-frequency communication and automotive packaging applications due to its superior electrical resistivity, lower dielectric loss, higher wear resistance, and dimensional stability at high temperatures. However, creating complex-shaped microfeatures in alumina is challenging due to its hard and brittle nature. Traditional contact-based methods fail to create microsized shapes in alumina; thus, the researchers are exploring novel machining methods, like abrasive, thermal, chemical, and hybrid micromachining processes. This review article comprehensively summarizes various micromachining methods used to create microfeatures in alumina ceramics. The mechanism, unique features, pros/cons, novelty, and applications of ultrasonic machining, laser ablation, electrochemical discharge machining, abrasive-jet machining, etc., are presented. The associated processing challenges in various alumina micromachining and the potential remedies to produce high-quality alumina microparts for microelectronics applications are discussed.

This article reports the improvement of the adhesion of the electroless seed layer deposited on glass substrates used in creating through-glass vias (TGV) by localized surface roughening. Four glass substrates having varying roughness characteristics were prepared by electrochemical discharge machining (ECDM) and ultrasonic machining (USM). The electroless nickel seed layer was deposited directly on glass without any adhesion layer, followed by electrodeposited copper layers. In-depth surface topography and morphology analysis reveal the mechanism behind the improved adhesion during standard peel and cross-hatch adhesion tests, which were used to determine the interlayer adhesion. Localized roughening techniques generated specific microfeatures, i.e., microgrooves (in USM) or ridges (in ECDM), increasing the surface area. These features acted as interlocking/nucleation sites to hold the electroless nickel atoms, resulting in higher interfacial adhesion. USM-roughened samples exhibited stronger interfacial adhesion than their ECDM-roughened counterparts, which indicated that the interlayer adhesion depends on topography and the roughened surface's morphology. The surface with negative skewness and positive excess kurtosis promotes mechanical interlocking, offering a promising strategy for enhancing interlayer adhesion. Finally, conformal deposition in a 6 x 6 array of through-holes having an aspect ratio of similar to 4 was also demonstrated.

A novel steady-dwell tool feeding approach is presented to create microfeatures in alumina substrate by ultrasonic-assisted electrochemical discharge machining (UA-ECDM). Comparisons among conventional ECDM, UA-ECDM, and UA-ECDM with steady-dwell feeding show distinct gas film formation. The impact of dwell time, step size, vibrational amplitude, and machining voltage on hole depth, overcut, and cross-sectional area removal rate (ARR) were assessed. Varying dwell time improved machining consistency,with material removal rates 1.8 to 2.3 times higher than continuous feeding. Ultrasonic assistance ensured uniform material removal beneath the tool, increasing ARR by 1.6 to 1.8 times. Combining steady-dwell tool feeding with ultrasonic assistance resulted in a 50% depth increase and a 33% ARR increase. The step size of 20 mu m yielded the best results regarding depth, ARR, and smaller overcut. An ultrasonic vibration amplitude of 8 mu m produced the maximum depth (365 mu m) and ARR (20 x 10-3 mm3/min); additionally, higher voltage correlated with higher depth, overcut, and ARR.

This article investigates the effects of mixing different alkaline electrolytes on the geometrical features created by the ECDM. Sodium hydroxide (NaOH) and potassium hydroxide (KOH) were mixed in varying volumetric proportions. Effect of critical process parameters on the depth and width of the microchannels and the associated tool wear was investigated. Pure NaOH electrolyte has resulted in the highest depth compared to the pure KOH electrolyte. Process mechanism behind the role of mixed electrolytes on the opening sizes and depths of microchannels is explained. Higher material removal by the NaOH electrolyte was due to the larger number of sodium (Na+) ions in the electrolyte, resulting in more aggressive electrochemical discharge; however, it also resulted in severe tool wear. Mixed electrolytes with a KOH yielded lower width and low tool wear. Increasing the volumetric proportion of KOH in the mixed electrolyte gradually decreased the machining depth, width, and tool wear.

A dynamic impact-based numerical model is presented to estimate the cross-sectional profiles of deep vias having depths up to 1 mm, created in glass by ultrasonic micromachining (USM). Finite element method (FEM) analysis was used to calculate the indentation volume caused by a single abrasive particle in a single impact. Considering the normal distribution of a large number of abrasive particles under the vibrating tool, the cross-sectional profiles were estimated. For the first time, the relationship between the velocity and the distance travelled by the abrasive in a viscous slurry after its impact with the tool is established. An exponential reduction in the abrasive velocity within the tool-glass gap was observed. This model predicted the minimum USM power, the minimum impact velocity and the maximum initial tool-workpiece gap required to cause significant machining. Experiment results confirmed that no machining happened at USM power 60 W, which the simulation model earlier predicted. Using this model, the initial gap required to prevent the glass breakage at different power ratings can also be estimated. In this work, the initial gaps were estimated to be 17 mu m, 30 mu m, 42 mu m, and 51 mu m for the USM power ratings of 60 W, 100 W, 140 W, and 180 W, respectively. The opening sizes and depths of vias, machined at varying USM power ratings, were predicted and later validated by detailed experiments. The percentage error in the simulation and experimental depths was within +/- 5%. High-aspect ratio through-holes were created in a 1.1 mm thick glass using optimized USM parameters, thus resulting in an etch rate of 350 mu m/min. The results conclude that the USM process can be used in various MEMS packaging and advanced interconnect applications thanks to its faster etching and room-temperature processing.

This chapter presents the fundamentals and advanced developments in the domain of electrochemical micromachining (ECM), which is used to create intricate components with superior surface finishes in electrically conductive materials. Based on the anodic dissolution at the atomic scale, ECM removes the material without any thermal or mechanical damage. The fundamental process parameters, emerging variants, and potential industrial applications are addressed. ECM-Based process innovations such as oxide-film masking, two-phase electrolytes, multi-wire ECM, and electrochemical jet machining are described. Recent applications, including surface texturing of free-form-shape using flexible electrodes, post-surface-finishing of additive-manufactured parts, and dressing of multi-tip array tools, are presented.