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The purpose of this paper is to investigate the reliability of wire bonds with three varying ball bond diameters, which are ball bonded with three different sizes of gold wires in light-emitting diode (LED) package under high-temperature environment. In automotive applications, “lifted ball bond” issue is a potential critical point for LED device reliability, as the wire bonds are usually stressed under high operating temperature during their lifetime. Moreover, the reliability of wire bonds in recent LED production has fallen under scrutiny due to the practice of reducing wire diameters to cut down production costs.

Three gold wires with sizes of 2, 1.5 and 1 mm were ball bonded on the LED chip bond pad via thermosonic wire bonding method to produce three different ball bond diameters, that is, 140, 120 and 100 μm, respectively. The reliability of these wire bond samples was then studied by performing isothermal aging at 200°C for the time interval of 30, 100 and 500 hours. To validate hypotheses based on the experimental data, COMSOL Multiphysics simulation was also applied to study the thermal stress distribution of wire bond under an elevated temperature.

Experimental results show that the interfacial adhesion of wire bond degrades significantly after aging at 200°C for 500 hours, and the rate of interfacial degradation was found to be more rapid in the wire bond with smaller ball bond diameter. Experimental results also show that ball bonds randomly elongate along an axis and deforms into elliptical shapes after isothermal aging, and ball bonds with smaller diameters develop more obvious elongations. This observation has not been reported in any previous studies. Simulation results show that higher thermal stress is induced in the wire bond with the decrease of ball bond diameter.

The reliability study of this paper provides measurements and explanation on the effects of wire diameter downsizing in wire bonds for automotive application. This is applicable as a reliability reference for industries who intend to reduce their production costs. Other than that, the analysis method of thermal stresses using COMSOL Multiphysics simulations can be extended by other COMSOL Multiphysics users in the future.

To resolve “lifted ball bond” issue, optimization of the bond pad surface quality and the wire bond parameter has been studied and reported in many studies, but the influence of ball bond diameter on wire bond reliability is rarely focused. Moreover, the observation of ball bonds randomly elongate and deform more into elliptical shape, and ball bond with smaller diameter has the highest elongation after isothermal aging also still has not been reported in any previous studies.

The purpose of this paper is to present a model that can be used to simulate the photopolymerization process in micro‐stereolithography (SL) in order to predict the shape of the cured parts. SL is an additive manufacturing process in which liquid photopolymer resin is cross‐linked and converted to solid with a UV laser light source. Traditional models of SL processes do not consider the complex chemical reactions and species transport occurring during photopolymerization and, hence, are incapable of accurately predicting resin curing behavior. The model presented in this paper attempts to bridge this knowledge gap.

The chemical reactions involved in the photopolymerization of acrylate‐based monomers were modeled as ordinary differential equations (ODE). This model incorporated the effect of oxygen inhibition and diffusion on the polymerization reaction. The model was simulated in COMSOL and verified with experiments conducted on a mask‐based micro‐SL system. Parametric studies were conducted to investigate the possibilities to improve the accuracy of the model for predicting the edge curvature.

The proposed model predicts well the effect of oxygen inhibition and diffusion on photopolymerization, and the model accurately predicts the cured part height when compared to experiments conducted on a mask‐based SL system. The simulated results also show the characteristic edge curvature as seen in experiments.

A triacrylate monomer was used in the experiments conducted, so results may be limited to acrylate monomers. Shrinkage was not considered when comparing cured part shapes to those predicted using COMSOL.

This paper presents a unique and a pioneering approach towards modeling of the photopolymerization reaction in micro‐SL process. This research furthers the development of patent pending film micro‐SL process which can be used for fabrication of custom micro‐optical components.

The purpose of this paper is to present the development and application of a numerical formulation for the structural dynamics and aeroelastic analysis of new generation helicopter and tiltrotor rotor blades. These are characterized by a curvilinear elastic axis, typically with the presence of tip sweep and anhedral angles.

The structural dynamics model implemented is based on nonlinear, flap‐lag‐torsion, rotating beam equations that are valid for slender, homogeneous, isotropic, non‐uniform, twisted blades undergoing moderate displacements. A second‐order approximation scheme for strain‐displacement is adopted. Aerodynamic contributions for aeroelastic applications are derived from sectional theories, with inclusion of wake inflow models to take into account three‐dimensional effects. The numerical integration is obtained through implementation within the COMSOL Multiphysics Finite‐Element‐Method (FEM) software code, considering the elastic axis of arbitrary curvilinear shape.

The computational tool developed is validated by comparisons with results available in the literature. These demonstrate the capability of the tool to accurately predict structural dynamics and aeroelastic behavior of curved‐axis rotor blades. In particular, the influence of sweep and anhedral angles at the blade tip is successfully captured.

The numerical tool developed is limited to the analysis of isotropic blades, with a simple sectional aerodynamic modeling for aeroelastic applications. However, the flexibility of the process through which the proposed tool has been developed is such that a moderate effort is required for its extension to composite blades and more accurate aerodynamic loads predictions.

The proposed computational solver is a reliable tool for preliminary design and optimal design processes of helicopter and tiltrotor rotor blades.

Computational tools for rotors with advanced‐geometry blades are not commonly available. Therefore, the presentation of a successful way to implement structural dynamics/aeroelastic mathematical formulations for rotor blades with curvilinear elastic axis in highly flexible, multiphysics, FEM‐based, commercial software may be of interest for designers and researchers.

Recent work has demonstrated the possibility of selectively sintering polymer powders with radio frequency (RF) radiation as a means of rapid, volumetric additive manufacturing. Although RF radiation can be used as a volumetric energy source, non-uniform heating resulting from the sample geometry and electrode configuration can lead to adverse effects in RF-treated samples. This paper aims to address these heating uniformity issues by implementing a computational design strategy for doped polymer powder beds to improve the RF heating uniformity.

Two approaches for improving the RF heating uniformity are presented with the goal of developing an RF-assisted additive manufacturing process. Both techniques use COMSOL Multiphysics® to predict the temperature rise during simulated RF exposure for different geometries. The effectiveness of each approach is evaluated by calculating the uniformity index, which provides an objective metric for comparing the heating uniformity between simulations. The first method implements an iterative heuristic tuning strategy to functionally grade the electrical conductivity within the sample. The second method involves reorienting the electrodes during the heating stage such that the electric field is applied in two directions.

Both approaches are shown to improve the heating uniformity and predicted part geometry for several test cases when applied independently. However, the greatest improvement in heating uniformity is demonstrated by combining the approaches and using multiple electrode orientations while functionally grading the samples.

This work presents an innovative approach for overcoming RF heating uniformity issues to improve the resulting part geometry in an RF-assisted, volumetric additive manufacturing method.

The substrate coupling and loss in integrated circuits are analyzed. Then, the authors extract impedances between any numbers of embedded contacts. The paper aims to discuss these issues.

The paper proposes a new substrate network 3D extraction technique, adapted from a transmission line method or Green kernels, but in the whole volume.

Extracting impedances between any numbers of embedded contacts with variable shapes or/and through silicon via. This 3D method is much faster comparing with FEM

Previous works consider TSVs alone, contacts onto the substrate. The authors do study entanglement between the substrate and the interconnections.

The paper describes a fast forward electromagnetic model built with help of commercial software. The purpose of this paper is to create an efficient and robust electromagnetic field model that could be easily plugged into a working microwave imaging system. The secondary purpose is to evaluate advantages and disadvantages of such a commercial packages for creating such a model.

In this paper the authors decided to build the model using COMSOL Multiphysics software suite, ultimately comparing its result to measurements of a real device. The numerical model was created in an iterative fashion in order to determine how much details are needed to make it reliable, while keeping it efficient.

The authors found that the commercial software seems like a viable platform for developing electromagnetic solvers. The resulting computer model is easy to prepare, run and integrate with external tools.

Using the experience in building numerical models of various systems the authors came to the conclusion that developing some in-house code is a very non-efficient technique as it slows down the progress of the research team once the team changes. Transfer of knowledge associated with the numerical tools is much easier when the tools are constructed using a common platform, i.e. commercial packages. It does not really matter if the software is free or proprietary as long as the platform provides efficient tools assisting in model preparation and data visualization.

One of the main advantages of using such a full field electromagnetic model is the ability to investigate an impact of different properties of the system (length of antennas, liquid parameters) on its performance. Thanks to the use of commercial software it is much easier to pass the project to new people too.

The presented numerical model utilizes a frugal meshing scheme which allows faster execution while keeping required accuracy of solutions. Using this model the authors were able to diagnose important geometrical details that could affect the performance of the system.

The purpose of this paper is to create a numerical model of electrode induction melting process for the gas atomization (EIGA) and process and investigate the complex interaction of the electromagnetic and thermal fields on the fluid flow with free surface.

The modelling approach is based on the free surface code SPHINX which includes time dependent electromagnetic, thermal and fluid flow with free surface modelling and the commercial software COMSOL for investigating 3D electromagnetic effects.

The melting dynamics, liquid film formation and the outflow free surface behavior are predicted by SPHINX using an optimized geometry. Quasi‐stationary AC electromagnetic solutions with COMSOL predict some 3D effects of the coil, including frequency dependent estimates of voltage, electric current and power.

The importance of magnetic forces controlling the free surface jet formation, partial semi‐levitation and the outflow superheat is uncovered by numerical modelling tools. An optimized geometry is presented for the EIGA process.

The purpose of this paper is to numerically investigate the effects of the shape on the performance of the cathode catalyst agglomerate used in polymer electrolyte fuel cells (PEFCs). The shapes investigated are slabs, cylinders and spheres.

Three 1D models are developed to represent the slab like, cylindrical and spherical agglomerates, respectively. The models are solved for the concentration of the dissolved oxygen using a finite element software, COMSOL Multiphysics®. “1D” and “1D axisymmetric” schemes are used to model the slab like and cylindrical agglomerates, respectively. There is no one-dimensional scheme available in COMSOL Multiphysics® for spherical coordinate systems. To resolve this, the governing equation in “1D” scheme is mathematically modified to match that of the spherical coordinate system.

For a given length of the diffusion path, the variation in the performances of the investigated agglomerates is dependent on the operational overpotential. Under low magnitudes of the overpotentials, where the performance is mainly limited by reaction, the slab-like agglomerate outperforms the spherical and cylindrical agglomerates. In contrast, under high magnitudes of the overpotentials where the agglomerate performance is mainly limited by diffusion, the spherical and cylindrical agglomerates outperform the slab-like agglomerate.

The current advances in the nano-fabrication technology gives more flexibility in designing the catalyst layers in PEFCs to the desired structures. If the design of the agglomerate catalyst is to be assessed, the current micro-scale modelling offers an efficient and rapid way forward.

The current micro-scale modelling is an efficient alternative to developing a full (or half) fuel cell model to evaluate the effects of the agglomerate structure.

Passive conducting elements are the important parts of textronic systems. This paper aims to study a possibility of creating well-conducting and durable elements in textile materials by combining two technologies – physical vapour deposition (PVD) and laser patterning.

Thin conducting metallic layers on common fabrics do not provide satisfactory resistance to bending and stretching; therefore, selected textile composite materials have been proposed as a substrate. The conducting elements were produced in two stage process – deposition of thin metallic layer on textile composite and creating conducting elements by laser patterning. Laser ablation process was optimized using modelling in Comsol Multiphysics package. Properties of conducting structures were investigated experimentally and by modelling.

This paper confirms the correctness of the choice of the textile composite as a substrate for conducting elements. The results have shown that combining PVD deposition of thin metallic layer and controlled laser ablation allow creating passive elements such as resistors, inductive coils and heaters. Computer simulations conducted in the Comsol Multihysics environment enabled to determine the temperature distribution around the heaters and to describe the dynamics of its changes. The obtained results allow to shorten time of the optimization process of structures with different geometry and assumed temperature distribution.

The novelty of this research can be summarized as following: choosing of textile composites as substrates for conductive elements instead of textiles used so far in textronics; creating conductive structures on textile composites using combined technologies, PVD and laser patterning, for the first time; modelling of laser ablation process of thin metallic layer; and optimization of properties of conducting elements by computer modelling.

With an eye to prevent derailment of high-speed trains, vis-à-vis unwarranted loss of lives and property, this paper aims to develop a formalism of designing a suitable control system with embedded decision support system.

A model of rolling contact fatigue (RCF) crack propagation in railway tracks is designed, simulating the alarming stress intensity factor around the advancing fatigue cracks. COMSOL multi-physics software is employed to design the RCF crack monitoring system with acoustic emission (AE) count signals, describing the damage threshold of railway tracks.

Simulation experiment on stress intensity factor for cracks in real life rail sections has enabled to describe the maximum working stress; it has been noticed that the threshold value of stress intensity factor (∼ 41 MPa m1/2) for the onset of unstable crack propagation is reached at a fatigue crack length of 11.5 mm. It is further noticed that the observed AE count at a particular instant of time in a specific location of railway track is a true indication of the vulnerability of rail failures.

The proposed model, a completely new of its kind, bears a high socio-technological value as it entails the design of an intelligent control system to prevent train accidents.