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The purpose of this paper is to propose a solution procedure to minimize/eliminate voiding and spattering defects in the assembly of 0201 chip components with micro via‐in pads and 95 wt.%Sn‐5 wt.%Sb solder alloy.

In total, four different micro via‐in pad designs were compared (via‐hole opening size): ultra small via‐in pads (d: 10 μm), small via‐in pads (d: 20 μm), and large via‐in pads (d: 60 μm), as well as designs with no via‐in pads and capped via‐in pads. Two process variables were also evaluated for the goal of achieving a high‐yield assembly solution in micro via‐in pad and lead‐free solder systems. Potential factors, such as the preheat conditions of the reflow profile and stencil aperture size, which might affect voiding and spattering in solder joints with micro via‐in pad, were investigated. Solder voiding frequency and size were also determined from X‐ray inspection and sample cross‐section analysis.

The results indicated that larger via‐holes were seen to create bigger voiding than smaller via‐holes. For smaller via‐holes, spattering is a greater problem than voiding in solder joints. Ultra small via‐in pads generated higher spattering compared to no via‐in pads and capped via‐in pads. Capped via‐in pads exhibited the best results in preventing voiding and flux spattering, and provided a wide process window for the selection of process parameters. It is also indicated that spattering was found to rapidly reduced with both increasing stencil opening size and use of reflow profile with long‐preheat conditions.

The findings provide certain process guidelines for surface‐mount assembly with via‐in pad substrate design. The strategy is to prevent voiding and spattering by adopting capped via‐in pads, if possible, when applying micro via with the 95 wt.%Sn‐5 wt.%Sb solder alloy system.

This paper aims to investigate voiding phenomena in solder joints under thermal pads of light-emitting diodes (LEDs) assembled in mass production environment by reflow soldering by using seven low-voiding lead-free solder pastes.

The solder pastes investigated are of SAC305 type, Innolot type or they are especially formulated by the manufacturers on the base of (SnAgCu) alloys with addition of some alloying elements such as Bi, In, Sb and Ti to provide low-void contents. The SnPb solder paste – OM5100 – was used as a benchmark. The solder paste coverage of LED solder pads was chosen as a measure of void contents in solder joints because of common usage of this parameter in industry practice.

It was found that the highest coverage and, related to it, the least void contents are in solder joints formed with the pastes LMPA-Q and REL61, which are characterized by the coverage of mean value 93.13% [standard deviation (SD) = 2.72%] and 92.93% (SD = 2.77%), respectively. The void diameters reach the mean value equal to 0.061 mm (SD = 0.044 mm) for LMPA-Q and 0.074 mm (SD = 0.052 mm) for REL61. The results are presented in the form of histograms, plot boxes and X-ray images. Some selected solder joints were observed with 3D computer tomography.

The statistical analyses are carried out on the basis of 2D X-ray images with using Origin software. They enable to compare features of various solder pastes recommended by manufacturers as low voiding. The results might be useful for solder paste manufacturers or electronic manufacturing services.

The purpose of this study is to obtain a general solution to the field equations of thermoelastic solid with voids and micro-temperatures under the gravitational field in the context of the three theories, namely, coupled theory (CT), Lord and Shulman theory and Green and Lindsay theory.

The normal mode analysis is used to obtain the exact expressions for the considered variables. Comparisons are made with the results obtained in the three theories with and without gravity. Some particular cases are also deduced from the present investigation.

The effect of the gravity on the displacement, the micro-temperature vector, the temperature distribution, the normal stress, the changes in the volume fraction field and the heat flux moments have been depicted graphically.

Some particular cases are also deduced from the present investigation.

The results of the physical quantities have been illustrated graphically by a comparison between three different theories in the presence and absence of gravity.

This study aims to investigate crack propagation in a moisture-preconditioned soft-termination multi-layer ceramic capacitor (MLCC) during thermal reflow process.

Experimental and extended finite element method (X-FEM) numerical analyses were used to analyse the soft-termination MLCC during thermal reflow. A cross-sectional field emission scanning electron microscope image of an actual MLCC’s crack was used to validate the accuracy of the simulation results generated in the study.

At 270°C, micro-voids between the copper-electrode and copper-epoxy layers absorbed 284.2 mm/mg³ of moisture, which generated 6.29 MPa of vapour pressure and caused a crack to propagate. Moisture that rapidly vaporises during reflow can cause stresses that exceed the adhesive/substrate interface’s adhesion strength of 6 MPa. Higher vapour pressure reduces crack development resistance. Thus, the maximum crack propagation between the copper-electrode and copper-epoxy layers at high reflow temperature was 0.077 mm. The numerical model was well-validated, as the maximum crack propagation discrepancy was 2.6%.

This research holds significant implications for the industry by providing valuable insights into the moisture-induced crack propagation mechanisms in soft-termination MLCCs during the reflow process. The findings can be used to optimise the design, manufacturing and assembly processes, ultimately leading to enhanced product quality, improved performance and increased reliability in various electronic applications. Moreover, while the study focused on a specific type of soft-termination MLCC in the reflow process, the methodologies and principles used in this research can be extended to other types of MLCC packages. The fundamental understanding gained from this study can be extrapolated to similar structures, enabling manufacturers to implement effective strategies for crack reduction across a wider range of MLCC applications.

The moisture-induced crack propagation in the soft-termination MLCC during thermal reflow process has not been reported to date. X-FEM numerical analysis on crack propagation have never been researched on the soft-termination MLCC.

The purpose of this paper is to investigate use of calabrian pine (pinus brutia) cone (CPC) dust along with borax (BX) to assess the effect of friction coefficient. Despite the number of research studies completed on the mechanism of friction in automotive brake lining materials, the phenomenon is still not fully understood. Complex mechano-chemical processes occurring on the friction interface of a composite friction material make it difficult to understand the correlation between the formulation of brake lining and the frictional performance.

In this study, the use of CPC dust along with BX has been investigated for assessing the effect on friction coefficient. CPC has resin in it. BX is a boron production which is widely used in boron glass production and in ceramic industry for increasing the heat- resistant and -forming abrasion resistant. Newly formulated brake lining material with five different ingredients has been tested under Friction Assessment and Screening Test. Friction coefficient, wear rate and scanning electron microscope for friction surface were examined to assess the performance of these samples.

Analysis of the experimental results shows that the brake lining material containing CPC and BX significantly improved the stability of the friction coefficient, fade and wear resistance.

Several investigations have been conducted to use different materials in brake pads. The brake pad standards have been provided in previous studies, as well as the aims for economical and sustainable production. In the present study, production of brake pads by CPC dust and BX has been executed. Parallel results have been presented between previously reported and present study, in view of brake characteristics and wear resistance. Use of the lower cost and productive organic sources of material are the main improvement of the present study.

The purpose of this paper is to understand the process of failure of scale and the corrosion resistance of scale to the substrate in an atmospheric environment.

The corrosion behaviour of X65 pipeline steel with different types of oxide scale was analysed using the natural environment exposure corrosion test, scanning electron microscopy analysis, electrochemical corrosion polarization curve test and other methods in a warehouse environment.

The results of this research show that one type of oxide scale, which is rough, has an uneven microstructure, and exhibits weak adhesion to the matrix, does not protect the substrate from corrosion. Conversely, the uniform, dense oxide scale, which exhibits strong adhesion to the matrix, provides effective protection to the steel. However, as the corrosion develops, the corrosion rate of the substrate tends to accelerate, especially when the structure of the oxide scale is damaged to a certain extent.

The corrosion mechanism of the oxide scale on hot rolled steel in an atmospheric environment has been proposed.

The purpose of this paper is to compare mechanical response of polypropylene in multi‐cycle tensile tests with strain‐controlled and mixed deformation programs and to develop constitutive equations that describe quantitatively the experimental data.

Multi‐cycle tensile tests are performed on isotactic polypropylene with strain‐controlled (oscillations between fixed maximum and minimum strains) and mixed (oscillations between a fixed maximum strain and the zero minimum stress) programs. A constitutive model is derived in cyclic viscoelasticity and viscoplasticity of semicrystalline polymers, and its parameters are found by fitting observations. The effect of damage accumulation of material parameters is analyzed numerically.

The model predicts accurately mechanical behavior of polypropylene in tests with numbers of cycles strongly exceeding those used to determine its parameters. In the regime of developed damage, material constants in the stress‐strain relations are independent of deformation program.

A novel constitutive model is derived in cyclic viscoelastoplasticity of semicrystalline polymers and comparison of its adjustable parameters is performed for different deformation programs.

Based on the random aggregate model of recycled aggregate concrete (RAC), this paper aims to focus on the effect of loading rate on the failure pattern and the macroscopic mechanical properties.

RAC is regarded as a five-phase inhomogeneous composite material at the mesoscopic level. The number and position of the aggregates are modeled by the Walraven formula and Monte–Carlo stochastic method, respectively. The RAC specimen is divided by the finite-element mesh to establish the dynamic base force element model. In this model, the element mechanical parameters of each material phase satisfy Weibull distribution. To simulate and analyze the dynamic mechanical behavior of RAC under axial tension, flexural tension and shear tension, the dynamic tensile modes of the double-notched specimens, the simply supported beam and the L specimens are modeled, respectively. In addition, the different concrete samples are numerically investigated under different loading rates.

The failure strength and failure pattern of RAC have strong rate-dependent characteristics because of the inhomogeneity and the inertial effect of the material.

The dynamic base force element method has been successfully applied to the study of recycled concrete.

This study aims at designing consistent and durable concrete by making use of waste materials. An investigation has been carried out to evaluate the performance of conventional and optimal concrete (including 5% GP) at high temperatures for different exposure times.

An experimental work is carried out to compare the conventional and optimal concrete with respect to weight loss, mechanical strength characteristics (compressive, tensile and flexural) after exposed to 100, 200 and 300 °C with 1, 2 and 3 h duration of exposure followed by cooling in furnace for 24 h and then air cooling.

The workability of granite powder modified concrete decreases as percentage of replacement increases. Compressive, tensile and flexural strengths all increased at 100 °C when compared to strength characteristics at normal temperature, regardless of the exposure conditions, and there was no weight loss noticed. For 200 and 300 °C, the strengths were decreased compared to normal temperature and an elevated temperature of 100 °C, as weight loss of concrete specimens are observed to be decreased at these temperatures. So, the optimum elevated temperature can be concluded as 100 °C.

Incorporating pozzolanic binder (granite powder) as cement replacement subjecting to elevated temperatures in an electric furnace is the research gap in this area. Many of the works were carried out replacing GP for fine aggregate at normal temperatures and not at elevated temperatures.