Mohd Faizul Mohd Sabri

A review on thermal cycling and drop impact reliability of SAC solder joint in portable electronic products

Currently, the portable electronic products trend to high speed, light weight, miniaturization and multifunctionality. In that field, solder joint reliability in term of both drop impact and thermal cycling loading conditions is a great concern for portable electronic products. The transition to lead-free solder happened to coincide with a dramatic increase in portable electronic products. Sn–Ag–Cu (SAC) is now recognized as the standard lead free solder alloy for packaging interconnects in the electronics industry. The present study reviews the reliability of different Ag-content SAC solder joints in term of both thermal cycling and drop impact from the viewpoints of bulk alloy microstructure and tensile properties. The finding of the study indicates that the best SAC composition for drop impact performance is not necessarily the best composition for optimum thermal cycling reliability. The level of Ag-content in SAC solder alloy can be an advantage or a disadvantage depending on the application, package and reliability requirements. As a result, most component assemblers are using at least two (and in many cases even more) lead-free solder sphere alloys to meet various package requirements.

High-Reliability Low-Ag-Content Sn-Ag-Cu Solder Joints for Electronics Applications

Sn-Ag-Cu (SAC) alloy is currently recognized as the standard lead-free solder alloy for packaging of interconnects in the electronics industry, and high- Ag-content SAC alloys are the most popular choice. However, this choice has been encumbered by the fragility of the solder joints that has been observed in drop testing as well as the high cost of the Ag itself. Therefore, low-Ag-content SAC alloy was considered as a solution for both issues. However, this approach may compromise the thermal-cycling performance of the solders. Therefore, to enhance the thermal-cycling reliability of low-Ag-content SAC alloys without sacrificing their drop-impact performance, alloying elements such as Mn, Ce, Ti, Bi, In, Sb, Ni, Zn, Al, Fe, and Co were selected as additions to these alloys. However, research reports related to these modified SAC alloys are limited. To address this paucity, the present study reviews the effect of these minor alloying elements on the solder joint reliability of low-Ag-content SAC alloys in terms of thermal cycling and drop impact. Addition of Mn, Ce, Bi, and Ni to low-Ag-content SAC solder effectively improves the thermal-cycling reliability of joints without sacrificing the drop-impact performance. Taking into consideration the improvement in the bulk alloy microstructure and mechanical properties, wetting properties, and growth suppression of the interface intermetallic compound (IMC) layers, addition of Ti, In, Sb, Zn, Al, Fe, and Co to low-Ag-content SAC solder has the potential to improve the thermal-cycling reliability of joints without sacrificing the drop-impact performance. Consequently, further investigations of both thermal-cycling and drop reliability of these modified solder joints must be carried out in future work.

A review on effect of minor alloying elements on thermal cycling and drop impact reliability of low-Ag Sn-Ag-Cu solder joints

Purpose – The purpose of this paper is to discuss the reliability of board level Sn‐Ag‐Cu (SAC) solder joints in terms of both thermal cycling and drop impact loading conditions, and further modification of the characteristics of low Ag‐content SAC solder joints using minor alloying elements to withstand both thermal cycle and drop impact loads.Design/methodology/approach – The thermal cycling and drop impact reliability of different Ag‐content SAC bulk solder will be discussed from the viewpoints of mechanical and micro‐structural properties.Findings – The best SAC composition for drop performance is not necessarily the best composition for optimum thermal cycling reliability. The content level of silver in SAC solder alloys can be an advantage or a disadvantage depending on the application, package and reliability requirements. The low Ag‐content SAC alloys with different minor alloying elements such as Mn, Ce, Bi, Ni and Ti display good performance in terms of both thermal cycling and drop impact loadi...

Enhanced Ethanol Gas Sensing Properties of SnO2-Core/ZnO-Shell Nanostructures

An inexpensive single-step carbon-assisted thermal evaporation method for the growth of SnO2-core/ZnO-shell nanostructures is described, and the ethanol sensing properties are presented. The structure and phases of the grown nanostructures are investigated by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. XRD analysis indicates that the core-shell nanostructures have good crystallinity. At a lower growth duration of 15 min, only SnO2 nanowires with a rectangular cross-section are observed, while the ZnO shell is observed when the growth time is increased to 30 min. Core-shell hierarchical nanostructures are present for a growth time exceeding 60 min. The growth mechanism for SnO2-core/ZnO-shell nanowires and hierarchical nanostructures are also discussed. The sensitivity of the synthesized SnO2-core/ZnO-shell nanostructures towards ethanol sensing is investigated. Results show that the SnO2-core/ZnO-shell nanostructures deposited at 90 min exhibit enhanced sensitivity to ethanol. The sensitivity of SnO2-core/ZnO-shell nanostructures towards 20 ppm ethanol gas at 400 °C is about ∼5-times that of SnO2 nanowires. This improvement in ethanol gas response is attributed to high active sensing sites and the synergistic effect of the encapsulation of SnO2 by ZnO nanostructures.

A review on the fabrication of polymer-based thermoelectric materials and fabrication methods.

Thermoelectricity, by converting heat energy directly into useable electricity, offers a promising technology to convert heat from solar energy and to recover waste heat from industrial sectors and automobile exhausts. In recent years, most of the efforts have been done on improving the thermoelectric efficiency using different approaches, that is, nanostructuring, doping, molecular rattling, and nanocomposite formation. The applications of thermoelectric polymers at low temperatures, especially conducting polymers, have shown various advantages such as easy and low cost of fabrication, light weight, and flexibility. In this review, we will focus on exploring new types of polymers and the effects of different structures, concentrations, and molecular weight on thermoelectric properties. Various strategies to improve the performance of thermoelectric materials will be discussed. In addition, a discussion on the fabrication of thermoelectric devices, especially suited to polymers, will also be given. Finally, we provide the challenge and the future of thermoelectric polymers, especially thermoelectric hybrid model.

Modeling and experimental validation of the performance of a silicon XY-microstage driven by PZT actuators

In this paper, the design and evaluation of silicon-based PbZrTiO3 (PZT) driven XY-microstages with total dimensions of 20 × 20 × 0.4 mm3 are presented. The PZT actuator has the advantage of having high accuracy and high intrinsic resonance frequency. However, its displacement is very small; thus Moonie amplification mechanisms are integrated to magnify the displacement. Finite element method simulation is carried out to obtain the microstage performance and identify its design parameters. It is demonstrated that an amplification factor of up to 18 times is possible using the silicon Moonie amplification mechanism, resulting in displacements of 82 µm and 60 µm at an applied voltage of 70 V for the X and Y directions, respectively. Furthermore, this microstage produces resonance frequencies of 261 Hz and 642 Hz in the X and Y directions, respectively.

Effectiveness Study of a Shell and Tube Heat Exchanger Operated with Nanofluids at Different Mass Flow Rates

Several challenging issues, such as global warming, greenhouse effect, fuel security, and the high price of energy, motivate people to think about energy savings. Energy can be saved by effectively using available materials and facilities. Heat exchangers play a significant part in the field of energy conservation, conversion, and recovery. Nanofluids can be used in the heat exchangers to reduce global energy losses. Thermal performance of a shell and tube heat exchanger operated with nanofluids has been analytically investigated at different mass flow rates and compared with water as the base fluid. Suspensions of ZnO, CuO, Fe3O4, TiO2, and Al2O3 nanoparticles in water (W) at 0.03 volumetric fractions have been considered. It is found that, for a certain mass flow rate (50 kg/min) of tube side and shell side fluid, the highest heat transfer coefficient (h) belongs to Al2O3-Wnanofluid and the lowest to CuO-W nanofluid. However, maximum energy effectiveness (ϵ) improvement took place by 43% for ZnO-W nanofluid and minimum ϵ improvement that was around 31% happened for Al2O3-W nanofluid. Furthermore, this energy effectiveness also improved with the decrease of the mass flow rates of nanofluids and increasing the mass flow rates of the base fluid. However, changing the base fluids mass flow rate has a limited effect on this improvement of energy effectiveness. For example, a maximum overall heat transfer coefficient was found to vary from 18.31 to 18.35 W/m² · K for Al2O3-W nanofluid when changing the mass flow rate of nanofluid from 50 to 70 kg/min. On the other hand, with the same changes of hot water mass flow rates, a maximum overall heat transfer coefficient was obtained to shift from 18.31 to 22 W/m².K for the same nanofluid. Viscosity and specific heat of nanofluids are responsible for these phenomena. However, energy effectiveness of the shell and tube heat exchanger can be increased by using metal oxide nanofluids, and better performance can be achieved by maintaining higher mass flow rates of shell side fluid and lower mass flow rates for tube side fluid.

Structure-electronics relations of discotic liquid crystals from a molecular modelling perspective

ABSTRACT Discotic liquid crystals (DLCs) have been researched for their potential in electronics applications, such as organic field-effect transistors, organic light-emitting diodes and organic photovoltaics. These molecules generally comprise a rigid planar core surrounded by aliphatic chains, and self-organise into columnar phases. Charge transfer is enabled along these columns, as the spatial overlap of the stacked π orbitals within the columns lead to a quasi-one-dimensional conductivity. An understanding of charge transfer and electronics orbitals in the field of DLCs is valuable for rational design of future DLC molecules in electronics applications. This paper provides a perspective that a range of molecular modelling tools may bring into our understanding on the structure, dynamics and electronics properties of DLCs. Whilst the description of charge transfer of DLCs has been substantially investigated, the understanding on the molecular orbitals had been relatively less explored. We introduce a multiscale molecular mechanics and quantum mechanics approach to understanding the relationship between the bandgap and density of states (DOS) and the structural parameters of a DLC. This investigation is expected to be the starting point for situations where knowledge of DOS for DLCs are of the essence, in applications such as current rectification and thermoelectricity. GRAPHICAL ABSTRACT

The bulk alloy microstructure and tensile properties of Sn‐1Ag‐0.5Cu‐xAl lead‐free solder alloys (x=0, 1, 1.5 and 2 wt.%)

Purpose – The purpose of this paper is to investigate the effect of Al addition on the bulk alloy microstructure and tensile properties of the low Ag‐content Sn‐1Ag‐0.5Cu (SAC105) solder alloy.Design/methodology/approach – The Sn‐1Ag‐0.5Cu‐xAl (x=0, 1, 1.5 and 2 wt.%) bulk solder specimens with flat dog‐bone shape were used for tensile testing in this work. The specimens were prepared by melting purity ingots of Sn, Ag, Cu and Al in an induction furnace. Subsequently, the molten alloys were poured into pre‐heated stainless steel molds, and the molds were naturally air‐cooled to room temperature. Finally, the molds were disassembled, and the dog‐bone samples were removed. The solder specimens were subjected to tensile testing on an INSTRON tester with loading rate 10−3 s−1. The microstructural analysis was carried out using scanning electron microscopy/Energy dispersive X‐ray spectroscopy. Electron Backscatter Diffraction (EBSD) analysis was used to identify the IMC phases. To obtain the microstructure, th...

Enhance protection of electronic appliances through multivariate modelling and optimization of ceramic core materials in varistor devices

E-waste comprises discarded low quality protected electronic appliances that annually accumulate million tons of hazardous materials in the environment. Protection is provided to control unwanted voltages that usually generate in associated electrical circuits by a multi-junction ceramic in a voltage dependent varistor. The ceramics microstructure consists of ZnO grains that are surrounded by the narrow boundaries of melted specific additives such as Bi2O3, TiO2 and Sb2O3. In fact, the boundaries manage the quality of protection through a certain volume of intrinsic oxygen vacancies transformation which depends on the amounts of the additives. Since these amounts are the ceramic fabrications initial input variables, the optimization process is capable of improving the quality of the protection (non-linear coefficient) as an output of the varistor devices. In this work, the fabrication was designed and then experimentally performed to calculate the non-linear coefficients of the produced varistors as actual responses. The responses were used to obtain an appropriate model for the fabrication by different semi-empirical methods. Afterward, the models predicted the optimized amounts of the additives which maximized the quality of the varistors. The predicted condition was fabricated as final varistors that were electrically characterized to compare their nonlinear coefficients as the quality indicator. The comparison demonstrated that the optimized amounts of Bi2O3 (0.5), TiO2 (0.47) and Sb2O3 (0.21) in mol% provided the very high protective varistor with nonlinear coefficients of 28.1. In conclusion, the optimization, which has industrial scale-up potential, warranties the electronic protection that controls global e-waste.