Suhana Mohd Said

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...

Blue phase liquid crystal: Strategies for phase stabilization and device development

Abstract The blue phase liquid crystal (BPLC) is a highly ordered liquid crystal (LC) phase found very close to the LC–isotropic transition. The BPLC has demonstrated potential in next-generation display and photonic technology due to its exceptional properties such as sub-millisecond response time and wide viewing angle. However, BPLC is stable in a very small temperature range (0.5–1 °C) and its driving voltage is very high (∼100 V). To overcome these challenges recent research has focused on solutions which incorporate polymers or nanoparticles into the blue phase to widen the temperature range from around few °C to potentially more than 60 °C. In order to reduce the driving voltage, strategies have been attempted by modifying the device structure by introducing protrusion or corrugated electrodes and vertical field switching mechanism has been proposed. In this paper the effectiveness of the proposed solution will be discussed, in order to assess the potential of BPLC in display technology and beyond.

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.

DNA hybridization detection by porous silicon-based DNA microarray in conjugation with infrared microspectroscopy

A method is described for the label-free detection of DNA hybridization on porous silicon (por-Si), based upon the pairing of oligonucleotide chemistry and standard silicon nanotechnology. Por-Si with a pore diameter of approximately 30 nm was used to immobilize probe DNA. Infrared microspectroscopy was employed to monitor the hybridization of probe-DNA immobilized on pore surfaces with its complementary DNA (target-DNA). The immobilization of probe DNA on por-Si facilitates hybridization detection for a small sensing area (approximately 50×50 μm2) with a high detection efficiency. In this study, we fabricated a porous silicon-based DNA microarray (por-Si-microarray) using photolithographic and Si anodizing techniques. We demonstrate that DNA hybridization can be detected on a por-Si-microarray through the analysis of infrared absorption spectral profiles in the region where the vibration modes of the bases appear. This present approach demonstrates that por-Si-microarray in conjugation with infrared micr...

Synthesis and characterization of protic ionic liquids as thermoelectrochemical materials

This unique work reports on the thermoelectrochemical potential of protic ionic liquid (PIL)-based electrolytes coupled with the I−/I3− redox couple. Two series of protic ionic liquids based on secondary and/or tertiary ammonium cations with the trifluoroacetate, methanesulfonate, trifluoromethanesulfonate and tosylate anions were synthesized for thermoelectrochemical cells. The complete study on PILs was carried out to determine the nature and efficiency for the generation of voltage through the electrochemical effect. The investigation was executed in a temperature range between room temperature and 90 °C. PILs show lower thermal conductivity and good ionic conductivity which leads to the success of good thermoelectric materials. The outcome was positive as our proposed PILs showed higher Se values of 420 μV K−1 obtained for TEHA TFMS than the reported values of the same I−/I3− redox couple. The most favorable thermoelectric figure of merit value (949.46 × 10−6) was achieved by BEHA TFMS. The power and the current output of the studied PILs are higher than those of some aprotic ionic liquids (AILs) reported.

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

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.

Fabrication and Characterization of Microstacked PZT Actuator for MEMS Applications

A microstacked PZT actuator of dimensions 8 mm × 0.8 mm × 0.4 mm and capable of 2.3-μm actuation under a voltage of 100 V was fabricated and characterized. This actuator was then integrated into a silicon microstage with dimensions of 20 mm × 20 mm × 0.4 mm requiring actuation by a miniaturized actuator. The microstage was designed containing a Moonie amplification mechanism in order to further amplify the actuation of the stacked PZT actuator. Experimental characterization of the microstage performance indicated that the combination of a stacked PZT actuator with the Moonie amplification mechanism was successful in enabling high amplification of the microstage to ~15 times the original displacement of the PZT actuator. A displacement of 16.5 μm at an applied voltage of 60 V and a resonant frequency of 456 Hz in the lateral vibration mode was observed. The relationship between the actuator parameters and the microstage design and performance was also discussed in order to show that the customized fabrication of a miniature actuator was imperative for the successful design of a high area-efficiency microstage. Analytical derivation of the displacement of the stacked PZT actuator was also carried out in order to evaluate the effectiveness of the fabricated actuator compared with the ideal stacked PZT structure.

High Thermal Gradient in Thermo-electrochemical Cells by Insertion of a Poly(Vinylidene Fluoride) Membrane.

Thermo-Electrochemical cells (Thermocells/TECs) transform thermal energy into electricity by means of electrochemical potential disequilibrium between electrodes induced by a temperature gradient (ΔT). Heat conduction across the terminals of the cell is one of the primary reasons for device inefficiency. Herein, we embed Poly(Vinylidene Fluoride) (PVDF) membrane in thermocells to mitigate the heat transfer effects - we refer to these membrane-thermocells as MTECs. At a ΔT of 12 K, an improvement in the open circuit voltage (Voc) of the TEC from 1.3 mV to 2.8 mV is obtained by employment of the membrane. The PVDF membrane is employed at three different locations between the electrodes i.e. x = 2 mm, 5 mm, and 8 mm where ‘x’ defines the distance between the cathode and PVDF membrane. We found that the membrane position at x = 5 mm achieves the closest internal ∆T (i.e. 8.8 K) to the externally applied ΔT of 10 K and corresponding power density is 254 nWcm−2; 78% higher than the conventional TEC. Finally, a thermal resistivity model based on infrared thermography explains mass and heat transfer within the thermocells.