Search results

An overview of the concerns involved in the operation of electronic hardware at elevated temperatures is presented. Materials selection and package design issues are addressed for a wide range of packaging elements from the semiconductor chip to the box. It is found that most elements of common high density device and packaging architecture can be used up to 200°C. However, gold‐aluminium wirebonds, eutectic tin‐lead solder joints and die attaches, and FR‐4 boards will seriously degrade at temperatures below 200°C. For these elements, alternative materials of construction are recommended. Comparisons are made between package design for high power dissipation and that for high temperature operation.

More electric aircraft (MEA) is defined as the extensive usage of electric power in aircraft. The demand for electric power in new generation aircraft rises due to environmental and economic considerations. Hence, efficient and reliable starter/generators (SGs) are trending nowadays. The conventional main engine starting system and power generation system can be replaced with an individual SG. The constraints of the SG should be investigated to handle the aviation requirements. Even though the SG is basically an electric machine, it requires a multidisciplinary study consisting of electromagnetic, thermal and mechanical works to cope with aviation demands. This study aims to review conventional and new-generation aircraft SGs from the perspective of electric drive applications.

First of all, the importance of the MEA concept has been briefly explained. Also, the historical development and the need for higher electrical power in aircraft have been indicated quantitatively. Considering aviation requirements, the candidate electrical machines for aircraft SG have been determined by the method of scoring. Those machines are compared over 14 criteria, and the most predominant of them are specified as efficiency, power density, rotor thermal tolerance, high-speed capability and machine complexity. The features of the most suitable electrical machine are pointed out with data gathered from empirical studies. Finally, the trending technologies related to efficient SG design have been explained with numeric datasets.

The induction motor, switched reluctance motor and permanent magnet synchronous motor (PMSM) are selected as the candidate machines for SGs. It has been seen that the PMSM is the most preferable machine type due to its efficient operation in a wide range of constant power and speed. It is computationally proven that the using amorphous magnetic alloys in SG cores increases the machine efficiency more. Also, the benefits of high voltage direct current (HVDC) use in aircraft have been explained by a comparison of different aircraft power generation standards. It is concluded that the HVDC use in aircraft decreases total cable weight and increases aircraft operation efficiency. The thermal and mechanical tolerance of the SG is also vital. It has been stated that the liquid cooling techniques are suitable for SGs.

The demand for electrical power in new generation aircraft is increasing. The SG can be used effectively and efficiently instead of conventional systems. To define requirements, constraints and suggestions, this study investigates the SGs from the perspective of electric drive applications.

This study aims to develop indium-based solders for cryogenic applications.

This paper aims to investigate mechanical properties of indium-based solder formulations at room temperature (RT, 27 °C) as well as at cryogenic temperature (CT, −196 °C) and subsequently to find out their suitability for cryogenic applications. After developing these alloys, mechanical properties such as tensile and impact strength were measured as per American Society for Testing and Materials standards at RT and at CT. Charpy impact test results were used to find out ductile to brittle transition temperature (DBTT). These properties were also evaluated after thermal cycling (TC) to find out effect of thermal stress. Scanning electron microscope analysis was performed to understand fracture mechanism. Results indicate that amongst the solder alloys that have been studied in this work, In-34Bi solder alloy has the best all-round mechanical properties at RT, CT and after TC.

It can be concluded from the results of this work that In-34Bi solder alloy has best all-round mechanical properties at RT, CT and after TC and therefore is the most appropriate solder alloy amongst the alloys that have been studied in this work for cryogenic applications

DBTT of indium-based solder alloys has not been found out in the work done so far in this category. DBTT is necessary to decide safe working temperature range of the alloy. Also the effect of TC, which is one of the major reasons of failure, was not studied so far. These parameters are studied in this work.

The purpose of this paper is to present the results of experiments performed to attach silicon dies (chips) to low‐temperature co‐fired ceramic (LTCC) substrates with Ag or AgPd pads using SnAgCu or SnPb solder and the results of the characterization of the solder joints.

LTCC substrates were fabricated by stacking and laminating four green tapes with the top layer screen‐printed with Ag or AgPd paste to form pads. Silicon die sizes of 1 × 1 mm and 2 × 2 mm with electroless nickel immersion gold plated were soldered to 2 × 2 mm pads on the LTCC substrates using SnPb or SnAgCu solder. The solder joints were then characterized using X‐ray, die shear, energy dispersive X‐ray and scanning electron microscopy techniques.

The joints made by AgPd pads with SnAgCu solder provided the best results with the highest shear strength having strong interfaces in the joints. However, the joints of Ag pads with SnPb solder did not provide high‐shear strength.

The findings provide certain guidelines to implement LTCC applications. AgPd pads with SnAgCu solder can be considered for applications where small silicon dies need to be attached to LTCC substrates. However, Ag pads with SnAgCu solder can be considered for lead‐free solder applications.

This paper seeks to review recent advances in wire bonding, flip chip and lead‐free solder for advanced microelectronics packaging.

Of the 91 journal papers, 59 were published in 2005‐2007 and topics related to wire bonding, flip chip and lead‐free solder for advanced microelectronics packaging are reviewed.

Research on advanced wire bonding is continuously performed for advanced and complex applications such as stacked‐dies wire bonding, wire bonding of low‐k ultra‐fine‐pitch devices, and copper wire bonding. Owing to its many advantages, flip chip using adhesive has gained more popularity. Research on the reliability of lead‐free solder joints is being conducted world‐wide. The new challenges, solutions and new developments are discussed in this paper.

Because of page limitation of this review paper and the large number of the journal papers available, only a brief review is conducted. Further reading is needed for more details.

This review paper attempts to provide introduction to recent developments and the trends in terms of the topics for advanced microelectronics packaging. With the references provided, readers may explore more deeply, focusing on a particular issue.

Tin-Silver-Copper is widely accepted as the best alternative to replace Tin-Lead solders in microelectronics packaging due to their acceptable properties. However, to overcome some of the shortcomings related to its microstructure and in turn, its mechanical properties at high temperature, the addition of different elements into Tin-Silver-Copper is important for investigations. The purpose of this paper is to analyse the effect of lanthanum doping on the microstructure, microhardness and tensile properties of Tin-Silver-Copper as a function of thermal aging time for 60, 120 and 180 h at a high temperature of 150°C and at high strain rates of 25, 35 and 45/s.

The microstructure of un-doped and Lanthanum-doped Tin-Silver-Copper after different thermal aging time is examined using scanning electron microscopy followed by digital image analyses using ImageJ. Brinell hardness is used to find out the microhardness properties. The tensile tests are performed using the universal testing machine. All the investigations are done after the above selected thermal aging time at high temperature. The tensile tests of the thermally aged specimens are further investigated at high strain rates of 25, 35 and 45/s.

According to the microstructural examination, Tin-Silver-Copper with 0.4 Wt.% Lanthanum is found to be more sensitive at high temperature as the aging time increases which resulted in coarse microstructure due to the non-uniform distribution of intermetallic compounds. Similarly, lower values of microhardness, yield strength and ultimate tensile strength come in favours of 0.4 Wt.% Lanthanum added Tin-Silver-Copper. Furthermore, when the thermally aged tensile specimen is tested at high strains, two trends in tensile curves of both the solder alloys are noted. The trends showed that yield strength and ultimate tensile strength increase as the strain rate increase and decrease when there is an increase in thermal aging.

The addition of higher supplement (0.4 Wt.%) of Lanthanum into Tin-Silver-Copper showed a lower hardness value, yield strength, ultimate tensile strength, ductility, toughness and fatigue in comparison to un-doped Tin-Silver-Copper at high temperature and at high strain rates. Finally, simplified material property models with minimum error are developed which will help when the actual test data are not available.

The paper aims to investigate the application of particle swarm optimisation and back propagation in weights optimisation and training of artificial neural networks within the mass appraisal industry and to compare the performance with standalone back propagation, genetic algorithm with back propagation and regression models.

The study utilised linear regression modelling before the semi-log and log-log models with a sample of 3,242 single-family dwellings. This was followed by the hybrid systems in the selection of optimal attribute weights and training of the artificial neural networks. Also, the standalone back propagation algorithm was used for the network training, and finally, the performance of each model was evaluated using accuracy test statistics.

The study found that combining particle swarm optimisation with back propagation in global and local search for attribute weights enhances the predictive accuracy of artificial neural networks. This also enhances transparency of the process, because it shows relative importance of attributes.

A robust assessment of the models’ predictive accuracy was inhibited by fewer accuracy test statistics found in the software. The research demonstrates the efficacy of combining two models in the assessment of property values.

This work demonstrated the practicability of combining particle swarm optimisation with back propagation algorithms in finding optimal weights and training of the artificial neural networks within the mass appraisal environment.

The purpose of this paper is to bridge the gap between physical and metaphysical entities in the context of product/system design. The paper talks about the grey area of human psychology and presents a theoretical framework for the identification and selection of psychological attributes for designers.

On the basis of a literature review, this paper identifies various psychological attributes affecting the performance of designers in a team environment and then analyses the same.

The paper talks about a new shift in engineering design and designs for maintainability of mechanical systems.

A procedure based on the analytic hierarchy process method is applied. The developed procedure is useful in the assessment and selection of coveted psychological attributes for personnel in general and for designers in particular.

The paper highlights the immense role of psychology in engineering design, especially in the design for maintainability of mechanical systems. The paper will be useful to researchers, designers, maintenance personnel and professionals from the domain of engineering design, irrespective of their field of application. This paper is equally useful for human resource and management professionals/researchers.

Since technological lifecycles do not always match hardware/software (HW/SW) lifecycles, obsolescence becomes a major issue in system lifecycle management as it can cause premature and unscheduled replacement of HW/SW subsystems. The purpose of this paper is to report a dynamic model to predict the obsolescence dates for HW/SW subsystems.

The dynamic model estimates obsolescence dates for HW/SW subsystems based on graph theory concept. The model depicts the stages of subsystem obsolescence through transmittances composed of probability and time-distribution elements. The model predicts probability and mean time to obsolescence for line replaceable units (LRUs) over the lifetime of the system. An illustrative example in signaling systems used in a train control system was used to demonstrate the application of this model.

Generally, the short timespan for HW/SW subsystems, which are periodically replaced with newer technologies, results in the development of new product lines by suppliers while they try to support legacy systems for a reasonable period of time. Obsolescence of HW/SW subsystems increases operation and maintenance costs as legacy systems are typically more expensive to maintain. The costs can be reduced by an optimum time to obsolescence derived from the model.

This research adds to the body of knowledge on asset management and maintenance strategy. This paper may be of particular interest to reliability, maintainability and availability practitioners and project managers.

The originality of this paper lies in developing a graph-based model that predicts probability and mean time to obsolescence for LRUs over the lifetime of the system.