Effective Solder for Improved Thermo-Mechanical Reliability of Solder Joints in a Ball Grid Array (BGA) Soldered on Printed Circuit Board (PCB)

Ball grid array (BGA) packages have increasing applications in mobile phones, disk drives, LC displays and automotive engine controllers. However, the thermo-mechanical reliability of the BGA solder joints challenges the device functionality amidst component and system miniaturisation as well as wider adoption of lead-free solders. This investigation determines the effective BGA solders for improved thermo-mechanical reliability of the devices. It utilised a conducted study on creep response of a lead-based eutectic Sn63Pb37 and four lead-free Tin-Silver-Copper (SnAgCu) [SAC305, SAC387, SAC396 and SAC405] solders subjected to thermal cycling loadings and isothermal ageing. The solders form the joints between the BGAs and printed circuit boards (PCBs). ANSYS R19.0 package is used to simulate isothermal ageing of some of the assemblies at -40℃, 25℃, 75℃ and 150℃ temperatures for 45 days and model the thermal cycling history of the other assemblies from 22℃ ambient temperature for six cycles. The response of the solders is simulated using Garofalo-Arrhenius creep model. Under thermal ageing, SAC396 solder joints demonstrate possession of least strain energy density, deformation and von-Mises stress in comparison to the other solders. Under thermal cycle loading conditions, SAC405 acquired the lowest amount of the damage parameters in comparison. Lead-free SAC405 and SAC387 joints accumulated the lowest and highest energy dissipation per cycle, respectively. It is concluded that SAC405 and SAC396 are the most effective solders for BGA in devices experiencing isothermal ageing and temperature cycling during operation, respectively. They are proposed as the suitable replacement of eutectic Sn63Pb37 solder for the various conditions.University of Derb

A comparison of processing techniques for producing prototype injection moulding inserts.

This project involves the investigation of processing techniques for producing low-cost moulding inserts used in the particulate injection moulding (PIM) process. Prototype moulds were made from both additive and subtractive processes as well as a combination of the two. The general motivation for this was to reduce the entry cost of users when considering PIM. PIM cavity inserts were first made by conventional machining from a polymer block using the pocket NC desktop mill. PIM cavity inserts were also made by fused filament deposition modelling using the Tiertime UP plus 3D printer. The injection moulding trials manifested in surface finish and part removal defects. The feedstock was a titanium metal blend which is brittle in comparison to commodity polymers. That in combination with the mesoscale features, small cross-sections and complex geometries were considered the main problems. For both processing methods, fixes were identified and made to test the theory. These consisted of a blended approach that saw a combination of both the additive and subtractive processes being used. The parts produced from the three processing methods are investigated and their respective merits and issues are discussed

Climate Smart Agriculture: An Option for Changing Climatic Situation

World population is increasing day by day and at the same time agriculture is threatened due to natural resource degradation and climate change. Production stability, agricultural productivity, income and food security is negatively affected by changing climate. Therefore, agriculture must change according to present situation for meeting the need of food security and also withstanding under changing climatic situation. Projected estimates based on food consumption pattern and population growth show that agriculture production will require enhancing by 65% to meet the need of burgeoning population by 2050. Agriculture is a prominent source as well as a sink of greenhouse gases (GHGs). So there is a need to modify agricultural practices in a more sustainable way to overcome these problems. Developing climate‐resilient agriculture is thus crucial to achieving future food security and climate change goals. It helps the agricultural system to resist damage and recover quickly by adaptation and mitigation strategies. Mitigation strategies reduce the contribution of agriculture system to greenhouse gas emission, and adaptation strategies provide agriculture production under changing scenarios. This chapter explains different mitigation and adaptation strategies, including farming practices and engineering approaches

Multi-sensor and data fusion approach for determining yield limiting factors and for in-situ measurement of yellow rust and fusarium head blight in cereals

The world’s population is increasing and along with it, the demand for food. A novel parametric model (Volterra Non-linear Regressive with eXogenous inputs (VNRX)) is introduced for quantifying influences of individual and multiple soil properties on crop yield and normalised difference vegetation Index. The performance was compared to a random forest method over two consecutive years, with the best results of 55.6% and 52%, respectively. The VNRX was then implemented using high sampling resolution soil data collected with an on-line visible and near infrared (vis-NIR) spectroscopy sensor predicting yield variation of 23.21%. A hyperspectral imager coupled with partial least squares regression was successfully applied in the detection of fusarium head blight and yellow rust infection in winter wheat and barley canopies, under laboratory and on-line measurement conditions. Maps of the two diseases were developed for four fields. Spectral indices of the standard deviation between 500 to 650 nm, and the squared difference between 650 and 700 nm, were found to be useful in differentiating between the two diseases, in the two crops, under variable water stress. The optimisation of the hyperspectral imager for field measurement was based on signal-to-noise ratio, and considered; camera angle and distance, integration time, and light source angle and distance from the crop canopy. The study summarises in the proposal of a new method of disease management through suggested selective harvest and fungicide applications, for winter wheat and barley which theoretically reduced fungicide rate by an average of 24% and offers a combined saving of the two methods of £83 per hectare

Bioenergy and Minigrids for Sustainable Human Development

Human-caused climate change and deep disparities in human development imperil a prosperous and just future for our planet and the people who live on it. Transforming our society to mitigate global warming offers an opportunity to rebuild energy systems to the benefit of those who are harmed by global inequality today. I examine this opportunity through the lens of two sustainable energy technologies: bioenergy and miniature electricity grids (minigrids). Bioenergy requires land to produce biomass and is inextricably connected to the surrounding environment, agricultural livelihoods, and food system. I apply data science tools to study aspects of land use and food security that may intersect with increasing bioenergy production. I assess the potential to use over one billion hectares of grazing land more intensively with an empirical yield gap analysis technique called climate binning. To clarify how agricultural and socioeconomic characteristics relate to national food security, I study the relative importance of several drivers using simple linear regressions with cross validation and random sampling techniques. Minigrids can supply clean, reliable electricity to un- and under-served communities, but small and hard-to-predict customer loads hamper their financial viability. To improve predictions of daily electricity demand of prospective customers, I test a data-driven approach using customer demographic surveys and machine learning models. I also investigate opportunities to grow loads by stimulating income-generating uses of minigrid electricity in twelve Nigerian agricultural value chains. I conclude by emphasizing the fundamental complementarity of energy and agriculture as change levers for human development, especially in rural communities with low energy access and high poverty. I also provide recommendations to support the effective use of energy to solve pressing agricultural problems and drive multiplicative human development benefits

The Brazil-China Soy Complex: A Global Link in ihe Food-Energy-Climate Change Trilemma

This paper traces the evolution, dynamics and implications of the Brazil-China soy complex, a trade link of global social-ecological significance. Recent scholarship, particularly in the environmental sciences, has critically analysed the social-ecological implications of Chinese imports of Brazilian soy. This paper contributes a socio-economic analysis of the soy complex as a manifestation of global linkages in the food-energy-climate change trilemma. The concept of the trilemma captures interconnections between food security, energy security and GHG emissions resulting from food and energy production ? particularly as a result of the conversion of non-agricultural land to cultivate food and energy crops. Recent scholarship has highlighted the need to bring socio-economic perspectives to bear on trilemma challenges (Harvey 2014), arguing that these develop differently in different contexts as a result of distinctive combinations of political-economies operating within particular resource environments. This paper builds on this work by exploring how global trade links in important food and energy commodities (soy in this case) influence trilemma development and resulting land-use change. The paper begins with an overview of the concept of the trilemma and a summary of recent scholarship arguing for the need to bring socio-economic perspectives to bear on trilemma issues. I then turn to the empirical case of the Brazil-China soy complex, where I develop a socio-economic account of its evolution, dynamics and implications for land-use and land-use change. The paper ends with a short discussion on implications and directions for further work

Optoelectronic devices based on van der Waals heterostructures

In this thesis we investigate the use of van der Waals heterostructures in optoelec- tronic devices. An improvement in the optical and electronic performance of specific devices can be made by combining two or more atomically thin materials in layered structures. We demonstrate a heterostructure photodetector formed by combining graphene with tungsten disulphide. These photodetectors were found to be highly sensitive to light due to a gain mechanism that produced over a million electrons per photon. This arises from the favourable electrical properties of graphene and the strong light-matter interaction in WS2 . An analysis of the photodetector per- formance shows that these devices are capable of detecting light under moonlight illuminations levels at video-frame-rate speeds with applications in night vision ima- ging envisaged. We also report a novel method for the direct laser writing of a high-k dielectric embedded inside a van der Waals heterostructure. Such structures were shown to be capable of both light-detection and light-emission within the same de- vice architecture, paving the way for future multifunctional optoelectronic devices. Finally we address a more fundamental problem in the properties of aligned grap- hene/hBN heterostructures. Strain distributions are shown to modify the electronic properties of graphene due to a change in the interlayer interaction. We demon- strates a method to engineer these strain patterns by contact geometry design and thermal annealing strategies.Engineering and Physical Sciences Research Council (EPSRC

Learning to change: the role of organisational capabilities in industry response to environmental regulation.

This thesis looks at the potential for environmental regulation to induce economically beneficial technical change in industrial activity. This question is explored in the context of the recent introduction of Irish legislation aimed at promoting such technical change. The research focuses on the experience of one industrial sector, the pharmaceutical manufacturing sector, in making the adjustment to the new Integrated Pollution Control regulations. The key question of interest is the importance of organisational capabilities in determining firms’ ability to adjust to a changed regulatory environment, to develop new organisational processes and to implement technical change. The thesis presents an analysis of competing theoretical approaches to analysis of regulation and technical change. The evolutionary theory of the firm, with its emphasis on organisational capabilities as the driver of technical change in firms, is identified as the most appropriate framework for the development of a coherent model of the relationship between environmental regulation and firm technical change. The empirical research was undertaken using two, complementary approaches. Measures of capability were constructed for all pharmaceutical firms licensed in the first phase of IPC implementation. This allows for comparative analysis of the role of organisational capabilities in the sector’s response to new environmental regulations. Further analysis of questions around the origins, significance and contingent nature of capabilities is explored in qualitative, case study research in five selected case companies. The research presented in this dissertation show that firms are differentially able to respond to technology-forcing regulations and that these differences are associated with differences in organisational capabilities. Firms with high performing dynamic capability were able to ensure effective environmental performance, preserving flexibility of action and supporting overall competitiveness