Transition zone: a training ethos designed to scaffold a PhD degree

The Transition Zone is our bespoke training programme to support transitions through different stages in a researcher’s career: (1) into doctoral studies as a high performing researcher, (2) through doctoral studies to make the most out of their doctorate and associated training and, (3) on exiting, to empower and equip them as highly employable graduates. This paper focuses on the first (i.e. ‘Transition In’) and the second transitions (i.e. ‘Transition Through’). The purpose of this paper is to offer a programme evaluation of these two transitions in order to assess whether the training ethos fulfils the three strategic aims (i.e. continuous learning as second nature, reflection in/on action, and deliberate employability boosters). Students have been encouraged to take ownership of their PhD and personal development from the outset (e.g. each student manages their own time, training, travel and consumables budget). The nature of the training activities has also been varied, accounting for to the student’s learning preferences, exposing students to both individual and group work, technical and non-technical training and with a strong flavour of externally-facing industry experience. A series of tests and self-awareness exercises have allowed the students to explore their own objectives and those of the program so that they dovetail, and allow an informed decision on training components to deliver a rounded engineer and/or scientist who not only is an expert in a research area but also possesses business acumen and industry readiness that are much sought after by employers in the current global market

3D acoustic-structure interaction of ultrasound in fluids for the manufacture of graded materials

Functionally graded materials engineered to meet specific requirements are being increasingly sought after for advanced engineering projects, yet the possibilities for their manufacture lag behind their design. The ability to control the porosity of a cellular material is one such method for adding functional gradients within materials. A novel technique using ultrasound to control the porosity in reacting polymers shows potential to effectively mass-manufacture porosity tailored polymeric foams. In this work the pressure field in a metastable polymer produced by multiple ultrasonic sources is modeled at distinct stages of the polymerisation reaction

Hybrid ToF and RSSI real-time semantic tracking with an adaptive industrial internet of things architecture

Real-time asset tracking in indoor mass production manufacturing environments can reduce losses associated with pausing a production line to locate an asset. Complemented by monitored contextual information, e.g. machine power usage, it can provide smart information, such as which components have been machined by a worn or damaged tool. Although sensor based Internet of Things (IoT) positioning has been developed, there are still key challenges when benchmarked approaches concentrate on precision, using computationally expensive filtering and iterative statistical or heuristic algorithms, as a trade-off for timeliness and scalability. Precise but high-cost hardware systems and invasive infrastructures of wired devices also pose implementation issues in the Industrial IoT (IIoT). Wireless, selfpowered sensors are integrated in this paper, using a novel, communication-economical RSSI/ToF ranging method in a proposed semantic IIoT architecture. Annotated data collection ensures accessibility, scalable knowledge discovery and flexibility to changes in consumer and business requirements. Deployed at a working indoor industrial facility the system demonstrated comparable RMS ranging accuracy (ToF 6m and RSSI 5.1m with 40m range) to existing systems tested in non-industrial environments and a 12.6-13.8m mean positioning accuracy

Excimer laser machining of microvias in glass substrates for the manufacture of high density interconnects

Machining of microvias in 100-50 μm thick CMZ glass using an excimer laser (248 nm) was investigated. The effect of various laser process parameters: pulse energy, repetition rate, irradiation time were studied to optimise the microvia drilling process and a process window was identified. Through-hole drilling of 100 μm diameter (entry hole) microvias was achieved at a fluence (energy density) as low as 2.3 J/cm with an irradiation time of 30-40 s at a repetition rate of 20 Hz, giving a taper angle between 22-24° relative to the vertical. However, by increasing the fluence to 4.5 J/cm , this reduced the machining time to 5-10 s and taper angle to 14°, giving an exit hole diameter of around 45-50 μm. With 50 μm thick glass, it was possible to machine through-hole microvias with smaller entry hole diameters down to 40 μm. Machined microvias were characterised to investigate debris, recast layer and microcrack formation. Debris and recast layer around the machined features was minimised by using a protective photoresist layer coating on the glass and through appropriate operating parameter selection. Microcracks along the sidewalls of the microvias could not be avoided, but their severity depended on the laser machining parameters used. © 2012 Springer-Verlag

Thermal interface materials - a review of the state of the art

The past few decades have seen an escalation of power densities in electronic devices, and in particular in microprocessor chips. Together with the continuing trend of reduction in device dimensions this has led to dramatic increase in the thermal issues within electronic circuits. Thermal management is therefore becoming increasingly more critical and fundamental to ensuring that electronic devices operate within their specification. Although a thermal management system may make use of all modes of heat transfer to maintain temperatures within their appropriate limits and to ensure optimum performance and reliability, conductive heat transfer is typically used to spread the heat out from its point of generation and into the extended surface area of a heat sink. To minimise the contact resistance, thermal interface materials (TIMs) are introduced to the joint to fill the air gaps and are an essential part of an assembly when solid surfaces are attached together. This paper reviews the conventional interface materials and then goes on to present a comprehensive review of the emerging state-of-the-art research in the use of carbon nanotube based materials. The paper also outlines the advantages and disadvantages of each TIM category and the factors that need to be considered when selecting an interface materia

A wavelet analysis on digital microstructure in microbumps

© 2015 IEEE. Heterogeneous three-dimensional system integration is the ultimate goal for packaging and integration, where materials are pushed to their physical limits. In this context, the microstructure of packaging materials, which exhibits a multi-scale nature, will be carefully designed and tightly controlled in both manufacturing and in-service conditions to ensure long-term reliability of the electronic products. A multi-level discrete wavelet transform using the haar wavelet is conducted on the dendritic structures, simulated with a phase field model, during solidification in microbumps with different sizes and geometries. The statistical data, e.g. the mean, standard deviation and energy, of the detail coefficients from the wavelet analysis reveal a wealthy of information on the features of the dendritic structure and its evolution during solidification at multiple resolutions. The size and geometry effects on the microstructure formed in the microbumps can thus be quantified by such data. Further studies using techniques such as principle component analysis and Radon transform can be conducted to evaluate the consistence of the result

Effects of stress and electromigration on microstructural evolution in microbumps of three-dimensional integrated circuits

Due to geometric scaling, the heterogeneous and anisotropic microstructures present in through-silicon vias and microbumps must be considered in the stress management of 3-D integrated circuits. In this paper, a phase field model is developed to investigate the effects of stress and electromigration on microstructural evolution in a Cu/Sn-microbump/Cu structure at 150 °C. External compressive stress is observed to accelerate the growth of Cu3Sn grains and cause the separation of continuous interfacial Cu 6 Sn 5 grains by β-Sn grains, whereas tensile stress promotes the growth of Cu 6 Sn 5 grains and the formation of a continuous Cu 6 Sn 5 layer. The roughness of the β-Sn-Cu 6 Sn 5 interface under compressive stress is greater than that under tensile stress. The morphological evolution of the β-Sn grains is also affected by stress. An external shear or compressive stress favors the growth of the β-Sn grains with their c-axis particular to the Y -direction. Furthermore, the interdiffusion flux driven by electromigration increases the roughness of the interfacial Cu 6 Sn 5 grains at the cathode. The strain caused by electromigration results in larger β-Sn grains, enabling faster interdiffusion along the current direction. The preferential growth of the β-Sn grains under stress or electromigration decreases the shear modulus of microbumps

An automated feature extraction method with application to empirical model development from machining power data

Machining shop floor jobs are rarely optimised for minimisation of the energy consumption, as no clear guidelines exist in operating procedures and high production rates and finishing quality are requirements with higher priorities. However, there has been an increased interest recently in more energy-efficient process designs, due to new regulations and increases in energy charges. Response Surface Methodology (RSM) is a popular procedure using empirical models for optimising the energy consumption in cutting operations, but successful deployment requires good understanding of the methods employed and certain steps are time-consuming. In this work, a novel method that automates the feature extraction when applying RSM is presented. Central to the approach is a continuous Hidden Markov model, where the probability distribution of the observations at each state is represented by a mixture of Gaussian distributions. When applied to a case study, the automated extracted material cutting energies lay within 1.12% of measured values and the spindle acceleration energies within 3.33% of their actual values

Crystallographic structure and mechanical behaviour of SnAgCu solder interconnects under a constant loading rate

With the continuing increase of the integration density in electronics, dimensions of interconnections for electronic components have been miniaturized to a scale that is comparable to those of their crystallographic structure. For instance, a SnAgCu solder joint in the flip chip package can contain only one or a few grains. In this case, the mechanical behaviour of the micro-joint is expected to shift from a polycrystalline-based to single-crystal one. Considering the further miniaturization, both the crystallographic structure and mechanics of each component (Ag3Sn, Cu6Sn5 and beta-Sn matrix) within a grain and the adjacent SnCu interface will play an important role in the reliability of the micro-joint due to their size comparable with that of a grain, irregular geometry, their heterogeneous distribution and considerably different properties. In addition, at such a small scale, the non-local effect on deformation of beta-Sn should be taken into account to interpret mechanical interactions between components. In this paper, a shearing test, in which it is possible to apply a constant loading to a SnAgCu joint is deigned to investigate mechanics of substructure within a SnAgCu grain and near the SnCu interface

Protrusion of Cu-TSV under different strain states

A phase-field-crystal (PFC) model is used to investigate the protrusion of blind TSVs under different strain states. The direction of loading applied to the TSVs has an effect on the protrusion, which is closely related to the copper grains and their orientations at the TSV edges. A nonlinear relation between protrusion and strain rate has been found, which can be explained by different mechanisms of deformation. A higher strain occurring near the top end of the TSVs leads to a larger protrusion of the bind TSVs