There is an increasing demand for electronics that can operate at temperatures in excess of 200 degrees C, well above the maximum operating temperature of traditional silicon microelectronics. Key application areas are in the power, automotive, aerospace and defence industries. Electronic devices capable of operating at such high temperatures are now available. However, new methods are also needed for integrating these devices into circuits and systems, and in particular for attaching them, both mechanically and electrically, to circuit boards and heatsinks. At present high-temperature devices are typically attached by soldering using high-melting-point, lead-rich solders. However, there is a strong environmental imperative to reduce the use of lead in all electronics, so this cannot be accepted as a long-term solution. Alternative solutions employing gold-rich solders or sintered nano-silver pastes can be used, but these are expensive and can suffer from reliability issues. Low-cost, lead-free high-temperature solder alloys are also available; however, these tend to require significantly higher soldering temperatures and longer processing times, leading to slower production and higher thermal load on the devices during soldering. This project will explore the use of quasi-ambient bonding (QAB) with reactive nanofoils as a route to lowering the process time and thermal load during packaging of high-temperature electronic devices. Reactive nanofoils are multilayer materials comprising alternating layers of two elements (typically nickel and aluminium) that react exothermically i.e. with the release of heat. Once the reaction is triggered, it is self-propagating and spreads throughout the foil. If the foil is sandwiched between two parts that are pre-coated with solder, the heat generated can be used to melt the adjacent solder layers momentarily and form a permanent bond. The heating is intense, but occurs over a short timescale, so that while the local temperature can reach up to 1500 degrees C, heating is confined to a narrow region around the foil, with negligible temperature rise occurring elsewhere. Up to now, quasi-ambient bonding applications have used traditional lower-temperature solders. In this project we will extend the application of QAB to a range of low-cost, lead-free high-temperature alloys. The primary aim will be to develop bonding processes tailored for applications in high-temperature power electronics and optoelectronics. We will also explore the use of QAB for sealing of hermetic packages which is another key area where low cost and low thermal load can be an advantage. The processes developed will be evaluated in terms of bonding strength and in-service reliability, and benchmarked against alternative processes based on lead- and gold-based solders. Alongside the process development and evaluation, we will carry out extensive modelling and characterisation aimed at gaining an improved understanding of the QAB process. Developments to date have been mainly empirical, and fundamental aspects of the process remain poorly understood. QAB is fundamentally different from traditional soldering because of the very short timescale over which the process takes place. In order for it to become established in mainstream electronics manufacturing, the potential detrimental effects of residual stresses and microstructural defects incorporated into QAB bonds need to be fully understood. The proposed research has the potential to provide a low-cost, sustainable joining technology for electronics manufacturing that can continue to meet the operating temperature requirements of high-temperature electronics for many years to come. At the same time it will yield new fundamental insights into processes involving rapid solidification of complex alloys that will be of wide interest to the materials science and manufacturing research communities.

To maintain continuity with MATCH Phase 1, it has been requested that MATCH Phase 2 follows the current programme breakdown in terms of Projects A-F from 2008-2013 / a vision that is described below. We note that MATCH changed dramatically in creating the projects A-F and that further changes in the themes are inevitable. An overview of these themes is given below.Projects A, B and C address economic evaluation and its impact in decision-making by companies, governments and procurement agencies. We have identified a major demand for such research, but note that there is some convergence between these themes (for instance, A and C may well coalesce under the Bayesian banner). In particular, a 'methodologies' theme is likely to emerge in this. Under the former theme, a truly integrated Bayesian framework for medical devices would represent a strategically important achievement.On the other hand, the business of delivering these developments to industry, and the organisations or franchises that might ultimately provide the best vehicle for doing so, still requires further exploration and negotiation, and at this point there is considerable uncertainty about how this will best be done. However the critical element has been established, namely that MATCH can provide useful tools for, and attract significant levels of funding from industry. To this extent, the applied side of Project A-F and Project 5 might well evolve into a series of programmes designed to spin out tools, training and best practice into industry. Project 5 remains for the present because we have set it up with a framework within which company IP can be protected, and within which we can expedite projects to company goals and time scales.A similar pattern is likely to emerge from the single User project (D), where there is considerable scope for capability, and methodological development / and the size of this team needs to increase. The aim is to develop a suite of methods, guidelines and examples, describing when a given method is useful and when user needs assessment must be cost-effective. We will gain and share experience on what approach works best where. Our taxonomy will recognise circumstances where the novelty of a proposed device may undermine the validity of user needs assessment conducted before the 'technological push' has had a fair opportunity to impact on the human imagination.Moreover, new research is needed to 'glue' some of these themes together. Some of this is already included (for instance, in Projects C and D below) to link the user-facing social science with the economics, or the pathway-changing experiences (F) with formal economic evaluation, will require new, cross-disciplinary research. This type of research is essential to developing the shared view of value, which MATCH is pursuing. Similarly, integrating supply-chain decision-making and procurement elements of theme (E) with economic evaluation would represent an important element of unification.To achieve this, we will need to bring in some news skills. For instance, we are already freeing up some funding to bring in an economics researcher at Ulster; more statistical mathematical support may be needed to further develop the Bayesian theme; and we need to bolster the sociological element within the team.Finally, this vision cannot be funded entirely within a research framework, and we expect critical elements to be achieved under other funding (for instance, Theme E by the NHS, in due course).