Effect of reflow profile and thermal cycle ageing on the intermetallic formation and growth in lead-free soldering

The formation and growth of intermetallic compound layer thickness is one of the important issues in search for reliable electronic and electrical connections. Intermetallic compounds (IMCs) are an essential part of solder joints. At low levels, they have a strengthening effect on the joint; but at higher levels, they tend to make solder joints more brittle. If the solder joint is subjected to long-standing exposure of high temperature, this could result in continuous growth of intermetallic compound layer. The brittle intermetallic compound layer formed in this way is very much prone to fracture and cold therefore lead to mechanical and electrical failure of the joint. Therefore, the primary aim of this study is to investigate the growth of intermetallic compound layer thickness subjected to five different reflow profiles. The study also looks at the effect of three different temperature cycles (with maximum cycle temperature of 25 0C, 40 0C and 60 0C) on intermetallic compound formation and their growth behaviour.. Two different Sn-Ag-Cu solder pastes (namely paste P1 and paste P2) which were different in flux medium, were used for the study. The result showed that the growth of intermetallic compound layer thickness was a function of ageing temperature. It was found that the rate of growth of intermetallic compound layer thickness of paste P1 was higher than paste P2 at the same temperature condition. This behaviour could be related to the differences in flux mediums of solder paste samples used.

Effect of long-term aging on the rheological characteristics and printing performance of lead-free solder pastes used for flip-chip assembly

Stencil printing of solder pastes is a critical stage in the SMT assembly process as a high proportion of the solder-related defects can be attributed to this stage. As the trend towards product miniaturization continues, there is a greater need for better understanding of the rheological behaviour and printing performance of new paste formulations. This fundamental understanding is crucial for achieving the repeatable solder paste deposits from board-to-board and pad-to-pad required for more reliable solder interconnections. The paper concerns a study on the effect of ageing on the rheological characteristics and printing performance of new lead-free solder pastes formulations used for flip-chip assembly applications. The objective is to correlate the rheological characteristics of aged paste samples to their printing performance. The methodology developed can be used for bench-marking new lead-free paste formulations in terms of shelf life, the potential deterioration in rheological characteristics and their printing performance.

Education and climate change – some systemic connections

Unlike most papers on education and ecology, this one is not concerned with the content of education but its organisation as a system and hence its purpose or finality. The central contention of the paper, which takes English education and training (or ‘learning’) as a case in point, is that in a new market-state formation the pursuit of short-term goals is tied to the global free-market economy over which any attempt at democratic control has been relinquished. At a time when humanity worldwide faces increasing change in the ecology that sustains it, this is considered to be ‘ecocidally insane’ and the opposite of any sort of learning from experience to alter behaviour in the future. The re-regulated new global market is seen in conclusion as a crisis response to the end of the previous Keynesian welfare nation-state formation. As such, it is argued to be unsustainable in any sense.

The knowledge is out there

Review Essay. On Bourdieu, education and society, by Derek Robbins, Oxford, The Bardwell Press, 2006, 596 pp., £75, ISBN 0-95-486836-6. Bringing knowledge back in, from social constructivism to social realism in the sociology of education, by Michael Young, London, Routledge, 2008, 247 pp.,£23.99, ISBN 9-78-041532-121-1. Personal knowledge, towards a post-critical philosophy, by Michael Polanyi, Chicago, University of Chicago Press, 1962, 428 pp., £18.99, ISBN 0-22-667288-3.

What Education Studies is and what it might be

Education Studies at the University of Greenwich is presented as an example of what Education Studies is – at least at one Higher Education Institution. As a field of practice to which a body of knowledge can be applied, Education Studies shares common features with other disciplinary fields of study. It is also unique in that its field – learning, is also what its students do – learn. What Education Studies isn’t is then discussed in relation to studies of schooling, the psychology of learning, sociology of education, traditional education degrees and teacher training. Lastly, what Education Studies could become is presented with reference to Ranson’s (1993) argument for the centrality of education as the common focus of all HE study. It is suggested that the subject could then contribute to expanding critical space in (higher) education through making research/ scholarship and creation an integral part of the Independent Study of all students at all levels of learning. This would be a necessary complement to the wider democratic transformation now demanded for human survival. It would also accord with what Marx called humanity’s “species being” as a “learning animal” (Morris). Such a social theory of learning can discriminate between information and competence at one level of learning and (corresponding terms) knowledge and skill at another more generalised level in relation to new divisions of knowledge and labour. Potentially these levels can be combined to create a new form of polytechnic learning, relating theory to practice, education to training and further to higher education.