Fracture mechanics analysis of cracks in solder joint intermetallic compounds

The trend towards miniaturization of electronic products leads to the need for very small sized solder joints. Therefore, there is a higher reliability risk that too large a fraction of solder joints will transform into Intermetallic Compounds (IMCs) at the solder interface. In this paper, fracture mechanics study of the IMC layer for SnPb and Pb-free solder joints was carried out using finite element numerical computer modelling method. It is assumed that only one crack is present in the IMC layer. Linear Elastic Fracture Mechanics (LEFM) approach is used for parametric study of the Stress Intensity Factors (SIF, KI and KII), at the predefined crack in the IMC layer of solder butt joint tensile sample. Contrary to intuition, it is revealed that a thicker IMC layer in fact increases the reliability of solder joint for a cracked IMC. Value of KI and KII are found to decrease with the location of the crack further away from the solder interfaces while other parameters are constant. Solder thickness and strain rate were also found to have a significant influence on the SIF values. It has been found that soft solder matrix generates non-uniform plastic deformation across the solder-IMC interface near the crack tip that is responsible to obtain higher KI and KII.

Psychology and interventions for pupils at risk of underachievement and school exclusion: the year 10 effect

Findings are presented from a longitudinal study of over 1,500 adolescents. Some were engaged in interventions aimed at reducing social disaffection. Participants completed measures of social-identification, academic self-concept and motivation, and social, emotional and behavioural difficulties. Consistent with our previous research, developmental trends in identity and self-concept were found - adolescents became more negative about some school-based factors and more positive about aspects of identity. Trends were less clear in the 120 adolescents receiving interventions. Findings demonstrate the importance of psychology in work with young people. [Source: (2008) 'Invited Address, IUPsyS Invited Symposium, Invited Symposium, Symposium, Paper Session, Poster Session', International Journal of Psychology, 43:3, 348 - 527]

‘The trouble with Year 10’: 13 – 16 year old school students’ attitudes to higher education

This study looked at the impact of Widening Participation interventions on the attitudes of young people towards higher education. A total of 2731 adolescents aged 13–16 years completed a self-report measure of their attitudes to higher education, general and academic self concept and identification with school, family and peers. This was matched with data on the students’ academic attainment and social backgrounds. As expected, attainment scores were significantly positively correlated with take up of Widening Participation activities aimed at increasing participation in higher education, attitudes towards going to university and academic motivation. However, attainment was negatively correlated with perceptions of family attending university and identification with family. Regression analyses found that perceptions of family views about attending university were not a predictor of taking part in Widening Participation activities but were a predictor of attitudes towards higher education. Students in Year 10 aged 14–15 were significantly more negative on most factors than either older or younger students.