Thermal, mechanical and optical modelling of VCSEL packaging

Hybrid OECB (Opto-Electrical Circuit Boards) are expected to make a significant impact in the telecomm switches arena within the next five years, creating optical backplanes with high speed point-to-point optical interconnects. OECB's incorporate short range optical interconnects, and are based on VCSEL (Vertical Cavity Surface Emitting Diode) and PD (Photo Diode) pairs, connected to each other via embedded waveguides in the OECB. The VCSEL device is flip-chip assembled onto an organic substrate with embedded optical waveguides. The performance of the VCSEL device is governed by the thermal, mechanical and optical characteristics of this assembly. During operation, the VCSEL device will heat up and the thermal change together with the CTE mismatch in the materials, will result in potential misalignment between the VCSEL apertures and the waveguide openings in the substrate. Any degree of misalignment will affect the optical performance of the package. This paper will present results from a highly coupled modelling analysis involving thermal, mechanical and optical models. The paper will also present results from an optimisation analysis based on Design of Experiments (DOE).

Shear strength analysis of ball grid array (BGA) solder interfaces

Ball shear test is the most common test method used to assess the reliability of bond strength for ball grid array (BGA) packages. In this work, a combined experimental and numerical study was carried out to realize of BGA solder interface strength. Solder mask defined bond pads on the BGA substrate were used for BGA ball bonding. Different bond pad metallizations and solder alloys were used. Solid state aging at 150degC up to 1000 h has been carried out to change the interfacial microstructure. Cross-sectional studies of the solder-to-bond pad interfaces was conducted by scanning electron microscopy (SEM) equipped with an energy dispersive X-ray (EDX) analyzer to investigate the interfacial reaction phenomena. Ball shear tests have been carried out to obtain the mechanical strength of the solder joints and to correlate shear behaviour with the interfacial reaction products. An attempt has been taken to realize experimental findings by Finite Element Analysis (FEA). It was found that intermetallic compound (IMC) formation at the solder interface plays an important role in the BGA solder bond strength. By changing the morphology and the microchemistry of IMCs, the fracture propagation path could be changed and hence, reliability could be improved

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]

Laser Doppler velocimetry measurements of particle velocity profiles in gas-solid two-phase flows

The measurement of particle velocities in two-phase gas-solid systems has a wide application in flow monitoring in process plant, where two-phase gas-solids systems are frequently employed in the form of pneumatic conveyors and solid fuel injection systems. Such measurements have proved to be difficult to make reliably in industrial environments. This paper details particle velocity measurements made in a two phase gas-solid now utilising a laser Doppler velocimetry system. Tests were carried out using both wheat flour and pulverised coal as the solids phase, with air being used as the gaseous phase throughout. A pipeline of circular section, having a diameter of 53 mm was used for the test work, with air velocities ranging from 25 to 45 m/s and suspension densities ranging from 0.001 kg to 1 kg of solids per cubic meter of air. Details of both the test equipment used, and the results of the measurements are presented.

‘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.