Students to Study the Effects of Microgravity on Solder Joints

A team of four materials undergraduates from Imperial College, London, will get the chance to perform their research in microgravity conditions after being selected to take part in the sixth Student Parabolic Flight Campaign 2003. The aim of their project is to investigate the mechanical and electrical conductivity of lead-free solders that have been solidified in microgravity conditions.

One of 30 finalists selected to take part in this year’s campaign organised by the European Space Agency (ESA), the team will experience on average 20 seconds of microgravity at a time in which they will melt and solidify 80 solder joints - processing four joints at a time. ‘The idea behind the project is to try and compare earth made and microgravity made solder joints to try and find the best way to repair plastic circuit boards in space,’ says Boris Thomas, team leader and undergraduate studying Materials Science and Engineering at Imperial College. ‘As far as we are aware we are the only research group trying to understand how flux works in microgravity.’

On earth, soldering on printed circuit boards (PCBs) is achieved by melting the solder paste or wire onto a copper base. A chemical flux contained in the solder removes the copper oxide from the surface to improve the wetting. During the chemical reaction, the residue evaporates from the solder/copper interface leaving an oxygen-free copper surface, which enhances the mechanical properties of the joint.

‘In microgravity we wouldn’t have this evaporation and it is very likely that porosity will remain at the interface, which will obviously decrease the properties of the joint,’ says Thomas. ‘We have ideas of what we can expect from the experiments but we may find out something else.’

The solder joints will be created in a specially built rig designed to withstand the stresses imposed by microgravity flight manoeuvres. Eighty solder joints will be created from three different solder pastes manufactured by Cookson Electronics - tin-lead (Sn-Pb), lead-free (Sn-Ag-Cu) and Sn-Ag-Cu flux-free. After two days of flying in a converted Airbus A300, which simulates microgravity during high-energy manoeuvres in flight, the team will determine the best lead-free solder system (flux or flux-free) that can be used in space, in relation to its mechanical and electrical properties. Mechanical shear tests will be performed using an Arcan-Voloshin method, while characterisation of the microstructure of the joints will be done using secondary electron imaging/back scattered imaging, X-ray diffraction and X-ray tomography

The student team, all members of the Institute of Materials, Minerals and Mining, also includes Kartik Rao, Andrew Spikins and David Tricker, all third year undergraduates studying Aerospace Materials. Boris Thomas, who would like to eventually work for the ESA is co-ordinating the project as part of his final year assignment. ‘The head of the department, Professor Kilner is really happy that I used my initiative to start this kind of project,’ he says. ‘Dr Dashwood, Director of Undergraduate Studies and the project’s supervisor, and Professor Atkinson, the project’s second supervisor, are also really supportive and would like to see this campaign running every year in the department.’

The team is currently finding means of funding the whole project. Having already received money from the Armourers and Braziers, they need a total of £5,000 to pay for the raw materials, manufacturing costs, electrical equipment and travel expenses. After the parabolic flight campaign there will be further developments to the website, a promotional video and a possible microgravity exhibition at the Science Museum.

Novespace provides the parabolic flight experience and the imperial College team will join other European research Students in Bordeaux, France, from 16-31 July. ‘I think we are going to have a lot of fun with the other students from all over Europe’, says Thomas. ‘I didn’t want to do a final year project that was just laboratory based. I wanted to do something that was more interesting and concrete - the down side is that during most flight, people do get sick.’


Posted May 2003


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