# Institute of Materials, Minerals and Mining – Materials Congress 2004

ISSN: 0305-6120

Article publication date: 1 December 2004

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## Citation

Goosey, M. (2004), "Institute of Materials, Minerals and Mining – Materials Congress 2004", Circuit World, Vol. 30 No. 4. https://doi.org/10.1108/cw.2004.21730dac.004

## Publisher

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Emerald Group Publishing Limited

## Institute of Materials, Minerals and Mining – Materials Congress 2004

Institute of Materials, Minerals and Mining – Materials Congress 2004

30 March-1 April 2004, London

Review of the Symposium on Packaging of Electronic Devices – 30 March 2004

Keywords: Conferences, Electronics industry, Packaging

The Institute of Materials, Minerals and Mining held its 2004 Materials Congress at the end of March and beginning of April in the magnificent historic buildings of Carlton House Terrace in the centre of London. The programme included around 40 plenary and keynote lectures and hundreds of contributed papers covering the main areas of materials science and engineering. Of particular interest to those involved in electronics was the Symposium on Packaging of Electronic Devices and it is this which is reported below.

The Symposium was chaired by Dr David Pedder, who was representing the EPPIC Faraday Partnership and TWI Ltd, and there was coverage of a wide range of interconnection and packaging topics by eight speakers from the UK, Belgium and the USA.

In a change to the advertised order, the morning session was opened by Chris Bailey, from the University of Greenwich, who gave a paper entitled "Reliability Predictions – Past, Present and Future". In his presentation, Chris discussed the physics of failure approach and how it combined accelerated testing with computational modelling. The methodology allowed behavioural predictions to be made based on product geometry, materials used and operating conditions. The modelling enabled predictions to be made of stresses from thermal, mechanical, chemical and electrical effects. An example given was that of wave soldering and the effects of oxygen levels at or near the solder bath on reliability. There was a need to minimise the amount of oxygen and computational fluid dynamics had been used to determine how oxygen entered the equipment when circuit boards were being soldered. Higher flow rates of nitrogen helped to reduce the amount of oxygen entering and modelling had helped both with the design of the nitrogen injectors and to determine the flow.

A second example given was the use of finite element analysis to optimise process conditions in order to minimise solder joint fatigue and stress in the die of a flip-chip assembly. Design parameters investigated included the Young's modulus and thermal expansion coefficient of the underfill, stand-off height and substrate thickness. The solder joint fatigue behaviour was studied for various combinations of the above properties.

There were a number of commercially available software packages that enabled this type of study to be undertaken. In the future it was predicted that we would see this type of modelling happening right across the supply chain. Chris concluded by referring to the new IEEE Reliability Prediction Standard (1413.1).

The next presentation was given by Dr Liz Logan on behalf of Jan Vordemann of Tech. Search International Inc., USA, who was unable to attend the meeting. In a presentation entitled "Semiconductor Packaging Materials: 2004 Outlook and Future Trends", Dr Logan highlighted the trend to area array packaging and the growth in the use of BGAs and how they offered higher margins regardless of pin count. The use of area array packaging was driving changes in both packaging materials and processes with, for example, the move away from wire bonding to flip-chip on to laminate within the packages. The market for semiconductor plastic packaging was set to grow from $7.9 billion in 2003 to$10.3 billion in 2006, with \$2.3 billion being accounted for by organic substrates. Eighty six percent of this would be in the Far East! Large growth was also predicted for flip-chip with solder bump growth for both 2004 and 2005 expected to be 48 percent. Most growth would be in flip-chip in a package, with only small growth occurring in flip-chip on board. Wafer level packaging was also expanding rapidly with the key issues being form factor and performance and major applications being in PDAs and mobile phones. The main materials used were BCBs but new types of polyimides were also coming on stream.

Clive Hall of Element Six in The Netherlands, then gave an overview of Diamond as a Thermal Management and Packaging Material and in his presentation Clive covered materials, properties and processing. Diamond based materials had found use in microprocessors, laser diodes, laser diode arrays and a variety of other applications and it was a very valuable material for dissipating heat. There were three main types of diamond and these were thick film CVD, thin film CVD and sintered diamond composites. The thin film CVD materials were generally lower in cost than the thick film materials and the diamond was typically deposited on a high thermal conductivity substrate such as silicon carbide or aluminium nitride in thicknesses of 20-40 μm. The sintered diamond composites offered thermal conductivities of around 600 W/ mK and thermal expansion coefficients of 3 ppm/°C. This was compared to the >1,800 W/mK for thick film diamond and 400 W/mK for copper, 260 W/mK for beryllia, 170 W/mK for commercial aluminium nitride and 35 W/mK for alumina. Pure diamond had a coefficient of thermal expansion of only 0.9 ppm/°C and was highly insulating with a resistivity of 1013 Ωcm, although it could be doped to increase its conductivity. Diamond is typically very optically transmissive over a broad wavelength band and is typically processed using conventional polishing techniques and laser cutting. Typical metallisation systems included titanium, platinum, gold coatings and solders such as gold-tin and indium-gold were used. Various examples were given of where diamond had been used to improve thermal performance and these included a 25 percent improvement in the temperature performance of a laser diode array. It was stated that if diamond is doped with boron it can be used as a thermistor and can be employed to track temperature changes with a very fast response.