03 Fakultät Chemie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/4
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Item Open Access Whisker formation on Sn thin films(2010) Sobiech, Matthias Lukas; Mittemeijer, Eric Jan (Prof. Dr. Ir.)The system Sn on Cu will usually be applied for interconnection of modern electronic systems, i.e. for mechanical, thermal and electrical “integration” of electronic components (e.g. composed of Cu) on rigid substrates (i.e. printed circuit boards) by (e.g. Sn) solder-joint technology. Nowadays Sn is the material of choice for this purpose because the up to now commonly and successfully used SnPb alloys for soldering and coating applications are prohibited by law since 1st July 2006 due to environmental concerns (Pb-free and “green” legislation). However, it is well known since nearly 60 years that pure Sn thin films deposited on Cu substrates are very prone to spontaneous formation of needle-like Sn single-crystals, called whiskers, during ageing at room temperature. Such filamentary Sn whiskers exhibiting growth rates of about 1 Å/sec constitute an issue of great technological relevance for Sn coated leadframe legs of modern microelectronic devices because whisker-induced short-circuit failures of various electronic devices have resulted in enormous financial damage including breakdowns of satellites, computer centres and military and medical devices. Unfortunately, profound knowledge on this controversially discussed phenomenon of whisker-growth is still lacking. Therefore, particularly in recent years, the electronic industry promotes scientific activities to arrive at fundamental understanding of Sn whisker formation in order to implement industrially reliable (accelerated) whisker tests and/or mitigation strategies. Against the above background, the present thesis focuses in particular on revealing the driving force for Sn whiskering in the system Sn on Cu during room temperature ageing and thus to devise a coherent understanding of the processes leading to the formation and growth of Sn whiskers. The obtained fundamental interrelations of microstructural evolution, phase formation, residual stress development and the associated whiskering of Sn thin films electro- and sputter-deposited on Cu as well as of SnPb thin films electrodeposited on Cu during ageing at room temperature have lead to a qualitative understanding of whisker growth in terms of localized Coble-creep. On this basis, whisker mitigation strategies can be proposed.