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O: Fachverband Oberflächenphysik

O 111: Oxides and Insulators: Adsorption II

O 111.3: Vortrag

Freitag, 16. März 2018, 11:00–11:15, MA 041

Corrosion mechanism in lead-free materials for the electronic industry — •Gabriele Saleh and Stefano Sanvito — Trinity College Dublin, College Green, Dublin 2, Ireland

Silver and tin constitute the major components (>99%) of alloys adopted to assemble printed circuit boards, ever since many countries have severely restricted the use of lead due to its toxicity. However, those alloys tend to suffer from corrosion issues, which represent an economic burden for the electronic industry. Although Ag-Sn surfaces play the main role in the corrosion process, their structure, composition and reactivity have never been investigated at the atomic level. In this contribution, we show how we bridged this gap by means of extensive ab initio simulations [Saleh et al., PCCP, submitted]. We investigated more than 70 surfaces (including non-stoichiometric ones) for all the known Ag-Sn alloys, thereby establishing which surfaces are most stable and will form in a real sample. Moreover, we systematically studied O and S chemisorption, and contextualized the results in the framework of corrosion tendency. The observed trends are rationalized in terms of structural and electronic features. Calculations on suitable model systems were performed to confirm the proposed rationale. On top of that, we present our preliminary results on molecular dynamics simulations ('ReaxFF' approach) to address what we call 'silver paradox', that is the experimentally observed preferable formation of silver sulphide over silver oxide despite O and S having almost identical chemisorption energies on Ag and Ag2S and Ag2O formation energies being almost identical.