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Gold in Flux-less Bonding: Noble or not Noble

Published online by Cambridge University Press:  01 March 2011

Marco Balucani ,
Paolo Nenzi ,
Fabrizio Palma ,
Hanna Bandarenka ,
Leonid Dolgyi  and
Aliksandr Shapel
Marco Balucani
Affiliation:
Department of Information Engineering, Electronics and Telecommunications, Sapienza – Università di Roma, Via Eudossiana, 18 – 00184 Roma (Italy)
Paolo Nenzi
Affiliation:
Department of Information Engineering, Electronics and Telecommunications, Sapienza – Università di Roma, Via Eudossiana, 18 – 00184 Roma (Italy)
Fabrizio Palma
Affiliation:
Department of Information Engineering, Electronics and Telecommunications, Sapienza – Università di Roma, Via Eudossiana, 18 – 00184 Roma (Italy)
Hanna Bandarenka
Affiliation:
Micro- and nano-electronics Department, Belarussian State University of Informatics and Radioelectronics, P. Brovka, 6 – 220027 Minsk, Belarus
Leonid Dolgyi
Affiliation:
Micro- and nano-electronics Department, Belarussian State University of Informatics and Radioelectronics, P. Brovka, 6 – 220027 Minsk, Belarus
Aliksandr Shapel
Affiliation:
Micro- and nano-electronics Department, Belarussian State University of Informatics and Radioelectronics, P. Brovka, 6 – 220027 Minsk, Belarus
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Abstract

This work highlights the solder joints reliability issues emerged during the development of a novel compliant contacting technology. The peculiar process in this technology is a mechanical lifting procedure in which a pulling force is exerted onto 63Sn-37Pb (eutectic) solder joints (realized by a flux-less thermo compression process), releasing metal traces from the substrate, to form free standing vertical structures. Since joints mechanical characteristics are critical for the successful fabrication of contacts, different bonding conditions (inert or forming atmosphere, temperature rates) and surface finishing (electroplated gold and preformed solder) have been tested. SEM and EDX analyses have been performed on failing joints to investigate failure causes and classify defect typologies. A constantly higher failure rate (percent number of failing joints) has been observed on gold finished surfaces. Analyses proved that such unusual rate was due to contamination of gold surface left by additives in the plating bath and to the embrittlement caused by gold diffusion into molten solder. Plating additives contamination reduces the wettability of gold surfaces. Concentration values of 3 wt.% for gold, considered safe for surface mount applications, caused embrittlement in solder bumps of 20-40 μm diameters.

Keywords

bondingAufracture
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1299: Symposium S – Microelectromechanical Systems—Materials and Devices IV , 2011 , mrsf10-1299-s09-04
Copyright
Copyright © Materials Research Society 2011

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References

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