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On the intermetallic corrosion of Cu-Al wire bonds

: Boettcher, T.; Rother, M.; Liedtke, S.; Ullrich, M.; Bollmann, M.; Pinkernelle, A.; Gruber, D.; Funke, H.-J.; Kaiser, M.; Lee, K.; Li, M.; Leung, K.; Li, T.; Farrugia, M.L.; O'Halloran, O.; Petzold, M.; März, B.; Klengel, R.

Postprint urn:nbn:de:0011-n-1725864 (3.6 MByte PDF)
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Erstellt am: 20.4.2013

Institute of Electrical and Electronics Engineers -IEEE-, Singapore Section, Reliability CPMT EDS Chapter; IEEE Components, Packaging, and Manufacturing Technology Society:
12th Electronics Packaging Technology Conference, EPTC 2010 : Singapore, 8 - 10 December 2010
New York, NY: IEEE, 2010
ISBN: 978-1-4244-8560-4
ISBN: 978-1-4244-8561-1
Electronics Packaging Technology Conference (EPTC) <12, 2010, Singapore>
Konferenzbeitrag, Elektronische Publikation
Fraunhofer IWM ()

A detailed description of the Cu-Al wire bond interface is presented, which can possibly explain the often observed corrosion failures in humidity reliability tests. Using micro-structural analysis techniques, it is shown that the unstressed interface contains up to three intermetallic phases, where the Cu-rich phases are located at the Cu-ball interface. Upon humidity stress test only the high-Cu containing intermetallic layers close to the Cu wire ball bond undergo a corrosion process, whilst the Cu-lean layers are stable in all environment stress tests. The failing layers consist out of an amorphous Al-based oxide matrix with embedded Cu precipitates. The failure process can be explained as galvanic corrosion of the intermetallic phases. The Cu-rich phases corrode faster compared to Al-rich phases, since they have an electrochemical potential lower than the Cu cathode and form, hypothetically, a less stable self-passivation oxide. The observed time-to-failure is then determined by the composition, thickness and volume of the intermetallic layers. This was verified by reliability test results performed on open wire bonds and on plastic encapsulated products. ©2010 IEEE.