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European R&D trends in wire bonding technologies

: Schneider-Ramelow, M.

45th International Symposium on Microelectronics, IMAPS 2012. Vol.1 : 9-13 September 2012, San Diego
Red Hook, NY: Curran, 2013
ISBN: 978-1-62748-095-6
International Symposium on Microelectronics (IMAPS) <45, 2012, San Diego/Calif.>
Fraunhofer IZM ()

Asian industry and development is currently very focused on replacing extremely expensive Au wire with Cu or Pd-plated Cu in IC (mass production) packaging technologies (ball/wedge bonding). In contrast, Europe traditionally is researching and developing in the field of wedge/wedge bonding using heavy wire (> 100 m) for power electronic modules or standard (thin) wire (< 100 m, mostly 25-50 m) for chip-on-board (COB) applications. One primary failure mechanism limiting the lifetime of power modules is Al wedge lift-off due to the different coefficients of thermal expansion (CTE) of the Al wedge and the chip (Si). This classical type of fatigue cracking can be reduced by using materials of higher strength and/or lower CTE. Key strategies include doping or alloying elements and/or optimizing bonding conditions to improve the microstructure. Cu-based wire or Cu-Al bimetal ribbons are another option, although these include changes to the chip structure and metallization. Al Si1 has been the industry standard bonding material in wedge/wedge thin wire bonding for many years. Its thermal stability is limited at temperature above 100°C due to recrystallization, grain growth and Si coagulation. For example, glob top material curing processes used in chip on board (COB) applications (e.g. several hours at 160°C) can decrease the strength of standard AlSi1 wire to less than 60% of its original value. Research and development is currently attempting to improve this situation by alloying and doping Al base material to increase high-temperature behavior or by using Al-coated Au or Cu wires. The presentation will give an overview of alternative wedge/wedge wire bonding materials and discuss the challenges to processing and reliability.