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|European R&D Trends in wire bonding technologies|
|Keywords: wire bonding, wedge/wedge bonding, new wire bonding materials|
|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 bond-ing). In contrast, Europe traditionally is researching and developing in the field of wedge/wedge bonding using heavy wire (> 100 µm) for power electronic modules or standard (thin) wire (< 100 µm, mostly 25-50 µm) 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 clas-sical 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. AlSi1 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 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.|
|Dr. Martin Schneider-Ramelow, Head of Department
Fraunhofer IZM Berlin