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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 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 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 100C due to recrystallization, grain growth and Si coagulation. For example, glob top material curing processes used in COB applications (e.g. several hours at 160C) 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
Berlin, Berlin
Germany


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