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Journal of ELECTRONIC MATERIALS, Vol. 42, No. 8, 2013
DOI: 10.1007/s11664-013-2576-1
2013 TMS
Copper Wire Bonding Concerns and Best Practices
PREETI CHAUHAN,1,3 Z.W. ZHONG,2 and MICHAEL PECHT1
1.CALCE Electronic Products and Systems Center, University of Maryland, College Park, MD 20742, USA. 2.School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore. 3.e-mail: [email protected]
Copper wire bonding of microelectronic parts has developed as a means to cut the costs of using the more mature technology of gold wire bonding. However, with this new technology, changes in the bonding processes as well as bonding metallurgy can affect product reliability. This paper discusses the challenges associated with copper wire bonding and the solutions that the industry has been implementing. The paper also provides information to enable customers to conduct qualication and reliability tests on microelectronic packages to facilitate adoption in their target applications.
Key words: Wire bonding, copper, gold, oxidation, corrosion, humidity
INTRODUCTION
Wire bonds form the primary interconnects between an integrated circuit chip and the metal lead frame in semiconductor packaging. They are generally considered a more cost-effective and exible interconnect technology than ip-chip interconnects. Gold (Au) wire has been used for wire bonding in the electronics industry for more than 55 years because of its mechanical and electrical properties, high reliability, and ease of assembly. However, due to the increasingly high cost of Au, alternative wire bonding materials have been considered. Copper (Cu) is the most preferred alternative material for wire bonding because of its lower cost, higher mechanical strength, lower electrical resistance, slower intermetallic growth on aluminum (Al) pads, and higher thermal conductivity compared with Au.
Cu wire bonding has been investigated for more than 25 years.14 Replacing Au wire with Cu wire in the wire bonding process presents many challenges. Cu wire bonds have the limitations of high oxidation rate, high hardness, and susceptibility to corrosion. Process and equipment changes are needed for conversion to Cu wire bonding, requiring new process optimizations and parameter adjustments for
ball bond and stitch bond formation, and to achieve the looping proles. To address Cu oxidation, bonding is carried out in an inert environment, e.g., in forming gas (95% N2/5% H2). In most cases, wire manufacturers adopt palladium-coated Cu (PdCu) wire, which...