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Overview of Actual Bonding Wire Technologies and Possible Solutions Based on Different Interconnection Materials
Keywords: Bonding Wire, Interconnection Technology, Advanced Packaging
The market for bonding wire is driven by different players and factors. For electronic applications using fine wires, actually replacing of old soft 4N5 wire types with new high strength 2N wire is taking place. Fine pitch and long loop applications require a mechanically stable and leaning resistant wire material. Currently, the average wire diameter used in market is between 17 and 20 m with 15m already in production and 10-12m in evaluation phase. The second driving force for development is the need of long time reliability in connection with Al based substrates. Here 2N and 3N wires show better performance compared with 4N wire types. The trade off for the reliability is lower electrical conductivity and narrower bonding window higher mechanical strength may be an advantage, so not necessarily a price to pay and harder free air ball that may cause pad crack or cratering during bonding. Although economical reasons to reduce cost of gold wire can be partly satisfied by using finer diameters combined with high reliability performance of 2N wires, there are also material based alternative solutions. Great attention is paid for copper wire and optimizing 1st and 2nd bond behavior in order to increase bonding window and therefore the yield for produced parts. Besides copper, which is already in production in various assembly houses and IDMs, different Au and Ag alloys are also being tested as alternative materials for special applications. For room temperature wedge-wedge wire bonding process, besides the commonly used AlSi wire, new specialized wire types have been developed to enable good bondability and corrosion resistance. For power applications in automotive and solar industry, which predominantly uses Al thick wire with diameters between 100 and 800m because of the high current throughput requirement. Al ribbon, due to the larger cross section of bonded areas and the higher stiffness of the loops, are getting more and more the attention of designers. Besides soft pure Al materials with excellent bondability, AlCu-clad could also provide advantages for high temperature applications due to high electrical and thermal conductivity of copper, but also with some limitation such as Galvanic cell effect in presence of moisture. In this presentation all areas of bonding wire interconnection will be described, including suitable packages and material properties, based on extensive experience of two leading bonding wire producers and their customers.
Dr. Tobias Mueller, Vice President
W. C. Heraeus GmbH
Hanau, Hessia 63450,
Germany


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