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Copper Wire Bonding for Mid to High I/O Count Packages
Keywords: copper wire bonding, fine pitch, process
Copper wire bonding has huge cost advantages over gold wire bonding. As a result of this low pin count heavy wire applications have already been converted to copper wire and many companies are in high volume production. Recently, with the price of gold skyrocketing, there has been an extensive amount of development activity that has targeted high pin count (>250 I/O) and high performance applications. As wafer features shrink and metal traces become closer together on the die, there is a need for materials, which have lower dielectric constants. Unfortunately these materials have lower fracture toughness and are more susceptible to damage during the wire bonding process. Also copper wire is about 33% harder then gold so the stress and strain that the pad experiences during the copper wire bonding process is much higher then with gold. This can result in difficulties with pad damage and cratering of the underlying structures, which is sometimes difficult to control. Advancements have been made to copper wire bonders, tools, and wire that have resolved many of these issues and made fine pitch copper wire bonding feasible. This paper describes the cost advantages of packages that are copper wire bonded with high I/O counts. It shows theoretical and analytical methods of characterizing the forces that the pad and underlying structures experience during copper bonding process and the reduction in these forces that new materials, tools and processes can provide. Process optimization techniques are identified that can result in a robust copper wire bonding process for ultra fine pitch applications. Example applications are demonstrated from set up through rel test to show viability.
Bob Chylak, Vice President Packaging and Process Integration
Kulicke and Soffa Industries Inc.
Fort Wahsington , PA
USA


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