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Physically Robust Interconnect Design n BOAC for Cu Wire Bond
Keywords: BOAC (bond over active circuitry), Cu wire bond, Al metallization
Economic challenges for small size IC design and manufacturing require: reduced die size without adding layers or other costs, bonding with Cu wire instead of Au wire, and maintained or improved reliability. Die size shrinking involves extensive use of bond over active circuitry (BOAC) to shrink the die size on IC's having at least two levels of metal. BOAC however, introduces more potential failure modes just as Cu wire bonding is more harsh to the pad and underlying structures. Dielectric cracks under the pad may be more hazardous with active circuitry present, and device electrical performance may shift due to strain. In short, bond pad cracks must be prevented while still lowering product cost. However, recommendations for improvement in both BOAC and Cu wire bonding in published literature are inadequate for many products. This paper discloses a practical solution for improving product yield and reliability issues of thin film deformation and cracking. This being caused from Cu wire bond directly over two or more layers of Al metallization interconnect encapsulated in SiO2 dielectric. The demonstrated solution is a methodology of modifying underlying circuitry to strengthen the pad structure against cracking. It is applicable in numerous technologies, facilitating Cu wire bonding on BOAC designs of current and future products.
Stevan Hunter, Principal Engineer
ON Semiconductor
Pocatello, Idaho
USA


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