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Thick Al Ribbon Interconnects: A Feasible Solution for Power Devices Packaging
Keywords: ribbon bond, reliability, aluminium
With the constant drive for smaller, cost effective power electronic systems with enhanced performance and reliability, Aluminium (Al) ribbon bonding has become an attractive alternative to the established thick Al wire bonding. Improved electrical performance and assembly cost reduction are the main expected benefits. Although ribbon bonding is viewed as a drop-in replacement for wire bonding, differences in the details of the joining process are to be expected. The potential effects of those differences on the bond formation and ultimately the bond reliability warrant a more detailed investigation. This work covers a first step, in which we analyze and report the effects of different target bond deformation levels on the strength and reliability of 80 x 8 mil thick Al ribbon bonded with different bond tools. The results show that good ribbon bonding was achieved over the range of bond deformation investigated. It was observed that increased deformation beyond a certain level only creates marginally higher average bond shear strength, but, with the tool designs tested, can cause increasing weakening of the heels of the bonds. The long-term strength and reliability of these ribbon bonds were assessed under thermal cycling between 60C to 170C. Bond shear testing was used to characterize bond strength. Micro-structural analysis was performed and the correlation between measured bond shear strength and crack length along the bond interface at increasing numbers of thermal cycles was studied. In summary, both the bond tool type and deformation setting play an important role in determining the thermal cycling reliability of the ribbon bond. All bond parameter combinations show high endurance under the extreme thermal cycling conditions. A next step will focus on design and process aspects to retain the observed level of bond strength and reliability, while minimizing damage to the bond heels due to bond over-deformation.
Wei-Sun Loh , Postgraduate Research Student
The University of Sheffield
Sheffield, South Yorkshire S1 3JD,
UK


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