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Accelerated Life Tests of Flip-Chips with Solder Bumps Down to 30 µm Diameter
Keywords: Flip-Chip, Reliability, Electromigration
In this study, a specially designed test coupon has been used to characterize lead-free micro solder bumps during accelerated life tests. As solder bump sizes continue to decrease, along with the shrinkage of the solder pads and the scaling of line/space geometries, thermal diffusion has even more impact on reliability and lifetime of the solder connections and current densities within single solder bumps increase. Electromigration of flip-chip interconnects is a significant reliability concern, especially when it comes to further miniaturization for high reliability applications. Combined with high operation temperatures, increasing power levels of ICs, as well as higher driving currents have a major impact on the electromigration performance. Flip-chips with 10 mmx10 mmx0.8 mm in size with a die layout providing a pitch of 100 µm for solder bump sizes of 60 µm, 50 µm, 40 µm, or 30 µm diameter, respectively, have been used. A daisy chain connection is integrated for each of the solder sphere sizes and each chip can separately be connected for online measurements during electromigration and reliability testing. The solder spheres were made of SnAgCu alloy and placed on a NiAu UBM realized in an electroless nickel process. A variety of current density and temperature combinations which is individually adapted to the respective solder sphere diameter has been tested. Lifetime data are collected using online measurement through the daisy chain. Cross sectioning has been used to analyze the influence of thermal diffusion as well as electromigration on the failure mechanism of the highly miniaturized solder joints. Additional, a prediction model for flip chip interconnects with solder spheres of 60 µm, 40 µm, and 30 µm will be outlined using Black's equation. The impact of down-scaling of wafer metallization and packaging feature sizes on the lifetime during temperature cycling will be considered as well. 1. Dohle, R., Schüßler, F., Friedrich, T., Goßler, J., Oppert, T., Franke, J., “Adapted Assembly Processes for Flip-Chip Technology With Solder Bumps of 50 µm or 40 µm Diameter,” Proc 3rd Electronic System-Integration Technology Conference (ESTC), Berlin, 2010. 2. Oppert, T., Dohle, R., Schüßler, F., Franke, J., “Solder Bumping and Processing of Flip-Chips with a Solder Bump Diameter of 30 μm or 40μm,” Proc International Conference on Electronics Packaging (ICEP) 2011, Nara, Japan, 2011.
Rainer Dohle, Dr.-Ing. Assembly & Test
Micro Systems Engineering GmbH
Berg/Oberfranken Bavaria 95180,

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