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Thin-Film Signal and Power Redistribution Layers Based on AL-X and Cu
Keywords: thin-film, redistribution, signal integrity
Use of unpackaged die in advanced integrated systems (i.e., 3-D integrated systems) calls for dense, high performance interconnection schemes with controlled impedance for high-speed signal routing and minimal impedance for efficient power distribution. We have evaluated a new material set for use in a thin-film-based redistribution layer (RDL) for dense signal and power routing between chips and from chip-to-board. The material set consists of Asahi Glass AL-X spin-on low-k dielectric polymer and electroplated copper metallization. This technology will allow fan-out and interconnection of high-speed signals and power to/from die pads on pitches sufficiently less than 100um directly to companion die over short distances or for transition to underlying board metallization for longer transmission distances that may require lower signal loss. This technology is demonstrated using both Si wafers and low-temperature co-fired ceramic (LTCC) substrates onto which the thin-film RDL is fabricated. We have developed and will describe the fabrication procedures used to construct multiple interconnected layers of AL-X / Cu, which are compatible with standard wafer level packaging (WLP) processes. Compatibility with Cu, excellent adhesion, good planarity, and desirable thermal expansion properties make this material set a promising one for 3-D integration purposes. Details of the fabrication procedure for these structures will be described. We have evaluated the performance of this technology for high-speed digital signal transmission by characterizing frequency parameters (i.e., S parameters) of varying lengths of single-ended and differential strip-line transmission line structures. We have optimized transmission line and transition geometries for transmission of signals at rates greater than 25Gbps. In addition to high-speed signal redistribution capabilities, we have characterized power redistribution capabilities of this technology. Results of the signal and power integrity measurements and simulations performed in this work will be presented.
John Bailey,
Auburn University ECE Department
Auburn University, AL

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