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This paper presents the design, fabrication and electrical characterization of a low loss and low cost non-traditional silicon interposer, demonstrating the high bandwidth chip-to-chip interconnection capability of the 3D silicon interposer, with equivalent or better performance than 3D ICs with TSVs, at a much lower cost. This scalable approach uses thin polycrystalline silicon in wafer or panel form, forms lower cost through-package-vias (TPVs) at fine pitch by special high throughput laser processes. The electrical performance is improved by thick polymer liners within the TPVs. Double side package processes for TPV metallization and RDL layers using dry film polymers and plating leads to significant cost reduction compared to single side TSV and BEOL wafer processes. Combined loss of 3mm long CPW lines and two TPVs in the low loss silicon interposer was demonstrated at less than 1dB at 10GHz. The fine pitch TPV capability and low loss of this non-traditional silicon interposer leads to 3D interposers with double side chips interconnected at equivalent bandwidth to wide bus I/O 3D ICs at a much lower cost and with better testability, thermal management and scalability.