We have developed a high-density wiring interposer for 10 GHz 3D packaging using a photosensitive multiblock copolymerized polyimide. This new polyimide can realize micron-sized fine patterns without pattern shrinkage because of the nonrequirement of high-temperature thermal curing. The polyimide has good electric properties such as high breakdown voltage and low dielectric constant. Therefore, it is considered that by introducing this photosensitive polyimide as an insulator of the interposer, a high-performance interposer for LSI packaging can be realized. We confirmed experimentally that the high-density wiring interposer can be fabricated using the polyimide and gold. We optimized the basic properties of the photosensitive polyimide film for the fabrication of the interposer. Fine metal wirings were smoothly covered by the polyimide, as confirmed by scanning electron microscopy (SEM) of the cross section of the fabricated balance pair strip line structure. From the time domain reflectometry (TDR) measurement, it was determined that the characteristic impedance of the strip line is within 55.2 Ω ± 11.5% at the center of the interposer chip.

We have developed a high-density wiring interposer for 10-Gbps signal propagation using a photosensitive polyimide. We optimized the basic properties of the photosensitive polyimide film for the fabrication of the interposer. We experimentally confirmed that the high-density wiring interposer could be fabricated using the optimized polyimide and gold multilayered structure. Fine metal wirings were smoothly covered by the polyimide film, as confirmed by scanning electron microscopy (SEM) of the cross section of the fabricated balanced pair strip-line structure. From the high-resolution differential time domain reflectometry (TDR) measurement, the differential impedance Z diff of a 12.5-µm-wide 12.4-mm-long balanced-pair strip-line was evaluated to be within 100 Ω ± 14.6 %. From the high-resolution differential time domain transmission (TDT) measurement, an insertion loss (S-parameter: S dd21 ) of -2.96 dB at 10 GHz through the differential strip-line was evaluated. Finally, we confirmed eye diagram measurement at 10 Gbps through the differential strip-line on the fabricated interposer. The aperture size of the measured eye diagram at 10 Gbps was sufficient for ultrahigh-speed signal propagation. IntroductionWith the increase in the operational speed and integration density of LSI chips, high-performance digital electronic systems have been realized. The clock frequency of a CPU-LSI chip exceeds the GHz range. However, to realize a computing system with a higher performance, the high-speed signal propagation performance of not only the LSI chips of computing systems but also LSI packages and interconnects must be improved. To obtain high-speed signal transmission in LSI packages and interconnects, line impedances should be

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A micro-contact printing (µCP) method has been applied to the fabrication of microstructures and electronics. We have successfully fabricated a copper wiring structure on flexible substrates using a combination of µCP, electroless plating, and electroplating. A nucleating agent ink pattern was printed by µCP onto polyethylene terephthalate, and polyethylene naphthalate. Nickel and copper thin films were electrolessly plated onto the pattern, and used as a conductive layer for subsequent copper electroplating. Copper wiring structures with a half-pitch of a 100 µm and a 250 µm line-and-space pattern, were successfully produced on flexible films at temperatures below 100 °C.

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