IWLPC (Wafer-Level Packaging) Conference Proceedings

Demonstration of SIC Interposers with High Density and Fine Pitch Microbumps

Authors: Hasan Sharifi, Melanie Yajima, Aurelio Lopez, Chuck McGuire, James Li, Zhiwei Xu
Company: HRL Laboratories, LLC and Chi-Tek, Inc.
Date Published: 11/11/2014   Conference: IWLPC (Wafer-Level Packaging)

Abstract: We describe our recent efforts in heterogeneous integration of diverse materials on Silicon Carbide (SiC) interposers. In this work, we have developed an ultra-high density, fine pitch (5µm and 10µm) Au microbump process for mixedsignal integrated microsystems with high-density I/O as well as RF/Microwave applications. Recently, the interest to achieve intimate device integration with an I/O pitch of less than 5um has been growing. The proposed microbump interposer offers a low-loss, high density, and technology agnostic system integration. A low temperature thermocompression bonding process as low as 125°C using Au-Au was developed. Silicon or glass interposers have been demonstrated for variety of applications. Silicon interposers are low cost, but have fairly high substrate loss due to the resistivity of silicon. On the other hand, glass interposers are fairly low cost with low substrate losses, but have a high CTE mismatch between disparate dies or chiplets as well as having poor thermal conductivity. SiC offers the best performance with high thermal conductivity, low electrical loss, as well as being CTE matched with silicon.

For the demonstration of 5um and 10um Au microbumps, we have designed and fabricated a fanout on a SiC substrate and chiplets that were fabricated on Si substrates. The arrays of microbumps consist of 50 rows, each with 50 microbumps. The Si chiplets have been hybridized on the SiC interposer using a high precision die bonder. We have conducted a design of experiments in order to determine the correlation between bonding temperature versus bonding force at a fixed bump resistivity. Experimental results indicate that low temperature bonding at higher forces provide a reliable, high-density interconnect. The DC measurements show that the microbumps can achieve a maximum resistance of 65mO per bump transition at a bonding temperature as low as 125°C with high yield. RF measurements of the microbump chains prove low loss (only 0.03dB) per bump at 20GHz. We have also conducted thermal cycling tests (-55°C to 85°C as well as -65°C to 150°C) and we did not observe any significant changes in electrical performance.

Key Words: 

Heterogeneous integration, interposer, fine pitch microbump

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