Planar Microspring—A Novel Compliant Chip-to-Package Interconnect for Wafer-Level Packaging

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In this paper, a novel compliant chip-to-package interconnect, planar microspring, is presented in terms of design consideration, wafer-level fabrication process and mechanical characterization. Several spring designs have been evaluated, and results indicate that a J-shaped spring design produces a combination of high 3D compliances and acceptable electrical parasitics. Further, numerical analyses on the J -shaped microspring interconnect examined the dependence of mechanical and electrical performance upon geometry parameters. A wafer-level fabrication flow combining complementary metal oxide semiconductor (CMOS) back-end-of-line (BEOL) process and 3-D surface micromachining technique has been successfully implemented to create planar microspring interconnect prototypes with a fine pitch (100 mum). The mechanical robustness of the prototype interconnects have been evaluated by nanoindentation. Finally, high-frequency electrical simulation suggested that the interconnect application can be extended up to ~35 GHz without significant power loss.