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This letter reports on the use of quasi-coaxial vertical via transitions fabricated with a selectively anodized aluminum substrate for 3-D packages to evaluate high frequency performances. The proposed method of fabricating quasi-coaxial vertical via transitions is easier and more cost-effective than other RF MEMS processes. Vertical interconnects with embedded anodized aluminum vias are first designed and fabricated. The optimized interconnect structure demonstrated RF characteristics with an insertion loss of less than 0.75 dB and a return loss of greater than 12.4 dB over a broad bandwidth ranging from 0.1 to 10 GHz. The experimental results suggest that the developed fabrication method, which is based on the use of a selectively anodized aluminum substrate, can be used in reasonable 3-D interconnect solutions.