A 3D coaxial transition with continuous ground wall fabricated by a 12-inch wafer-level packaging method for radio frequency applications

Purpose - This paper aims to realize the vertical interconnection in 3D radio frequency (RF) circuit by coaxial transitions with broad working bandwidth and small signal loss. Design/methodology/approach - An advanced packaging method, 12-inch wafer-level through-mold-via (TMV) additive manufacturing, is used to fabricate a 3D resin-based coaxial transition with a continuous ground wall (named resin-coaxial transition). Designation and simulation are implemented to ensure the application universality and fabrication feasibility. The outer radius R of coaxial transition is optimized by designing and fabricating three samples.Findings - The fabricated coaxial transition possesses an inner radius of 40 pm and a length of 200 pm. The optimized sample with an outer radius R of 155 pm exhibits S11 < -10 dB and S21 > -1.3 dB at 10-110 GHz and the smallest insertion loss (S21 1/4 0.83 dB at 77 GHz) among the samples. Moreover, the S21 of the samples increases at 58.4-90.1 GHz, indicating a broad and suitable working bandwidth.Originality/value - The wafer-level TMV additive manufacturing method is applied to fabricate coaxial transitions for the first time. The fabricated resin coaxial transitions show good performance up to the W-band. It may provide new strategies for novel designing and fabricating methods of RF transitions.