A novel fully additive fabrication approach for creating double-stacked copper spiral inductors

The development of miniaturized embedded inductors holds crucial significance in advancing modern electronic devices, contributing to their size reduction, enhanced efficiency, and improved performance. This study introduces a groundbreaking, fully additive manufacturing process designed for fabricating miniaturized embedded double-stacked copper spiral inductors. The Sequential Build Up-Covalent Bonded Metallization (SBU-CBM) method serves as the foundation for this novel approach. The experimental process evolves in three stages. In Stage I, the first layer of polyurethane (PU1) is initially spin-coated onto the FR-4 base substrate. The lower embedded copper spiral inductor is then fabricated on top of PU1, employing the SBU-CBM method. Moving to Stage II, the second layer of polyurethane (PU2) is spin-coated onto the existing PU1 layer. Subsequently, a single microvia is created and copper-plated using the SBU-CBM method, establishing a crucial vertical connection between the upper and lower embedded copper spiral inductors. Finally, Stage III involves the fabrication of the upper embedded copper spiral inductor on PU2, utilizing the SBU-CBM method. Optical microscopy and X-ray Computed Tomography (XCT) images confirm the successful formation of embedded double-stacked copper spiral inductors, a configuration where two embedded copper spiral inductors are interconnected through a copper microvia. Notably, the copper strip lines within the spiral inductor configuration are miniaturized to a width of 10 μm, while the diameter of the microvias is reduced to 10 μm, indicating the miniaturization precision achieved through this novel additive manufacturing process.