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42 DESIGN007 MAGAZINE I DECEMBER 2025 UHDI layer types include core, sequen- tial lamination build-up; microvia; embedded and passive antennas and inductors; and embedded functional, protective, and hybrid rigid-flex layers. Together, they enable ultra-fine features, dense interconnects, high-frequency per- formance, and miniaturized system designs. Sequential Lamination Build-up (SBU) UHDI typically requires multiple SBU cycles, where thin dielectric and copper layers are drilled for microvias, plated, imaged, and laminated sequen- tially to build up to the final design from the inside out (Figure 1 above). Embedded Passive Layers Embedding passives directly into dielectric layers saves space and reduces parasitic effects, enhanc- ing power and signal integrity. Antennas and Inductors Antennas and inductors are often integrated directly into UHDI substrates as embedded func- tional layers. This approach saves space, reduces parasitic losses, and improves performance com- pared to discrete components, which is critical for 5G/6G, IoT, wearable, and implantable electronics. Inductive layers are created by spiral or meander- shaped copper patterns within UHDI dielectric lay- ers, and can be implemented as planar inductors, solenoidal geometries, or integrated magnetic-core structures. This technology reduces parasitic capac- itance and enhances power integrity by lowering impedance in power distribution networks. Thermal Layers As UHDI enables ultra-compact, high-performance systems (AI, HPC, 5G/6G, medical implants), thermal management becomes critical. Thermal U H D I F U N DA M E N TA LS BY A N AYA VA R DYA , A M E R I CA N STA N DA R D C I RC U I TS An Overview of UHDI Layer Types Figure 1: Chart showing the impact of sequential lamination.