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22 DESIGN007 MAGAZINE I OCTOBER 2024 channel (conductors per channel). When these channels are restricted further, the designer will need to consider sub-surface circuit rout- ing to achieve interconnection. Industry roadmaps consistently point to materials and process refinement as the key enablers for improving product performance and manufacturing efficiency. By address- ing these concerns, the laminate industry has made significant refinements to all packag- ing and substrate-related materials. For HDI applications, the base structure selected must be mechanically stable enough to withstand the process temperatures experienced during board fabrication and throughout each phase of the assembly process. Regarding multilayer circuit board fabrication, although a mature and widely available service, each supplier's process sequence and methods can vary. When component and circuit complexity require a higher circuit density solution, many circuit board fabricators have the expertise to furnish circuit boards that enable a higher-density cir- cuit. ere are, however, physical limits that oen restrict the interconnect potential for the circuit board: • Limited PCB surface area • High ratio component density • Greater semiconductor I/O • Very fine-pitch terminal spacing Implementing HDI technology has the potential to overcome most of the barriers associated with implementing the increasingly complex semiconductor products. e factors that define the limits of circuit interconnect routing ability on a circuit board include: • Pitch/distance between via-holes or plated through-holes • Number of conductors routed between land pattern features • Established limit on the number of signal layers required Most of the interconnect challenges can be solved by efficiently utilizing small-diameter micro via holes and more advanced multilayer fabrication methods. HDI and UHDI Process Refinement Process refinement for PCB manufacturing includes implementing more efficient imaging capability and greater utilization of alterna- tive hole-forming techniques, applying more advanced etching and plating chemistry, and the refinement of lamination methods. e more technically competent PCB fabrication companies can produce conductors as nar- row as 25 microns (~0.001") but they will rely on dielectric materials that are furnished with very thin copper foil. When conductor lines and space widths must be reduced further, the