Introduction: High-density HDI PCBs for optical interaction require precise 3 mil/3 mil trace/Area, Rogers or Panasonic M6 substrates, and electrolytic hard gold complete for reputable 8-layer, 3–5 cm² https://bookmarktiger.com/story21622256/assortment-conditions-for-high-density-hdi-pcb-boards-in-optical-communication