Introduction: High-density HDI PCBs for optical interaction require precise 3 mil/3 mil trace/space, Rogers or Panasonic M6 substrates, and electrolytic tricky gold end for reputable 8-layer, 3–5 cm² https://letsbookmarkit.com/story21650822/collection-requirements-for-high-density-hdi-pcb-boards-in-optical-interaction