Introduction: large-density HDI PCBs for optical interaction involve precise 3 mil/3 mil trace/space, Rogers or Panasonic M6 substrates, and electrolytic hard gold end for responsible eight-layer, 3–5 cm² https://ilovebookmark.com/story21525294/assortment-standards-for-prime-density-hdi-pcb-boards-in-optical-interaction