Introduction: significant-density HDI PCBs for optical interaction need precise 3 mil/3 mil trace/space, Rogers or Panasonic M6 substrates, and electrolytic tricky gold finish for dependable eight-layer, 3–5 cm² https://nimmansocial.com/story11793264/assortment-conditions-for-high-density-hdi-pcb-boards-in-optical-communication