How can you distinguish between first-, second-, and third-order HDI boards?

As electronic products continue to evolve toward higher density and miniaturization, the application of high-density interconnect (HDI) printed circuit boards is becoming increasingly widespread. HDI technology enables efficient connections between multiple layers through micro-blind vias and buried vias, thereby significantly improving circuit routing density and electrical performance. In HDI structures, first-order HDI is relatively simple in structure, with mature manufacturing processes that are easy to control. However, as the number of layers and structural complexity increase, second-order HDI boards face greater technical challenges during design and manufacturing, particularly in critical process steps such as alignment accuracy, microvia processing, and plating quality, which place higher demands on manufacturing capabilities. First-order HDI boards are relatively simple and easy to control. Second-order processes become more complicated; one reason is alignment issues, and