HDI circuit boards, or high-density interconnection PCBs, utilize advanced technologies such as micro-blind and buried vias to achieve high circuit density. They are crucial for meeting the demands of miniaturization in portable product designs, particularly with components like BGA packages with pitches smaller than 0.65mm. These boards are widely used in high-end applications such as mobile phones and GPS systems due to their ability to connect inner PCB layers efficiently without penetrating the entire board (blind vias) and to connect traces between inner layers invisibly from the surface (buried vias).