Definition

Any-layer (or every-layer interconnect) HDI uses micro-vias throughout the stackup, allowing vias between any two adjacent layers. Unlike conventional HDI with specific build-up sequences (1+N+1, 2+N+2), any-layer construction typically uses all cores or RCC build-up with no mechanical through-holes. This maximizes routing freedom and density, enabling escape routing from ultra-fine-pitch components. Stacked micro-vias must be copper-filled for reliability. Any-layer is the most advanced HDI type, used in smartphones and other high-density applications.