HDI, high-density interconnect, describes boards that use microvias, thin dielectrics, lines and spaces of 100 micrometres (4 mils) or less, and often several sequential lamination cycles that build layers up around a core. Structures are named by the number of microvia layers on each side, such as 1+N+1 or 2+N+2, and any-layer HDI uses stacked copper-filled microvias throughout. Phones, wearables and fine-pitch BGA designs depend on it.
With the 0.35 mm pitch processor we're looking at 2+N+2 HDI, so budget for two extra lamination cycles.
Also heard as
- high-density interconnect
Related terms
Microvia
Very small laser-drilled via, typically 0.15 mm or less across, spanning one thin dielectric layer.
Blind via
Via that starts on an outer layer and ends at an inner layer without passing through the whole board.
Via-in-pad
Via placed directly in a component pad, filled and plated over so solder cannot drain down it.
Stackup
Ordered arrangement of copper layers, cores and prepregs that makes up a multilayer board, with each thickness.