HDI PCBs, (High Density Interconnector) are printed circuit boards that incorporate a very dense interconnection between the component(s) and the circuit board itself. In order to accomplish this, there are many different design technologies that need to be implemented into the circuit board to be able to accomplish such an extreme pad density.
Most applications are using trace width/space that are 3mils or less, and micro-vias that are 4mil and smaller, that require a Via in PAD design. Via in PAD requires that the via has to be filled in almost all cases with a conductive material, or at least have a conductive material on the top of the via for connection purposes.
HDI PCB capabilities
1+N+1 – PCBs contain 1 "build-up" of high-density interconnection layers.
i+N+i (i≥2) - PCBs contain 2 or more "build-up" of high density interconnection layers. Microvias on different layers can be staggered or stacked. Copper filled stacked microvia structures are commonly seen in demanding designs.
Any Layer HDI - All the layers of a PCB are high density interconnection layers which allows the conductors on any layer of the PCB to be freelyinterconnected with copper filled stacked microvia structures. This provides a reliable interconnect solution for highly complex large pin-count devices, such as CPU and GPU chips utilized on handheld and mobile devices.
Multilayer copper filled stacked micro via structure