HDI Structures and Constructions

There are several types of HDI board constructions that offer different advantages:

1. Build-Up HDI

This uses a conventional PCB core (typically FR-4) with additional build-up dielectric and copper layers laminated on top to form the HDI structure. The I/O pads connect through the core layers to the build-up layers.

2. Coreless HDI

As the name implies, coreless HDI boards eliminate the core FR-4 layers and implement the HDI build-up layers directly on a thick copper foundation. This enables the thinnest constructions but are prone to warpage without a core for stability.

3. Any-Layer HDI

Any-layer HDI incorporates microvias in every layer of a multilayer board, rather than just the outer build-up layers. This maximizes connection options between layers but requires advanced drilling precision.

4. Sequential Build HDI

Sequential build HDI involves successive lamination of dielectric and copper foil layers, with each lamination fully imaged and etched before the next is added. This allows greater control and yields the finest features.

5. High-Density Interconnect Flex

HDI technology has also expanded into flex PCB fabrication, combining the flexibility of flex circuits with the integrated capabilities of HDI to offer robust solutions where bending is required.