What is a HDI PCB Board?

HDI stands for ‘High Density Interconnects’. An HDI PCB is a dense version of a printed circuit board where the components are placed closer to each other allowing the overall board size to be smaller. HDI printed circuit boards use optimized routing, smaller components, BGA component footprints and optimized vias to make connections between the components on the board.

In regular PCBs we use through hole vias to connect multiple layers of the board to each other. A traditional via goes from the top of the PCB to the bottom, connecting all the layers, as seen in the image below. These vias are easy to deploy as they can be drilled through the board from top to bottom using a regular drill. The main disadvantage of regular vias from a space optimization point of view is that this via will connect all the layers of the board, even those that do not need to be connected to each other and thus can result in wastage of space within some layers of the PCB.

An HDI PCB uses different types of vias – microvias, buried vias and blind vias to optimize the space requires for interconnections between the layers and components.

Microvias are ultra-small vias which can be drilled using lasers. They are much smaller in diameter than regular vias.

A Blind via connects the outer layer to an inner layer, with access to only one external layer. 

A Buried via can connect inner layers of the same substrate or multiple substrates, with no access to external layers as seen below.

Blind or buried via gives access to only functionally required layers, and as a result do not occupy space on all the layers at a given time. This provides more space for components with enhanced routing within the traces. A designer can mount more components to increase the board density or can reduce the board size as per the requirement.

Advantages of an HDI PCB Board:

• HDI PCBs allow for increased component placements on both sides of the PCB thereby making the board smaller and lighter
• HDI PCBs can reduce the amount of laminate material required. This can result in lower pricing of a board when using a very expensive laminate material
• HDI boards can improve signal transmission along with a reduction in signal loss and delays as connection paths are shorter
• Provides better heat dissipation

Click here to see a list of HDI Printed Circuit Board Manufacturers.