Main Types of Vias in HDI PCB

Vias are the conductive holes that connect and allow electrical (or thermal) signals to be transmitted through the multiple layers of an HDI PCB. Vias have different names depending on their position and their construction:

Through-Hole Vias: are copper-plated holes or cylinders that traverse the entire printed circuit board from top to bottom. They form conductive paths that connect all of a board’s layers. Through-hole vias are the least costly vias to fabricate.

Blind vias: are copper-plated holes or cylinders that connect the top or bottom layers of a PCB to one or more of its inner layers. Unlike through-hole vias, blind vias do not go through the entire board thus they are only visible from one side of the board.

Buried Vias: are copper-plated holes or cylinders that connect two or more of the inner layers of a board but do not penetrate either outer layer of the board. Buried vias thus are not visible from either side of a board.

Microvias: are particularly tiny vias that interconnect two adjacent layers. They have a diameter less than 150 microns, making them the smallest and most space efficient type of via. Microvias are rarely found in traditional PCBs but are common in HDI PCBs. Microvias may be through-hole, blind or buried.

HDI PCB Stackup

The Institute for Printed Circuits (IPC) provides six design structures for HDI printed circuit boards. These designs are defined by the IPC-2226 standard. Every structure can be represented by the notation i+[C]+i, with i indicating the number of layers on each side of the “core”: which is represented as [C]. The core of a PCB is the rigid base material onto which copper traces are imprinted. Below are the three most commonly used structures in the manufacture of HDI printed circuit boards.

What is HDI PCB?

A high density interconnector printed circuit board (HDI PCB) is a circuit board that has a higher wiring density per unit area as opposed to conventional circuit boards. This allows for more components to fit in the total available space. HDI PCBs are useful for increasing electrical performance while reducing the weight and size of equipment.

HDI PCBs have minor vias, capture pads, finer spaces and lines, and higher connection pad density making them a better option for boards where space is a concern. HDI technology is regularly used in products like mobile phones, personal computers, MP3 players, game consoles, and more.

TYPE 1 HDI PCB Stackup: Include 1 layer of microvias on one or both sides of the core as well as through vias.

TYPE 2 HDI PCB Stackup: Include 1 layer of microvias on one or both sides of the core combined with through vias and blind/buried vias.

TYPE 3 HDI PCB Stackup: Include 2 layers of microvias on one or both sides of the core together with through vias and blind/buried vias.

Benefits of HDI PCBs

There are multiple benefits of using HDI PCBs, and the major one is the density of the packaging. You can add more components on a smaller board and further reduce the size of the device. Other benefits include:

HDI circuit boards are smaller and lighter and thus don’t increase the weight of the device.

They have low power consumption and enhance the electrical performance of the device.

They increase the speed by faster routing, more component space, and easily placed SMD components.

Improved signal integrity leads to decreased interference.

Fewer layers and components can be added on both sides of the layers.

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