What Is a High Density Interconnect HDI PCB?

High Density Interconnect HDI PCB

A high density interconnect HDI PCB is a printed circuit board that uses smaller traces and vias to fit more components in a smaller space. This technology is crucial for reducing the size of electronic devices without sacrificing performance or functionality. Typically, HDI PCBs are found in high-end or space-constrained products that require higher signal transmission quality and greater power efficiency. They’re also a common choice for advanced technology systems, including smartphones and game consoles. In the medical industry, HDI PCBs are helping to produce more accurate monitoring equipment and medical diagnostics.

An HDI PCB is a complex PCB that requires special manufacturing processes to create. These include laser drilling, plugging and laser direct imaging. They also feature thin specialty materials and sequential lamination cycles. Because of these requirements, HDI boards can be more expensive than standard PCBs. However, their smaller size and better electrical performance can offset these costs.

To improve routing density on an hdi pcb, designers utilize a variety of stack-up arrangements. Typically, this involves using different layers for ground and power planes and drilling the vias between them. This reduces the number of inner layers and makes it easier to achieve optimal signal integrity. Alternatively, the design can also use microvias in a pattern called “via-in-pad” to increase signal connections between adjacent layers.

What Is a High Density Interconnect HDI PCB?

The design of an HDI PCB must be carefully planned to minimize the amount of material used and keep the layout efficient. This includes ensuring that the shortest possible trace lengths are used to preserve signal integrity. The layout must also ensure that there are sufficient grounds and power planes for reliable operation. In addition, it is important to plan the layer thicknesses and the locations of the drilled holes.

There are two main types of HDI PCBs: a build-up structure and an any-layer structure. Both structures have a core that is made of prepregs that are layered together. The prepregs are then heated and liquified to stick the layers together. The top and bottom of the core are then etched and the layers are placed on top of each other, then laminated to form the finished product.

A build-up structure has copper-filled staggered or stacked microvias between each of the outer layers. This type of structure is commonly used for BGAs, as it supports lower ball pitch and greater I/O counts. It is also a good option for complex ICs with a large footprint, such as QFNs. The any-layer structure allows any layer to connect to any other layer.

Both structures have a cost advantage over traditional multilayer PCBs, but any-layer designs are more flexible and can be produced with fewer lamination cycles. This is particularly the case for multi-layer boards with a low number of inner layers. Ultimately, the decision between any-layer and build-up structure should be based on the layout requirements and cost of the final product.