What Is HDI PCB 2 n 2 ?

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The newest line of electronics uses printed circuit boards, or PCBs, for all application requirements. Printed circuit boards are superior to their traditional counterparts for several reasons. One of the most important factors for their growing popularity is the many different types of PCBs in the market.

Consequently, this innovation has started a cycle of need-based designs springing up in the circuit board sector. PCBs are so customizable that designers keep on creating increasingly newer versions of them to keep up with the growing complexity of electronic products.

Some of the more prevalent PCB types include flex PCBs, rigid PCBs, rigid-flex PCBs, and HDI PCBs. In this article, we will expand upon HDI PCBs and the many different types of HDI PCB structures.

What Are HDI PCBs?

High Density Interconnect, or HDI, printed circuit boards refer to PCBs with higher wiring density compared to traditional circuit boards. Higher wiring density means HDI PCBs have enhanced electrical performance and can handle higher electrical loads.

Moreover, HDI PCBs have smaller vias copper traces, higher connection pad density, and refined lines. In a time when technology is becoming increasingly smaller and more complex, inventors are beginning to demand well-crafted components that are able to handle increasingly larger electrical loads. Smaller application size also limits the number of circuit boards that can be used.

As a result, HDI PCBs offer the best solution in the form of their small and compact size, higher wiring density, and lower layer count. HDI PCBs are lighter in weight, more compact in size, and are required in less number than standard printed circuit boards. Where a design application would require 5 PCBs to meet the electrical requirements, using only one HDI PCB would prove to be sufficient.

What Are HDI PCB Benefits?

HDI printed circuit boards offer a number of benefits, such as:

• Reduced power consumption by offering deployment of more transistors
• Improved copper etching technology compared to traditional PCBs
• Reduction in overall costs by decreasing the number of PCBs required for an application design
• Increased reliability due to use of microvias with smaller aspect ratio compared to through holes
• Faster manufacturing speeds and time-to-market because of enhanced design efficiency and better electrical output.

Types of Microvias in HDI PCBs

HDI printed circuit boards allow free signaling between their layers with the help of microvias. These are tiny conductive holes that increase the electrical efficiency of HDI PCBs. Depending on the HDI design model and application requirements, there are different types of microvias:

• Blind Vias: an expensive variant that is used in multilayered HDIs. It can only be seen from one side of the board.
• Microvias: small laser-cut holes approximately 150 microns in size. Their small size allows them to connect dense PCBs to be connected to single layers.
• Through Hole Vias: come in the form of plated through holes with copper pads or non-plated through holes with no pads and are the most cost-effective of the four types.
• Buried Vias: these are present within the layers of an HDI PCB and cannot be seen from the outside. An electroplated hole is also drilled in the layers to allow for free signaling.

Types of HDI PCB Structures

There are many types of HDI PCB structures just like other categories of printed circuit boards. HDI structures are layering or stack-up options for the fabrication of printed circuit boards. Depending on an application design and the PCB requirements of the creator, there are several types of HDI PCB structures, including the following:

i. HDI PCB 1+n+1: Simplest HDI
ii. HDI PCB 2+n+2: Moderate Complex HDI
iii. Every Layer Interconnection (ELIC): Most Complex HDI

HDI PCB 2+n+2: Moderate Complex HDI

HDI PCB 2+n+2 is a Type III construction in which resin-filled holes, though vias, and plated microvias are used for interconnection. The type refers to a sequential buildup of X+n+X.

In the case of a 2+n+2 buildup, a minimum of two, if not more, high density interconnection layers are used on at least one side of the substrate core to design the HDI PCB. The substrate core can have any number of layers with buried vias for interconnection and is manufactured using traditional PCB guidelines. It can be flexible or rigid depending on the application requirement.

The microvias can be stacked or staggered on different layers. This design allows signals to pass freely between the layers with the help of these microvias. Although a sequential lamination process is also required for microvias due to the small drill diameters and vias aspect ratio requirements, stacked microvias technology allows designers to route fine pitch components using buried or blind vias.

Challenging designs, incorporating copper-filled stacked microvias, are usually incorporated in application designs requiring a high-level signal transmission performance. HDI PCB 2+n+2 design is the preferred choice in appliances that demand increased routing density but a thin finish of printed circuit board thickness.
Similarly, HDI PCB 2+n+2 designs are very suitable for Ball Grid Arrays, or BGAs, because they have high I/O counts and a smaller ball pitch. As a result, their demand has considerably grown in the manufacturing of game consoles, cameras, and cell phones.

It should also be noted that the common design model for an X+n+X buildup is 2+n+2, but structures can climb to higher numbers as well, depending on the mechanical and electrical requirements of an appliance. Main factors in increasing or reducing the buildup of types of HDI PCB structures include cost and complexity of manufacturing.


We hope you learned a good deal about the types of HDI PCB structures and the HDI PCB 2+n+2 buildup. It is becoming an increasingly popular type of printed circuit board due to stacked and stagged microvias technology. Since the designs are very complex due to increased wire density and layer issues, we recommend contacting PCB manufacturing experts like Hemeixin Electronics Co., Ltd.

Hemeixin Electronics is one of the leading manufacturers of printed circuit boards. They offer cheap and affordable solutions in the electrical appliances sector without compromising on quality. They pride themselves on state-of-the-art PCB technology and client satisfaction. Visit Hemeixin Electronics today, and get a quote on your custom HDI PCB 2+n+2 designs!

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