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What is HDI PCB? Meaning, Manufacturing and Cost

An example of HDI PCB or high interconnect PCB
HDI PCB or high interconnect PCB
An example of HDI PCB or high interconnect PCB
Resource: https://www.semanticscholar.org

An HDI PCB packs more components in a small space, making circuit boards with fewer layers possible — and smaller electronic devices a reality. With the growing demand for miniaturized electronics, this type of PCB is becoming even more important. In this article, we introduce you to the world of the HDI printed circuit boards; their features, design, fabrication, and cost considerations.

What is HDI PCB?

HDI PCB is the name given to a type of printed circuit board that features a high number of interconnections. Put in another way, it means a PCB that’s designed to have more components and circuits in a unit area than a normal PCB.

This intricate design is the basis of many electronic products today, from mobile phones to computers and other devices. So what does HDI mean and how is it used in the HDI circuit board design and stack-up?

HDI PCB Meaning

Now that you understand what it is, let’s dive into the HDI PCB definition: HDI means “high density interconnects” and signifies the high number of connections that have been placed on the board.

To achieve HDI, everything is miniaturized, and the board made smaller and lighter. HDI technology effectively caters to the performance and size demands of modern electronic products and which include the following:

HDI PCB Stack up

One of the most important aspects of high density interconnect circuit boards is their stack-up, or the arrangement of their different layers. The fact that you can pack many components in a very small area practically reduces the number of layers required.

But that also requires a proper selection of the dielectric, or the insulating layer between the conductive copper layers. Generally, the type of material used must offer excellent dimensional stability, be able to withstand laminations, and be easy to work with. Options range from FR4 and FR5 to polyimide films.

In an HDI multilayer PCB, different arrangements are possible. Examples include the 0-N-0, 1-N-1, and 2-N-2. Depending on the application type, this type of PCB board can also be rigid, rigid flex, or the flex type. In the next section, we’ll see how this board differs from normal PCBs.

high interconnect PCB
A high interconnect PCB
Resource: https://designhelp.fedevel.com

HDI PCB vs. Standard PCB

The HDI PCB differs from the standard type of the board in many different ways: size, weight, number of components per square inch, and other aspects. To make the difference between HDI vs. standard PCB clear, here is a table with a comparison of the different features.

Feature

HDI PCB

Standard PCB

Component Density

More components per inch squared

Fewer components per inch squared

Component Size and Weight

Smaller and lighter high-performance components

Components are larger and weigh more

Via Types

Blind vias, buried vias as micro vias

Uses through holes

Number of Layers

Fewer layers

More layers

Imaging and Hole Drilling

Direct laser imaging and mostly laser drilling

Photo film imaging and mechanical drilling

As you can see, the HDI PCB offers better and more advanced features. That, in turn, means better performance and other benefits, such as reliability exceptional versatility, signal integrity, and compactness. Next, we’ll take a look at its manufacturing process, from the design stage to fabrication and testing.

HDI PCB design
HDI PCB design
Resource: https://www.youtube.com/watch?v=Q01okxqaV2Y

HDI PCB Manufacturing

The HDI PCB manufacturing process, although almost similar to that of the standard PCB, features a few differences. Just like any other board, it starts with the engineer producing the board’s design, then the prototyping stage and finally, the fabrication process where the HDI board comes to life.

HDI PCB Design

The board is first designed, taking into account the unique features that characterize it, such as component density. Also, the fact that’s these must be a laid out in a way that will not compromise signal integrity and board performance. During the HDI PCB design phase, the following features are determined.

  • The type of material to use
  • The number of layers or stack-up. The HDI PCB stack-up is typically composed fewer layers than the standard board.
  • The types of vias to use with options being buried, blind and microvias
  • The number and types of electronic components. Mostly, these will be surface mount devices with many pins or pads.
  • EMI reduction strategies like optimizing the size of traces, component grouping and spacing, the use of ground planes, etc.
  • Routing and layout optimization

The HDI PCB design is actualized in PCB design software. After that, the designer sends it to the manufacturing section for prototyping before the actual production process can begin.

HDI PCB Prototype

Before full-fledged production can begin, a test board or prototype is made. The HDI PCB prototype has all the required features to test its different capabilities. These results will then form the basis for corrections, if any, to ensure the board satisfies every performance and reliability requirement.

HDI PCB Fabrication

This is where the HDI design is actualized and made into a real product. The HDI PCB fabrication process is similar to that of conventional circuit boards, with only a variation in the type of technologies used to print the board circuitry and drill holes.

Because HDI PCB circuit boards require smaller traces and vias, mechanical film printing and mechanical hole-drilling are less viable options. So laser machines are used to do the job. Laser etching and drilling— despite being more expensive — offers not only precision, but also the ability to work with very small surfaces.

To print the circuitry, laser direct imaging technology is used. For vias, a concentrated beam of laser light is aimed at a spot. The resulting heat when the material absorbs this energy vaporizes the spot, essentially creating a tiny hole. Note that mechanical drilling may also be used, especially if only a few boards are needed.

HDI multilayer PCB design
HDI multilayer PCB design
Resource: https://electronics.stackexchange.com

HDI PCB Cost

As you may have guessed, the intricate nature of HDI printed circuit boards makes their fabrication a demanding process that requires complex design considerations. It also mostly requires advanced manufacturing technologies.

But while the mentioned requirements could increase the estimates for HDI PCB cost, the reduced layer count ends up lowering it considerably. Generally, the cost of HDI boards depends on these variables:

  • The amount and types of materials used.
  • The board stack-up features (number of laminations and board thickness).
  • The types of vias used or the technology to make them (laser-drilled vias are more expensive).

Different HDI PCB manufacturers will also price their board manufacturing services differently, so you can expect the figures to vary a lot. To reduce your expenses, it’s crucial that you optimize your board for the different features. You may also want to only include what’s crucial and necessary for your board.

Conclusion

With the world of digital technology becoming more and more advanced, the demand for the HDI PCB board continues to grow. This type of circuit board packs many components in a small area, making miniaturized electrical circuits and devices possible.

And even though that also means a longer and more demanding process to make them, modern HDI circuit boards are becoming more and more affordable, thanks to the use automation and other manufacturing technologies.

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