What Are the Basics of HDI PCB Design, and How Is It Different from Other PCB?

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The amazing performance stats we get from small devices like smartphones are only because of PCB advancements. Today, we can pack more power in small PCBs while achieving high performance. This technique ok packing more components in smaller sizes is known as high density interconnect technique.

What is an HDI PCB design?

The HDI PCB design designs PCBs with denser connection traces, thinner lines, and lesser spaces between components. An important factor of this design is using small components to maintain less space between all the components.

This design enables these HDI PCBs to have a faster connection time. On the other hand, when we consider other PCBs, the main focus is on implementing the circuit to get the desired output without emphasizing compactness and reliability.

The major differences between HDI PCB and other PCB design

Several technical and practical differences exist between the regular PCB design and the HDI PCB design. Here are the 3 major differences that you must know:

Material selection

When designing other PCBs, material selection is not a thing to consider. It is only considered once the circuit design is finalized and is moved to the production phase. However, material selection must be considered during the HDI PCB design process.

As these PCBs are made with different layers of dielectric materials, checking the material for its reliability, thermal capability, chemistry with other materials, adhesion, and several other qualities is necessary.

Ball Grade Array

An important factor of the HDI PCB design is using BGAs or the ball grade arrays. It makes the design more complex but, at the same time, allows us to work with layers of PCB with different components. BGAs allow putting much smaller chips on the PCB for higher functionality. However, adding the same functionality on a regular PCB with individual components may take a lot of space and circuit traces.

Drilling technology

Drilling is a part of HDI PCB design leaned more toward the physical end. Standard PCB design uses traditional drilling practices. It is because those PCBs' layers and circuit traces are not that complexly designed.

Usually, there are no layers, and even on the double-sided PCBs, drilling is much easier. With HDI PCB design, micro laser drilling is standard as it provides precision drilling results in the places needed. So, the chances of accidentally damaging the circuit traces decrease.


What is the process of HDI PCB design?

The HDI PCB design process differs slightly from the regular PCB design process. For regular PCBs, the design can be made first, and once it is made, it is implemented physically. However, HDI PCB designing is different, and the following steps are followed during its process.

Determining the layer count

The first step of this process is determining the number of inner and outer layers of your HDI PCB. These layers will be used for routing signals, and to count the layers, you can check the location of the largest BGA on the PCB. The direction and interface counter regarding this BGA will help determine the layer count, which will be vital in HDI PCB design.

Choosing the right materials

Once you know the number of outer and inner layers of your HDI PCB, you must select the right material. You may get information about all the dielectric materials and their properties from the fabrication place. Choosing the right material will be vital because it plays a role in the stack-up structure of your HDI PCB design.

Routing style selection

Now you will decide which routing style you will be going with. It depends on the thickness of your design and the layer count. Another important thing to consider is yielding max efficiency from the design when routing signals from the inner layer. It is a critical part of the design process, as the wrong selection may result in a lack of performance of the PCB even when everything else is perfectly selected.

Reliability assessment

Till now, it has been all planning, and to begin implementation of the design, reliability assessment is essential. This testing ensures that all the design elements, routing style, and material selected for this PCB work are as intended. The results from this assessment can help during production and assembly as well as during the operation of the PCB.

Determining the design rules and implementation

For every HDI PCB design, there may be varying design rules. So, the final step will be selecting your design rules for maximum reliability in the final product. With that, you can select a fabricator considering the services they offer and leave everything up to them.

Is HDI PCB design simple, just like other PCB designs?

The HDI PCB design process is not only different from other PCB designs but is also more complex. While we have to follow all the steps above for HDI PCB design, simple PCB design only takes a schematic that we can upload in software and get the PCB design. The HDI PCB design involves other challenges that make the process even more complex. Those challenges include:

  • Space management according to components on both sides
  • Availability of small components
  • Availability of labs and tools to work on HDI PCB design
  • Keeping routes between components short is essential
  • The design gets very complex as you are dealing with multiple layers simultaneously.

Main qualities we focus on during HDI PCB design.

HDI PCB design process focuses on many things more than regular PCB design. Here are the details about the main qualities focused on during the HDI PCB design process.

Compact design

While working on the HDI PCB design, compactness is one of the main qualities to focus on. As most of the signal routing will be done between layers, achieving it can be easier with the right component placement. Compact design is why HDI PCB becomes so fast and well-performing while staying small.

Circuit reliability

Physical reliability is the next quality to focus on as the PCB design goes through a lot. With layers of this design carrying signals, it must be reliable against environmental factors. While standard PCBs are not too good against environmental factors, a huge part of HDI PCB designing is protecting traces and components. In this way, the circuits can go through a lot and maintain the same performance.

Signal integrity

Signal integrity is what makes the HDI PCB design so consistent. HDI PCBs are designed to prevent interference with the signals flowing through the circuit. Thus, the output values are correct every time. Keeping signal travel distances short is very helpful because less traveling means fewer chances of interference. Signal integrity differs significantly between the HDI PCB and other PCB designs we use.

Thermal reliefs

With higher performance, it is not strange that the components of HDI PCB will get hot. If this heat is not dissipated effectively, the HDI PCB may lose its performance, and over longer exposure to heat, there could be reliability issues. So, managing thermal reliefs by efficient component placement is another quality of the HDI PCB design process. This quality ensures the right performance stats and a longer PCB life.

Signal strength

The signal strength is way better in HDI PCB design than in standard PCB designs because of the lesser distance between components. The delays are decreased, and signals can travel faster than before. As the signals and traces of HDI PCB go through different layers of non-conductive and conductive materials, thoughtful designing can improve signal strength.

How has HDI PCB design revolutionized the digital world?

Every field of life uses digital products, from healthcare to business, telecommunication, and defense. Most of them use the HDI PCB because of its qualities and benefits over regular PCBs. Some fields where HDI PCB are widely used include:

  • Automobile industry
  • Military applications
  • Smartphones and computers
  • Healthcare products and tools
  • Aerospace
  • Wearable gadgets

In all these applications, the smaller products are better, and with the HDI PCB design, we can pack more power in smaller packages.

Where do other PCB designs work better than HDI PCB designs?

Even though the HDI PCB design brings more power in a much smaller size, sometimes it is just overkill. There are several instances where the standard PCB design makes a better option than the more complex HDI PCB design. These include products where we are not more performance-oriented and don't worry about signal integrity.

Such products also don't need to be better with thermal relief. Wall clocks, digital calculators, and some old-school electronics are good examples of applications where standard PCB designs are more effective in terms of cost and performance than the HDI PCB design.


Most devices around us today have HDI PCBs working in them, and the HDI PCB design is the reason behind the wide success of several products due to higher performance capabilities than ever before. Due to this efficient design practice, smartphones fitting in the palm of our hands are more powerful than many computers and other devices collectively. The best part is that the HDI PCB designs to ensure accurate, reliable, and efficient results.


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