What Is an HDI PCB Stackup?

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HDI PCB stackups are a new innovative circuit board design that offer several benefits over conventional PCBs and are therefore the preferred circuit board design for many modern-day devices such as smartphones and smartwatches. This article will explain what an HDI PCB is and how it differs from a conventional PCB. So, keep reading.

An Overview of HDI PCB Stackup Technology

High-density interconnect PCBs, more commonly known as HDI PCBs, according to the IPC-2226 standards, are printed circuit boards that have been specifically designed to have a wiring density that is higher compared to your run-of-the-mill printed circuit boards.

In order to pull off such a design, a designer must use smaller traces, smaller vias, and fewer layers in comparison to conventional PCBs. Additionally, for these PCBs to have the desired formfactor, components are crammed into a more compact packaging.

Furthermore, HDI PCBs employ a variety of different via technologies, including built-up laminations, blind and buried vias, and microvias. Implementing this allows for more flexible routing and creates room for more components.

In the past, adding more components to a traditionally designed circuit board required the designer to add more layers. On top of this, there was only one kind of connectivity available. However, the discovery of HDI technology now allows for a greater number of sub-connections between layers.

Since HDI PCB design allows for a multitude of connections and sub-connections from a single layer, the number of required layers is lower than for conventional PCBs. Needless to say, fewer layers means that the PCB can accommodate a more compact circuit board formfactor.

Compact boards are generally more reliable and have a smaller aspect ratio, especially those with a reduced thickness. These boards have a smaller drill-to-copper ratio and narrower trace width. Moreover, these boards also have a superior signal integrity than traditional PCBs because of the close connections and lower power needs.

The Layout Design of HDI PCB

The layout design of an HDI PCB consists of a variety of components, thinner traces, microvias, and lower signal levels. All elements of the board play a vital role in its functioning and therefore, the proper selection of all its components is crucial for these boards.

Via-in-pads with an offset design makes it easier to provide more wiring space. The wiring requirement is the total length of connections needed to link all the components. The substrate capacity is the amount of wiring that can be used to link all of these components. The substrate capacity should always be greater than the wiring demand in high-density connection boards.

Using the via-in-pads method, vias can be inserted into the flat lands' surface. The via is capped and plated over, making it nearly unnoticeable, after being filled with non-conductive or conductive epoxy.

While it may sound easy, this unusual process requires an additional eight steps on average. To create the ultimate undetectable via, technicians at Hemeixin use specialized equipment and their years of experience in the industry to continuously monitor the procedure and drive it to success.

Via fill materials come in a wide variety of forms, including conductive epoxy, non-conductive epoxy, electrochemical plating, and copper- and silver-filled epoxy. These fill materials enable the creation of a via that is completely soldered inside of a flat piece of land. Concealed under SMT lands, vias and microvias are blinded, drilled, or buried, filled, then plated and covered.

It takes time and sophisticated equipment to process vias of this kind. Adding further to the process time are the many drill cycles and controlled depth drilling.

Smaller microvias will leave a greater amount of room for installation of more components and technology on the board, that is why a manufacturer must aim to drill the smallest possible microvia.

The high influence laser used by Hemeixin, with a beam diameter of 20 microns (1 mil), can penetrate through glass and metal to create the tiniest through hole. Newer materials, such as uniform glass materials with low dielectric constants and laminates can facilitate the use of smaller holes because of their increased heat resistance for lead-free assembly.

HDI PCB Stackup Structure

HDI PCBs can be found in a variety of layout variations, the most popular ones being 1-n-1 and 2-n-2 PCB. The simplest type of HDI printed circuit board is a 1-n-1 PCB, which consists of a single batch of highly dense interconnected layers which are sequentially laminated on each side of the core.

The 2-n-2 PCB features two sequentially laminated HDI layers and enables the stacking or staggered placement of microvias. Copper-filled stacked microvia structures are commonly used in sophisticated designs.

Structures can go well beyond a 2-n-2 PCB level for instance, a 3-n-3 PCB, 4-n-4 PCB, or even higher than that. However, the complexity and cost of production usually prevent this from happening.

The any layer HDI is another option worth considering. To allow conductors on any layer of the PCB to freely interface with the laser microvia structures, a very dense HDI arrangement is used. These structures are commonly used in CPUs, GPUS, smartphones, and other portable devices.

Benefits of HDI PCB boards

Following are some of the main benefits that HDI PCBs offer you over conventional circuit boards:

  • Smaller formfactor and reduced space requirement.

The use of microvias, buried vias, and blind vias, reduces the overall space required and allows for a more compact design.

  •  Enhanced signal integrity

An HDI PCB design enjoys a shorter signal path thanks to components being placed close together. This reduces signal attenuation translating to better signal integrity and quality.

  •  Improved Reliability

The smaller aspect ratio makes the PCB more reliable.

  •  More cost-effective

The number of layers required is less with HDI PCBs thanks to multiple sub-connections between each layer. Fewer layers can potentially reduce the manufacturing cost of the PCB.

Conclusion

Modern-day technological trends lean towards compact size and space-efficiency across all gadgets, especially smartphones and smartwatches. This has led to an increase in the demand for HDI PCB stackups since space savings are one of the main advantages of these circuit boards. Hemeixin is an industry-leading electronics manufacturer that specializes in all types of PCBs including HDI PCB stackups. If you want to learn more about our services and what we can do for you, head on over to our website now!

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