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Selecting the Right HDI PCB Stack-up

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Even if you're not an expert in HDI PCB design, it is clear to see how a layer stack for HDI PCB can impair the board's signal integrity. For this reason, that an HDI PCB manufacturer should prioritize the stack-up layout throughout the whole design process. Manufacturers are usually eager to assist clients in finding the best answer for their needs. Here is what you should know about HDI PCB stack-ups.

What is Meant by an HDI Stack-up?

HDI refers to the usage of buried, blind, and microvias, and any layer HDIs, to make small circuits. HDI has a number of advantages over typical multilayer designs, including the clear advantage of compressing the same board capability into a compact size. These include lower power consumption, improved signal integrity, fewer layers, and better electrical performance.

The notion that minimizing signal paths across your board boosts signal integrity and electrical performance automatically is the basis of these advantages, assuming you can appropriately account for EMI/EMC constraints.

When determining the type of stack-up your HDI PCB requires, you should be aware of the following points:

  • Microvias are very small laser-drilled vias having a 1:1 aspect ratio.
  • Buried vias interconnect one or more inner layers of a circuit without making any contact with the board's outside layers.
  • Without piercing the entire board, blind vias link an outside layer to at least one internal layer.
  • The use of stacked copper-filled microvias to link several layers of a PCB is referred to as any layer HDI.

There are technically six types of stack-ups for HDI PCBs, but types IV, V, and VI are usually accompanied by design and price challenges, which is why we will only focus on the first three in this article.

Type I

The board's structure will feature a laminated core along with one or multiple microvia layers on both sides or either. The type I stack-up standard prohibits the use of buried vias; however, blind and plated through-hole or vias are permitted.

When it comes to the overall layer count, keep in mind that using thinner FR-4 dielectrics may result in delamination at a high temperature, which could be required for using the lead-free soldering approach. Furthermore, the length-to-hole-diameter ratio is important for durability, and it should normally be kept below 10 for plated through-holes.

Type II

Type II features a laminated core. On a laminated core, an HDI PCB manufacturer can combine buried and blind vias, as well as microvias. One or more micro vias layers must also be placed on at least one side, if not both. According to the buried vias, manufacturers may stack or stagger them or sway microvias from the others.

Experts recommend this strategy for an HDI PCB, but you should be aware of the same limits as with the type I procedure. Microvias can only be placed on exterior layers, which limits the applications that can use them. It would also be helpful to remember that many trace routing buildup levels are recommended by experts to boost effectiveness.

Type III

The main distinction between type II and type III is that this technique necessitates the use of two or more microvias layers on the sidewalls. The laminated core will have buried and blind vias, along with microvias.

The ability to use the exterior layers for energy and the ground plane is a significant benefit of type III. This can be accomplished by including microvias in the inner layers and assuring that there are enough layers for signal routing. Stacked vias can increase the routing density but will also increase the cost of production.

The type III stack-up is most suitable for an HDI PCB with multiple layers and several large BGAs with fine-pitch features. Most HDI PCB manufacturers prefer using a Type III stack-up design, which is in line with industry norms. This method enables the use of many micro-via layers on the board's sides. It is not necessary to position them on both sides of the printed circuit board, but it is an alternative that is ideal for dense boards.

Why is the HDI PCB Stack-up an Important Design Feature?

If you've ever purchased printed circuit boards, you're aware that the designing process is just as vital as the fabrication. All methods must consider the board's end-use, usability, and dependability. The characteristics, performance, and dependability of your HDI printed circuit board is all affected by the HDI PCB stack-up type.

It is important to emphasize, however, that the designer should consider production capabilities. To put it another way, the design should be not only be ideal for the purpose but also feasible to produce. A handful of PCB manufacturers specialize in HDI PCB manufacture and assembly, and they can fit high layer counts with thin, compact traces. This crucial task will initially improve profitability in your manufacturing process while also ensuring a higher yield.

Last Words

Layer count, component count, and net count are the restrictive parameters dictating routing density in HDI designs, which are being pushed to become progressively smaller. Hence, you should give importance to your HDI PCB stack-up if you're building advanced items that push boundaries of element and routing density.

Manufacturing PCBs has evolved into a systematic set of activities requiring particular expertise and equipment. HDI PCB design necessitates the assistance of an HDI PCB manufacturer who is familiar with the complexities of this cutting-edge technology and can advise you on the right HDI PCB stack-up for your product.

As one of the first companies to supply HDI PCBs in bulk to customers, Hemeixin's expertise and commitment to providing a holistic service to our customers contribute to resolving early design issues, shortening the production process, and delivering a high-quality, cost-effective product. Visit this link to get an online quote.

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