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HDI PCB – Which Stackup Type is Right for Your PCB

Do you believe that an HDI printed circuit board is the right choice for your product? In that case, you need to know more about HDI PCB Stackup methods.

The selected Stackup method can determine the reliability and performance of a printed circuit board. That is why this article will provide valuable information regarding high-density PCB Stackups and how to choose the right one for your application. Don't hesitate to start reading to improve your knowledge about the topic!


1、HDI PCB--Basic Overview



A printed circuit board with electric components

Image 1: A printed circuit board with electric components


The abbreviation HDI PCB might not mean a lot to you. However, you will understand better if we tell you that we are talking about high-density interconnect printed circuit boards.

HDI technology is becoming more popular due to its particular specifics. The main idea of using an HDI board is to optimize the size of the PCB while ensuring maximum performance and reliability.


1.1. HDI PCB--What Are the Benefits of Using HDI Technology?



Here is a brief overview of why you should consider using this approach:

• You can keep the board small and light while adding more components to it. The main reason for this is that high-density boards allow you to place pieces on both sides.

• It has a relatively low power consumption, making it suitable for applications that use batteries, such as smartphones and tablets.

• It has a durable and robust design, and it slows down thermal degradation, which also contributes to durability.

An HDI Stackup type can significantly affect your printed circuit board's specifics, performance, and reliability. That is why we will discuss different types and how to choose the right one for your PCB.


2、HDI PCB Stackup Types



A multilayer PCB with components and microcontroller

Image 2: A multilayer PCB with components and microcontroller


If we discuss PCB Stackups, we should mention that the manufacturers have three approaches during the assembly process.

These include:

Regular lamination, which involves using plated through-holes or vias

Using Micro vias for lamination buildup

Using bling plated through and buried vias for sequential lamination




Institute of Printed Circuits Standards



IPC (Institute of Printed Circuits) has adopted a standard that recommends manufacturers use one of six different Stackups for high-density interconnect boards.

These types have categories from I to VI (marked with Roman numbers). However, the classes marked with IV or higher might not be an excellent choice for HDI PCB. One of the reasons is the production cost, which makes it unsuitable for mass production. On top of that, there are specific design and assembly challenges for which the manufacturers still haven't found the right solution.


3、Which Type Is the Right Choice for Your PCB?



A printed circuit board with multiple layers

Image 3: A printed circuit board with multiple layers


Due to the price and design challenges, we will immediately eliminate HDI PCB Stackup types IV, V, and VI. That leaves us with three choices for your application, and here is what you should know about each of the types.


3.1. HDI PCB--Should I Choose Type I?



If you look at the board's structure, you will notice a laminated core with one or more Micro vias layers. These layers can be on both sides, but they can also be kept on a single side.

The Type I standard doesn't allow you to use buried vias, but you are welcome to apply bling and PTH vias.

As for the total layer number, you should consider that going with FR-4 dielectrics that are thin may lead to delamination under extreme temperatures, which may be needed to apply the lead-free method of soldering.

Additionally, the ratio between length and hole diameter may be crucial for reliability, and you should always aim to keep that ratio under 10 for the plated through-hole.


3.2. HDI PCB Type II Details



In this type, you can use buried and blind vias and Micro vias on a laminated core. You also need to place one or more Micro vias layers on the sides. You do not have to put them on both sides, but at least one is mandatory. Manufacturers sometimes go with stacking or staggering them depending on the buried vias, or they can sway Micro vias from others.

The experts consider that this method is far more suitable for high-density boards, but you should keep in mind the same limitations as the type I approach.

You can only place Micro vias on outside layers, which implies certain limitations for some applications. It would help if you also kept in mind that the experts recommend placing multiple trace routing buildup layers to improve effectiveness.


3.3. Why Type III Can Be a Good Choice



The crucial difference between type II and III is that this approach requires placing two or more Micro vias layers on the sides (you do not have to put them on both sides). Apart from that, you also have buried and blind vias and Micro vias on a laminated core.

The configuration of this Stackup can be an excellent choice for high-density PCBs with multiple layers and use several big BGAs that have fine-pitch features. As for FR-4 thin dielectrics and PTH holes, the same limitations apply.

The significant advantage of type III is using the outside layers for power and the ground plane. You can achieve that by placing Micro vias in the inner layers, ensuring sufficient layers, the manufacturers can use for signal routing.

If you are willing to increase the cost, you may also use stacked vias for great routing density.


4、Other Tips to Successfully Design HDI PCBs



PCB layout routing design process

Image 4: PCB layout routing design process


If we are discussing the process of assembling a PCB, there are some things you should keep in mind. For example, the process flow for manufacturing an HDI board with four layers is not that different compared to assembling a standard board.

You start with mechanical drilling and then move on to through and blind holes. The process may be different if the HDI board uses six layers with two stacking.

Another crucial thing to consider is the layout of the components on the board. It is not easy to design a high-density board because you should maintain solderability, installability, and maintainability.

The critical thing to keep in mind is spacing, so the PIN spacing for standard components should be at least 20mil. Additionally, it would help if you kept at least 40mil between standard PIN & SOP and other features. Finally, the distance between PIN and BGA and further details should be at least 80mil.

Another essential tip to stick to is keeping signals with high power as far away as possible from other signs.

As for the tracking, the process may be wise to include a definite isolation effect for the bottom and top layer components. That way, you can decrease the inner layer signal crosstalk. If your primary priority is signal quality, you can even consider drilling blind holes directly on the pad.


5、HDI PCB--Why Choose OurPCB for Your Printed Circuit Boards



A CNC machine used for PCB processing

Image 5: A CNC machine used for PCB processing


If you need a printed circuit board to use with your product, you should work with a reliable manufacturer that knows all the trade tricks.

OurPCB was established in 2005, which means that the company has been around for over a decade. Over that time, they became an industry leader in manufacturing reliable PCBs that will deliver consistent and impressive performance.

Here are some of the advantages of OurPCB:

• Experienced and knowledgeable staff – the company employs a team of experts with years of experience in manufacturing PCBs.
Additionally, they have all the necessary qualifications and skills to meet any demands of the clients.

• Quick quote and delivery times – you can easily place an order via the company's website. You will receive a formal quotation in the shortest possible timeframe. Upon finalizing your order, the experts will complete and deliver the boards as soon as possible.

• Reliable support – in case you have any PCB-related questions, the company is at your service.

Finally, the manufacturing capabilities of OurPCB are impressive. You can order boards with up to 32 layers and choose the desired specifications depending on your needs.


6、HDI PCB--Conclusion



We hope that you now know all the HDI PCB Stackup details. That should help you when you are planning a suitable board for your next project. If you want to maintain maximum reliability and performance, you should have a premium manufacturer in your corner. A company like OurPCB can help you determine which PCB is the best choice for you and quickly complete your order.