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
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 optimise the size of the PCB while ensuring maximum performance and reliability.
1.1. 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 components on both sides.
• It has a relatively low power consumption, which makes it suitable for applications that use batteries, such as smartphones and tablets.
• It has a strong and durable design, and it slows down thermal degradation, which also contributes to durability.
An HDI Stackup type can greatly affect the specifics, performance, and reliability of your printed circuit board. That is why we will discuss different types and how to choose the right one for your PCB.
2、HDI PCB Stackup Types
Image 2: A multilayer PCB with components and microcontroller
If we are discussing PCB Stackups, we should mention that the manufacturers have three approaches that they use during the assembly process.
• Regular lamination, which involves using plated through holes or vias
• Using Microvias for lamination buildup
• Using bling, plated through, and buried vias for sequential lamination
2.1. Institute of Printed Circuits Standards
IPC (Institute of Printed Circuits) has adopted a standard that recommends manufacturers to use one of six different types of Stackups for high-density interconnect boards.
These types have categories from I to VI (marked with Roman numbers). However, the categories marked with IV or higher might not be a great 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 certain 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?
Image 3: A printed circuit board with multiple layers
Due to the price and design challenges, we will immediately eliminate an 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. Should I Choose Type I?
If you take a look at the structure of the board, you will notice a laminated core with one or more Microvias 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 ration under 10 for the plated through hole.
3.2. HDI PCB Type II Details
In this type, you can use buried and blind vias, as well as Microvias on a laminated core. You also need to place one or more Microvias layers on the sides. You do not have to put them on both sides, but at least one is mandatory. Manufacturers some time go with stacking or staggering them depending on the buried vias, or they can stagger Microvias 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 with type I approach.
Now, you can only place Microvias on outside layers, which implies certain limitations for some applications. You should also keep 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 you to place two or more Microvias layers on the sides (you do not have to place them on both sides). Apart from that, you also have buried and blind vias, and Microvias on a laminated core.
The configuration of this Stackup can be a great choice for high-density PCBs that have 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 big advantage of type III is that you can use the outside layers for power and ground plane. You can achieve that by placing Microvias in the inner layers, which ensures that there are 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
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 when it comes to manufacturing an HDI board that has 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 key thing to keep in mind is spacing, which is why the PIN spacing for standard components should be at least 20mil. Additionally, you should keep at least 40mil between standard PIN & SOP and other components. Finally, the distance between PIN and BGA, and other components should be at least 80mil.
Another important tip to stick to is that you should keep signals with high power as far away as possible from other signals.
As for the tracking process, it may be wise to include a solid isolation effect for the bottom and top layer components. That way, you can decrease inner layer signal crosstalk. If your primary priority is signal quality, you can even consider drilling blind holes directly on the pad.
5、Why Choose OurPCB for Your Printed Circuit Boards
Image 5: A CNC machine used for PCB processing
If you need printed circuit board to use with your product, you should work with a reliable manufacturer that knows all the tricks of the trade.
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 when it comes to 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 that have years of experience in manufacturing PCBs.
Additionally, they have all the necessary qualifications and skills to meet any demand of the clients.
• Quick quote and delivery times – you can easily place an order via the company’s website. You will receive a formal quote in the shortest possible timeframe. Upon finalising your order, the experts will ensure to complete and deliver the boards as soon as possible.
• Reliable support – in case you have any PCB-related question, 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.
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 to determine which PCB is the best choice for you and complete your order quickly.