The application of HDI PCB has brought about the improvement of the portability of electronic products worldwide. HDI PCB has made it possible to produce smaller electronic devices, and with no loss of quality or functionality. In case you want to learn the HDI PCB's history, uses, designing, and implementations, please continue reading and answer your curiosity.
1. What Is HDI PCB?
HDI stands for High-Density Interconnector. Therefore, HDI PCB is described as a printed circuit board that has a higher electrical connections density per unit area when compared with a standard board. They come with better spaces and lines, small capture pads, small vias, and high electrical connections pad density compared to the traditional PCBs. HDI PCBs benefit from laser drilling engineering and require little room.
It has made it possible for the circuit boards to be as compact as you may want. Regardless of this decline, the performance of your product would remain uncompromised. Differently put, you can call every PCB with about one hundred twenty to sixty pins that are one square inch as an HDI PCB.
(It depicts a PCB with many signal routes)
2. What Are the Differences Between an Ordinary and HDI PCB?
2.1 HDI VS Standard PCB: The Differences
The following are the three major areas in which you can see variations between ordinary and HDI PCBs:
- The density of the circuit – When the designers build HDI PCBs, they often choose to cover the wires that link to the next layer. You can use micropore processing to do this. It will allow you to maximize the PCB circuit density, which can be useful for small electronic applications.
- Manufacturing technology - HDI PCBs are once again relying on advanced micropore technology, particularly in comparison to the traditional drilling procedures that standard PCBs utilize during manufacturing.
- Electrical performance and signal – HDI PCBs micropore contacts lead to a high level of interruption security, which provides safety from signal interferences. It is one reason you can improve the performance of an HDI board over a normal one.
The table in the next section further differentiates between an ordinary and HDI PCB.
2.2 Tabular Differences between HDI PCB and Standard PCB
1.Reduced number of layers
A higher number of layers
2.Higher component density in every square inch
Average Component density in every square inch
3.Small aspect ratio
Large aspect ratio
4.Operates flawlessly with low pitch packages and high pin count
Many compatibility problems with low pitch packages
5.Laser drill technology
6.Blind, buried, and micro-vias technology
No micro-vias, only through-hole, buried, and blind vias are present.
8.Smaller and lightweight boards
Heavier and cumbersome boards
(It illustrates a standard industrial PCB)
3. What Are the Advantages/Benefits of HDI PCBs?
3.1 Lightweight and Compact Sized
HDI PCBs are compact in size and lightweight, fulfilling many designer requirements, such as making smartphones as lightweight as possible. With HDI PCBs, you can fix several electronic components on a small-sized board, this too with full functionality.
3.2 Maximize Cost-Effectiveness
With HDI PCBs, you can make your every penny invested count. HDI PCBs will preserve the optimum performance of your product and ensure that you don't spend more than required on the components. In several examples, HDI PCBs allow you to pack all functions in one board rather than in several standard PCBs.
3.3 Improved Performance
The distance between adjacent electronic parts will affect your PCB's performance. Thankfully, you can reduce this gap when it comes to HDI PCBs. Further, you can also add transistors to enhance electrical performance, and at the same time, reduce HDI PCB's power consumption.
3.4 Quick Delivery Times
The PCB manufacturers can also build HDI PCBs more conveniently. It is just because creating a board that does not use a lot of components and materials takes less time. As a consequence, you will quickly get your product and can introduce it to the market as soon as possible.
4. How to Choose HDI PCB Material
4.1 HDI Stackup Overview
The design approach of an HDI PCB requires a high level of circuit density. It will not be simple because you can manage small capture vias and pads, and fine lines and spaces.
You can select from various varieties of HDI Stackups, but they usually have a laminated and mechanically drilled core, along with a plated mechanical drill. The manufacturing steps can also include forming inner layers, successive lamination, and the shaping of final through-holes and laser-drilled vias.
4.2 The Importance of Dielectric Materials
If you would like your HDI PCB to work correctly, you must choose the correct resin or dielectric material. The characteristics you want look into include temperature of the glass transition, decomposition temperature, coefficient of thermal expansion, and delamination time. You must look for materials that can function well in these areas, but be aware that this can also raise the expenses.
For instance, PDAs and mobile telephones may perform relatively well in the places mentioned above. But you need the finest available components if you plan to create a product for avionics, military applications, or high-speed telecommunications.
4.3 What Are Material Types Suitable for Your Application?
Are you planning on you using HDI PCB for your electronics project? You must choose the correct material in this situation, and the following list will make things easier:
- Ultra-low loss, high speed - if you search for HDI PCB materials for utilizing radiofrequency and microwave applications, you must consider those with a relatively low loss and excellent signal integrity.
Low loss, high speed – In this type, there's a much flatter curve between the frequency response and dielectric constant. You will get a 50 percent lower loss than you can get with materials having an average loss.
- You can also push stuff to the next level and choose an HDI PCB material that maintains exemplary signal quality and thus further reducing electric noise.
- Average loss and speed –the term 'average' is the secret, and which is why so many clients agree on using FR-4 PCB materials. These may not be appropriate for all applications, but they may be an ideal choice for some digital/analog GHz applications.
5. HDI Structures
You can typically build HDI PCBs in many respects. The following are three ways:
1.1+N+1: In this type of HDI PCB structure, printed circuit boards have only one high-density interconnection layer.
2.i+N+i: This demonstrates that in PCBs, there are two or more high-density interconnection layers. You will also need to stagger or stack together micro-vias on various layers.
3.Any layers: Every layer in this framework is an HDI layer that allows all layers to be linked. It is appropriate for complicated devices such as computer CPU chips or GPU chips on smartphones.
(It shows a microchip CPU made up of HDI PCB)
So now that you are familiar with the basics of HDI PCBs, you can grab the concepts of HDI PCBs. In our next section, explore our best tips for designing HDI PCBs.
6. HDI Design Rules and Tips
6.1 Tip No. 1 - Adopt a DFM Strategy
Our first suggestion is relatively easy and familiar. You must integrate design for manufacturing strategy (DFM) with HDI PCBs. In this strategy, the purpose is to design a product that you develop quickly and cost-effectively. You need to make sure that you are creating something that is also practically feasible.
When you design an HDI PCB that goes well beyond your PCB manufacturer's abilities, the design may be pointless. It would help if you created the HDI board by keeping in mind that it delivers all the advantages of the HDI PCB, and manufacturers can fabricate it conveniently at the very same time.
6.2 Tip No. 2 – Choose the Type of Via
Deciding the via type is a critical choice as it defines the machine and equipment that you will require in the production line. It can affect both the cost of the process and its duration. By limiting the number of layers and materials, micro-vias can decrease the production duration and expenses. You may, however, choose among various kinds of vias. These may comprise of via in pad and near pad versions.
Therefore, you must select one which costs either you or your HDI PCB manufacturer the lowest, without sacrificing on the HDI PCB's electrical performance.
6.3 Tip No. 3 – Check Availability and Size of the Components
The number of components you want to use for HDI PCBs is another aspect. Note that the primary goal of the HDI PCB is to bring down costs and surface area. You must, therefore, ensure that they are lightweight, economical, and in a small number.
How you put the components will decide trace width, hole size, and backup dimension. However, you must note the quality and reliability of these modules. Or, you may need to redesign the entire HDI PCB.
6.4 Tip No. 4 – Do Not Overcrowd Components
Although the compact design can push you to place components nearby, you should not usually do it. High-powered devices can contribute to Electromagnetic Interference (EMI), which might influence the signal integrity.
Furthermore, near pad inductances and capacitances may influence signal strength and slow down communication. Moreover, you should place all the parts so that it spreads vias symmetrically over the surface. It will also help reduce stress, which avoids any distortion in effect. It would help if you also considered the maintenance and installation stages so that you can quickly rework and solder at a later stage.
6.5 Tip No. 5 – Choose a Stackup Design
The method of PCB stacking can also evaluate any manufacturing problems during production. The number of layers in the stack configuration and the material type strongly influences the frequency of laminates and the drilling duration. Make sure anything you choose is efficient but cost-effective.
7. HDI PCB Stackup
7.1 Types of HDI PCB stack-ups
Type I: 0-N-0 – Laser Microvia
In this type of HDI PCB, the manufacturers first laminate the core and then drill it mechanically. After that, you will plate the mechanical drill and use laser technology to hit it further and form vias. Finally, the HDI PCB manufacturer will then make the through-hole. The micro vias can be on a single side of the laminated core or both of its sides.
Type II: 1-N-1 – Laser Microvia& Buried Via
Here, the '1' reflects the sequential lamination on both parts of the core. It indicates that on either side of the center, there are two HDI layers. The method is equivalent to the 0-N-0. The only difference is that you will create an internal layer after platting the mechanical drill. The HDI PCB manufacturers then laminate this inner layer with two extra layers such that a buried via made from the mechanical exercise. Finally, laser drilling technology makes more vias.
Type III: 2-N-2 with Microvia
Here, the '2' indicates two lamination layers on both sides of the core. Therefore, you might assume that there will be four layers of copper and that there are overall six total layers.
7.2 Which Type Is the Right Choice for Your PCB?
Should I Choose Type I?
The Type I does not permit buried vias; however, you can use plated through-holes (PTH) and blind vias. For the total number of layers, it is necessary to consider thin FR-4 dielectrics that may contribute to deformation in temperature extremes, which could be essential for the application of the lead-free soldering process. Furthermore, to achieve reliability, you must aim at keeping the length to hole diameter ratio less than 10 for PTH.
Can I go with HDI PCB Type II?
In this kind, you can use buried, blind vias and micro vias on a laminated core. You must also put one or maybe more layers of micro vias on the sides. You do not need to place them on both sides, but one is necessary. The professionals believe that this approach is much more appropriate for high-density boards. You can also improve the effectiveness of HDI PCB by putting many trace routing buildup layers. Limitations for type I also apply here.
Why Type III Can Be a Good Choice
The primary difference between Type II and Type III is the fact that this needs you to put two or more micro-vias on both or one sides. Besides, in a laminated core, you can also have blind, buried, and micro vias. This configuration can be perfect for high-density PCBs with multiple layers and many large BGAs with fine-tuning capabilities.
The great benefit of type III is that you can use the exterior layers for ground and power terminals. For sufficient signal routing, you can place several micro vias in the inner layers. For even higher routing density, you can stack vias, but that will also increase the cost. However, for thin dielectric FR-4 and PTHs, the limitations of type I also apply here.
7.3 Design Perfect Stackup for Your Application
7.3.1 Why Is the Design of a Layer Stackup for HDI PCBs Important?
You must design HDI Stackup layers by keeping in mind the manufacturing facilities. It means that the design must be practical, and manufacturers can produce it efficiently. It would help if you did not design it by only considering the application; you must also consider HDI PCB's reliability and usability. In industries, many HDI PCBs stack up designs are of Type III.
188.8.131.52. Designer Tips for HDI PCBs
Here are several suggestions that you can use to design an HDI PCB:
- You can choose to stack or arrange micro vias by placing them optimally against each other and other board vias.
- Use the outer layers for ground connection as it can improve EMI/EMC requirements. The inner layer will accommodate the power plane and micro vias for signal routing. It is ideal for an HDI PCB with eight layers or more.
- For an HDI PCB board with many layers, you may stack the vias. It may be more expensive but will provide you with flexibility and more signal routing efficiency.
(It shows an HDI PCB material for EMC)
7.3.2 HDI PCB--How Can Stackup Design Affect Signal Integrity?
An immature HDI PCB stack-up design will affect signal integrity if it doesn't fulfill the manufacturing specifications. There is a chance the manufacturing options are not able to implement the design requirement such as copper thickness, selected material, and trace width. So, in the end, it is all on you to again make the changes.
However, even in this case, some reliable HDI PCB manufacturers can go beyond their capabilities to find an optimal solution for their customer's HDI PCB. It could include discovering an appropriate PCB material with similar properties.
(It shows a possible trace data of HDI PCB)
7.3.3 HDI PCB--Stackup Design Standards
The manufacturers typically use three methods or standards for designing. Firstly, for standard lamination, they use through-hole vias because of better reliability and less cost. However, this approach is not famous these days due to the limited layer count.
Thus, to meet the client's requirements of more layer number, HDI PCB manufacturers are using blind and buried vias and sequential lamination. It reduces hole size and is ideal for signal routing. However, its main reason for still being unpopular is the problem with trace widths.
7.3.4 How to Improve Routing in Layer Stackup for HDI PCB
It would help determine how to place HDI PCB vias on BGA pads to improve signal routing in your design. One way could be to go for smart placement as HDI PCBs use fine pitched BGAs. Another way could be to use a dog-bone pattern, in which you place vias next to the pads.
If you choose to develop the most excellent density possible, the via-in-pad solution is prudent to use. This design can offset and partial; however, the former ensures more reliable signal routing. It is crucial as it eventually decreases manufacturing cost by reducing the layer count.
If you select the outer layer of HDI PCB for the ground plane, it will optimize the EMI shield and improve signal integrity. You can also place VCC to the nearby layers, which will reduce the number of bypass capacitors that a BGA needs. Therefore, you may also use pull-up resistors and bypass capacitors to give more room to signal routing layers. It may also minimize crosstalk and optimize return paths. For providing power in no small BGA, you must consider split planed or a dedicated voltage layer rather than a new voltage supply.
8. HDI PCB Prototype
An HDI PCB prototype is a simplified model of a manufactured HDI PCB to evaluate different designs. You can ask your HDI PCB manufacturer to develop such prototypes for testing. They also have a small layer count and size because of the high density of wires. These prototypes must have stacked, staggered, blind, and buried vias so that you could decide the best combination. Additionally, the HDI PCB prototype will assist you in selecting the vias size and highly effective aspect ratio.
(Automatic machine is testing HDI PCB prototype in the industry)
9. HDI PCB Application
HDI PCBs have a substantial impact on the medical sector. Hospitals use medical equipment usually composed of HDI PCB. For example, tiny devices such as imaging equipment, implants, and lab.
The small HDI PCBs mainly draw the automotive industry because it creates additional space within the vehicle.
9.3 Tablets and Smartphone
The smartphone, tablet, or laptop you are currently using to read this article is HDI PCB. PCB manufacturers are using HDI PCBs for developing portable and lightweight electronic products.
9.4 Wearable Technology
HDI PCBs also support products such as VR headsets, apple watch, and other wearable tech devices.
9.5 Aerospace and Military
The military is also implementing HDI PCBs for their defensive hardware and communication strategies. Further, HDI PCBs are compliant with dangerous and challenging environments that allow them to be ideal for military and aerospace industries.
10. The Future of HDI PCB
HDI PCBs are taking technologies to the next level. It is playing an essential part in electronic devices production. With its advances, this technology meets the most significant challenges. HDI PCB is a technology for you. Especially if you are looking for technology that allows you to work anywhere, anytime efficiently. Therefore, the potential of this technology is very promising as demand continues to increase and not to decline.
Phew, we know that was a lot to take in. Don't worry, you only need to understand these terms; you do not need to be an expert. You need to select a reliable HDI PCB manufacturer with a competent team of engineers. They will do your work for you. We, here at OURPCB, also manufacture HDI PCBs. We can optimize your designs and calculate tolerances that will allow you to adjust the HDI PCB designs. This, too, without influencing its fitness for your particular application.