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All You Should Know about HDI PCB Design Guidelines

Technology is evolving, and the need to pack more capabilities into small packages is also increasing. The PCBs are devised with the help of HDI, or High-Density Interconnect techniques, and are smaller in size. It’s mainly because more components are packed within a smaller space.

In an HDI PCB Design, micro, blind and buried vias, along with thin traces and vias pads, are packed together within a smaller area. With the help of HDI PCB design, you can easily build powerful HDI boards.

The term HDI PCB came to light when the high-density interconnect, or HDI technology printing of circuit designs and fabrication began in 1980. This was when the researchers began investigating various ways to lessen the size of the vias in PCBs.

The first-ever sequential circuit boards appeared way back in 1984. Since then, many fine-pitch components manufacturers and designers have looked for ways to pack many more functions within a single printed circuit board and a chip.

These days, the HDI PCD design and fabrication have been codified in IPC-6016, IPC-2315, IPC-4104, and IPC-2226 standards.

HDI PCB: A Brief Description

HDI Pcb structure
HDI Pcb structure

Higher-Density Interconnect is a printed circuit board that contains a higher wiring density when opposed to a conventional board known as the HDI PCB. The HDI PCBs carry finer lines and spaces, along with high connection pad density, capture pads, and minor vias.

These circuit boards are helpful in lessening the equipment’s size and weight and magnifying performance. The HDI PCBs are a much better option for their expensive laminated HDI boards and high layer count.

Apart from its electrical requirements for high-speed signal integrity, these HDI boards or circuit boards should come with various features, which are:

  • Lessening duplicative radiation
  • Impedance control
  • High-frequency transmission power
  • Many more

Moreover, the HDI board or the printed circuit board must be improved within the density because of the collections and miniaturization of the electrical parts. Besides the outcome from the assembly procedures of leadless, direct chip bonding, and the fine pitch package, the HDI boards or the circuit boards are featured with higher density.

You will also come across various benefits of higher density interconnect or HDI technology, such as:

The HDI board or the printed circuit board also serves as the main part of laptop computers, mobile devices, and personal computers. At present, the HDI PCBs are mainly used in user-end products, such as game consoles and MP3. The high-density interconnect, or HDI PCBs, also take advantage of all the advanced technologies.

These technologies exist to amplify the functionality of the circuit boards by a little or similar amount of space. The development of this printed circuit board technology is motivated by the semiconductor packages and tinniest parts, which assist all the top-notch characteristics in innovative products, such as touch screen tabs.

Challenges to Overcome When Planning HDI Board Design

Second-order HDI PCB Design
Second-order HDI PCB Design

When you have made the plan to design the HDI boards or high-density interconnect circuit boards, there are some HDI PCB manufacturing and design challenges that you have to overcome. Here is a list of challenges you will encounter when designing the HDI PCBs:

  • Plenty of trace routes are needed for the HDI Board design
  • Long trace routes will produce longer signal flight times
  • Tighter space and smaller components are needed for designing these circuit boards
  • A massive number of elements on both sides of the HDI PCBs stack up
  • Limited higher density interconnect or HDI board workplace area

When you have the right set of routing tools and layout created on a design engine, which is completely rules-driven, it will enable you to violate the HDI PCBs’ design rules. Doing so will allow you to create powerful and exceptional high-density interconnect PCB designs effectively.

If you work with fine pitch components and high PCB routing density will become easy when you use the HDI PCB technology or software, which is created for all the HDI printed circuit boards design. With this software, you can plan the HDI PCB manufacturing process and design the HDI printed circuit boards without hassle or problems.

Discrepancy Between HDI PCB Designing and Manufacturing

When it comes to the HDI manufacturing process differs greatly when compared to the traditional PCB manufacturing process in important yet simple ways. The main point about this board technology is that the prevaricator restriction will curb the design freedom and set limits on how the printed circuit boards can get routed.

The usage of smaller components, more or fewer layers, small vias, and thinner traces can easily be adjusted in the design tools or software. But adapting the DFM or Design for Manufacturing needs will allow you to take full advantage of the mechanization in the design software.

But the exact DFM needs will depend heavily on the HDI manufacturing process and also the materials which are used for building the printed circuit boards. Apart from that, the DFM needs also become pretty crucial when you consider the dependability needs.

During the time for material selection for designing the printed circuit boards, here are some of the questions that need to be answered:

  • Will the dielectric utilize chemistry consistent with the existing chemistry utilized by the substrate material?
  • Will the dielectric carry plated copper adhesion? [Many OEM or original equipment manufacturers want 6lb./in. Per 1 oz. of copper]
  • Can the dielectric offer reliable and adequate dielectric space between the inner layers or outer layers?
  • Does it have the ability to meet all the thermal requirements?
  • Can the dielectric offer a high Tg for rework and wire bonding?
  • Is it able to survive the thermal shock with numerous SBU layers [These are thermal cycles, solder floats, and numerous reflows]

In the HDI PCB substrates, 9 dielectric materials are used. IPC slash sheets, such as the IPC-4104A and IPC-4101B, are known to cover many of these materials. But some of them are not yet specified by the IPC standards. All these 9 materials are:

  • Thermoplastics
  • Photosensitive Liquid Dielectrics
  • Conventional FR-4 prepregs and cores
  • Polyimide Flexible Film
  • Thermally Cured Liquid Dielectric
  • Thermally Cured Dry Films
  • New Spread Glass Laser Drilling or Laser Drillable Prepregs
  • RCC or Resin Coated Copper Foil, both Reinforced and Dual Layers
  • Resin-coated copper (RCC) foil, dual-layer and reinforced

When it comes to the HDI PCB printed circuit boards, the design procedure is quick, and it’s all thanks to the advanced features of the software. Also, the routing efficiencies for the HDI PCB are completely dependent on the PCB stackup, design rules, via architecture, electrical performance, BGA components or fanout, and parts placement.

Also, the most crucial part when planning the HDI layout is to consider the stacked vias size, the trace widths, and the escape or placing routing of the BGA elements. Be sure to check the HDI printed circuit board house so that you can adequately determine the fabric procedures of the HDI PCB design manufacturing work.

You also have to determine the limits of the fabrication procedure because it will influence the feature sizes, which can place within the layout. According to experts from the PCB industry, the ball pitch on the BGA elements can determine the size of the via that you have to use. This can help determine the HDI manufacturing process needed to make the multilayer boards.

One of the central features of the HDI PCB is the micro vias, which you have to design precisely to adjust the routing density between the layer pairs.

HDI PCB Manufacturing and Designing Process: An Overview

HDI PCB Board Laminate Structure-Blind and Buried vias-3
HDI PCB Board Laminate Structure-Blind and Buried vias-3

There are several steps under the PCB manufacturing work, but the HDI PCB design utilizes several specific steps that are not utilized in other board designs. The HDI process for the board design method begins just like all the other procedures. These steps are

  • Step 1: Determine the outer/inner layer count needed to route all the signal layers by utilizing the direction and interface counter from the biggest IC found on the board. Otherwise, you can also utilize the biggest BGA element available on the board.
  • Step 2: Get in touch with the fabrication house to get all the dielectric information and choose all the materials to make the PCB stackup.
  • Step 3: According to the layer thickness and counter, you need to decide on the via style, which will be utilized for the route signals right through the inner layers.
  • Step 4: You need to conduct a reliability assessment to identify that all the materials do not stress the high-density interconnection during operation and assembly processing.
  • Step 5: Based on the fabricator’s dependability needs [trace width, clearances, teardrops, etc.] and capabilities, you need to determine the design rules. Doing so can ensure reliable assembly and manufacturing.

The stackup determination and creation of the designing rules are the main points because they can determine the power to route the reliability and the board of the end product. When all these points get completed, an HDI PCB designer will implement all their fabricator’s reliability and DFM needs.

This will be done according to the HDI PCB designing rules of the ECAD software. It’s crucial to get this done at the front end because it will aid in ensuring the board design is manufacturable, routable, and reliable at the same time.

Various Types of Via Found in the HDI PCB Designing Work

Several types of via styles are utilized in the high-density interconnector or HDI PCB routing and layout. These are stacked visas, staggered vias, and blind and buried vias. All these via styles carry a low aspect ratio, below 1, even when many manufacturers claim that the aspect ratio is 2, including for the stacked micro-vias.

Conventional buried vias are found right in the middle of the PCB stackup and offer a connection through the thicker layer. This particular inner layer buried via might have a bigger aspect ratio because it will be drilled through the mechanical drilling process.

When the dielectric thicknesses and the layer count have been decided, the HDI PCB designer can create the vias against the aspect ratio limits effectively. Obeying all the aspect ratio limits on the microvias is essential to reliability. This is because these boards go through the reflow. Otherwise, they are deployed within a setting with repeated mechanical cycling or thermal shocks.

The Sequential Buildup: Things to Know!

A sequential lamination process creates a high-density interconnection or HDI stackup construction in a layer-by-layer style. This particular procedure is used for all multilayer PCBs, and it’s pretty crucial for HDI or high-density interconnection. Because of the high density, thin dielectrics are assembled in separate layers surrounding the viscous core.

Due to such reasons, the lamination takes place in several steps to construct the stackup, known as the sequential lamination process. Now, let’s check out all the steps of this particular process.

  • Photoresist Direction and Residue: This is utilized for defining all those areas that need to be engraved that will leave back a dent of conductors on the laminate.
  • Cleaning and Engraving: According to the current electronics industry, the etchant is a ferric chloride solution. Once the etching work is completed, you can reclaim the remaining photoresist and clean up the consequential conductor design.
  • Via drilling and formation: All the vias have to be defined through laser drilling or mechanical drilling, and for higher via thickness, you can chemically eliminate the via holes.
  • The Via Metallization: When all the vias have been defined properly, they get metalized to create a conductive and continuous interconnect.
  • The Buildup: Both the top and bottom layers are stacked up within the multiple lamination cycles to construct the stack right before the exterior layer processing.

HDI PCB: Taking a Look at Its Benefits!

hdi technology in pcb
hdi technology in pcb

The demand for HDI PCBs is extremely high in this modern era, but there are also some unique benefits that you must know.

1. Having Tighter Designs

Due to their high-density nature, the PCBs can take up less space. HDI features, such as the buried and blind vias [these features can cut down on the space, which is utilized for linking between the PCB layers], offers a compact construction. In return, it makes the circuit boards a lot more versatile.

2. Light-Weight Material

Common PCBs utilize a diverse range of materials. But on certain occasions, it uses a mixture of aluminum, fiberglass, copper, and various other metals, which can be bulky. But the HDI PCBs can be cooler and lightweight at the same time.

When you check out a list of materials used by HDI, you will not just find the specifics but also learn how much every material is utilized. These materials can offer excellent performance without making them too heavy or overheating the PCBs.

3. Higher Reliability

The particular designs of the HDI PCBs make them highly reliable so that the connections do not get compromised. Besides that, the stackedup vias’ implementation shields these multilayer PCB boards from various environmental conditions.

4. Sharper Signal Integrity

This is the most vital because the PCBs are pretty compact, so the signals do not have much distance to travel during the transmission work. This clearly shows the difference when compared with other PCBs, but it will lead to a much sharper performance for all those who are executive creative projects.

5. Lessens the Heat Transfer

When it comes to thermal management in HDI PCB, the heat transfer is lessened dramatically. It’s mainly because there is not much distance for the heat to travel right before it can easily escape the HDI PCB. Moreover, HDI PCBs also go through less stress because of the thermal expansion, extending their life.

6. Manage the Conductivity

The laser drilled vias contain a lot of non-conductive or conductive materials, which promote the transmission work between the component lead, relying heavily on the board design. It also improves the functionality of the “via-in-pad,” and blind vias enable all the components to get closer to each other.

When transmission range from one element to another gets lessened, it reduces the crossing delays and transmission times significantly and increases the signal strength.

7. It has a Compact Design

The mixture of the micro, buried, and blind vias can easily reduce the board space needed, leading to a compact design.

Checking Out the Various Applications of HDI PCBs

You will be surprised to know that the HDI PCB has numerous applications under its belt. Are you interested to know which are they? Let’s find out through this section.

1. Healthcare

Even though the healthcare sector is growing at a rapid pace, HDI PCB is also making a massive impact on this industry. All the medical devices are completely HDI, and it’s mainly because they fit perfectly into all the smaller devices, such as imaging and laboratory equipment and implants.

Medical equipment plays a vital part I n providing life support and diagnosing various diseases. Some examples are monitoring and diagnostic facilities and pacemakers. Besides that, devices like small cameras are used for checking the interior parts of patients.

This can help in identifying the problem, and doctors can establish the correct diagnosis. Furthermore, even though the cameras are becoming smaller but the picture quality is not getting compromised. All these advancements have been made possible through HDI technology.

Cameras that should be inserted through the open ends have decreased in size but offers an excellent picture quality. Now, it has become much easier to get a colonoscopy and will not hurt the patient during the process. With the help of PCBs, providing medical treatment and services has become a lot easier.

2. Tablets and Smartphones

In today’s era, all smartphones come with the Every Layer Interconnection or ELIC and HDI PCBs construction. This technology is completely responsible for making smaller and thinner portable electronic gadgets. These devices are not just useful, but you can also carry them anywhere you go.

3. Automotive

Vehicle or car manufacturers have become attracted to all the small-sized PCBs. It’s mainly because they can easily save up a lot of space within a vehicle. Universally popular vehicle brands like Tesla have launched the first-ever futuristic vehicles.

Here, the main focus of vehicle makers is to provide a high-quality and excellent driving experience by integrating electronic devices. These days, vehicles contain front and back cameras, in-built phone systems, Wi-Fi, music systems, maps, and even television.

All these features will make the whole car driving experience comfortable and smooth at the same time.

4. Aerospace and Military

Just like all the other industries, the military and aerospace sectors have also started to use this technology. HDI has been completely incorporated into the communication devices of the military. It is also used in various other equipment, such as the defense system and missiles.

Moreover, experts say that the HDI PCB technology is much more suited for extreme hazardous and also environmental conditions. Due to such reasons, this particular technology has become ideal for all military and aerospace applications.

5. The Wearable Technology

When it comes to wearable technology, one company that comes into everyone’s head is Apple. The introduction of wearable watches and other devices like VR devices has made HDI become one of the prime stakeholders within the consumer market.

In this digital realm, wearable technologies have gained a lot of popularity among the younger generation. It’s mainly because of its outstanding functionalities. Through these wearable devices, you can call, send a message, set up a timer, and even send emails without worries.

Ending Note

The PCBs have completely revolutionized the electronic sector greatly. They are utilized in various electronic devices or gadgets, such as smartphones, tablets, desktop computers, laptops, and so on. The demand for PCB is pretty high and also appears a lot promising.

It’s mainly because they are used in numerous industries, and the HDI PCBs have also received momentum in the past several years because of their versatility. Currently, the 10-layer HDI is the main driver in today’s market. With the help of the HDI PCB designing process, professional manufacturers and designers can easily make smaller devices or products.

These devices will be packed with enhanced signal integrity and will enable all the electronics to fit perfectly anywhere possible. In this post, you will learn a lot more about HDI PCBs so that you can know their importance, benefits, and the various sectors they are utilized in.




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