HDI PCBs have a higher density per unit circuit than traditional PCBs. They use a combination of buried and blind vias and microvias (0.006 inches in diameter or less). A high-density board is a PCB that has one or more of the following features:

Through and buried vias
Through surface-to-surface vias
At least two layers with vias
Coreless structures with layer pairs
Passive substrate structures without electrical connections
Alternative structures to coreless structures built with layer pairs
Combination of buried and blind vias
HDI technology in printed circuit boards and other areas has been a key driver in the development of many of today’s electronic products, especially those that have seen a significant reduction in size and weight in recent years. The smaller the device, the more likely it is to use HDI technology.

The tight tolerances of HDI printed circuit boards mean you need to work with an experienced supplier. Even small defects or layout mistakes can cause serious problems. As a leading HDI printed circuit board supplier, Millennium Circuits Limited can provide top-notch boards with circuit densities far higher than traditional PCBs.

Benefits of using HDI technology
HDI technology offers a variety of advantages over other options that can improve project results. With the right design and the right supplier, using HDI boards in your product can improve the overall quality and performance of your product, as well as customer satisfaction and profits. Other benefits include:

Smaller Size and Lighter Weight: With HDI boards, you can affix more components on both sides of the bare PCB, allowing you to get more functionality in less space and expand the overall functionality of your device. HDI technology enables you to add functionality while reducing the size and weight of your product.

Improved Electrical Performance: Shorter distances between components and a higher number of transistors result in better electrical performance. These features reduce power consumption, which improves signal integrity. The smaller the size, the faster the signal travels, and the greater the reduction in overall signal loss and crossover delay.

Improved Cost-Effectiveness: With proper planning and manufacturing, HDI boards can be more cost-effective than other options because they are smaller in size and require fewer layers, which requires less raw material. For products that once required multiple traditional PCBs, you may only need one HDI board. You get more functionality and value in a smaller area and with less material.
Microvias have smaller aspect ratios
Shorter production time: Using less material (even less board) and the design efficiencies associated with HDI technology can reduce production time and shorten the time it takes to get your product to market. Components are relatively easy to place in HDI PCBs, and high electrical performance reduces the time required for testing and troubleshooting.
Enhanced reliability: Smaller aspect ratios and high-quality microvia structures can improve the reliability of your boards and products. The increased performance and reliability provided by HDI PCBs will reduce costs and improve customer satisfaction.

HDI PCB Design Considerations
The processes involved in producing HDI PCBs are generally different from other types of PCBs. Here’s what you need to know about HDI board production and some design considerations to keep in mind throughout the production process:

Sequential lamination: During the lamination process, the PCB core is bonded to the copper and prepreg layers of multi-layer PCBs by applying heat and pressure. The heat and pressure required vary from board to board. After the lamination stage is complete, the PCB manufacturer will drill the holes. Unlike other types of PCBs, HDI boards need to go through this process multiple times. These sequential laminations help prevent shifting and breaking during the drilling process.
Via-in-pad Process: The via-in-pad production process allows you to place a via on the surface of a planar pad on a PCB by plating the through hole, filling the via with one of a variety of fill types, capping it, and finally plating over it. Via-in-pad is typically a 10- to 12-step process that requires specialized equipment and skilled technicians. Via-in-pad is a smart choice for HDI PCBs because it simplifies thermal management, reduces space requirements, and provides one of the shortest capacitor bypass methods for high-frequency designs.
Via Fill Type: The via fill type should always match your specific application and PCB requirements. The via fill materials we frequently use include electrochemical plating, silver fill, copper fill, conductive epoxy, and non-conductive epoxy. The most common type of via fill is non-conductive epoxy. You need to choose a via fill that sits flush with the planar pad and can be fully soldered, just like a traditional pad. The filler must allow microvias and standard through-holes to be blind, buried, or drilled and then plated to hide them beneath SMT pads. We often use multiple drilling cycles with precise depth control to ensure that each drilling process is completed correctly. This level of control requires specialized equipment and longer development time.
Common HDI PCB Structures
HDI Structures: There are several different layout options for HDI PCBs. The most common are 1-n-1 PCBs and 2-n-2 PCBs. 1-n-1 PCBs contain a single structure of high-density interconnect layers, so it is the “simplest” form of HDI printed circuit board. It requires one continuous lamination on each side of the core. 2-n-2 PCBs have two HDI layers, allowing microvias to be staggered or stacked across layers. Complex designs often use copper-filled stacked microvia structures. Structures can reach very high XnX levels, but complexity and cost usually limit this structure. Another important option is any-layer HDI. This involves extremely dense HDI layouts so that conductors on any given layer of the PCB can freely interconnect with laser microvia structures. These designs appear in GPU and CPU chips in smartphones and other mobile devices.
Laser Drilling Technology: Any-layer HDI designs often require the use of laser drilling to create laser microvias. These drills can produce diameters up to 20 microns, which can easily cut through metal and glass to form very small but clean holes. You can use materials such as uniform glass with a lower dielectric constant to achieve even smaller holes.
LDI and Contact Imaging: Being a leading HDI printed circuit board supplier means constantly pushing the limits.KKPCB is able to provide finer lines using cutting-edge technology and cleanrooms, ensuring safe and reliable processing. For these fine details, repairs are impossible, so it must be done correctly and extremely accurately the first time. We alternate between contact imaging and LDI imaging depending on the needs of verifying your device. LDI is the preferred choice for fine lines and tiny pitches because it can verify the most demanding processes, continuously expanding our capabilities and allowing for smaller form factors.
HDI PCB Cost Considerations
Many different factors can affect the cost of an HDI board. Keep the following considerations in mind to determine your budget and ensure your PCB order is as cost-effective as possible:

Type and quantity of vias, through-holes, or micro-vias: The vias, micro-vias, or through-holes you choose for your HDI PCB will affect its cost, as will the number of these features you require. Smaller vias cost more than larger ones because they require more precision. Of course, adding more vias will also increase the price.
Stack Height and Number of Layers: The type of stack-up required will also affect the cost. A 2-n-2 high-density PCB layout is more complex than a 1-n-1, and therefore more expensive. Additional layers increase the price. You should aim for the most cost-effective and efficient number of layers.
Materials Used: You may have a number of choices for the materials your board is made of. The core material may be FR4, metal, fiberglass, or something else, depending on the application. For the surface finish, you can choose ENIG, HASL, immersion tin, immersion silver, gold, and more. ENIG is the most common material for HDI due to its flatness and ease of soldering.
Number of consecutive laminations: The number of layers and the type of via structure determine the number of consecutive laminations required. While more laminations means more processing time and higher costs, increasing the number of laminations can improve product performance and cost-effectiveness.
Stacking vs. staggering: There may also be a difference in cost between stacked and staggered setups. Stacked vias can be filled with copper, but staggered microvias cannot. Filling vias means more material and time are required to complete the project.
Cost Differences Between Stacked and Staggered Setups
Pad Size: To reduce costs, you should determine pad size early. Knowing the appropriate pad size helps you plan your design efficiently and economically.
Turnaround Time: If you request an expedited order, you may incur higher costs because additional resources are required to complete the expedited order. Sometimes, last-minute circumstances are beyond your control, but planning orders in advance can help improve cost-effectiveness. KKPCB offers fast turnaround times and quick customer service.
PCB Supplier: The partner you choose can also have a significant impact on the cost of your HDI boards. You need to choose a supplier that is competitively priced and can also deliver high-quality products efficiently to ensure cost-effectiveness. It is better to order a high-quality product once than to have to repair or replace components afterward.
HDI PCB Industries and Applications
HDI technology is a key component of many of today’s advanced technologies. The miniaturization of electronic components, including PCBs, has enabled manufacturers to produce smaller, more cost-effective devices without sacrificing performance or reliability. Here are a few industries that use HDI PCBs and how they are used:

Consumer Electronics: Computers once took up entire rooms, but now, thanks in part to HDI technology, devices as small as smartwatches are essentially miniature personal computers. You can find HDI boards in laptops, smartphones, tablets, and wearables, as well as other consumer electronics such as digital cameras and GPS devices. HDI PCBs play a vital role in making these powerful technologies accessible to everyday consumers. They are also an essential component of IoT devices in the home, including smart thermostats, refrigerators, and many other connected devices available. As these smart devices become more common, HDI boards are becoming more common as well.
Communications: In addition to smartphones and laptops, HDI PCBs are found in the devices that make these devices function, such as routers, switches, modules, and semiconductors. Whenever you use electronic communications, computerized gadgets, or devices that use radio waves, there’s a good chance you’re using an HDI board. Digital video and audio devices also often use HDI technology. These boards are found in devices used for personal communications as well as networks used by businesses.
Automotive and Aerospace: HDI PCBs enable manufacturers to fit more functionality into smaller spaces and lighter devices. This is especially useful in the automotive and aerospace industries, where less weight means more efficient operation. Like nearly everything else, cars are becoming more connected and computerized. Today’s cars have around 50 microprocessors in them, which play a role in engine control, diagnostics, safety features, and other convenience features. Many new features, such as in-car WiFi and GPS, rearview cameras, and backup sensors, rely on HDI PCBs. As automotive technology continues to advance, HDI technology is likely to play an increasingly important role.
50 microprocessors in a car
Medical devices: Advanced electronic medical devices, including certain types of equipment for monitoring, imaging, surgery, laboratory analysis, and other uses, may employ HDI boards. High-density technology improves the performance of devices and reduces their size and improves the cost efficiency of devices, potentially improving the accuracy of monitoring and medical tests.
Industrial uses: Industrial equipment is also becoming more computerized, and IoT devices are becoming more common in manufacturing, warehousing, and other industrial settings. Many advanced devices incorporate HDI technology. Today, businesses use electronic tools to track inventory and monitor equipment performance. More and more machines are equipped with smart sensors that can collect usage data and connect to the internet to communicate with other smart devices, as well as pass information to management and help optimize operations.