HDI PCB A Complete Guide for Beginners

Today, you might come across different PCB manufacturers including HDI PCB manufacturer, SMT PCB Assembly, Aluminum PCB Manufacturer and PCB Manufacturer that develops every type of PCB. Since it is impossible to avoid incorporating PCBs into your electronics, thus it is a good idea to learn about its basics.

If you know the basics of the Printed Circuit boards, it will allow you to choose a good manufacturer. After all, you would not like to rely on manufacture that does not offer quality and high production rates.

To ensure that you tend to get the maximum out of your Printed Circuit Board, you need to know about different designing and production techniques. We would recommend that you always use modern and sophisticated techniques to produce and assemble your PCBs. In the course of this article, we are going to provide you complete detail on a modern and up to date HDI boards.


Table of Content

  • What is HDI PCB?
  • HDI Printed Circuit Board Vs Conventional Printed Circuit Board
  • Advantages of HDI Printed Circuit Boards
  • Why use HDI Technology?
  • Summary


What is HDI PCB?

High-Density Interconnector Printed Circuit Board is a circuit board with higher wiring density in comparison to the traditional boards.  The boards have been around for 20 years now, however, they did not make big among the manufacturer until recently.

HDI Printed Circuit boards are a sophisticated form of PCBs, thus they come with finer lines, spaces minor vias and higher connection pad density. These boards are the consumer’s first choice, especially when they want to enhance electrical performance while reducing the equipment size and weight. If the objective is to acquire costly laminated and high-layer count boards, then we firmly believe that HDI is a perfect choice.

The board has the ability to meet s the electrical needs for high-speed signals. It incorporates several features including decreases redundant radiation, impedance control, high-frequency transmission capability among others. The board is high density mainly due to the array and miniaturization of the electronic parts.

The basic idea of an HDI Printed Circuit Board is to pack as many components as possible on the board to ensure high performance.


HDI Printed Circuit Board Vs Conventional Printed Circuit Board


For starter, you need to learn about the major differences between the conventional Printed Circuit Board and the HDI Printed Circuit Board. After having the basic identifying of their difference, you shall focus on the three main keys to designing an effective HDI Printed Circuit Board.

An HDI board is different from the conventional board in many ways. However, there are three main differences and we have listed them below.


Circuit Density


Circuit Density is extremely useful for small-sized electronics. The PCB manufacturers are able to come up with an HDI design that allows them to hide the wiring connecting the next layer. In order to hide the wiring, they incorporate a sophisticated form of technology, Micropore Technology.

The technology enhances the overall appeal of the HDI boards, thus making them the best choice for consumers offering small size, yet advanced electronics.


Construction Technology


Unlike the traditional Printed Circuit Boards that require drilling, HDI boards use Micropore technology. The old PCBs were difficult to improve due to the aperture size was not less than 0.15mm and outdated drilling tools. On the contrary, HDI boards incorporate laser drilling technology. It is possible to have an aperture that ranges from 0.076 to 0.152 mm along with a width of 0.076 to 0.10mm.

This drastic decrease in the aperture range and the width size makes it possible to decrease pad size significantly. Thus, allowing the incorporation of more components in the same unit area.


Electrical Signal and Performance


Of course, with increased density, and a number of components the board is bound to perform better. The micropore connections provide high-level protection against all sorts of interference.  The lack of interference makes it possible for the HDI board to perform better in comparison to the conventional boards.


Three main keys to designing an effective HDI Printed Circuit Board


Whether you are an Aluminum PCB manufacturer, SMT PCB assembly manufacturer or a generic Printed Circuit Board manufacturer, you will have to consider certain things to create PCBs. Below are some important factors of an HDI PCB.




The first thing that you need to focus on is the Aperture ratio. It is very important for a thorough hole, buried and blindhole design PCBs. In the case of the conventional PCBs, the aperture hole is greater than 0.15 mm. The drilling equipment does not allow having a smaller hole. The board with 0.15 mm should have 8:1 aperture ratio.

In some cases, the aperture ratio can be 12:1 or above. However, this happens only for some special cases. You will not have to face these limitations in the HDI Printed Circuit Board case. Since HDI boards use a laser hole, thus it is possible to decrease their size. These holes can range can be of 3 to 6 mil. Most manufacturers use the 4 mil hole while having 1:1 aperture ratio.

The thickness of the board has a direct impact on the aperture. So, if you use a thick board, you will have a smaller aperture. Using laser hole technology makes it difficult for the anything especially the chemical solution to penetrate during the plating process. The solution is not able to in the drilling hole.


There are different categories of HDI PCB layer stack-up. These categorizes are basically defined by the way the layers are placed with blind holes. Below are some of the basic categories:


Stacked and Resin 2-HDI- Filled


See the figure below for hole information. 1-8 through-hole, 3.6 buried hole, 7-6 resin and stacked blind hole, 8-7 stacked blind hole, 2-3 resin and stacked blind hole, 1-2 stacked blind hole.


1-HDI- Buried Holes

If you see the picture below, you will notice that 8-5 are blind hole, 1-2 blind hole, 1-6 are through-hole and 2-5 are buried hole.


Non-resin Filled Stacked 2-HDI1-8 through

See the Figure below for the hole details. 1-8 through-hole, 3-6 buried hole,7-6 stacked blind hole, 8-7 stacked blind hole, 2-3 stacked blind hole, 1-2 stacked blind hole.


Non-Stacked 2- HDI- Buried Holes

Have a look at the picture below, the holes are as follows: 1-8 through-hole, 3.6 buried hole, 7-6 non-stacked blind hole, 8-7 non-stacked blind hole, 2-3 non-stacked blind hole and 1-2 non-stacked blind hole.


Process Flow

We will discuss the process flow of 6-layer HDI having 2 stacking and 4-layer HDI with one stacking. Please see the examples below.


6 Layer HDI with Two Stacking


6 layer HDI with 2 stacking has the same process flow as any ordinary Printed Circuit Board. However, the sequences of drilling holes are different in HDI. The drilling in HDI start with mechanical drilling of buried holes on 3-4 layer, then the holes are buried on 2-5 layer. After this, the manufacturer drill buried holes in the layer 5-4 and 2-3 layers.

After all the above-buried holes, we have the through holes on 1-6 layers. Finally, there is the drilling of blind hole 1-2 and then 6-5.
For buried holeHDI PCB manufacturer uses laser technology. The high temperature of the laser drilling cauterizes the hole wall. This then leads to the generation of the coke button. The hole wall tends to absorb this coke button effectively.

A good idea is to implement the pre-operation before you go on with the implementation of electroplating. The removal of the coke button can be a challenging task due to the small aperture of the blind holes. So, manufacturers tend to use filling and plating for the blind holes. This may generate effective results, but the downside is a significant increase in the overall cost.


Although it seems a sophisticated form of Printed Circuit boards, but we do not recommend this except when really needed. The reason being, the 6-layer HDI having two stacking are in need of counterpoints. These counterpoints lead to increase scrap rate.


4-Layer HDI with One Stacking

Like the 6-layer HDI, the process flow of 4-Layer HDI with One stacking is similar to the conventional Printed Circuit board. However, they have different drilling hole sequences. For the 4 Layer HDI with one Stacking, the manufacturer starts with mechanical drilling o the buried holes of 2-3 layers. They then move to the drilling of through-holes of 1-4 layer, 1-2 blind hole and blind holes on 4-3 layer.

After this, comes the direct drilling of holes on either 4-3 layer or 1-3 layers. The key point to remember here is that drilling is conducted without 2-3 conversion. This leads to difficulties in the fabrication process as well as a drastic increase in scrape rate and the production cost.

To ensure that you do not pay extra for the hole drilling and to decrease the overall cost of your Printed Circuit board, you need to pick a right technique. We would suggest that you pick a technique that corresponds to the design and fabrication process of your Printed Circuit Boards.


To ensure the right spacing between the components, you need to see the table below. The right spacing ensures that the board remains stable, maintainable and tolerable once deployed.


HDI component Spacing
Ordinary Pin and SOP of other components  >40 mil
 Ordinary Component Pins   > 20mil
Other Components Pin and BGA  > 80 mil



The above parameters are to meet the demand of ordinary soldering. However, during the actual production process, the spacing needs to be altered in order to ensure the maintainability and stability of the Printed Circuit Board.



The uniformity of track, control spacing and the minimum line width are among the most common factors that need consideration during the tracking process. The trouble with any of the above factors can lead to serious issues in the HDI PCB.

For instance, if the spacing is not of the right size, it can lead to clipping film problem.  It means there is a high probability of short-circuiting due to the residue of film. Likewise, the manufacturer might face flowing speeds at different points along with the lack of uniformity of the copper thickness. To ensure the successful working of the Printed Circuit Board, you need to ensure that track and copper uniformity during the design phase.


Advantages of HDI Printed Circuit Boards


There are several advantages of an HDI PCB. We will be dividing these advantages into two main categories, functionality and Deployment.




In terms of functionality HDI PCB offer stabilized power along with outstanding performance. In addition, the HDI boards will have a denser tracerouting and there is a drastic decrease in the interference inductance. You will also see a decrease in capacitance.

HDI PCB offer high signal integrity and lead to faster performance. It also offers reliable and efficient results.



With laser technology and other sophisticated technique, it is possible to offer fast and reliable turnaround time. One of the reasons behind the fast turnaround time is an easy placement of SMD components. Also, there is no need for constant relocation of the components.


Why Use HDI Boards Technology


Using HDI PCB will ensure that you are able to deliver the best possible results. You can offer outstanding quality as well as amazing results with these boards. Below are some reason, why consumers prefer using HDI PCB for their electronics.


Compact Size and Lightweight


When it comes to Printed Circuit Boards, it is never about the smallest boards. On the contrary, it is all about the placement of a maximum number of components on the board. The more components you have on board, the better functionality. HDI boards not only offer maximum functionality, but they are also of compact size.

Likewise, the lightweight makes it the best choice for the applications. For instance, smartphone manufacturers are trying their best to introduce smartphones that are extremely lightweight. Incorporating lightweight PCBs will help the manufacturer to keep a close check on the electronic weight.



It more about making each invested cent count then saving money. With HDI Printed Circuit Boards, you will be able to maximize performance while spending on material only when necessary. Another way you can save money is that one HDI board can offer functionalities that would need multiple conventional Printed Boards.

Improved Performance

The distance between 2 components has a direct impact on the performance of a PCB. If you are using an HDI board, you can enjoy short distances, thus making it possible for you to add more transistors. The increased number of transistors will improve the electrical performance of the board along with the optimizing of power consumption.


Quick Delivery Time


Since the boards do not use a lot of material, thus it is possible to manufacturer this board efficiently. Due to efficient manufacturing, you can effortlessly release product sooner in the market then you had initially anticipated.







HDI PCBs have become a huge success over time. There endless functionalities and advantages make them the best choice for modern-day consumers. To ensure high-quality HDI boards, you need to opt for the right manufacturer.

KingPCB manufacturer has indebted knowledge about the design, development, and deployment of all kinds of Printed Circuit Boards. Their knowledgeable staff and outstanding production team make it possible for them to produce high-quality boards in no time. They have the ability and the experience to work on all size projects.

So, allow KingPCB to be your first choice for board manufacturers. You can reach out to them around the clock and their outstanding customer service will reach out to you as soon as possible.

By hqt