It covers both basic and advanced aspects about HDI printed circuit boards, from definition, design, benefits, design, applications, and many more.
By the end of this guide, you’ll be an expert in the HDI PCBs.
What is an HDI PCB?
When using these PCBs, you will notice they have fine lines and spaces, capture pads, minor vias, and high connection pad density.
These serve the function of facilitating electrical performance and minimizing the application’s size and weight.
The effectiveness of these boards serves as an alternative to the use of high-layer laminated boards, which are expensive.
As we shall see later on, the characteristics of these boards, such as lightweight, high electrical speed, and frequency, make them ideal for several applications.
Benefits of an HDI PCB
Using HDI Printed Circuit Boards in your application comes with a wide variety of advantages. These advantages are what make various manufacturers use these HDI PCB.
But what are these benefits that you will experience when using HDI PCB?
Well, here is a look at these benefits.
Keep reading.
Reduced heat transfer
One of the benefits of having an HDI PCB is that there will be a minimal transfer of heat. This is because heat travels for a short distance before escaping the HDI PCB.
The design of the HDI PCB enables it to go through a high thermal expansion which in turn increases the lifespan of the PCB.
Managing thermal conductivity
The availability of vias helps the HDI PCB to transmit current between the components. You can fill the vias with either conductive or non-conductive materials.
You can also improve the functionality of the HDI PCB by placing the blind vias and via-in-pad components together.
Reducing the transmission distance between the components reduces the transmission times and the crossing delays.
The result of this is a strong signal for your HDI PCB.
Smaller form factors
HDI PCB is the ideal PCB when it comes to saving space. You can quickly minimize the number of layers when designing your HDI PCB.
For instance, you can easily replace a PCB that has 8- a layers through the hole with a 4-layer HDI that has via- in- pad solution.
By doing so, you end up with a smaller PCB with vias that are visible to a person and increase performance.
Minimal power usage
One of the benefits of having an HDI PCB is that it will consume less battery power. This is due to the technology used in the manufacturing process.
Such technology includes keeping the electrical components together and minimizing energy loss.
The effect of this is that there is an extension of the lifespan of your battery.
Using vias instead of through holes also makes HDI PCB ideal for reducing power usage.
Incorporation of components
Since you can minimize the space on the PCB for the components, you can incorporate as many details as you want on the board.
Also, you can reduce or increase the number of layers depending on the design of your PCB.
The other consideration you can use to incorporate the components is populating both sides of the boards. This, of course, will depend on your HDI PCB’s design and application.
Different designs
By using HDI PCB, you can have different designs for your application. HDI PCB comes in different types that you can choose for your application.
For instance, you can have flexible, rigid, or a combination of the two for your application. Later on, in this guide, we will discuss each type of HDI PCB you can select when designing your PCB.
HDI PCB Manufacturing Process
Manufacturing HDI PCBs is one of the most straightforward processes you can quickly learn.
Even though there are a few technical steps that you will encounter, you can counter them by understanding all the requirements.
Here are the steps that you need to follow when manufacturing HDI PCB.
1. HDI PCB Designs and Layout
There are various designs and layouts that you can have for your HDI PCB.
However, there are several considerations that you have to check when selecting the PCB design and layout which will fit your application.
First, you have to check the size of your application. This is in terms of dimensions to ensure that all the angles fit perfectly.
The other consideration you need to check is the environment in which your HDI PCB will operate.
This is essential to determine which materials you will use, especially if the environment is of high temperature.
Lastly, most HDI PCBs don’t consume a lot of electricity.
You, therefore, need to check on the energy output requirement levels for your application to ensure that you design the correct HDI PCB.
2. HDI PCB Fabrication Process
You can follow the following steps when fabricating your HDI PCB.
·Design and output
The first step in manufacturing your HDI PCB is to develop a plan that will fit your application. Various software exists that you can use to design your HDI PCB.
The common ones include Altium Designer, OrCAD, Pads, KiCad, Eagle, etc.
You are identifying which software will inform your manufacturer of the production procedure to use.
Therefore, you need to inform your manufacturer of the software you will be using.
·Checking on the signal frequency that your HDI PCB requires
The next step involves identifying the correct power and voltage needs of the various electrical components on the board.
This includes checking if you can accommodate trace length and controlled impedance on the board.
Your manufacturer will come in handy here to ensure that you accurately know what they have as the minimum tolerance needs for the PCB.
At the same time, ensure you have a plan to minimize noise from the HDI PB.
·Documenting the board stack up a plan for manufacturing purposes
In this step, you must record all you require to stack up the plan. Again, in this step, a manufacturer will help determine the specifications for your HDI PCB.
The details to check include the type of material to use and the constraints specified for your HDI PCB.
You can have FR-4, Nelco, or Rodgers types of material for your HDI PCB.
Other strategies that you can have for the stacking-up plan include the use of a signal layer. You can place this side by side with the adjacent layer, offering an efficient return path for the signals.
Another option is to route the high-frequency signals present on the inner layers of the HDI PCB between the planes.
This is important to protect against any radiation that the signals emitted externally.
On your stack-up, you can have ground planes. This is important as it reduces the reference hindrance, minimizing the radiation effect on the circuit.
·Floor planning
The crucial step of your HDI PCB manufacturing process. Here, you will have to partition your PCB into logical parts.
Among the considerations to note when you are partitioning is if you will place all the subcircuits separately or into a larger design.
This step is essential, especially when dealing with analog and digital sections, which need isolation to reduce interference. Also, you need to identify the direction of the circuit.
·Understanding the ground and power planes
This step involves understanding the details of your HDI PCB. You must identify and understand the ground plane and check if it is complete.
The routed signal should stay within your ground plane. Division on the ground plane will force you to rotate the available void, which may affect the EMI and the signal timings.
In case it is a must that you divide the ground plane, you need to include a resistor on the signal trace. The function of this is to facilitate the signal by creating a bridge so that there can be facilitation of the return path.
·Check on the size of the land patterns
You must ensure you have the correct land pattern for your PCB. The right size must accommodate all the components to function correctly. Other strategies that you can have for the stacking-up plan include the use of a signal layer. You can place this side by side with the adjacent layer, offering an efficient return path for the signals.
Another option is to route the high-frequency signals present on the inner layers of the HDI PCB between the planes.
This is important to protect against any radiation that the signals emitted externally.
On your stack-up, you can have ground planes. This is important as it reduces the reference hindrance, minimizing the radiation effect on the circuit.
·Floor planning
The crucial step of your HDI PCB manufacturing process. Here, you will have to partition your PCB into logical parts.
Among the considerations to note when you are partitioning is if you will place all the subcircuits separately or into a larger design.
This step is essential, especially when dealing with analog and digital sections, which need isolation to reduce interference. Also, you need to identify the direction of the circuit.
·Understanding the ground and power planes
This step involves understanding the details of your HDI PCB. You must identify and understand the ground plane and check if it is complete.
The routed signal should stay within your ground plane. Division on the ground plane will force you to rotate the available void, which may affect the EMI and the signal timings.
In case it is a must that you divide the ground plane, you need to include a resistor on the signal trace. The function of this is to facilitate the signal by creating a bridge so that there can be facilitation of the return path.
·Check on the size of the land patterns
You must ensure you have the correct land pattern for your PCB. The right size must accommodate all the components to function correctly.
Generally, your PCB pad needs to be around 30% of the size of the component pins. The advantage of this is that it will offer mechanical strength to your PCB while minimizing parasitic capacitance.
·Routing high-frequency signals
By routing high-frequency signals, you will maximize the shielding effect of your HDI PCB. High-frequency signals emit high levels of radiation while moving from the source.
This radiation can interfere with two different signals. You can route the frequency signals in two ways to avoid this interference.
One is that you can reduce the long and parallel signals, minimizing the coupling of the movements. The second option is increasing the distance of the traces of the signals.
Alternatively, you can route the signal to a different layer if they are noisy. Routing of the frequency signals on different layers must be orthogonal.
For instance, on a signal layer, you can include either vertical or horizontal traces.
·Ensure you have an efficient return path
You need to ensure that every signal has a route originating from the source and ending at the sign via the path. The path needs to have a minimum of obstruction.
Using via might be necessary for certain situations to ensure a smooth path. The via minimizes the chances of the current spreading over the splits on your PCB.
This can lead to loss of quality of the signal. If you use the via to reverse the current to the source, ensure tight coupling.
Tight coupling ensures the timely arrival of the signals. You can place the reverse near the signal to minimize the distance the signal needs to travel.
·Use the 3W rule to minimize trace coupling
Line coupling can affect the quality of signal transmission. However, you can prevent this by using a 3W valve.
This rule states that the distance of separation between traces should be thrice the width of one single trace measured from end to end. This rule increases the distance between the traces, minimizing the coupling effect.
To increase the gains of reducing line coupling, you must increase the separation distance to ten from three.
·Use the 20H rule to minimize the coupling of the plane
Coupling happens between the ground plane and the power, which poses a risk to your HDI PCB. The coupling allows for the absorption of fringe to the ground plane instead of radiating out externally.
The 20H rule indicates that you should ensure that the dielectric thickness between the adjacent power plane and the ground is 20 times thicker than the power plan.
·Check the routing guidelines
Lastly, you must ensure you have followed your HDI PCB’s routing guidelines. First, avoid using the 90-degree bends on the traces because they can bring about single reflections of the frequencies.
Also, ensure you have all the signals from the different pairs of the same signal and gap. The advantage of this is that it will increase the cancellation of the electromagnetic field.
Lastly, as you design your transmission lines, ensure that you use microstrip traces. The purpose of these traces is to offer a single reference plane that is separated using a dielectric.
HDI PCB Working Principle
Understanding how an HDI PCB works can be hectic for beginners. All one can see are green shapes and tons of different parts assembled.
However, if you are keen, it is easy to understand how this board functions. Let me simplify this for you. To start, when viewing the board, you need to look at it from the perspective of a city. Another way of looking at it is to take a flight and look down.
All you can see is a well-organized city, different from when you are walking on the streets. You can view roads, buildings, people, and vehicles interacting to form a town.
Now translate that perspective to the HDI PCBs. These PCBs are a complete system with components that interact harmoniously.
Let’s use the analogy of the city and its components to see how the PCB functions.
·Talk of HDI PCB Traces (Let’s Equate this to Roads and Cars)
When you look at the PCB, you will observe that lines run on the entire board while connecting different components. Just like roads in which cars move around, electrons run along these lines transferring power from one element to another.
These lines are made of copper, known as traces when we are talking of HDI PCBs.
·Integrated Circuits (Let’s Equate this to Downtown)
In a city, the downtown area is where a lot of activities occur. Here, you have all sorts of businesses, from big offices to small businesses and markets.
Downtown also exists when we are talking of PCBs. Here, they are the square black shapes that are on the PCB. They are called Integrated Circuits.
During fire calculation activities, it is here where all the work takes place.
·Components on HDI PCB
The design of HDI PCB is such that you will fix various components on the board.
Normally, the nature of the components will depend on the main application of function of the DDI PCB.
For example, you can have:
- Resistors
- Diodes
- Inductors
- Capacitors, etc.
·HDI PCB Pads
These are areas on the HDI PCB, where you can solder components on the board.
Or, you can talk of it as a section that support components on the PCB.
It looks like this:
·Silkscreen on HDI PCB
They are all the white or at times gold paintings that you will see on the PCB.
They are known as the silkscreen.
They serve the function of directing the people who are fixing or assembling the PCB to know which part is for a particular location.
In most cases, they are on the component side, and have vital information such as component interface, identifiers, settings, etc.
·Vias
These are holes that allow for interconnecting various section of the PCB or components.
For instance, vias allows you to connect various layers of the PCB.
Besides, you can join pads or traces.
It looks like this:
Types of HDI PCB
There are different types of HDI PCBs available in the market. These HDI PCBs though different in terms of designs, they all serve the same function.
However, the choice of which type of HDI PCB that you select will depend on your application.
So, what are these types?
Here is the answer to this question
1)Flex HDI PCB
The composition of this kind of HDI PCB is flexible plastic. This material allows the board to shape into different shapes, which is advantageous when you compare it to rigid boards.
The board’s flexibility allows you to bend or move quickly during the application process without damaging the circuits on the board.
The only disadvantage of this type of board is that it is expensive to design and manufacture. However, they have numerous advantages.
For instance, you can replace the heavy wiring in advanced equipment such as satellites with these PCBs. They utilize little space and are lighter, which makes them ideal for such use.
The other advantage of this board is that it comes in different designs, such as double-sided, single-sided, or multilayer designs.
2)Rigid HDI PCB
The difference with this type of HDI PCB is that in addition to its number of sides and layers, you can have it in different rigidities. Rigid HDI PCB constitutes a tough but solid substrate material like fiberglass.
Such a material prevents the HDI board from bending. However, when mentioning these PCBs, most consumers think they are circuit boards.
An example of a typical application of this HDI PCB is the tower on most desktops.
3)Rigid- Flex HDI PCB
Rigid-flex HDI PCB combines both stiff and flex circuit HDI board technology. The rigid-flex HDI PCB consists of a rigid circuit board that attaches to a flexible circuit board.
The complexity of the design depends on your application.
4)Multilayer HDI PCB
Multilayer HDI PCB incorporates the advanced technology of the double-sided board. These boards have multiple layers of substrate boards with insulating material separating each of these layers.
Just like double-sided HDI PCBs, you can use holes or vias to connect the electrical circuits in the board.
The advantage of using a multilayer HDI PCB is that it consumes less space than a double-sided HDI board.
The most common types of Multilayer HDI PCB include 4, 6,8, or even ten layers. However, you can have a multilayer HDI PCB with more layers per your specification.
The standard applications for this type of HDI board include servers, medical machinery, computers, and handheld devices.
5)Double-Sided HDI PCB
Double-sided HDI PCBs have the characteristics of having electrically conductive metal layers on both sides. Also, the conductive components and circuits are attached on both sides.
With holes on both sides, electrical circuits on one side are connected to electrical circuits on the opposite side of the HDI PCB. There are two methods through which the electrical circuits can connect.
You can connect by using ether surface mount technology or through-hole technology. Through-hole technology entails feeding tiny wires, also known as leads, through the holes.
You then solder each of these holes to the relevant circuit or component. On the other hand, surface technology excludes the use of wires.
Instead, you solder the leads directly onto the HDI PCB.
Surface technology allows you to use more circuits even with a small space on the HDI PCB.
The implication is that the HDI PCB can perform many functions at a lesser weight and a faster speed than through-hole boards.
6)Single- Sided HDI PCB
The main characteristics of this HDI PCB are that it has only one layer of the base material or substrate. A thin layer of metal, usually copper, covers one side of the board.
The use of copper is mainly due to it being an excellent conductor of electricity.
On top of the metal, you will have a protective solder mask, and then you can have a silkscreen coat on top of the protective solder mask.
The purpose of the silkscreen is to label the parts of the HDI PCB. Single-sided HDI PCBs usually have electronic circuits and components on one side of the board.
You can conveniently use this board for simple electronic applications. You can easily design and manufacture this PCB at home since it is less costly and complicated.
However, since they are common in basic applications, it is rare to find these boards in large-scale use.
Definition of HDI PCB terms
There are various terms that you will encounter while handling HDI PCBs.
Some of these terms may appear difficult to understand initially, but you will find them comfortable in due process.
Let me take you through these terms so that you can be in a position to understand them.
·Buried Via
The buried via refers to a connection between two or more inner layers of the PCB. However, this does not pass through the outer layer of the PCB.
You can have several advantages when selecting a buried via for your PCB application.
First, it allows you to perform more functions on the board in a bit of space since the vias don’t pass through the outer layer.
Secondly, buried vias is a cost-effective method of designing your HDI board. A lot of manufacturers prefer the use of buried vias when manufacturing the HDI PCB.
·Micro-via
Micro-via is the minute holes that a laser drilled on the HDI PCB.
These holes are essential in generating an electrical link between the layers of a multilayer HDI PCB.
Once the laser drills these holes, you can fill them with different types of materials depending on the design of your HDI PCB.
For instance, you can use epoxy resin, a conductive and non-conductive material, or electroplated copper.
The use of micro-via can lead to an increase in the component design of your HDI PCB. However, the reliability structure of the HDI PCB is the main limitation of the application of micro-vias.
·Blind Via
A blind via is a connection between the outer layer of the PCB and one or more inner layers. However, this connection only passes through part of the board.
In basic terms, via will consists of a barrel, a pad, and an anti-pad. While drilling blind people, you will have to put into consideration several factors.
First, you must check on the depth you want the via to have.
Also, you need to check the quality of the plating of the PCB.
Lastly, you need to select which build-up plan you will use when drilling the vias.
- SBU (Sequential Build-Up)
This is a technology whose use is expected in the manufacturing of HDI PCBs.
It consists of subsequent building up multilayer boards with a minimum of 2 pressing steps.
You can add several layers in sequence to a board that already has multiple layers.
While using this technology, blind and buried vias play an essential role in combining layers to the board.
You can have several advantages by using sequential build-up technology on your HDI PCB.
They include cost-effective benefits, adding more components to the board, and using little space on the board.
Chapter 7: Applications of an HDI PCB
Having come all this way, you might wonder where to apply these crucial boards.
The truth is there is a vast area of applications that you can use HDI PCBs.
This ranges from basic applications to complex ones. Here are some of the applications that you can use for HDI PCBs.
·Consumer electronics
Consumer electronics refers to the basic devices that you will find very many people using.
They include laptops, computers and smartphones, entertainment systems, home appliances, and recording devices.
Due to the nature of some of these gadgets, there is a need to have lighter PCBs. These boards need to carry still the same electrical components maintaining their flexibility.
Since HDI PCBs meet these qualities, they are commonly used by different manufacturers to produce these gadgets.
However, manufacturers need to adhere strictly to the regulations in place.
This avoids situations where they come up with different designs that affect the quality of the devices.
- Medical equipment
Electronics play a significant role in the well-being of our health. However, the PCB components of this equipment are always understated.
There is a high specialization of PCBs in the medical industry to ensure that they meet the standards.
This includes having a small size of these HDI PCBs incorporate all the details that will be useful.
Also, they must adhere to the health standards set to ensure the safety of the patients. There are several devices that you will find HDI PCB necessary.
They include monitors, scanners, internal devices such as heart pacemakers, control systems, and scientific instruments.
·Industrial applications
HDI PCBs are standard in high-powered industrial applications because they consume less energy while ensuring maximum output.
Also, they can withstand the harsh environment in which they are as they perform their functions.
Most HDI PCBs incorporate thick copper on the boards, which aids in faster battery charging and high current application. You can find these PCBs in a variety of industrial applications.
They include industrial equipment such as electric drills, measuring equipment used to measure pressure and temperature.
Also, they are present in power equipment such as solar power panels and generators.
·Automotive applications
Automotive is the other area of application where you can find HDI PCBs in use. Most automobiles rely on electronic parts to function correctly.
You can apply a combination of HDI PCBs and a few other technologies, like high-frequency signals present in RF, to sensor applications typical in automotive.
Other technologies such as radar technology are also finding their way in the automobile industry. All these technologies depend on HDI PCBs to function.
Among the common applications include car control systems such as engine management systems. Others applications include navigation devices, audio, and video devices and surrounding motors.
·Aerospace applications
The durability and precision that HDI offers make them an ideal in most aerospace applications. The harsh and turbulent environment that airplanes and jets go through require equipment that can stand such stress.
To find a solution for this, most airplanes use flexible HDI PCBs which are small in size while being light in weight.
They are also resistant to the vibration effect.
These HDIs need to meet certain standards to be used in the aerospace industry since the safety of the airplanes relies on them.
Among the common applications include monitoring equipment such as accelerometers and pressure sensors.
Also, you can find them in testing equipment which collects information during flight testing.
·Lighting application
HDI PCBs have everyday use in a wide range of LED applications. LED are increasingly becoming popular due to the change in technology.
The advantage of these lights is that they consume less power and are highly efficient. At the core of LED, you will find HDI PCBs.
The features that make these lights stand out include the HDI PCB using little space; hence they will be small. Also, the fact that the components are close together means less energy is lost to the surrounding, thus ensuring maximum output.
LEDs are standard in a wide range of industries. They include automotive lights, home lights as well as in medical theatres.
Conclusion
I hope I have addressed all your concerns about HDI PCBs. Of importance when selecting an HDI PCB for your application is to check on the specifications.
Specifications you can check include the materials you are using and the design of your HDI PCB.
Also, there are various manufacturers of HDI PCB in the market. However, not all of them are genuine. Always check the manufacturer’s details before engaging them to manufacture your HDI PCB.
You can avoid all the speculation by engaging us to manufacture your HDI PCB. We assure you of our quality and timelines in manufacturing your HDI PCB.
