Your Reliable HDI PCB Manufacturer in China

As we mentioned before, the HDI printed circuit boards are not the same as the typical PCBs, so you need to keep some facts while doing the HDI PCB design.

As a PCB designer, you should follow the following HDI PCB design guidelines.

Keep Space Priority In Mind

As the main objective of HDI PCBs is the density of the components, you must think about as many components as you can implement. Along with a lot of components, you must consider the future maintenance of the PCBs.

On the other hand, ensure the proper spacing among the components. Keep in mind that you must give importance to the via diameter, trace width, pad diameter for the flawless HDI PCB manufacturing process.

Understanding Via Essence

Vias are one of the most important factors in HDI PCB design. You must understand the via implication on your HDI circuit board design.

Understanding Via Is Essential for Designing HDI Circuit Boards

The vias play a vital role in making the HDI boards. They also affect the signal performance of the HDI printed circuit boards.

The uses of vias are different from through-holes.

Keep Solder Related Issues In Mind

To avoid shoddy connections, avoid the use of a via-in-pad. If not possible for valid reasons, then use a solder mask to cover the via-in-pad. Be careful while using a solder mask, as there are different complications of the solder mask itself.

HDI PCB Stackup

Select and implement the right HDI PCB stackup. Because the PCB stackup for the HDI multilayer PCBs impacts the drilling cycles.

The video below demonstrates how to incorporate HDI technology into printed circuit boards.

Vias are holes in PCBs that connect the different layers in the PCB electrically. Using multiple layers and connecting them using vias reduces the PCB size.

As the main goal of HDI circuit boards is to reduce their size, vias are one of the most important factors for them. Vias are available in different types.

Various Types Of Vias In PCB

Through-Hole Vias

It passes through the whole PCB, from its surface layer to its bottom layer, and is known as a through-hole via. By this point, they connect all of the layers of the printed circuit board. But, through-hole vias take more space and reduce space for components.

Blind Vias

Blinds vias just connect the external layers of the PCBs with the internal layers. No need to drill the entire PCBs.

Buried Vias

Buried vias are used to connect the internal layers of the PCBs. Buried vias are not visible from the outside of the PCBs.

Microvia

Microvia is the smallest via size less than 6 mils. You need to use laser drills for forming micro vias. So, basically, micro vias are used in HDI circuit boards.

It is because of its size. As you need component density and no way to waste space in HDI PCBs, it is wise to replace other common vias with micro vias. Also, micro vias don’t create thermal expansion issues (CTE) as they have short barrels.

Let’s see how to set up micro vias in PCB.

Depending on the design requirements and application, HDI PCBs are formed in different structures.

Let’s have a look at a quick illustration of the HDI PCB construction in the next section.

1+N+1: The Simplest Structure

A “build-up” high-density connectivity layer is included in the 1+N+1 construction. In this configuration, there are fewer I/O counts available in BGA.

Micro vias, tiny lines, and registration technologies are all found in 1+N+1. These can produce a 0.4-mm ball pitch. Furthermore, the mounting stability and reliability of this design are exceptional. It also has a copper-filled vial in it.

This HDI structure is used in cell phones, GPS devices, memory cards, and other devices.

2+N+2: Moderate Complex HDI Structure

Basically, there are at least two connecting layers in this architecture. More layers of build-up might also be employed. Micro vias are utilized in various PCB layers, and they may be stacked or staggered in their placement.

A 2-4-2 Construction Of High-Density Interconnect PCB

This structure is often utilized in the construction of high-level signal transmission systems. This unique structure facilitates the routing procedure in complex design situations.

By the way, this is particularly well suited for BGAs. Where the BGAs have tiny ball pitches and a high I/O count, the BGAs are superior.

This HDI structure is used by portable video recorders, mobile phones, and gaming consoles.

Every Layer Interconnection (ELIC): Most Complex HDI Structure

Every layer is powered by high-density interconnects in this topology. This also enables all layers to communicate with one another through micro vias.

It is the HDI design’s most complicated structure. This very complicated topology provides huge pin connectivity options for large pin-count devices. CPUs and GPUs, as well as cell phones, are examples.

This complicated HDI structure is used by GPUs, CPUs, cellphones, and computer gadgets.

As HDI printed circuit boards are designed with complex and highly advanced technology, high-end electronics use them.

The devices that use HDI circuit boards are highly complicated and generate excellent performance.

HDI Printed Circuit Boards Are Used In Varieties Of Applications

The following are the applications mentioned of HDI PCBs according to industries.

Consumer electronics: smartphones, touch screens, laptops, digital cameras, 4,5 G network communications, military communication system, etc.

Aerospace industries: use HDI circuit boards where decreased weight is a concern.

The automotive industry: is becoming more computerized and highly microprocessor-dependent. Smart cars are increasing the use of auto control, GPS, rear cameras, backup sensors, etc., through HDI PCBs.

Medical equipment: such as monitoring, imaging, surgical, laboratory devices, etc., are using HDI.

Industrial automation and IoT are becoming more popular. HDI PCBs are the common power providers of them.

HDI PCBs are capable of doing a lot with a little size. The fundamental objective is to make electronics smaller.

As a result, HDI circuit boards are compact, take up less space and perform better. HDI printed circuit boards enable the deployment of more transistors by reducing the distance between the trace space. In addition, HDI uses less electricity and provides better signal transmission.

HDI Circuit Boards Are Compact In Size And Lightweight

Aside from these, the following advantages are found using HDI PCBs.

• HDI is cost-effective when you properly plan and implement the design manufacturing.
• HDIs are advantageous with faster production.
• Micro vias are used in HDI printed circuit boards. they are reliable, dependable, less space-consuming, and allow more space for the components.

Base materials are used for HDI PCB in different categories. They are categorized as follows.

Regular Speed And Dielectric Loss Tangent

These types of materials are from the FR4 family. They are loss-prone to the dielectric. The regular speed materials are used in a particular range of bandwidth. Isola 70HR is an example of this material family.

FR4 Family Materials Are Used In Making HDI Printed Circuit Boards

Moderate Speed And Loss

Responsive frequency curves are a kind of material. Also, holds a moderate Dk level as well. Dk loss is half that of standard speed materials in this case. These materials are appropriate for frequencies up to 10 GHz. Nelco N700-2 HT is one of the examples of moderate speed and low loss materials.

High Speed, Low Loss

These types of materials are high-frequency based and lose low dielectric. The use of high-speed and low-loss materials results in a considerable reduction in noise. For example, Isola I-Speed material.

Large High Speed, Signal Integrity, And Deniable Loss

They are highly responsive to frequency, produce high frequency, and allow the lowest Dk loss. This high-end material is used for higher bandwidth. An example: ISOLA Tachyon 100G.

Laser Direct Imaging is the abbreviation for LDI. The HDI circuit boards portions, on the other hand, are processed using LDI and contact imaging.

LDI is more costly than contact imaging in this case. However, if you want a finer line, spacing, or annular ring, you’ll need a lot more control.

Laser Direct Imaging Is Perfect For Small-Sized PCB Processing

LDI is superior to contact imaging, yet contact imagery is still commonly utilized. In an SC100 room, contact imagery is employed.

The utilization of LDI is expanding day by day as long as demand and technology demand the latest innovation.

Because for the smaller-sized PCBs, LDI is extensively accurate. Electronics like smartphones, cameras, laptops are getting lightweight day by day because of HDI lightweight technology.

In this case, the need for cutting-edge and accurate technology like LDI is required for HDI processing.

Surface mount technology is a component placement technology on PCBs. It allows mounting components on the PCB without drilling the PCB for components.

As SMT components don’t need any drilling, they occupy smaller space. So, the components could be mounted in a compact space.

Surface Mount Technology Needs No Drilling For Component Placement

For this reason, SMT is used in higher-density designs like HDI.

There are many advantages of SMT technology. Theta er as follows.

• A smaller and compact PCB design is possible with SMT technology as you can mount more components in a compact space.
• SMT mounting process is faster and leaves fewer leads and leftovers.
• High-frequency PCB, fast signaling, etc., are created with SMT.
• You can mount the components on both sides of PCBs.
• SMT components create less electromagnetic interference.
• As the components are small and lightweight, the weight of the PCBs is reduced.

As we mentioned that the HDI circuit board is different from typical standard PCBs, you will face some challenges designing and manufacturing it. Let’s have a look at them.

Circuit Design

As might be assumed, the circuitry on HDI PCBs is more sophisticated than the circuitry on any other PCB type. The circuit has become denser, and the trace patterns have become closer to one another.

HDI Circuit Design Is Fairly Complex Than Standard PCBs

Drilling Holes (Vias)

Drilling holes are one of the most significant features of high-density interconnect (HDI) printed circuit boards. Because of the smaller and more compact design, it is not envisaged that typical holes will be present.

For HDI PCBs, you must utilize laser drilling or laser direct imaging as opposed to conventional methods.

Because conventional drilling will result in larger holes, which are not acceptable with HDI technology, traditional drilling is not recommended. In order to reduce the amount of wasted space in HDI, micro vias are used.

The length of the hole will rise in proportion to the increase in the number of layers. The maximum diameter of micro vias in HDI PCBs, on the other hand, is 50 µm.

While designing HDI printed circuit boards, you should consider some design facts in your mind. Since HDI is different from standard PCB design, it demands special consideration as expected.

Fill The Vias Holes In PCB

• Be precise for component selection. HDI boards need a high pin count SMD and BGA that is less than 0.65 mm. You need to select them wisely as they impact the via type, trace width, and HDI PCB stackup.
• You need to use micro vias in HDI boards. This will allow you to get double spaces than through-hole or other vias.
• It is necessary to use materials that are both effective and efficient. It is critical for the manufacturability of products.
• For getting a plain PCB surface, you should fill the vias’ holes.
• Try to select materials for all layers with the same CTE rate.
• Keep an eye on thermal management. Make sure you properly design and organize layers that can properly dissipate the excessive heat.

As an HDI board designer, you must know the following IPC standard for the HDI PCBs.

IPC-2315

HDI structures, as well as micro vias, are covered in detail in this chapter.

IPC-2226

High-definition interface (HDI) boards are described in detail in the IPC-2226 standard. These include the production of micro vias, the characterization of materials, the interconnection of structures, and so on.

IPC/JPCA-4104

IPC-4104 assists you in determining the kind of material used in HDI boards. This document also contains a description of the performance and qualification standard for the high-density structure of the printed circuit boards.

IPC-6016

This covers the features of the HDI materials that are consistent across time. Additionally, the performance and specifications of the HDI construction are described.

There are different types of HDI printed circuit boards in terms of layer counts, application, frequency ability, etc.

They are as follows.

HDI Multilayer PCB

Multi-layer reflects its name. There are at least three conductive layers that make a multilayer PCB. However, all layers are joint through vias in the PCB.

Multilayer PCB Stackup

The layer count could be 4,6,8, up to 40 layers, or more.

Rigid PCB

HDI PCBs are constructed from stiff materials, which are referred to as rigid PCBs. Rigid printed circuit boards (PCBs) are stiff and cannot be bent or twisted.

Flexible PCB

The PCBs that are made of flexible substrates are called flexible PCBs. High-grade flexible materials such as polyamide, TEFLON, etc are used in flexible circuit board design.

Rigid-Flex PCB

Rigid-flex printed circuit boards (PCBs) are a hybrid of rigid and flex PCBs. Essentially, a stiff board is joined to another flex board and then bonded together to make the fundamental shape.

The layout of an HDI circuit board ensures the component and wire density along with ensuring the smallest possible size of the PCB.

The layout of the HDI board means the techniques to keep the trace width under 8 mils. The HDI layout consists of the following things.

A Visual Representation Of HDI PCB Layout

Vias Sized Small

Basically, micro vias are used in HDI circuit boards. They consume smaller space that ensures more space for the component placement. The size of the PCB becomes compact due to this reason.

Traces with Thinner State

Connecting circuits and vias is accomplished by the use of finer traces. Additionally, they are available as in-pad vias. Thinner traces are responsible for creating increased trace density in the background.

Layer Count Remains Higher

The HDI PCB layout contains a higher layer count. Counting 20 layers is a normal fact in HDI boards.

Low Signal Level

HDI circuit boards are not used for higher current flowing applications. The lower signal level is another fact in the HDI circuit board layout.

The HDI board’s sequential stack-up aids in the layer-by-layer construction of the HDI PCB stackup. Although this technology is used to create multilayer printed circuit boards, it is especially important for high-density to interconnect (HDI) printed circuit boards.

The sequential buildup is as follows.

Photoresist Deposition and Exposure

You will be able to specify the etching region of the PCB using this procedure. It will result in a pattern of conductors on the PCB laminate as a consequence of this.

Etching and Cleaning

Etch the traces with ferric chloride to make them more visible. After the etching process is completed, clean the surface of the PCBs. ensure that no photoresist is left on the surface

Via formation and Drilling

Drill the board using a laser direct imaging method to add micro vias. The remaining via holes are then chemically removed.

Sequential Layer Stackup In HDI Circuit Board

Metallization Of Vias

After you have established and structured the vias, you must metalize them in order to allow connections between the layers to be made.

Stack-up

The inner layers are now stacked in preparation for the outer layer processing.

Metalization is the process of depositing a thin copper coating on a dielectric surface. The metalized dielectric surface is located inside the vias that are drilled into the PCB layers in order to link them together.

When sequential construction is being carried out, it is essential to guarantee that each layer is metalized to the highest possible standard.

Metalization Process In HDI Printed Circuit Board

As a side note, you should be careful about the cracking of the vias and internal body of the printed circuit boards.

However, four types of PCB metallization are there. They are conventional electroless and electroplating copper, conductive pastes, conventional conductive graphite, and fully and semi-additive electroless copper.

The HDI PCB stackup is the organizing of the layers one by one. The number of layers or stackup could be determined based on the needs. However, this could be 8 layers to 40 layers or more.

But the exact numbers of layers are dependent on the density of traces. The multilayer stackup helps you to reduce the PCB sizes. It also reduces the cost of manufacturing.

By the way, to determine the layer count of your HDI PCB, you need to determine the trace sizing, and nets per layer. After determining them, you can calculate your required layer stackup of your HDI circuit board.

It is true that HDI circuit design takes more effort due to its complexity. For this, you must choose the right HDI PCB manufacturer for manufacturing this complex PCB to be done.

Because of the intricate nature of the design, the maker must possess exceptional qualifications. When looking for a manufacturer, you should look for the following characteristics.

• To make HDI PCBs, a manufacturer must be equipped with cutting-edge technology and production capabilities.
• They must have a quality management system that is integrated across the organization.
• Must hold IPC certification.
• Must have extensive experience in the field.
• The office staff must be highly trained and skilled.

The mentioned criteria will make a manufacturer fit for manufacturing the complex HDI printed circuit boards.

HDI PCB manufacturing is one of the toughest and most complex tasks in PCB manufacturing. You must have extensive infrastructure and experience to design and manufacture HDI circuit boards.

As you gain a brief knowledge about HDI printed circuit boards, you may realize the toughness of designing them.

So, there is no alternative to a highly experienced and organized PCB manufacturer to select.

PCBMay is your one-stop PCB manufacturer that manufactures extensively qualitative HDI PCBs.

You may contact us for the best quote today.