What Is HDI High-Density Interconnect?

Printed circuit board (PCB) technology has evolved significantly over the last few years. It calls for much faster and more compact products. Today, high-density interconnect boards are much smaller in size. They have minute vias, spaces, copper traces, and pads.  

A high-density interconnect (HDI) is a printed circuit board with a much higher wiring density per unit than conventional printed circuit boards. Usually, HDI PCBs are best described as printed circuit boards with blinds, microvias, buried vias, high signal functioning, and built-up laminations.

Thus, HDIs have denser wiring, which leads to a much lighter weight, lower layer count, and more compact PCBs. Now, instead of using many PCBs in a device, one high-density interconnect board is sufficient enough to house the functionality of the previously used boards.

What is HDI High-Density Interconnect?

The world of technology has evolved completely. There is a constant need to place advanced technology into smaller packages. Thus, it leads to a high demand for a high-density interconnect. Printed circuit boards (PCBs) devised using HDI practices tend to be tinier as more workings are crowded in a lesser space.

High-density interconnect printed circuit scheming and construction began in the 1980s. It was because researchers wanted to reduce the size of existing PCBs. And today, the HDI board design and manufacture are categorized in the following standards: IPC-2315, IPC-2226, IPC-4104, and IPC-6016. They use a combination of the blind, buried vias, and microvias less equivalent to 0.0006 diameters.

Considering the key design and fabrication challenges when planning an HDI PCB board design is crucial. Here are some of the most shared difficulties:

• There are more traces needed to finish the board
• You need to fit/design smaller components in a much tighter spacing
• There is a very limited workspace area
• It has a limited board workspace area
• There are a greater number of components on both sides of your PCB stack up

What Are the Different Types of Vias In HDI PCB?

Vias is a small conductive hole that joins several layers in a high-density interconnect PCB. It grants signals to move across them effortlessly. Subject to the operations of a PCB, four types of vias are pierced into an HDI PCB.

These are:

• Through-hole vias

This hole is drilled using a drill or laser across the PCB from top to bottom. It helps link all the layers of the multi-layer PCB. Not only is it simple to construct, but these are one of the most economical vias. They’ve been divided to broaden them into plated-through (with copper pads) holes and non-plated-through holes (without copper pads).

• Blind vias

The hole is pierced with the help of a laser or a drill to join the peripheral layer of a multi-layer high-density interconnect PCB with the inner layer. The thing about this hole is that you can only see it from one side of the PCB board; thus, it is referred to as the blind via. However, you must remember that this type of hole is pricey and challenging.

• Buried vias

The buried vias aid in linking two inner layers of the multiplayer HDI PCB. It is permanently on the inside of the printed circuit board, and they are not visible from the outside, which is where it derives its name from. This via is also an electroplated hole that requires a separate drill file. The layer count in a buried via is even in number, i.e., 2,4,6, 8, and so on.

• Microvias

As you can tell by the name, the microvias is the tiniest form with a diameter of fewer than 150 microns. It is also pierced using a laser. These are one of the most everyday types of vias found in HDI PCB to help link one layer of the PCB to its adjacent layer. Moreover, it has a tiny diameter compared to mechanically drilled vias like the through-hole. Their size and power to link one layer to the next layer enable them to get denser printed circuit boards with more challenging designs.

In comparison to microvias and through-hole vias, HDI technology poses numerous advantages, comprising:

• Better consistency: HDI PCBs have reduced features and more compactly packed interconnections, which makes them, to a lesser extent, prone to destruction and more dependable than conventional PCBs.
• Enhanced functioning: HDI PCB have a higher density of interconnections, are compliant for quicker signal transmission, and upgraded electronic device functioning.
• The advanced density of interconnections: HDI technology accepts a higher density of interconnections, which states more improved connections can be built in a limited area. It is imperative for generating tinier and more intricate PCBs.

What Are the Benefits of Using High-Density Interconnect (HDI) Technology?

High-density interconnect offers plenty of benefits over the extra options available. These can help boost the overall results of your project. If you’re a thoughtful designer and a suitable supplier, you can use HDI boards to enhance the overall quality and performance and exceed customer satisfaction rates.

Here is a list of benefits you get by using high-density interconnect (HDI) technology:

Compact And Lightweight

A high-density interconnect board allows you to get more components on either side of the bare PCB, permitting you to get more performance out of a compact space and escalating the overall abilities of the equipment. HDI technology assists you in adding functionality while decreasing the volume and mass of your products.

Upgraded Electronic Functioning

There is an increased electrical performance with a reduced component gap and greater transistors. These characters enable lower power consumption, which enhances signal integrity. Reduced sizes relate to signal transmissions and provide a drop in overall signal losses and crossing intervals.

Economical

Once you build and scheme correctly, your HDI board can be more economical than other options. They demand lesser raw materials owing to their tiny size and require an even lower number of layers. Now you can easily use a single HDI board for a product that you once needed multiple conventional PCBs. You can certainly get more performance and value from less area and less material.

Prompt Manufacturing Times

It allows you earlier production times. With the ability to use only a few materials and fewer boards, it combines design efficiencies linked to HDI technology and can translate quicker production times and a shorter timeframe needed to get your product to market.

Components are comparatively simple to set in HDI PCBs, and the high electrical functioning lowers the time needed for testing and troubleshooting.

Greater Dependability

Advanced microvias can enhance the dependability of your board and your product. The greater functionality and consistency HDI PCBs offer will lower costs and please customers.

Increased Routing Density

Blind vias allow signals to be transmitted among internal layers of the PCB, allowing the creation of more multifaceted and densely packed circuit designs. It is most beneficial in high-density applications where many connections are needed in a small area.

HDI PCB Manufacturing Method & HDI Design Essentials

1.    Design

You start by designing the circuit outline utilizing computer-aided design (CAD) software. This design will help identify where the component will be placed and the interconnection of the components set on the PCB.

To form an HDI board, you must be of utmost accuracy, as the circuit plan is liable for the device’s appropriate performance. Computer-aided design (CAD) software is used to simplify the overall design process. It helps ensure accuracy as compared to a manual method. With the help of this tool, a designer can successfully plan their layout and initiate the electrifying device creation process.

You can use computer-aided design (CAD) software to test different production techniques, including laser cutting and pick-and-place. This makes it practical to build unique devices quickly and with the least effort. Computer-aided design (CAD) software is essential in HDI board design and formation, from its primary concept to prototyping and the final production.

2.    Photomask Formation

A photomask is a clear film that contains the complete circuit layout. It is essential in fabricating HDI boards. This template includes metal trace patterns and forms part of the substrate etching process. However, you need to be highly accurate, as this filter must-have several tiny components and intricate detail that cannot be shaped manually.

Thus, innovative photolithography machinery, along with etching processes such as reactive ion etch, produce specific traces that are highly suitable for complex high-density interconnect board designs, are used.

Even the slightest deviance from the specified place can lead to a lack of interconnectivity and substantial board failure. Thus, utmost attention is dedicated to photomask creation within an HDI fabricator’s facility.

3.    Photoresist Application

A photoresist is applied to the surface of the PCB. This photosensitive material is built to shield specific areas of the board through chemical processes and simplify a consistent etch pattern. It helps protect areas where conductive tracks or pads are essential on the PCB.

The clear-cut patterns generated by the photoresist require challenging tolerances and accurate imaging practices; else, problems might occur throughout later stages of production.

4.    Photolithography

The printed circuit board (PCB) is set in a photolithography tool. This device employs UV light to selectively show the photoresist material that was earlier applied on the PCB board. Thus, when it is not exposed to this UV light, the photoresist will be removed from these spaces utilizing chemical etching.

Moreover, this technique is also used to generate patterns and qualities on combined circuits and other exclusive components. It is mainly responsible for driving today’s miniaturization efforts in many industries dependent on electronics and related products.

5.    Layering & Via Formation

Layering and via creation are applied in the fifth step when constructing an HDI board. It entails producing multiple copper layers used in the PCB design to adapt circuitry, routing signals, and much more. These processes might include etching, silver-plating, and drilling.

Additionally, vias are built to provide link between circuit traces/layers on various edges of the board to permit signal routing past numerous layers. By employing both layerings and via creation in this step of the HDI board-making process, beneficial features, including high-frequency functioning or higher density levels, can be acquired from even slimmer boards than beforehand.

6.    Testing

After cautiously designing and forming HDI boards, one last critical step is to put them through all-inclusive testing. This testing phase is crucial to validate full functionality and guarantee that the boards are enhanced and securely functioning to industry standards. Testing involves gauging parameters, including signal integrity, current consumption, and component tolerances, permitting the detection of any possible problem before a board is put into use.

Creating effective HDI boards entails utmost dedication and attention to detail during every stage of their production; furthermore, extensive testing of the end product ensures these components are fit for purpose.

What Are the Design Consideration for HDI PCBs?

As HDI technology has progressed, innovative manufacturing techniques have been established, including plasma design to eliminate excess material from the PCB and laser drilling to build via holes. The recent progress has enabled the formation of intricate and high-level HDI designs and facilitated the extensive acceptance of HDI technology in diverse electronic applications.

Today, HDI technology has continued to develop, with new materials and methods facilitating the design of even more complex HDI designs. These advances have reduced electronic devices and developed innovative and upgraded electronic products. HDI has transformed how electronic devices are designed in terms of performance, weight, and size.

Here are a few considerations for HDI PCBs:

Progressive Lamination

The printed circuit board core/s are merged with copper and pre-preg layers for multi-layer PCBs by employing the right amount of heat and pressure in the lamination process. The extent of temperature and force that you need to apply on a board differs from one board to another.

Once the lamination phase is over, the PCB manufacturer will drill vias. Dissimilar to other types of PCBs, HDI boards require going through the process several times. These serial laminations will benefit in averting being uneven and disintegrating through drilling.

Via-In-Pad Procedure

The via-in-pad manufacturing process enables you to set vias in the even surface of the flat lands on your PCB by plating the via, padding it with one of the several fill types, covering it, and electroplating over it.

Via-in-pad is usually a 10-to-12-step procedure that needs expert equipment and expert technicians. Via-in-pad is a wise option for HDI PCBs because it makes thermal management straightforward. Not just that, it lowers space requests and offers one of the shortest ways to bypass capacitors for high-frequency designs.

Via Fill Types

The thing with via-fill types is that they should always match your specific application and PCB needs. Via fill materials we work with daily comprise electrochemical silver-plating, copper-filled, silver-filled, and conductive epoxy. The most standard via-fill type is nonconductive epoxy.

Fills must enable microvias and usual vias to be unsighted, suppressed, and pierced, then ingrained to hide them underneath SMT lands. We frequently use several drill cycles at exactly measured intensities to ensure the drilling process is done right each time. This level of control demands expert machinery and extended development time.

HDI Structures

HDI PCBs come in a few diverse layout choices. Some of the most standard ones are 1-n-1 PCB and 2-n-2 PCB. A 1-n-1 PCB comprises a single build-up of high-density interconnected layers. Thus, it’s the easiest method of HDI printed circuit board. It demands one serial lamination on either side of the core PCB.

The 2-n-2 printed circuit board comes with a dual HDI layer and enables microvias to be arranged through layers. Complex designs frequently integrate copper-filled piled mircovia structures. Structures can climb to very great X-n-X levels. Nevertheless, complexity and expense classically restrict the build-up. An additional essential choice is the any-layer HDI. It contains an easy and dense HDI layout, so conductors are on any given layer of smartphones and other mobile devices.

Laser Drill Technology

Any-layer HDI designs frequently require laser microvias generated with laser drills. These drills produce a laser up to 20 microns in diameter, which can smoothly pierce through metal and glass, generating minute yet clean holes. You can get even smaller holes employing materials, including uniform glass, which has a low dielectric constant.

LDI and Contact Imagery

Being a leading HDI printed circuit board (PCB) supplier implies going above and beyond. You must be able to deliver finer lines with progressive technology and clean rooms that certify, protect, and secure processing. Since when these details are taken into consideration, you can’t go back and repair everything. Thus, it is bound to be done right the first time and with great accuracy.

Sophisticated PCB Materials for HDI PCB Production

High-Density Interconnect (HDI) Printed Circuit Boards (PCBs) depend upon innovative materials to generate the most competent and profitable results. Signal and space management are key factors in an enhanced design. It can be accomplished using HDI techniques and high-quality base materials incorporating laser microvia laminates, copper foils, surface mount adhesive films, and surface treatment photosensitive dry films.

It is crucial to use the current PCB materials with consistent adhesion powers and circuit traces to achieve all manufacturing standards. This is important for a strong and versatile performance under severe temperatures and other environmental conditions.

Manufacturers can guarantee first-rate product excellence for all HDI applications once they combine sophisticated PCB materials with progressive technologies, including a plating-thru-hole process for blind/buried vias or inkjet printing incorporating silver nanoparticles for enhanced signal transmission.

Greater Thermal Dependability

PCB fabrication employing high-density interconnect technology offers numerous advantages, including greater thermal reliability. Through careful board design and manufacture, HDI PCBs offer exceptional thermal security, even in difficult operating situations. Layering copper unswervingly to the surface of these boards creates ideal thermal dissipation, confirming that an amplified component count does not compromise operational functioning, even over extended periods.

RoHS Compliant

RoHS is one of the most requested standards in PCB fabrication currently. This standard recognizes materials used in manufacturing electronic components and products that include dangerous amounts of lead, mercury, cadmium, and other environmental pollutants.

Complying with RoHS ensures that customers purchase high-quality Printed Circuit Boards (PCBs) made without illegal or dangerous substances.

Halogen-Free PCB

The usage of halogen-free PCB for HDI PCB fabrication is progressively widespread due to the heavy-duty importance of product protection and environmental security in many trades. By employing halogen-free technology, engineers can create long-lasting devices that meet the stringent needs established by governing agencies.

Such HDI boards are frequent champs of greater thermal steadiness, chemical resistance, flexibility, and electrical insulation than conventional designs, making them highly suitable for various industrial applications and environments. Moreover, the reduced risk of corrosion from halogen-free designs can help reduce costly maintenance by eliminating environmental factors as a source of system failure.

Ultra-Low Loss HDI PCB

Ultra-Low Loss, HDI PCB creations swiftly become the gold standard in circuit boards. This PCB is a potent tool for enhancing complete electrical performance, with ultra-low losses and dielectric constants rivaling ceramic substrates.

There are many ways to design an ultra-low-loss HDI PCB:

• Making use of high-quality materials
• Using low-loss connectors
• Enhancing trace breadth and width
• Using controlled depth microvias
• Employing differential pairs
• Using impedance-controlled routing
• Using low-loss laminates

Conclusion

High-density interconnect (HDI) offers the required means to get products to market quickly and sustain high standards. Where time is concerned, HDI delivers the ultimate solution that doesn’t sacrifice quality or performance.

Thus, to stay ahead, it is critical to be well-informed about HDI technology and how it can profit your business. And since we are moving towards more compact electronics, HDI will become even more dominant in a few years. Once you recognize what HDI is and how it works, you will surely make well-informed decisions about employing this technology in your products and designs.