High Density Interconnect (HDI) Printed Circuit Board(PCB)

High-density interconnects (HDI) printed circuit board(PCB) is a combination of non-printed islands, floating ground connections, and high-density vias that are fabricated on this surface which means the board has a higher wiring density area compared to traditional PCB boards. 

HDI board helps in optimizing the electrical performance by reducing the weight and size of the equipment. Usually, HDI PCB is the best choice for the higher-layer boards. High-density interconnects (HDI) printed circuit board(PCB) is developed using a combination of various materials like stainless steel, copper foil, aluminum foil, and silicon resin. The printing procedure is a batch process, while the other manufacturing process is a continuous flow. It has the highest value of fill factor among any other products in the industry. High-density interconnection printed circuit boards (PCB) are flexible and durable, and allow for them to be optimized for system performance. This enhances the quality of the product. It is a new technology that allows manufacturers to increase the number of pins on their PCBs. This results in more functionality, longer life, and enhanced performance in a single process. Besides, it has additional advantages like small size, high frequency, and high speed. The most popular HDI PCB features include high-frequency transmission capability, which decreases redundant radiation.

Six types of various HDI boards are available which are as follows:

• Through vias from surface to surface
• Through vias and buried vias
• Coreless Constructions with layer pairs
• Two or more layers of HDI with vias
• Availability of alternative constructions of coreless builds with layer pairs
• Passive substrate constructions without electrical connection

High-Density Interconnect PCB features a uniform high density of copper, enabling the development of high-performance passive devices. The PCB is designed to be installed in space-constrained boards and also has low thermal resistance to enable it to be used in small form factor devices. High-Density Interconnector PCB provides the connection of signal, power, and ground together to increase design flexibility and reduce signal loss. Our high-density interconnector boards are high-performance, economical, and easy to use. 

The less size and weight of HDI mean the less chance to get mechanical shocks. The placement of the components in HDI PCB requires extra precision than traditional PCB because of the minimum pads and fine pitch of the circuit on the board. For leadless chips to be fabricated and repaired, special soldering techniques need to be used.

The major application area of this HDI PCB includes Portable Computers, mobile phones, MP3 players, Personal Computers, and game consoles. 

HDI PCB Structures

HDI PCB (1+N+1): Simplest HDI

This is the simple HDI PCB layout design that contains 1 build-up of high-density interconnection layers that is more useful for lower I/O counts of Ball Grid Array. In addition, it is capable of 0.4 mm ball pitch and has a fine line, micro vias, and registration technologies, which have excellent mounting stability and reliability. Some of its application areas include PMP, Cell Phones, MP3 players, Memory Card, etc.

HDI PCB (2+N+2): Moderate Complex HDI

This HDI PCB is constructed by stacking or staggered micro vias on different layers of high-density interconnections. Micro vias can be staggered or stacked. In challenging designs requiring high signal transmission performance, copper-filled stacked micro vias are commonly used. In a complicated design, these can provide increased routing density while maintaining a thin finished board thickness, which is suitable for BGAs with smaller ball pitches and greater I/O counts. Some of its application areas include Cell Phones, Game consoles, PDA, and Portable Video Recording Devices. 

ELIC (Every Layer Interconnection): Most Complex HDI

This HDI PCB structure includes high-density interconnecting layers that permit copper-filled stacked micro via structures to connect conductors on any layer of the PCB. The resulting interconnect solution provides a reliable solution for complex large-pin-count devices, such as CPU/GPU chips for handheld devices and mobile devices. The application area of this structure includes Cell Phones, Ultra-Mobile PC, Memory Cards, MP3s, Small Computer Devices, etc. 

Why is HDI PCB Popular?

HDI PCB is one of the fast-growing technology in the PCB market industry. The HDI technology uses finer lines and space, higher connection pad densities, and smaller vias because of its higher circuitry density. 

The HDI PCB has the capability of doing more with less use of components with the use of copper etching technology for better precision. The major factors in any PCB i.e. signal integrity are improved due to smaller distance connection. This also improves the power requirement. Besides, the other factor that makes the HDI PCB so special is its stable voltage rail, closer ground planes, lower RFI/EMI, distributed capacitance, and minimal stubs. 

Another feature that makes HDI PCB popular is its weight and size. It has provided the designer with more space to work allowing to place the smaller components closer together. This HDI PCB has now been used in various advanced technologies because of its effective and better working quality for any complex mechanism in technologies. 

Advantages of HDI PCB

High Reliability

HDI PCB boards are very reliable as it provides a super shield against extreme environmental conditions because of the use of stacked vias. The reliability also increases because of the smaller aspect ratio of micro vias than typical through holes. 

High Flexibility

HDI PCB provides better flexibility for the engineer for creating a better and more flexible design. The components can be placed on both sides of the PCB if necessary. 

Better Thermal Properties

Laser Drilling in HDI PCB produces smaller holes improving the thermal properties of the board. Besides, due to thermal expansion, HDI PCBs undergo the lesser stress that extends their life PCB.

Better Signal Integrity

The signal is transferred at a faster rate due to denser trace routing. The routing also reduces the interference due to capacitance and inductance. This improves the overall performance of the PCB improves. 

Cost Effective

HDI PCB provides a better layer reduction option. For example, the traditional 6-layer PCB could be replaced by 4 layer HDI PCB board without compromising the quality. This results in smaller PCB sizes with vias that are invisible to the naked eye. 

Space management

The combination of blind vias, micro vias, and buried vias reduces the board space requirement. 

Different kinds of Vias in HDI PCB

Vias are the holes for conductivity that pass through the layers of the board. Each of the holes works as the conductive path where the electrical signal in between circuit layers is passed. 

Although there are various available vias that provide the basic purpose, one suitable type of vias is more effective and suitable for specific PCB designs. The type of vias in HDI PCB includes:

Microvia

Vias that are under 150 microns are called micro vias, that is used in many HDI boards. Micro vias have smaller size of holes that consumes less space on board that the holes that required more drilling. The layers in the micro via are connected to each other with copper plating. 
There are many advantages to micro vias, these include their versatility, ability to be stacked together as well as the ability to sit on the top of a buried via. However, they are expensive to fabricate. 

Blind Via

Blind Via is another via presented in HDI PCB. As a blind via is drilled and electroplated, it is quite not possible to see through it to the other side of the PCB when viewed from either the top or bottom of the board, facing the light. In blind vias, laser drilling or mechanical drilling are used. The depth of drilling must be accurate. It is possible to drill blind vias directly on a PCB. However, electroplating is more difficult as well. PCB manufacturer creates holes in the circuit board where the layer is piled up for creating the blind vias and electroplating them. 

Buried Vias

Buried Vias are other via present in HDI PCB. They are drilled and electroplated in between the PCB’s inner layers. These vias are there to connect the circuit between two or more inner layers. The PCB manufacturer can only drill holes on the required PCB layers which are then piled up for electroplating. If a buried via connects three or more inner layers, it cannot be directly drilled on the PCB. 

Through-Hole Vias

It is one of the most common PCB vias. These through-hole vias are drilled from the upper layer of PCB to the bottom layer. Most of the through-hole vias are PTH i.e. Plating Through Hole and NPTH i.e. Non-Plating Through Hole vias. NPTH vias are used for mechanical connections with screws or connectors to fix the PCB, whereas PTH vias are used for PTH assembly. One of the drawbacks of through-hole is it takes more PCB space. Because of this, it is not much popular in HDI PCB design. 

The use of vias in PCB depends on the technology of PCB, the need for circuitry, and the estimated cost for PCB. In addition to this, the other factors to consider while selecting vias are as follows:

Aspect Ratio

The smallest drill size acceptable for creating a standard via should be based on the thickness of the circuit board. Drills with mechanical motors can only drill through a certain amount of material before they become unreliable. PCB fabricators will typically require a drill size aspect ratio of no more than 10:1 based on the relationship between board thickness and drill size. 

Annular Ring

One of the essential considerations is the size of the via pad. Angular right must be ensured to be large enough after the via is drilled. Without a sufficient annular ring, the via could suppose to breakout.

Signal Integrity

Even if vias are only a little longer than a conductor, they can still cause problems with tight signal integrity requirements. On a ten-layer board, a thru-hole via connecting the top two layers will have 8 layers of unnecessary metal that may cause interference. By back drilling the via, the unused metal can be removed from the line and prevented from acting as an antenna, so you can find problems such as these and correct them. 

Routing Density

A designer should avoid blocking routing channels or ground plane return paths with vias when routing dense areas of the board. When there are hundreds of vias in one small area on dense parts like high pin-count BGAs, this can occur. In planning out a circuit, blind vias and micro vias become critical.

Application of HDI PCB

HDI PCB has wide application areas and is used in various industries. Some of the most common application areas of HDI PCB are as follows:

1. Healthcare

Healthcare is one of the most critical areas where HDI PCB is contributing and making progress. It has led to new possibilities. In the health sector, PCB design should have a very high standard and quality for ensuring the complications with the medical regulators. HDI PCBs provide the high transfer rates needed by medical devices in small packages. Any implants should allow high-speed signal transmission and also should fit enough in the human body like Pacemaker. Besides, other medical devices and equipment like CT scans, emergency monitor rooms, etc. also use the HDI PCB.

2. Automotive

HDI PCB has opened a wide road in the automotive industry since much more innovations are now possible using high-speed circuitry. The performance of the vehicles could be increased while more space could be saved. Some of the common applications of PCBs in vehicles include Navigation, Control systems, Proximity Monitors, and Control Systems. 

3. Industry

Business motive industries with manufacturing and production lines are having huge benefits from PCB. Besides being indispensable in day-to-day processes, these electronic components are also key to automation, which can reduce costs and eliminate human error. In the industrial sector, PCBs are designed specifically to withstand demanding environments and high-power applications. Measuring Equipment using HDI PCB could control the temperature, pressure, and other essential factors in the industry.

4. Electronics

Consumer electronics are the most common sectors where the PCB is used. Electronics have been one of the daily essential parts of humanity since many of us depend on these devices. All the daily used things like mobile phones, computer devices, coffee makers, and many other home appliances have the circuit board within them. Some of the common areas of these HDI PCBs include communications, home appliances, entertainment areas, etc. 

5. Wearable technology

HDI is becoming a major stakeholder in the consumer market as Apple Watch and other wearable devices are launched. Young people are becoming more interested in wearable technology due to its outstanding features.

HDI PCB Manufacturing Methods

The manufacturing process of the HDI PCB is similar to that of the other PCB designs. The only difference is in the hole drilling and stacking up. Laser drilling is used since HDI boards required smaller drill holes for vias although they are limited by depth. Thus, once at a time, a limited number of layers can be drilled. The multilayer HDI contains blind and buried vias for which the multiple drilling process is required. 
HDI PCB manufacturing is an advanced technology that requires the best expertise. Besides, it requires laser drills, a special clean room environment, and laser direct imaging capability.
 
The manufacturing methods of HDI PCB depend on HDI builds and the manufacturing of sequential laminating. The PCB structure 1+N+1 is similar to that of multilayer PCB manufacturing. For example, four-layer HDI PCB with structure 1+2+1 is manufactured as:

The two outer layers of PCB is manufactured and two inner PCB layer are manufactured and laminated.

The two outer layers are laminated using inner layers and the inner layer’s blind vias are electroplated.

 
Similarly, for the structure of 2+N+2, the manufacturing method is as follows:

• The 4 inner layers of PCB are first manufactured and laminated. Then layers 2 and 7 are then manufactured. 
• Using mechanical drilling, the inner layer is drilled while layers 2 and 7 are drilled using laser drilling.
• The inner layer in blind vias is electroplated while layers 2 and 7 are laminated with inner layers.
• Layers 2 and 7 with micro vias are then electroplated.
• Layers 1 and 8 are then manufactured and HDI PCB manufacturers use laser drilling for drilling the holes after locating the place of micro vias.
• With the finished PCB layers, layers 1 and 8 are laminated.
• The manufacturing of staggered HDI PCBs is somehow easier than the manufacturing of stacked-via HDI PCBs as the micro vias do not need high precision for stacking and locating. 

HDI PCB Design Tips

1. Adopt DFM Strategy

HDI PCB is to be integrated for design for manufacturing. The aim is to design a product that is efficient and cost-effective. The HDI PCB design that goes beyond the ability of the PCB manufacturer could ruin the design. 

2. Choose via types

The selection of vias is one of the critical decisions to take since it determines the manufacturing steps and equipment requirements. It also determines the processing time and cost. The number of layers and the cost of materials is also reduced with the use of micro vias, buried, and blind vias. The choice of selecting the pad vias impacts the process complexity.

3. Minimum Components 

Component Selection Optimization is the more critical part of the HDI board. The components present in the HDI board determine the locations, size, type of drill holes, trace width, etc. In addition to performance capability, availability, packaging, and traceability are to be considered. Redesigning the layout with proper substitute components can optimize fabrication time and cost.

4. Space Components

A board may experience warpage when component placement results in asymmetrical distribution of via locations. Producing usable boards per panel may be significantly affected by this factor. Electromagnetic interference (EMI) can affect signal quality if components are spaced too closely together. In addition, nearby pins or pads may have parasitic capacitances or inductances that impact signal quality. Due to this, parasitics components should be extracted from EMI models during design.

5. Route Traces

Signal propagation is one of the important units of PCB. HDI PCB has a better ability to use the smaller trace widths that helps in proper signal propagation. The aim is to achieve the best signal integrity by reducing trace widths, using the shortest trace lengths, proper grounding, analog, digital, and power signal isolation, and a consistent path impedance. 

6. Stackup for material cost

HDI PCB electronics manufacturing costs are also significantly influenced by PCB stack-up selections. Depending on the material type and the number of layers, lamination and drilling cycles may need to be repeated multiple times. It is important to consider costs when making these decisions.

7. Signal Integrity

HDI layout requires high-speed design guidelines with high-frequency guidelines when working with an RF board. The impedance-controlled routing is required in the HDI board thus traces and stack-up is to be designed for ensuring the impedance with the signaling standard of the board. 

8. Opt for fewer layers

More of the assembly steps and manufacturing cost result from the high layer count boards. The cost per board is to be reduced following the necessary guidelines. 

9. Placing micro vias against each other and other board vias can be stacked or arranged optimally.

10. EMI/EMC requirements can be improved by using the outer layers for ground connection. A power plane and micro vias for signal routing will be accommodated in the inner layer. PCBs with eight or more layers would benefit from it.

Difference Between HDI PCB and Standard PCB

HBI PCB and Conventional PCB have many differences, from the manufacturing process to the outcomes there is a huge difference between these two PCBs.
Some of the major differences areas of HDI PCB and basic PCB are as follows:

1. Manufacturing Process

HDI PCB is generally manufactured with laminated methods. The technical level of the board is determined by these lamination layers. While the ordinary HDI PCBs are single-time laminated. Thus, in manufacturing, HBI PCB adapts two or more stacking technology and uses the latest and most advanced PCB technologies like hole stacking, direct drilling by laser, and hole filling by electroplating. On the other hand, the standard PCB is manufactured using the conventional drilling method. 

2. Use of Vias

HDI PCB uses the blind, buried, and micro vias while on the other hand traditional PCB uses the through-hole, buried, and blind vias.

3. Overall Performance

The overall working performance of HDI PCB is better compared to standard PCB. HDI PCB performs better in almost every section like electromagnetic wave interference, electrostatic combustion, radio frequency interference, signal quality, etc. 

4. Size and Weight

The HDI PCB is smaller and lightweight compared to the standard PCB board as HDI technology can make a more compact terminal product design 

Order HDI PCB Online Today

Are you seeking a reliable and qualitative HDI PCB manufacturer? If so then NextPCB is here to solve every of your problem regarding circuitry to any embedded solution. 
NextPCB has many years of working experience in HDI PCB manufacturing. The NextPCB team finds a great way to provide you with the best quality of HDI PCB services.  Our team has been delivering quality services for many years. We provide you with every PCB solution based on your requirement. Our priority is quality and customer satisfaction.  You can check more about our services from this PCB online quote page.