HDI PCB-10 Guide To Perfect Know High Density Interconnect

The increased portability of electronic devices has been made possible thanks to HDI PCB’s use around the world. Electronic devices can now be manufactured in smaller sizes without sacrificing quality or functionality thanks to HDI PCB’s innovations. If you’re interested in learning more about the HDI PCB’s history, applications, design, and implementation, keep reading.

Table of Contents

What HDI is in PCB?


HDI stands for High Density Interconnection. Simply put, it is a multilayer board that is made with blind micro vias and the lamination method. (That is, the traditional method starts with getting a core board with no plated through holes (PTH). Then, thin lines and micro blind holes are added to both sides of the outer layer to make a multilayer board.



In the PCB industry, a micro-hole is a hole with a diameter of less than 150um (6mil).


Buried hole: A buried hole is one that is hidden in the inner layer of the hole and can’t be seen from the outside. (An advantage of a buried hole over a through-hole is that it doesn’t take up space on the PCB’s surface, so more parts can be put on the PCB’s surface.)


Blind hole: A blind hole can be seen in the finished product. The main difference between a through-hole and a blind hole is that a through-hole can be seen from both sides, but a blind hole can only be seen from one side. When compared to through holes, blind holes have the advantage that they can be wired from below.





Because electronic products are getting smaller and integration is becoming more important, PCBs need to be able to fit more components in less space and send high-frequency signals better. Because of this, high density interconnect (HDI) PCBs are also one of the PCB technologies that is growing the fastest. Because it has more circuits than traditional circuit boards, HDI PCB designs can use smaller vias and capture pads and more connection pads per square inch. HDI boards have blind and buried vias, and they usually have microwells that are 0.006 inches or less in diameter.




Most HDI PCBs are made with the lamination method, and the technical grade of the board goes up as the number of laminations goes up. Normal HDI boards are only laminated once, but higher-order HDI uses two or more times of lamination along with advanced PCB technology like stacked holes, plated-filled holes, and laser direct punching. When the PCB has more than eight layers, the cost of making it with HDI will be less than with the traditional, complicated lamination method.

medical board
medical board

HDI boards are better than traditional PCBs in terms of how well they work with electricity and how well the signals work. HDI boards also have better improvements for RFI, EMI, static discharge, thermal conductivity, and many other things. High Density Integration (HDI) technology makes it possible to make smaller end products that meet higher standards for how well and how efficiently electronics work.




HDI boards are made with blind holes and then pressed together twice, in first-order, second-order, third-order, fourth-order, and fifth-order. The first-order ones are easier and have well-controlled processes and steps. The alignment problem is the biggest problem with the second order, and the hole punching and copper plating problem is the second biggest problem. There are many different second-order designs. One is to put each order in a different place. To connect the next neighboring layer, you have to run a wire through the middle layer, which is the same as doing two first-order HDIs. Second, two first-order holes overlap, and the way to get to the second order is through superposition. Processing is the same as for two first-order, but there are many points in the process that need special control. This is what was said above. The third type is to punch holes straight through from the outer layer to the third layer (or N-2 layers). This is a very different process from the first two, and it is also harder to punch holes. For the comparison between the third order and the second order, that is.




Since HDI costs more in PCB proofing, most manufacturers are reluctant to use it. GESP can make HDI blind-buried PCB boards, which other companies won’t do. At this point, GESP’s HDI technology has broken through the highest layer count of 20 layers, a blind hole order of 1/4, a minimum hole diameter of 0.076mm, and a laser drilling process.





Advantages of HDI PCBs

  1. HDI technology helps bring down the cost of PCBs.


  1. Line density gets better with HDI PCB.


  1. HDI technology makes it easier to use more advanced packaging.


  1. The electrical and signal performance of HDI PCBs is better.


  1. You can count on HDI technology more.


6.High density PCB makes it easier to get rid of heat.


7.PCB HDI makes it easier to design.




More flexibility HDI PCB Layout


Engineers now have more design freedom and flexibility than ever before because of how high-density PCB technology has changed. If they want to, designers who use HDI high density interconnect methods can now put more parts on both sides of the raw PCB. Basically, an HDI PCB gives designers more room to work with and lets them put smaller parts even closer to each other. This means that a PCB with a high density of interconnects will allow signals to be sent faster and with better quality.






Multilayer HDI PCB that is lighter


HDI PCB is often used to reduce the weight and size of a product, as well as to improve its electrical performance. The high-density PCB is often used in cell phones, devices with touch screens, laptops, digital cameras, and 4G network communications. The HDI PCB is also a big part of many medical devices and electronic parts and components for airplanes. With high-density interconnect PCB technology, it seems like there are almost no limits to what can be done.


Function improved by HDI PCB


1.Routing of Denser traces


2.Power that is steadier


3.Lessen the effects of interference inductance and capacitance


4.Make high-speed designs with better signal integrity


Use HDI printed circuit boards to speed up development.


1.Easier to place SMD components

2.Faster routing

3.Reduce frequent relocation of components

4.More component space (also by Via-in-Pad)







Interconnections at the first, second, third, fourth, and any other layer


1st-order HDI structure: 1+N+1 (two times press-fit, one time laser)


Structure of a second-order HDI: 2+N+2 (3 times pressed together, 2 times laser)


Structure of a third-order HDI: 3+N+3 (4 times pressed together, 3 times laser)


Structure of the 4th order HDI: 4+N+4 (pressed together 5 times, laser 4 times)




What does HDI Material


Some of the new requirements for HDI PCB materials are better dimensional stability, anti-static mobility, and no adhesives. RCC materials are often used for HDI PCBs (resin-coated copper). RCC comes in three different forms: metalized polyimide films, pure polyimide films, and cast polyimide films.




RCC has many benefits, such as a small thickness, a light weight, flexibility, the ability to burn, compatibility, impedance, and excellent size stability. In the process of making an HDI multilayer PCB, chips can be used instead of the traditional bonding sheet and copper foil as an insulating layer and a layer that conducts electricity. The micro-through-hole connections are then made using non-mechanical drilling methods, such as lasers.




RCC drives the development and use of PCB products from SMT (Surface Mount Technology) to CSP (Chip Level Packaging), from mechanical drilling to laser drilling, and promotes the development and improvement of PCB microvia, which all become the leading HDI PCB material for RCC.




Most RCCs used today are FR-4 standard Tg 140C, FR-4 high Tg 170C, and FR-4 and Rogers combination laminate. As HDI technology improves, HDI PCB materials must meet more requirements. This means that the main trends of HDI PCB materials should be popular on the market in the future.




HDI PCB Design Tips

Smart Component Selection


Most HDI boards have SMD (0.65 mm) and BGA (0.65 mm) components. The pitch or space between pins should be chosen carefully because it affects the width of the trace, the type of through-hole, and how the PCB is stacked.



How to Use Microvias






Use techniques like microvia or continuous stacking (0.15 mm), which can help designers save more space. Microvias are good for high-speed applications, connecting power supply surfaces with decoupling capacitors, and reducing noise because they have a low inductance.




Material Selection


Every PCB design needs to choose the right materials. But it needs to be said here that it is even more important for HDI-pcb. The goal of the designer is to choose materials that can be made and that meet temperature and electrical standards. When thinking about the aspect ratio of the microvias to be plated, it is important to think about how thick the material is.




HDI PCB Stackup problems


Different layer materials have different CTE values and rates of water absorption, which causes layered PCB designers can stop this from happening by using the same material or a material with the same CTE value for each layer.



HDI PCB Testing


HDI designs are tested using functional or JTAG methods, not ICT. ICT is important, but a thorough node analysis is needed.


 Heat Radiation 





IPC-2226, which talks about thermal issues, can help you manage the design better. Because HDI circuits have a lot of parts, designers need to pay more attention to how heat affects the circuit. Together, thinner dielectrics and microvias help get rid of heat. To get the most heat out, you might want to add thermal vias.



Cabling requirements and substrate capacity


Cabling requirements are the total length of connections needed to link all the parts on the PCB. Substrate capacity is the length of wires that can be used to connect all the parts. The capacity of the substrate should be more than what is needed for the wiring. This way, there will be enough space for wiring to finish the design with the least amount of cost.


Printed Wiring Board Density


Calculate a design’s PWB density to find out how complicated it is. The average length of a trace per square inch is used to measure the density of a printed circuit (Wd) (including all signal layers).


PWB density is calculated by assuming that each electrical network has an average of three nodes and that each component lead is one of those nodes.


Density of PWB (Wd) = ([Cd]) (Cc)


= β√([(per square inch.)] ) × (average lead per part) (average lead per part)


Where. Cd is the average number of parts per square inch in the design.


Cc = component complexity = average number of possible customers per part


= constant, 2.5 in the high analog/discrete region, 3.0 in the analog/digital region, and 3.5 in the digital/dedicated IC region.






This formula can be used as a guide, but there is no one rule that all designs should follow.


HDI PCB Processing & Stackup


Microvia manufacturing



The main problem with making HDI PCBs has been making micro-through-holes. There are two main ways to drill.


Mechanical drilling is always the best choice for common through-hole drilling because it is fast and cheap. With the improvement of mechanical machining, it is becoming easier to use in micro-through-hole.


There are two ways to drill with a laser: photochemical ablation and photothermal ablation. The first term refers to the process of heating the operating material until it melts and evaporates through the hole made when the laser’s high energy is absorbed. This is the result of high-energy photons in the UV range and laser lengths that are longer than 400 nm.


For flexible and rigid panels, there are three types of laser systems: excimer laser, UV laser drilling, and CO 2 laser. Laser technology can be used not only to drill, but also to cut and shape things. Even some manufacturers make HDI with lasers. Laser drilling equipment is expensive, but it offers higher precision, stable processes, and technology that has been used for a long time. Because laser technology has so many benefits, it is the most common way to make blind/buried through-holes. Today, laser drilling is used to make almost all of the HDI microvia holes.




Through metallization


The hardest part of through-hole metallization is making sure that the plating is even. For micro-through hole deep hole plating technology, the plating solution on the plating device should be upgraded over time. This can be done by strong mechanical stirring or vibration, ultrasonic stirring, or horizontal spraying. Also, the through-hole wall’s humidity needs to be raised before plating.




In addition to process improvements, HDI through-hole metallization methods have seen improvements in major technologies like chemical plating additive technology, direct plating technology, etc.



Fine Line



Fine lines can be made through both traditional image transfer and direct laser imaging. Chemical etching is the same process as conventional image transfer when it comes to making lines.



For laser direct imaging, you don’t need photographic film. Instead, the laser makes the image right on the photosensitive film. UV light is used for operation, which makes it possible for liquid solutions to meet the needs for high resolution and easy operation. No photographic film is needed to avoid unwanted effects caused by flaws in the film. This makes it possible to connect directly to CAD/CAM and shortens the manufacturing cycle, so it can be used for both small and large production runs.


HDI PCB Prototype


An HDI PCB prototype is a smaller version of a real HDI PCB that can be used to compare different designs. You can ask the company that makes your HDI PCBs to make prototypes for testing. Because there are so many wires, they have few layers and are small. These prototypes need to have stacked, staggered, blind, and buried vias so that you can figure out which ones work best together. Also, the HDI PCB prototype will help you choose the size of the vias and the best aspect ratio.



HDI PCB Application


Mobile communication gear and boards for laptop computers. The number of holes, lightness, length, size, and strength.


Equipment for high-end computers and networks, as well as large boards for peripheral equipment. The number of holes is small, and there are a lot of layers of conductors. The integrity of the signal being sent and control of the characteristic impedance are also important.


large-scale integrated circuit packaging chip carrier board, such as pressure-soldering board (also called wire, Wire Bonding Board) and overlay board (Flip Chip Board) and so on. Small line width and spacing (usually less than 2mil), high precision, small hole diameter (1–2mil), small hole spacing (5mil), good heat resistance of the substrate, and a small coefficient of thermal expansion.

The Future of HDI PCB


With the development of electronic equipment toward thin, short, high-performance, and multi-functional, and the progress of electronic assembly technology, the printed circuit board products for electronic component interconnection from the through-hole insert technology (THT) stage to the surface mount technology (SMT) stage, towards the chip-level packaging (CSP) stage, and is slowly moving towards the system-level packaging (SIP) stage. In the PCB industry, a new generation of HDI board products has been planned, set up, and developed. This new generation will be the norm for the next generation of printed circuit boards because the conductor holes are getting smaller and the wires are getting better.



Your Reliable HDI PCB Manufacturer


XFDC Technology has a wide range of HDI structures and processes to meet your PCB needs. This gives you a better balance between technology and cost.


No matter what industry you work in, you are probably already thinking of ways that high-density interconnect PCBs could make the electronics you make or use better. Get in touch with us and we’ll talk about it. Use our “Contact us” page to send us your needs and production documents. Within 24 hours, we will get back to you.

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