HDI PCB is the short form of high-density interconnect printed circuit board, a kind of printed circuit board manufacturing technology. An HDI PCB is a circuit board with a relatively high circuit density that uses micro-blind and buried “via”—or the copper-plated holes in PCBs—technology. HDI PCBs are compact products designed for small-capacity users, costing much more than standard PCBs.

HDI PCB boards, one of the fastest-growing technologies in the PCB industry, are now available at HonLynn Circuit. HDI PCB contains both the blind via and buried via hole varieties and has a higher circuitry density than traditional circuit boards. We are capable of manufacturing HDI PCBs up to 36 layers.


HDI PCB stack-up suggestions

The following is a breakdown of the various structures offered by HonLynn:

1+N+1 – PCB contains 1 “build-up” of high-density interconnection layers.

i+N+i (i≥2) – PCB contains 2 or more “build-ups” of high-density interconnection layers. Microvias on different layers can be staggered or stacked.

Copper-filled stacked microvia structures are commonly seen in challenging designs.

4. Any Layer HDI – All the layers of a PCB are high-density interconnection layers, which allows the conductors on any layer of the PCB to be interconnected freely with copper-filled stacked microvia structures (“any layer via”). This provides a reliable interconnect solution for highly complex, large pin count devices, such as central processing unit (CPU) and graphics processing unit (GPU) chips utilized on handheld and mobile devices.

Our HDI PCB capabilities

A micro via maintains a laser-drilled diameter of, typically, 0.006″ (150µm), 0.005″ (125µm), or 0.004″ (100µm), which are optically aligned and require a pad diameter of typically 0.012″ (300µm), 0.010″ (250µm), or 0.008″ (200µm), allowing additional routing density. Microvias can be via-in-pad, offset, staggered or stacked, non-conductive filled and copper-plated over the top, or solid copper filled or plated. Microvias add value when routing out of fine-pitch ball grid arrays (BGAs) such as 0.8 mm pitch devices and below.

Step HDIHDI StructuresType of   Micro viasMass ProductionSmall-Middle   BatchPrototypeAvailable

1+N+1Blind viasYesYesYes4 Layers+
2 Step2+N+2Blind/Buried   staggered viasYesYesYes6 Layers+
2 Step2+N+2Blind/Buried   stacked viasYesYesYes6 Layers+
3 Step3+N+3Blind/Buried   staggered viasYesYesYes8 Layers+
3 Step3+N+3Blind/Buried   stacked viasYesYesYes8 Layers+
4 Step4+N+4Blind/Buried ViasYesYesYes10Layers+
5 Step5+N+5Blind/Buried   ViasYesYesYes12 Layers+

Additionally, micro vias add value when routing out of a 0.5 mm pitch device where staggered micro vias can be used. However, routing micro-BGAs such as a 0.4 mm, 0.3 mm, or 0.25 mm pitch device requires using Stacked MicroVias using an inverted pyramid routing technique. 

We are capable of manufacturing HDI PCBs up to 36 layers.

HDI PCB material

Some new requirements are being put forward for HDI PCB materials, including better dimensional stability, antistatic mobility, and non-adhesives. The typical material of HDI PCBs is resin-coated copper (RCC). There are three types of RCCs: polyimide metalized film, pure polyimide film, and cast polyimide film.

The advantages of RCCs include small thickness, light weight, flexibility and reduced flammability, compatibility characteristic impedance, and excellent dimensional stability. In the HDI multi-layer PCB process, instead of the traditional adhesive sheet and copper foil as the insulating medium and conductive layer, the RCC can be suppressed with the chip using traditional suppression technology. Non-mechanical drilling methods such as lasers are then used to form micro via interconnections.

RCC promotes the development of PCB products from surface mount technology (SMT) to chip-scale packaging (CSP), from mechanical drilling to laser drilling—and promotes the development and progress of PCB microvias, all of which have become RCC’s leading HDI PCB material.

In the actual PCB manufacturing process, for the selection of RCC, there are usually FR-4 standard Tg 140C, FR-4 high Tg 170C, and FR-4 and Rogers combined lamination, which are mainly used now. Given the development of HDI technology, HDI PCB materials must meet more requirements. Therefore, the main trends of HDI PCB materials are:

1. Development and application of flexible materials without adhesives;

2. The thickness of the dielectric layer is small, and the deviation is slight;

3. The development of LPIC;

4. The dielectric constant is getting smaller and smaller;

5. The dielectric loss is getting smaller and smaller;

6. High welding stability; and

7. Strictly compatible with coefficient of thermal expansion (CTE).

HDI PCB advantages

1. HDI technology can reduce the cost of PCB, although when the density of PCB increases beyond eight layers, it will be more expensive to manufacture with HDI.

2. The traditional and complex pressing process is low.

3. Increased circuit density: traditional circuit boards and parts are interconnected

4. Conducive to the use of advanced construction technology

5. Have better electrical performance and signal accuracy

6. Better reliability

7. Can improve thermal properties

8. Can improve radio frequency interference/electromagnetic wave interference/electrostatic discharge (RFI/EMI/ESD)

9. Greater design efficiency

HDI PCB application

While advancements in electronic design continue to improve the performance of the whole device, the trend is also moving towards reducing its size. In small portable products ranging from mobile phones to smart weapons, “small” is an eternal pursuit. High-density interconnect (HDI) technology can make terminal product designs more compact while meeting higher electronic performance and efficiency standards. HDIs are widely used in mobile phones, digital cameras, MP3s, MP4s, notebook computers, automotive electronics, and other digital products, among which mobile phones are the most widely used. HDI boards are generally manufactured using the build-up method.

6 layer Blind via hole HDI PCB

The greater the build-up times, the higher the technical level of the board. Ordinary HDI boards are one-time build-up. High-end HDIs use two-time or more build-up technology. Advanced PCB technologies such as stacking holes, electroplated hole filling, and laser direct drilling are also used. High-end HDI PCB boards are mainly used in 3G, 4G, and 5G mobile phones, advanced digital cameras, IC carrier boards, etc.

Assuming the upward trend of high-end HDI PCB boards, 4G boards or IC carrier boards continues, future growth is expected to be very rapid: the world’s 5G mobile phone use will grow by more than 50% in the next few years, and China will issue 5G licenses. Moreover, IC carrier board industry consulting agency Prismark predicts that China’s forecast growth rate from 2020 to 2030 will be 80%, which is a microcosmic of the direction of PCB technology development.

HDI PCB manufacturing technology

HDI PCB manufacturing is difficult because microvias are made through metallization and thin wires.

1. Microvia manufacturing

Microvia manufacturing has always been the core issue of HDI PCB manufacturing. There are two main drilling methods:

1. Mechanical drilling, which is for ordinary through-hole drilling, is always the best choice because of its high efficiency and low cost. With the development of machining capabilities, its application in microvias is also constantly developing.

2. Laser drilling, of which there are two types: photothermal ablation and photochemical ablation. The former refers to a process by which the operating material is heated to melt and evaporate through the formed hole after the high-energy laser is absorbed. The latter refers to the result of high-energy photons and lasers exceeding 400nm in the ultraviolet region.

Three types of laser systems are applied to flexible and rigid boards: excimer lasers, ultraviolet laser drilling, and CO2 lasers. Laser technology is suitable not only for drilling but also for cutting and forming. Some manufacturers even use lasers to manufacture HDIs. 

Although the cost of laser drilling equipment is high, they have higher precision and stable and mature technology. The advantages of laser technology make it the most commonly used method in blind/buried through-hole manufacturing. Today, 99% of HDI microvias are obtained by laser drilling.

2. Through metallization

The biggest challenge of through-hole metallization is that it is difficult to achieve uniform plating. For the deep-hole electroplating technology of microvias, in addition to using an electroplating solution with high dispersibility, the plating solution on the device should be upgraded in time. This can be done through mechanical solid or vibration, ultrasonic stirring, and horizontal spraying. In addition, the humidity of the through-hole wall must be increased before plating.

In addition to process improvements, HDIs’ through-hole metallization method has also seen significant technological improvements, such as chemical plating additive technology, direct electroplating technology, etc.

3rd. Tiny circuit

The realization of thin lines includes traditional image transmission and direct laser imaging. Traditional image transfer is the same as forming lines by ordinary chemical etching.

No photographic film is needed for direct laser imaging, and the image is formed directly on the photosensitive film by laser. The ultraviolet (UV) lamp is used for operation so that the liquid anticorrosion solution can meet high-resolution requirements and be operated. No photographic film is needed to avoid adverse effects associated with film. CAD/CAM can be directly connected to shorten the manufacturing cycle and make it suitable for limited and multiple production.

HDI PCB types

HDI PCB comes in different types. Although they are different in design, they have the same function. The type you decide to choose depends on the application you are using. Let’s quickly consider the types.

* Flex HDI PCB

Flex HDI PCB is composed of flexible plastic. This material permits the board to form different shapes. This offers lots of benefits when compared with rigid boards.

The board’s flexibility also allows you to move or bend easily during the application process without damaging the circuits on the board. One disadvantage with this board type is that designing and manufacturing it costs a lot. However, they come with numerous benefits.

The heavy wiring in advanced equipment like satellites can be replaced with these PCBs. They are lighter and use little space, making them great for such use. Another benefit is that it features multilayer, single-sided, or double-sided designs.

* Rigid HDI PCB

Aside from the number of layers and sides this HDI PCB has, it also comes in different rigidities. They comprise a solid and rigid substrate material such as fiberglass. This kind of material prevents the bending of the HDI board. The application of this HDI PCB can be found on most desktop towers.

* Rigid-Flex HDI PCB

This comprises a rigid circuit board, which attaches to a flexible board. The design’s complexity depends on whatever application you are using.

* Multilayer HDI PCB

These boards have substrate boards of multiple layers with an insulating material that separates these layers. Like HDI PCBs with double sides, either vias or through holes can be used to connect the board’s electric circuits. Multilayer HDI PCBs are very beneficial because they use less space. This HDI board’s standard applications include medical machinery, servers, handheld devices, and computers.

Mass production lead time

lead   time
Lead Time (Wroking   days,ex-factory
4+N+4To be determined based on case

The above lead time is based on:

1. Conventional Material

2. All engineering consultations are confirmed.

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