HDI Printed Circuit Boards

2022-11-07 15:49:07 HDI Printed Circuit Boards 394 Viewed

SummaryHDI printed circuit boards are circuit boards with relatively high circuit distribution density using micro-blind and buried via technology. The HDI printed circuit boards have inner layer lines and outer layer lines, and then uses drilling, in-hole metallization and other processes to realize the internal connection of each layer of lines....

HDI printed circuit boards are circuit boards with relatively high circuit distribution density using micro-blind and buried via technology. The HDI printed circuit boards have inner layer lines and outer layer lines, and then uses drilling, in-hole metallization and other processes to realize the internal connection of each layer of lines. HDI printed circuit boards are generally manufactured by the lamination method.

The more the number of laminations, the higher the technical grade of the board. Ordinary HDI printed circuit boards are basically one-time buildup, and high-end HDI printed circuit boards use two or more buildup technologies, while using advanced HDI printed circuit boards technologies such as stacking, electroplating, and laser direct drilling.

Classification of HDI Printed Circuit Boards

HDI printed circuit boards usually include laser blind vias and mechanical blind vias; general through buried vias, blind vias, stacked vias, staggered vias, cross blind buried, through vias, blind via filling plating, fine line small gaps. The technology of realizing the conduction between the inner and outer layers by processes such as micro-holes in the pad, usually the diameter of the blind buried is not more than 6mil.

HDI printed circuit boards are divided into: 1st level, 2nd level, 3rd level, 4th level, and any layer interconnection.

1.1st-level HDI printed circuit boards structure: 1+N+1 (2 times of lamination, 1 time of laser)

2. 2nd-level HDI printed circuit boards structure: 2+N+2 (3 times of lamination, 2 times of laser)

3. 3rd-level HDI printed circuit boards structure: 3+N+3 (4 times of lamination, 3 times of laser)

4. 4th-level HDI printed circuit boards structure: 4+N+4 (5 times of lamination, 4 times of laser)

From the above structure, it can be concluded that the laser once is a first-level HDI printed circuit boards, twice is a second-level HDI printed circuit boards, and so on. Of course, any layer interconnection can start lasering from the core board. What needs to be lasered before lamination is any layer interconnection HDI printed circuit boards.

Application of HDI Printed Circuit Boards

While electronic design is constantly improving the performance of the whole machine, it is also trying to reduce its size. In small portable products, from mobile phones to smart weapons, "small" is the eternal pursuit. HDI printed circuit boards technology enables more miniaturization of end product designs while meeting higher standards for electronic performance and efficiency. HDI printed circuit boards are currently widely used in mobile phones, digital (camera) cameras, MP3, MP4, notebook computers, automotive electronics and other digital products, among which mobile phones are widely used. HDI printed circuit boards are generally manufactured by the build-up method. Ordinary HDI printed circuit boards basically one-time buildup, and high-end HDI printed circuit boards uses two or more buildup technologies, while using advanced HDI printed circuit boards technologies such as stacking, electroplating, and laser direct drilling. High-end HDI printed circuit boards are mainly used in 3G mobile phones, digital cameras, IC substrates, etc.

Advantages of HDI Printed Circuit Boards

This HDI printed circuit boards have grown rapidly on the basis of prominent advantages:

1. HDI printed circuit boards help to reduce PCB costs;

2. HDI printed circuit boards increase the linear density;

3. HDI printed circuit boards facilitate the use of advanced packaging;

4. HDI printed circuit boards have better electrical performance and signal validity;

5. HDI printed circuit boards have better reliability;

6. HDI printed circuit boards are better in heat dissipation;

7. HDI printed circuit boards can improve RFI (Radio Frequency Interference)/ EMI/ ESD (Electrostatic Discharge);

8. HDI printed circuit boards improve design efficiency;

Materials of HDI Printed Circuit Boards

Several new requirements have been placed on HDI printed circuit boards materials, including better dimensional stability, antistatic mobility, and non-adhesives. A typical material for HDI printed circuit boards is RCC (Resin Coated Copper). There are three types of RCC, namely polyimide metallized film, pure polyimide film, cast polyimide film.

The advantages of RCC include: small thickness, light weight, flexibility and flammability, compatibility characteristic impedance and excellent dimensional stability. In the process of HDI multilayer PCB, instead of the traditional adhesive sheet and copper foil as insulating medium and conductive layer, RCC can be suppressed with chips through traditional suppression technology. A non-mechanical drilling method, such as a laser, is then used in order to form the microvia interconnects.

RCC promotes the occurrence and development of HDI printed circuit boards products from SMT (Surface Mount Technology) to CSP (Chip Scale Packaging), from mechanical drilling to laser drilling, and promotes the development and progress of HDI printed circuit boards micro-vias, all of which have become RCC's leading HDI printed circuit boards material.

In the actual HDI printed circuit boards manufacturing process, for the selection of RCC, there are usually FR4 standard Tg 140, FR4 high Tg 170℃ and FR4 and Rogers combined lamination, which are mostly used now. With the development of HDI printed circuit boards technology, HDI printed circuit boards materials must meet more requirements, so the main trends of HDI printed circuit boards materials should be:

1. Development and application of adhesive-free flexible materials;

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

3. 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;

7. Strictly compatible with CTE (Coefficient of Thermal Expansion);

Technology of HDI printed circuit boards Manufacturing

The difficulty of HDI printed circuit boards manufacturing lies in the micro-through fabrication, through metallization and fine lines.

1. Micro-via manufacturing

Microvia fabrication has always been a core issue in HDI printed circuit boards fabrication. There are two main drilling methods:

a. For common through hole drilling, mechanical drilling is always the best choice for its high efficiency and low cost. As machining capabilities have grown, so has its use in microvias.

b. There are two types of laser drilling: photothermal ablation and photochemical ablation. The former refers to a process in which the operating material is heated to melt and evaporate through the formed through-holes after high-energy absorption of the laser light. The latter refers to the results of high-energy photons in the ultraviolet region and laser lengths exceeding 400 nm.

There are three types of laser systems applied to flexible and rigid boards, namely excimer laser, UV laser drilling, CO2 laser. Laser technology is not only suitable for drilling, but also for cutting and forming. Even some manufacturers make HDI printed circuit boards by laser. Although the cost of laser drilling equipment is high, they have higher precision, stable process and mature technology. The advantages of laser technology make it the most common method for blind/buried via fabrication. Today, 99% of HDI printed circuit boards microvias are obtained by laser drilling.

2. By metallization

The biggest difficulty with through hole metallization is that the plating is difficult to achieve uniformity. For the deep-hole electroplating technology of micro-through holes, in addition to using the electroplating solution with high dispersing ability, the plating solution on the electroplating device should also be upgraded in time, which can be achieved by strong mechanical stirring or vibration, ultrasonic stirring, and horizontal spraying. In addition, the humidity of the through-hole walls must be increased prior to electroplating.

In addition to process improvements, HDI printed circuit boards' through-hole metallization methods have also seen improvements in major technologies: electroless additive technology, direct plating technology, and more.

3. Thin line

Thin line implementations include conventional image transfer and laser direct imaging. Traditional image transfer is the same process as ordinary chemical etching to form lines.

For laser direct imaging, photographic film is not required, and the image is formed directly on the photosensitive film by the laser. UV wave lamps are used for operation, enabling liquid corrosion protection solutions to meet the demands of high resolution and simple operation. Photographic film is not required to avoid adverse effects due to film defects, and can be directly connected to CAD/ CAM, shortening the HDI printed circuit boards manufacturing cycle, making it suitable for limited and HDI printed circuit boards productions.


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HDI Printed Circuit Boards Description

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Advantages of HDI printed circuit boards

HDI printed circuit boards can not only make the terminal product design more miniaturized, HDI printed circuit boards can also simultaneously meet higher standards of electronic performance and efficiency. The increased interconnect density of HDI printed circuit boards allows enhanced signal strength and improved reliability. HDI printed circuit boards have better improvement for RF interference, heat conduction, etc.

Processing difficulties of HDI printed circuit boards

HDI printed circuit boards significantly increase the consumption of processing capacity. The level of HDI printed circuit boards is determined by the number of repetitions of the sub-outer layer processing in the production process. Therefore, compared with the 1st-level HDI printed circuit boards, the 2nd-level HDI printed circuit boards with the same area need to use more pressure in the sub-outer layer processing. The production capacity of processes such as bonding, copper reduction, and laser needs to be doubled, and the production capacity required for the 3rd-level or any-level HDI printed circuit boards is more than three times that of the 1st-level.

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