What are the differences between high-density multi-layer boards and ordinary multi-layer boards?

With the development of 5G communication, artificial intelligence, new energy vehicles and high-end consumer electronics, PCB circuit boards are constantly upgrading towards higher density, higher speed and higher reliability. Among them, high multilayer boards, as an important representative of high-end PCB products, are widely used in servers, communication equipment, industrial control and automotive electronics, etc. So, what are the differences between high multilayer boards and ordinary multilayer boards? What are the differences between the two in terms of structure, process, performance and application?

What is an ordinary multi-layer board?

An ordinary multilayer board is a PCB board formed by pressing together multiple layers of conductive copper foil and insulating material.

Common levels include:

Four-layer board

Six-layer board

Eight-layer board

Some products will also use 10-layer boards.

Ordinary multi-layer boards are mainly produced through processes such as inner-layer circuit fabrication, lamination, drilling, electroplating and surface treatment.

Its characteristics are:

The manufacturing process is mature.

The cost is relatively low.

Suitable for most electronic products

Common applications include:

Household appliances

Security equipment

Industrial control board

Power module

Consumer electronic products

What is a high-density multi-layer board?

High-density multi-layer boards usually refer to PCB products with a large number of layers, complex structures, and high processing accuracy requirements.

Although there is no unified standard within the industry, it is generally believed that:

Above the 10th floor

Above the 12th floor

Above the 16th floor

All of them can be classified under the category of high multi-layer boards.

Some high-end products even reach:

24th floor

32th floor

Above the 40th floor

The high-rise panels not only have more layers, but also usually possess:

High-density wiring

High-speed signal transmission

Strict impedance control

High reliability requirements

Therefore, it is widely used in high-end electronic devices.

The main differences between high-density multi-layer boards and ordinary multi-layer boards

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1. Different levels of structure

The most obvious difference is the number of layers.

Ordinary multi-layer board:

4 floors

6 floors

8th floor

The structure is relatively simple.

High-density multi-layer board:

10th floor

12th floor

Sixteen floors

Above the 20th floor

As the number of layers increases, the internal wiring space expands significantly.

For example:

PCBs of the same size,

The number of lines that a 16-layer board can accommodate is far greater than that of a 6-layer board.

Therefore, it can meet the design requirements of complex systems.

II. Different line densities

The circuit design of ordinary multi-layer boards is relatively loose.

Common line width and spacing:

4mil/4mil

5mil/5mil

And for high-rise buildings, the following are usually required:

3mil/3mil

2.5 mil / 2.5 mil

More detailed and precise circuits

The reason is:

The pins of high-end chips are becoming increasingly numerous.

For example:

CPU

FPGA

GPU

AI chip

More lines are needed to complete the connection.

Therefore, the high multi-layer board has a higher wiring density.

III. Different Signal Transmission Capabilities

Ordinary electronic products have relatively limited requirements for signal speed.

And the high-rise buildings usually undertake:

High-speed data transmission

High-frequency signal processing

Large-capacity information exchange

For example:

PCIe bus

DDR memory interface

5G communication module

Optical module equipment

These high-speed signals require:

Precise impedance control

Stable reflux path

Good electromagnetic compatibility

Therefore, for high-density multi-layer boards, strict signal integrity analysis needs to be conducted during the design stage.

4. Different complexities of the pressing process

The ordinary multi-layer boards require fewer pressing operations.

The manufacturing process is relatively simple.

And for high multi-layer boards, as the number of layers increases:

Needs to be faced:

Multilayer Positioning

Control of interlayer thickness

Thermal expansion control

Warp control

For example:

During the lamination process of the 20-layer PCB, any minor deviation could affect the final quality.

Therefore:

High-density multi-layer boards have higher requirements for lamination equipment and process management.

V. Different levels of drilling difficulty

As the number of layers increases:

The depth of the hole keeps increasing.

The holes in ordinary multi-layer boards have a larger diameter.

The drilling process is relatively easy.

For high multi-layer boards, the following aspects need to be controlled:

Quality of deep holes

Porcelain wall surface roughness

Thickness of copper tube

Some products will also incorporate:

Blind hole

Burial hole

Back drilling process

Improve the quality of the signal.

Therefore, the difficulty of drilling processing has significantly increased.

Six. Different impedance control requirements

In many cases, ordinary multi-layer boards do not require strict impedance control.

And high-density multi-layer boards are usually used for:

Communication equipment

Data Center

High-speed server

Therefore, it is necessary to control:

Single-ended impedance

Differential impedance

Common Requirements:

50 ohms

90 ohms

100 ohms

The control accuracy is even required to reach:

±5%

High-end products can achieve:

±3%

This places higher demands on the materials, the wiring, and the pressing accuracy.

Seven. Different Materials Selection

Most ordinary multi-layer boards are made of standard FR-4 material.

And for high multi-layer boards, they may be designed according to application requirements as follows:

High TG material

Improve heat resistance.

Low-loss materials

Reduce signal attenuation.

High-frequency materials

Suitable for RF and 5G devices.

For example:

Rogers Materials

Megtron material

Panasonic materials

The prices of these materials are significantly higher than those of ordinary FR-4.

VIII. Different Production Cycles

The ordinary multi-layer board manufacturing process is mature.

The production cycle is relatively short.

The high multi-layer board is due to:

More process steps

More testing items

The yield control is more stringent.

The production cycle is usually longer.

In particular:

Products above the 16th floor level

It often requires a longer period of time for process verification and quality inspection.

IX. Significant Cost Variations

The high cost of high-density multi-layer boards mainly comes from:

Increase in material costs

The number of pressing operations has increased.

The difficulty of drilling has increased.

The yield rate requirement is higher.

The cost of testing is higher.

Therefore:

At the same size,

The price of high-grade multi-layer boards is usually much higher than that of ordinary multi-layer boards.

In which fields are high-density multi-layer boards mainly applied?

Communication equipment

Including:

5G base station

Optical communication equipment

Core Switch

These products require the processing of a large amount of high-speed signals.

Data center server

The server motherboard usually adopts:

12th floor

Sixteen floors

PCB above the 20th layer

Meet the requirements of complex calculations.

Automotive Electronics

Applied to:

Autonomous driving system

Domain Controller

Battery Management System

Require high reliability and stability.

Medical equipment

For example:

CT equipment

MRI equipment

Medical monitoring system

Requires long-term stable operation.

Industrial Automation

High-end control systems require complex signal processing capabilities.

High-density multi-layer boards can meet the requirements of high integration.

How can one determine whether a manufacturer possesses the capability for high-quality multi-layer board production?

When choosing a supplier, the following aspects should be given particular attention:

Do you have experience in mass production of high-rise panels?

Key points to understand:

Cases involving more than 16 floors

Cases above the 20th floor

Does it have advanced pressing equipment?

The pressing ability directly affects the quality between layers.

Does it have the capability for deep hole machining?

Check:

Maximum thickness-to-diameter ratio

Drilling accuracy

Whether it has the ability for impedance control

High-speed products are particularly important.

Does it have a complete detection system?

Including:

AOI inspection

X-ray inspection

Slice analysis

Impedance testing