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PCB develops towards HDI - from single-layer to substrate-like PCB (SLP)

HDI is the abbreviation of high density interconnector, which is a circuit board with a relatively high circuit distribution density using micro-blind buried hole technology. While electronic design is continuously improving the performance of the whole machine, it is also striving to reduce its size.

From mobile phones to small portable products such as smart weapons, HDI technology can make the design of terminal products more miniaturized, while meeting higher standards of electronic performance and efficiency.

Table of Contents

High density and small aperture PCB – more and more mature

High density and small aperture PCB-more and more mature
High density and small aperture PCB-more and more mature

At present, PCB is upgraded from the early single-layer PCB, double-layer PCB and multi-layer PCB boards to HDI Micro via PCBs, HDI Any Layer PCBs, and the current hot substrate-like PCB, and the product line width and line spacing are gradually reduced.

PCB develops towards HDI
PCB develops towards HDI

Compared with traditional PCB, HDI PCB can achieve smaller aperture, thinner line width, less number of through holes, save PCB routing area, greatly increase component density and greatly improve radio frequency interference/electromagnetic wave interference, etc.

Compared with HDI boards, SLP (substrate-like PCB) can shorten the line width/line distance from HDI’s 40/50 microns to 20/35 microns, and the number of electronic components in the same area can reach twice that of HDI. It has been used in high-end mobile phone products such as Apple and Samsung.

The process of PCB board products is upgraded, the number of layers of copper clad laminates(CCL) is increased, and the performance level of key technical indicators is improved. With the upgrading of PCB products, the production process is also adjusted and changed. At present, there are three main production processes for PCB and IC substrates, namely subtractive method, additive method and improved semi-additive method.

The yield rate of the subtractive method is very low in the production of fine circuits, while the additive method is suitable for making fine circuits, but the cost is high and the process is immature. The semi-additive method can make the signal lines more tightly wired and the distance between the conductive paths is shorter, which can greatly improve the yield, and is mainly used in the production of SLP (substrate-like PCB).

With the increase of product density, the number of layers of copper clad laminates increases, and copper clad laminates account for about 30% of the total cost of PCB boards, which will significantly increase the cost of PCBs. The performance of the copper clad laminate directly affects the speed and quality of signal transmission in the PCB board. Generally, the dielectric constant (Dk) and dielectric loss factor (Df) are used as the inspection indicators. Dk affects the propagation speed of the signal, and the Df value mainly affects the signal transmission quality.

At present, in high-speed PCB, high-frequency PCB, and RF board products, the Dk value and Df value have been significantly reduced to ensure information transmission. The improvement of PCB board performance has gradually increased the production capacity and technical level requirements of core equipment such as presses and drilling rigs, and increased the capital investment requirements of enterprises.

PCB application – rapid growth in the server field

PCB application-rapid growth in the server field
PCB application-rapid growth in the server field

PCB is widely used in communication, consumer electronics, computer, automotive electronics, industrial control, military, aerospace, medical equipment and other fields.

According to relevant data, the largest downstream application of the global PCB market in 2021 was the communications field, accounting for 32%; followed by the computer industry, accounting for 24%; consumer electronics, accounting for 15%; and the server field accounting for 10%, the market size is 7.804 billion US dollars, and it is expected to reach 13.294 billion US dollars in 2026, with a compound growth rate of 11.2%. It is the fastest growing field in the downstream, higher than the industry average of 4.8%.

Growth rate of global PCB downstream applications
Growth rate of global PCB downstream applications

Other downstream application fields are rapidly expanding and continuously upgrading, and PCBs in the server field are developing towards high speed and high frequency. PCB is developing in the direction of miniaturization, portability and multi-function.

For example, in the field of consumer electronics, due to the continuous development of miniaturization and functional diversification of smartphones and tablet computers, PCBs need to carry more components and reduce their size . In the field of computers and servers, in the high-speed and high-frequency 5G era and the wave of AI, the communication frequency and transmission rate have increased significantly. PCBs need high-frequency and high-speed operation, stable performance, and can undertake more complex functions to meet the requirements of low dielectric constant and medium. Specification requirements for loss factor and low roughness.


At present, servers/memory require six to sixteen layers of boards and packaging substrates. High-end server motherboards have more than sixteen layers, and back planes have more than twenty layers. In the future, as the demand for servers increases, the technical level of PCBs needs to be improved, non-stop upgrading.

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