In the core architecture of electronic devices, PCB is like a complex neural network, carrying the signal transmission and energy supply between electronic components. With the rapid development of electronic technology towards miniaturization and high performance, a more advanced type of PCB has emerged – HDI board. HDI board is significantly different from ordinary PCB in many aspects, which profoundly affects the performance and development direction of electronic equipment.

Definition and structural differences

Ordinary PCB is a printed board that forms point-to-point connections and printed components on an insulating substrate according to a predetermined design. Its structure is relatively simple. It is generally made of copper-clad boards through drilling, circuit etching, electroplating and other processes. The circuit layout and via settings are relatively conventional, and it is suitable for electronic devices that do not require high space and performance.

HDI boards emphasize high-density interconnection. It uses micro-hole technology and advanced means such as laser drilling to achieve more electrical connections in a smaller space. HDI boards usually have thinner substrates and finer circuits, and the number of layers is relatively large. They can integrate more functions in a limited space, greatly improving the integration of electronic devices.

 Production process comparison

Drilling process

Ordinary PCB drilling mostly adopts mechanical drilling method, and the drill bit rotates on the copper clad board to drill the required hole diameter. Although this method is low-cost, the hole diameter is relatively large, generally above 0.3mm, and it is easy to have deviations for high-precision drilling of multi-layer boards.

HDI boards widely use laser drilling technology, using high-energy-density laser beams to instantly melt or vaporize the board to form micro-holes, and the hole diameter can be as small as 0.1mm or even smaller. Laser drilling has extremely high precision and can realize special hole types such as blind holes (only connecting the outer layer and the inner layer) and buried holes (connecting the inner layer and the inner layer), which greatly improves the flexibility and density of line connections.

 Line etching process

When etching lines on ordinary PCBs, the control over line width and line spacing is limited, and the line width/line spacing is generally around 0.2mm/0.2mm. During the etching process, problems such as rough line edges and uneven lines are prone to occur, affecting the quality of signal transmission.

The production of HDI boards requires extremely high circuit etching accuracy. Advanced HDI board production lines can achieve line widths/line spacings as low as 0.05mm/0.05mm or even finer. By using more sophisticated exposure equipment and etching processes, the line edges are ensured to be neat and the line widths are uniform, meeting the stringent requirements of high-speed and high-frequency signal transmission on line quality.

Lamination process

The lamination process of ordinary PCBs mainly involves bonding multiple layers of copper-clad boards together by hot pressing, with the focus on ensuring the basic connection firmness between the layers. During the lamination process, the requirements for interlayer alignment accuracy are relatively low.

Due to the large number of layers and complex structure of HDI boards, the lamination process requirements are extremely strict. Not only must the layers be tightly fitted, but also high-precision interlayer alignment must be ensured to achieve precise connection between tiny holes and circuits. During the lamination process, parameters such as temperature, pressure, and time need to be precisely controlled to prevent defects such as interlayer offset and bubbles, and to ensure the overall performance of the HDI board.

 Differences in performance characteristics

Electrical properties

Ordinary PCBs have certain limitations in terms of signal transmission speed and frequency. As the signal frequency increases, problems such as signal attenuation and crosstalk gradually become prominent. This is because its relatively thick lines and larger vias will produce larger resistance, inductance and capacitance, affecting the integrity of the signal.

HDI boards rely on fine lines and micro-hole design to greatly reduce line resistance, inductance and capacitance, effectively reducing losses and interference during signal transmission. It performs well in high-speed and high-frequency signal transmission, and can meet application scenarios such as 5G communications and high-speed data storage that have extremely high requirements for signal transmission quality.

Mechanical properties

The mechanical strength of ordinary PCBs mainly depends on the material and thickness of the substrate, and there are certain bottlenecks in miniaturization and thinness. Due to its relatively simple structure, it is prone to problems such as board deformation and solder joint cracking when subjected to complex stress.

HDI boards use thinner, lighter and stronger substrates, and at the same time improve the overall mechanical stability by optimizing the multi-layer structure design. While ensuring thinness, it can withstand a certain degree of mechanical stress such as vibration and impact, and is suitable for mobile electronic devices and other fields that have strict requirements on device volume and weight.

Different application fields

Ordinary PCBs are widely used in some electronic devices that do not have high requirements for performance and space due to their low cost and relatively simple manufacturing process, such as ordinary household appliances (such as televisions, washing machines), low-end consumer electronics products (such as ordinary radios, simple remote controls) and non-core circuit parts in some industrial control equipment.

HDI boards are mainly used in high-end electronic equipment due to their excellent performance and high-density integration capabilities. For example, smartphones need to integrate a large number of functions in a small space, and HDI boards can meet their needs for high-speed signal transmission, miniaturization, and thinness; in the computer field, server motherboards, high-end graphics cards and other components with extremely high performance requirements also use HDI boards in large quantities to ensure high-speed data processing and transmission; in addition, in high-precision fields such as aerospace and medical equipment, HDI boards also play a key role, providing support for the stable operation of complex electronic systems.

There are significant differences between HDI boards and ordinary PCBs in terms of structure definition, manufacturing process, performance characteristics and application areas. With its advanced technology and excellent performance, HDI boards play an important role in promoting the development of electronic equipment towards miniaturization and high performance, while ordinary PCBs continue to show their cost advantages in mid- and low-end application areas. Understanding the difference between the two will help electronic equipment manufacturers choose appropriate circuit board solutions according to product requirements and promote the continuous development of the electronics industry.