In the context of multilayer PCB, a frequently mentioned concept is interlayer connection or interlayer interconnect. This technique involves the electrical connection between different circuit layers of a PCB through vias, enabling information transmission and power supply across layers. This ensures multilayer connectivity and signal transmission within the circuit. In this article, we will delve into this topic for a comprehensive understanding.
How is Interlayer Connection Achieved
As we know, the internal structure of a PCB is formed by alternating layers of copper foil and insulating materials. Electrical signals flow within the copper layers and reach the designated layer through the insulating layers. The core of achieving this interlayer connection lies in the use of vias.
PCB vias are a primary technology used for connecting different layers. Depending on the project requirements, vias come in different types. These include through-holes that penetrate the entire PCB to achieve electrical connections between different layers; blind vias that penetrate from the outer layer to an internal layer without going through the entire board; and buried vias that exist solely between internal layers without exposing themselves on the outer surface. As the trend toward miniaturization of electronic devices intensifies, HDI PCB increasingly utilize microvias to achieve more complex interlayer connections within limited space.
For high-power applications, such as power modules and high-frequency circuit boards, conductive pillars are also used for interlayer connection. This technique involves filling the vias with conductive materials to enhance the stability of the electrical connection and improve heat dissipation performance, thereby addressing challenges posed by high power or thermal loads.
Design Considerations for Interlayer Connection
A well-thought-out interlayer connection design is crucial to the overall performance of a PCB, covering multiple aspects such as electrical performance, thermal management, and manufacturing costs. First, in terms of electrical performance, since electrical signals may experience interference when transmitting between different layers, especially in high-speed signal transmission, appropriate routing strategies should be considered during design to minimize issues like signal distortion and noise. Additionally, optimizing the via size, spacing, and the number of routing layers can ensure impedance consistency in interlayer connections, thereby reducing signal reflection and distortion.
Further Reading: PCB Layout Design Guide for Beginners
Beyond electrical performance, thermal management is equally critical, especially in high-power projects, as the transmission of electrical signals generates more heat, directly impacting the reliability of the PCB. Different materials perform differently under high-temperature conditions, so material selection during design should be carefully considered based on specific project requirements and environmental factors. This involves key parameters such as thermal conductivity, heat dissipation performance, and thermal expansion coefficient.
While ensuring electrical performance and thermal management, manufacturing costs are also a key factor that cannot be overlooked during the design process. PCB manufacturing costs are closely related to the materials used, via types, and services provided by the manufacturer. In interlayer connection design, the type of vias is most directly related to cost. Standard vias, due to their versatility and lower manufacturing costs, are suitable for most application scenarios. Blind and buried vias, although relatively more expensive to manufacture, can enhance circuit complexity and performance, especially for high-end applications. Microvias, although the most expensive to manufacture, hold significant value in devices with extremely high space and performance requirements, such as smartphones and high-performance computing equipment.
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