Layer Structure: In multi-layer PCBs, layers are typically arranged in an even number, such as 4, 6, 8, 10, or more, and are sandwiched together with insulating material known as the substrate or core.

Conductive Layers: Conductive layers are composed of copper traces forming the electronic circuits. Signals and power planes are strategically distributed across various layers to optimize performance.

Insulating Layers: Insulating layers, often made of prepreg or core material, ensure electrical insulation between adjacent conductive layers.

Vias: Vias are tiny holes drilled through insulating layers to establish connections between conductive traces on different layers. Vias can be plated or non-plated based on design requirements.

Advantages: Multi-layer PCBs offer numerous benefits, including reduced size and weight, enhanced signal integrity, and improved thermal performance. They enable higher component density and intricate circuit designs.

Complex Designs: Multi-layer PCBs are integral to complex electronic devices like computers, smartphones, and networking equipment, thanks to their ability to accommodate sophisticated circuitry.

Signal Integrity: The use of multiple layers allows for the separation of sensitive signals from noisy ones, contributing to superior signal integrity. 

Power and Ground Planes: Multi-layer PCBs often incorporate dedicated power and ground planes to efficiently distribute power and minimize noise.

Manufacturing Process: Manufacturing multi-layer PCBs involves intricate processes like layer stacking, lamination, and via drilling, making it more complex than single or double-layer boards.

Cost and Complexity: While multi-layer PCBs may be pricier and more complex to produce than single or double-layer counterparts, the performance and space-saving advantages justify the investment.

Overall, multi-layer PCBs play a critical role in modern electronics, enabling compact designs and enhanced performance across a wide range of applications.