In PCB design, the term "layer" refers to the various copper layers used for routing signals. These include the top and bottom signal layers, which are commonly used for wiring, as well as the silkscreen layers (top and bottom) and the non-copper layer (such as the solder mask or paste). On the other hand, a "plane" refers to an internal copper layer that is typically used for power (VCC) or ground (GND) connections in multi-layer boards (typically 4 layers or more). A board can have up to 16 internal planes, depending on its complexity.
The **layer** is considered a "positive film," meaning that where there is a trace, it represents copper. In contrast, the **plane** is a "negative film," also known as the "anti-etch" method. This means that the plane itself is a solid copper area, and when you draw lines on it, you are removing copper—essentially creating openings or cutouts in the copper layer.
Planes are often used for grounding because they allow for automatic connections through vias or pads. Although both layers and planes contain copper, the plane's design helps reduce data processing load, especially in large boards or older systems. For this reason, tools like Allegro use negative films for planes, which significantly reduces file size and improves performance.
When working with software like Altium Designer, you can access the "Layer" option for signal layers and the "Plane" option for internal planes. You'll notice that the Layer is listed under Signal Layers, while the Plane is found under Internal Planes. Adding vias to a plane layer will show cross symbols, indicating their connection to the plane.
Additionally, a plane can be split into multiple regions using traces, allowing each section to be connected to different networks. This technique is known as "internal layer splitting." It’s a common practice to assign specific nets to each region of the plane for better power distribution and signal integrity.
Overall, understanding the difference between layers and planes is essential for efficient PCB layout. While layers are used for signal routing, planes are primarily used for power and ground, offering advantages in terms of connectivity, performance, and design efficiency.
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