With the rapid development of high-speed circuits and the increasing number of chip pins, PCBs have become more complex. Traditional 2-layer boards are no longer sufficient for high-speed circuit design. To prevent interference from electrical factors, signal layers and power layers must be separated, which necessitates the use of multilayer PCBs. Before designing a multilayer PCB, the number of layers—whether 4, 6, 8, or more—must be determined based on project requirements and circuit complexity.
Once the number of layers is decided, the placement of internal power and ground planes must be arranged, along with the distribution of different signals across the layers. Stack-up design is a key factor affecting the electromagnetic compatibility (EMC) performance of a PCB. A well-planned stack-up can significantly reduce electromagnetic interference (EMI) and crosstalk between high-speed signals.
Below is a summary of common stack-up configurations:
2-layer board: top – bottom
Note: In a typical 2-layer board, both layers are used for signal routing. These boards are suitable for low-speed applications since there is no dedicated power or ground plane, and thus no stack-up considerations are involved.
4-layer board: signal – ground – power – signal
Note: This is the most common 4-layer configuration. The top layer is typically used for optimal signal routing. Sometimes, the power layer is also used for routing. In some cases, all four layers are used for signal routing, depending on actual needs. However, it is generally recommended to maintain at least one solid ground plane.
6-layer board: signal – ground – signal – power – ground – signal
Note: This is a common 6-layer configuration, suitable when signal lines are relatively few. Signal routing is typically done on layers 1, 3, and 6. This stack-up offers good electromagnetic compatibility.
8-layer board: signal – ground – signal – ground – signal – power – ground – signal
Note: This is a typical 8-layer stack-up. Both this and similar configurations can achieve excellent electromagnetic compatibility performance.