The number of layers in a PCB is determined by the complexity of the circuit board. From a PCB manufacturing perspective, multi-layer PCBs?are created by stacking and laminating multiple "double-sided PCBs." However, the layer count, the stacking sequence between layers, and the choice of materials are decisions made by the PCB designer. This is what we refer to as "PCB layer stack design."
The number of layers and stacking scheme in PCB design?are determined by several factors:
- Hardware Cost: The number of PCB layers is directly related to the overall hardware cost. More layers result in higher costs. Consumer electronics products, such as laptops, typically have a limit on the number of layers, usually ranging from 4 to 6 layers, with very few exceeding 8 layers.
- High-Density Component Routing: High-density components, like those in BGA packages, often dictate the number of layers required for routing on the PCB.
- Signal Quality Control: For PCB designs with concentrated high-speed signals, an emphasis on signal quality may necessitate reducing adjacent layer routing to minimize signal crosstalk. This can lead to an increase in the number of PCB layers. Conversely, if signal quality control is not a strict requirement, adjacent layer routing can be used to reduce the number of layers.
- Signal Definition in Schematics: The definition of signals in the schematic design plays a crucial role in ensuring smooth PCB routing. Poorly defined signals in schematics can lead to non-optimal routing and an increase in the number of layers.
- PCB Manufacturer's Manufacturing Capability: PCB designers must consider the manufacturing capabilities of the PCB manufacturer, such as their fabrication processes, equipment capabilities, and commonly used PCB material types when proposing layer stack designs, including layer count, stack-up methods, and layer thickness.
Designing a PCB layer stack involves seeking a balance and setting priorities among the aforementioned factors.
