The processing of the power plane plays a very important role in PCB design. In a complete design project, the processing of the power supply can usually determine the success rate of the project by 30%~50%. Today, 2PCB will introduce the 3 basic factors that should be considered in the processing of the power plane during PCB design.
1. When processing the power supply, the current carrying capacity should be considered first, which includes 2 aspects:
a) Whether the width of the power line or the width of the copper foil is sufficient to consider the power line width.
First, we need to understand the copper thickness of the layer where the power signal processing is located. Under conventional processes, the copper thickness of the outer layer (TOP/BOTTOM layer) of the PCB is 1OZ (35μm), and the copper thickness of the inner layer will be 1OZ or 0.5OZ according to the actual situation. For 1OZ copper thickness, under normal circumstances, 20mil can carry a current of about 1A; for 0.5OZ copper thickness, under normal circumstances, 40mil can carry a current of about 1A.
b) Whether the size and number of holes when changing layers meet the current carrying capacity of the power supply.
2. Secondly, the power path should be considered
a) The power path should be as short as possible. If it is too long, the voltage drop of the power supply will be more serious. Excessive voltage drop will cause project failure.
b) The power plane segmentation should be kept as regular as possible. Thin strips and dumbbell-shaped segmentation are not allowed.
c) When the power supply is segmented, the segmentation distance between the power supply and the power plane should be kept at about 20mil. If it is in some areas of the BGA, the segmentation distance can be kept locally at 10mil. If the distance between the power planes is too close, there may be a risk of short circuit.
d) If the power supply is processed on adjacent planes, try to avoid parallel processing between copper foil or traces. This is mainly to reduce interference between different power supplies, especially between some power supplies with large voltage differences. The overlap of the power plane must be avoided. If it is difficult to avoid, consider adding a ground layer in the middle.
3. When doing power segmentation, try to avoid the situation where adjacent signal lines are split across
The signal will have impedance mutation due to the discontinuity of the reference plane at the cross-segmentation point (as shown in the figure below, the red signal line has a cross-segmentation phenomenon), which will cause EMI and crosstalk problems. When doing high-speed design, cross-segmentation will have a great impact on signal quality.