A few basic elements of Power plane processing in PCB design
The processing of the power plane plays an important role in PCB design
The processing of the power plane plays an important role in PCB design. Usually, it determines 40%~60% of the success rate in a complete design project. Now let introduce some basic elements of power plane processing in PCB design.
When designing the power supply, we must consider its current carrying capacity first, which contains two aspects:
1) Consider the power line width: Whether the power line width or the width of the copper is sufficient.
First, figure out what the copper thickness of the layer where the power signal is processed. Normally the outer layer of the PCB is BOTTOM and TOP layer, the copper thickness is 1OZ (35μm), and the inner layer copper thickness will be 0.5OZ~1OZ according to the actual situation. For 1OZ copper thickness, under normal circumstances, 18mil~20mil can carry about 1A current; for 0.5OZ copper thickness, under normal circumstances, 35mil~40mil can carry about 1A current.
2) When changing layers, whether the size and the number of holes meets the current flow capability of the power supply.
First, we must understand the flow capacity of a single via. In the normal case of a 10 degrees temperature rising, refer to the table below.
vias diameter (mm)
Power flow and through hole aperture capacity comparison table
As can be seen from the above table, a single 10 mil via can carry 1 A current, so if the power supply is 2 A current when designing, at least 2 or more vias should be used when using a 10 mil via for hole punching. Generally, we’ll consider to design more holes in the power channel to maintain a certain margin.
Secondly, we have to consider the power path. The following are the two main aspects.
1) The power path should be as short as possible. If it is too long, the voltage drop of the power supply will be serious. If the voltage drop is too large, the project will fail.
2) The power plane should be divided as regular as possible, and no sliver and dumbbell split.
3) If the power supply is treated in an adjacent plane, it is necessary to avoid parallel processing between the copper or the traces. This is mainly to reduce the interference between different power supplies, especially between power supplies with large voltage differences, it must manage to avoid the overlapping issue, If it is difficult to avoid, consider adding the interlayer in the middle.
4) When dividing the power supply, the distance between the power supply and the power plane should be kept as close as possible to 20 mil. If it is in the BGA area, a 10mil distance can be maintained locally. If the distance between the power planes is too close, there may be a risk of short circuit.
When doing power splitting, try to avoid the situation where adjacent signal lines are split. Since the reference plane is discontinuous, there will be a sudden change in impedance, which will cause EMI and crosstalk. When doing high-speed design, cross-segmentation will have a great impact on signal quality.
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