The processing of power plane plays a very important role in PCB design. In a complete design project, the processing of power supply can usually determine the success rate of 30% – 50% of the project. This time, we will introduce the basic elements that should be considered in power plane processing in PCB design.
1. When doing power processing, the first consideration should be its current carrying capacity, including two aspects.
(a) Whether the power line width or copper sheet width is sufficient. To consider the power line width, first understand the copper thickness of the layer where the power signal processing is located. Under the conventional process, the copper thickness of the outer layer (top / bottom layer) of PCB is 1oz (35um), 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 conditions, 20MIL can carry about 1A current; 0.5oz copper thickness. Under normal conditions, 40mil can carry about 1A current.
(b) Whether the size and number of holes meet the power supply current flow capacity during layer change. First, understand the flow capacity of a single through hole. Under normal circumstances, the temperature rise is 10 degrees, which can be referred to the table below.
“Comparison table of via diameter and power flow capacity” comparison table of via diameter and power flow capacity
It can be seen from the above table that a single 10mil via can carry 1A current. Therefore, in the design, if the power supply is 2A current, at least 2 vias should be drilled when using 10mil vias for hole replacement. In general, when designing, we will consider drilling more holes on the power channel to maintain a little margin.
2. Secondly, the power path should be considered. Specifically, the following two aspects 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 serious. Excessive voltage drop will lead to project failure.
(b) The plane division of power supply shall be kept as regular as possible, and thin strip and dumbbell shaped division are not allowed.