Single and Double-Sided PCB Stackup
The printed circuit board stackup arrangement is the basis of the entire PCB design system. Any deficiencies in the stackup design will ultimately affect the overall EMC performance.
In general, the design of the PCB stackup mainly comply with two rules:
1.Each alignment must have an adjacent reference layer (power or ground);
2.Keep the minimum spacing between adjacent main power and ground so as to provide a larger coupling capacitance.
For the two-layer PCB board, there is no problem with the stackup due to the small layer number. EMI radiation control is mainly considered from the wiring and layout.
Electromagnetic compatibility issues of single- and double-layer PCB become more and more prominent and serious. The main reason for this phenomenon is because the signal loop area is too large, not only produce a strong electromagnetic radiation, but also make the circuit sensitive to external interference. The easiest way to improve the electromagnetic compatibility of a line is to reduce the loop area of critical signals.
The key signal: From the electromagnetic compatibility point of view, the key signal mainly refers to those that can produce strong radiation and be sensitive to the external environment. Signals that produce strong radiation are typically periodic signals, such as low-level signals of clocks or addresses. Signal that is sensitive to interference refers to those analog signals with low level.
Single- and double-layer PCB boards are typically used in the low-frequency analog which is below 10KHz:
1.Power lines on the same level are routed radically and minimize the sum of the length of the lines;
2.Add a ground line next to the key signal line, and this ground should be as close to the signal line. This results in a smaller loop area, reducing the sensitivity of differential mode radiation to external interference. When a ground line is added next to a signal line, a loop of the smallest area is formed, and the signal current will certainly pass through this loop instead of the other ground path.
3.If it is a double-layer circuit board, you can place a ground wire along the signal line on the other side of the circuit board, just under the signal line, and try to make the line as wide as possible. The loop area thus formed is equal to the PCB board thickness multiplied by the signal line length.