If the density of the component on the 4 -layer board is relatively large, it is better to use 6 layers. However, some overlapping schemes in the 6 -layer board design are not good enough for the shielding of the electromagnetic field, and the reduction of the transient signal of the power supply flow discharge is very small. Two examples are discussed below.

     First of all, the power supply and land are placed on the second and fifth floor. Due to the high copper covering impedance of the power supply, it is very unfavorable to the control of the co -mode EMI radiation. However, from the perspective of the impedance control view of the signal, this method is very correct.

     The second case is placed on the third and fourth layers of the power supply and land. This design solves the problem of copper -covered impedance of the power supply. Due to the poor electromagnetic shielding performance of the first and 6th layers, the differential model EMI has increased. If the number of signal lines on the two outer layers is small, the length of the wiring is very short (shorter than the 1/20 of the signal high wavelength), then this design can solve the problem of differential mode EMI. Fill the non -component and non -wiring areas on the outer layer and fill the copper cover area (every 1/20 wavelength to the interval), and the suppression of the differential mode EMI is particularly good. As mentioned earlier, the copper -paving area should be connected to the internal ground floor.

     General high -performance 6 -layer board design generally uses the first and 6th layers of cloth as the formation, and the 3rd and 4th layers take the power supply and ground. Because between the power layer and the ground layer are the dual -micro -signal line layer of the two layers, the EMI suppression ability is excellent. The disadvantage of the design is that there are only two layers of the wiring layer. As mentioned earlier, if the outer wiring is short and copper in the no wiring area, the traditional 6 -layer board can also be used to achieve the same stack.

     Another 6 -layer plate layout is signal, land, signal, power, land, land, signal, which can realize the environment required for high -level signal integrity design. The signal layer is adjacent to the ground layer, and the power layer and ground layer pair. Obviously, the deficiencies are stacking imbalances.

     This usually causes trouble for processing and manufacturing. The method of solving the problem is to fill all the blank areas on the 3rd layer of the third floor. If the copper cover density of the 3rd layer is close to the power layer or ground layer after the copper is filled, this board can not be counted as a structural balanced circuit board. Essence Filling the copper area must be connected to the power or ground. The distance between the connecting holes is still 1/20 wavelength, and it is not necessarily connected everywhere, but ideally should be connected.