One, microstrip line microstrip line
The strip trace on the surface of the PCB, as shown in the figure, the yellow part is the copper skin, the green part is the PCB solder mask layer, the yellow-green part in the middle is the plate, and the yellow part above is the microstrip line.
Second, the strip line stripline
The strip trace buried inside the PCB, as shown in the figure, the yellow part is the copper skin, the yellow-green part in the middle is the plate, and the yellow part in the middle is the stripline.
Three, EMC analysis:
One side of the microstrip line is exposed in the air (with a layer of solder mask attached to the surface), which can form radiation to the surrounding or be disturbed by the surrounding radiation, while the other side is attached to the insulating dielectric of the PCB, so part of the electric field it forms is distributed in the air , and the other part is distributed in the insulating medium of the PCB.
The stripline is embedded in the middle of the board and loaded between two layers of copper skin, so the electric field it forms is distributed in the PCB, and will not radiate energy, nor will it be disturbed by external radiation.
4. SI analysis:
The signal transmission rate is related to the dielectric constant of the adjacent medium of the line. The larger the dielectric constant, the slower the signal transmission. The dielectric constant of the air is 1, the dielectric constant of the sheet is 4-5, the dielectric constant of the solder mask is generally 3-4, and the solder mask layer is thin. It can be seen from the above model that the signal transmission speed of the microstrip line is faster than that of the strip line, which is its outstanding advantage.
Five, practical application analysis:
The above analysis shows that the EMC of the microstrip line is poor, but the signal transmission is fast; the EMC of the strip line is good, but the signal transmission is slow. In the actual design, we have to consider these factors.
Taking DDR3 wiring as an example, data lines/address lines of the same length are required in the group, try to go on the same layer, and avoid some strip lines and some microstrip lines. Because if part of the stripline and part of the microstrip line are used, even if the equal-length constraint rule is set and the signal line is controlled by equal length, the signal timing is still affected due to the different transmission speeds of the stripline and the microstrip line, which may seriously cause DDR communication fails or does not reach the designed rate. Let me say one more thing, vias will also affect the signal transmission rate, so the number of vias in the same group of signal lines should be consistent .
If the microstrip line is used, EMI issues must be considered. It is generally recommended to add a shield to the DDR3 running the microstrip line to avoid excessive electromagnetic radiation.
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这是一段测试代码
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//为了防止系统判断推荐受影响
# deb cdrom:[Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)]/ xenial main restricted
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial main restricted
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates main restricted
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial universe
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates universe
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial multiverse
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates multiverse
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security main restricted
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security universe
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security multiverse