Explanation of common PCB terms – stripline and microstrip line

The types of wiring on the PCB mainly include signal lines, power supply, and ground wires. Among them, signal lines are the most common wiring, and there are many types. According to the physical structure of the wiring, it can be divided into strip lines and microstrip lines.

A stripline is a line of copper tape placed in the middle of dielectric between two layers of conductive planes, buried inside the PCB.

PCB Stripline

The blue part is the conductor, the green part is the insulating dielectric of the PCB, and the stripline is a strip wire embedded between the two layers of conductors.

Because the stripline is embedded between two layers of conductors, its electric field is distributed between the two conductors (planes) surrounding it, and it will not radiate energy or be interfered by external radiation. But because it is surrounded by dielectric (dielectric constant is greater than 1), the signal transmission speed in the stripline is slower than in the microstrip line!

Stripline can better prevent RF radiation, but it can only be used at lower transmission speeds because the signal layer is between two reference planes, and there will be capacitive coupling between the two planes, resulting in a reduced edge change rate of high-speed signals. . The capacitive coupling effect of stripline is more significant when the edge change rate is faster than 1ns.

Microstrip is a strip conductor (signal line) separated from the ground plane by a dielectric.

PCB Microstrip

The blue part is the conductor, the green part is the insulating dielectric of the PCB, and the blue piece above is the microstrip line.

PCB Microstrip

The yellow part is epoxy organic material.

Since one side of the microstrip line is exposed in the air (which can form radiation to the surroundings or be interfered by surrounding radiation), and the other side is attached to the insulating dielectric of the PCB, part of the electric field it forms is distributed in the air, and the other side is Part of it is distributed in the insulating medium of the PCB. However, the signal transmission speed in microstrip line is faster than that in stripline (stripline). This is its outstanding advantage!

Microstrip lines provide PCBs with RF immunity while also allowing for faster clock or logic signals than strip lines. The disadvantage of microstrip is that the external signal layer of the PCB will radiate RF energy into the environment unless there is metal shielding above and below this layer.

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