The first time I heard a presentation on high speed design techniques, it went straight over my head. Since this was at the beginning of my career as a , I’m sure that it was my inexperience that caused the confusion. The whole concept of stripline and microstrip routing didn’t make any sense to me and I thought that the instructor was talking about a completely different type of PCB designs that I wasn’t familiar with. Fortunately, my confusion was quickly straightened out when I learned that it isn’t the PCB schematic itself that is considered to be stripline or microstrip. Instead, stripline and microstrip are different methods of routing high speed transmission lines on a PCB design.
Understanding stripline and microstrip can be difficult. So whether you are new to PCB design schematic or if you are looking for a refresher on the topic, this basic review is for you.
Understanding Stripline and Microstrip
Stripline and microstrip, what are they?
Stripline and microstrip are methods of routing high speed transmission lines on your PCB design. Stripline is a transmission line trace surrounded by dielectric material suspended between two ground planes on internal layers of a printed board. Microstrip routing is a transmission line trace routed on an external layer of the board. Because of this, it is separated from a single ground plane by a dielectric material.
With the transmission line on the surface layer of the board, microstrip routing has better signal characteristics than stripline. board fabrication is also less expensive with microstrip since the layer structure of one plane and one signal layer makes the manufacturing process simpler. Stripline can be more complex to manufacture because is requires multiple layers to support the embedded trace between two ground planes. However, the width of a controlled impedance trace in stripline is less than an impedance trace in microstrip of the same value. This is because of the second ground plane. These smaller trace widths enable greater densities, which in turn enables a more compact design. The internal layer routing of stripline also reduces EMI and provides better hazard protection.
Stripline and microstrip have different benefits. The decision of which is the better method should be based on the needs of the design. In a dense high speed design, a mixture of both methods on a multi-layer board is often used to accomplish the design goals.
Furthermore, it is extremely important to maintain controlled impedance across the design when routing transmission lines on a high speed design. The layer of the PCB that the transmission line is routed on, the physical characteristics of the transmission line trace, and the characteristics of the
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