In Printed circuit Boards, traces are generally given two names depending on their placement in the stack of a PCB; Microstrip and Stripline. In a circuit board, both microstrip and stripline offer two distinct structures of line used in the layout of a PCB. Both strip lines and microstrips come in differential varieties and coplanar. Each of them gives off specific types of benefits while using high-frequency and high-speed signals. This article helps you understand the difference between strip lines and microstrips and guides you through the different benefits and routing styles each of them incorporates.
However, before getting into the details, it is crucial to understand the basic factor that makes both strip lines and microstrips differ from each other. For the strip lines located inside the stack of a PCB, the traces are fully disclosed to the material of the dielectric. At the same time, the properties of dielectric material will have a better impact on the propagating signal along the strip lines. Read along; you will get to know what factors cause differences between both types of traces.
What Is A Stripline?
A stripline lies inside the material substrate with around two planes (ground) sandwiching the substrate and stripline. This impregnation depicts that the transmission lines can only be available in the internal routing layers of a PCB. Thus, strip lines are mostly found in multilayered printed circuit boards. Also, the structure protects the stripline, reducing emissions.
What Is A Microstrip?
A microstrip refers to a planar communicating line that lies outside the material of the dielectric. The material of the PCB insulates and splits the tace signal from the ground plane. This means that the transmission line possesses air over it. Hence, the transmission line can only lie over the lower and upper PCB layers. Moreover, the air constant of the dielectric and the material of the board affect the impedance of the trace.
Differences: Stripline Vs. Microstrip
However, it’s hard to directly say which routing style suits you better or perfectly. Therefore, the difference helps you determine to choose the right one for your application. So, let’s discuss different areas that depict differences.
Location
As discussed above, the main difference between both strip lines and microstrips is their placement or location. Striplines lie inside the internal layers, particularly between two ground planes, whereas microstrips lie on the outer layers of a PCB.
Usage
Typically, you can select between whether to go with microstrips or stripline while routing the designs. Though, you need to consider some things before selecting between any routing styles.
- Choose a stripline routing style if you are looking for high-density tolerance impedance for your application. A stripline possesses greater density for impedance-controlled routing as compared to a microstrip. Thus, a thin and small stripline will offer the same value of impedance as a wider and bigger microstrip gives.
- Whereas you don’t have to choose any routing method if your circuit board contains short traces between close electronic components. However, you can still choose microstrips only if you need impedance control in your application.
- Furthermore, strip lines do not go well with ultra-high frequencies. Unfortunately, the Via integrating with the internal layer will behave like a distinct transmission line. This allows the surrounding parasitic capacitance to develop impedance continuity and signal losses.
- You can go for strip lines also if you want greater isolation between the layers of your design. This stripline routing style develops isolation in the internal layer, which seems impossible with microstrips. At the same time, this style of design doesn’t guarantee greater isolation between straplines of the same layer. Hence, you have to consider crosstalk before moving forward with the design.
- Last but not least, you can use both routing methods with high pin-count electrical components.
Characteristics Impedance
The characteristic impedance of the strip lines relies on the dielectric constant, the center conductor of the strip, and the cross-sectional geometry of ground planes. Furthermore, the characteristic impedance of the stripline decreases when the width of the strip increases. Whereas on the contrary, the characteristic impedance of the microstrip changes with increasing frequency.
Stripline Vs. Microstrip: Transmission Line
The calculation of routing requires parameters like the dielectric constant used in the dielectric layer of the PCB.
Microstrip
The microstrip routing on the upper and lower level of the circuit board reduces dielectric losses greater than stripline routing. This occurs because of negligible losses of air. Moreover, in microstrip routing, the conductor strip lies at the outside layer, which makes the fabrication process simple.
Whereas microstrip radiates greater energy because of air exposure. However, the constant of dielectric inside the layers of PCB is generally 1.4, whereas 1 for air. These variations determine the difference in impedance value between microstrips and strip lines.
Striplines
On the contrary, the stripline routing method has the benefit of sandwiching the traces of signals between planes (reference). This structure allows the manufacturing of narrower transmission lines over the same values of impedance needed for microstrip routing. Furthermore, the sandwich structure makes better insulation with the material of dielectric. Thus, allowing you to compress the trace routing.
Advantages and Drawbacks of Stripline Vs. Microstrip
Both microstrip and stripline offer their own types of benefits. Let’s see a glimpse of the pros of each routing style.
Stripline Benefits
- Striplines can protect and shield traces of signals from unknown invasive frequencies.
- The performance of this routing method will enhance up to 50MHz.
- Moreover, strip lines also offer low impedance, which leads to minimum crosstalk and emissions.
- Furthermore, this certain routing method also offers greater EMI characteristics.
Microstrip Benefits
- Microstrips contain open transmission line structures which make connections between the electrical components and the surface of the PCB easily.
- Moreover, you can also stack up microstrips on HD channels with lesser crosstalk. This makes it the perfect design for microwave IC and RF.
- Microstrips contain planar topology, which gives them a little immunity to circuit board fabrication tolerances.
- Furthermore, they also offer faster times of propagation.
- Last but not least, this routing method offers mechanical support and heat sinking simultaneously.
Cons
Similarly, each method of PCB routing does have disadvantages too. Let’s dive into the details to know more about them.
Stripline Drawbacks
Tough microstrips come in compact sizes and less price, but they seem loosier as compared to strip lines, waveguides, CPW, and coaxial lines.
Microstrip Drawbacks
- Striplines have implanted signal traces which makes them complex to debug. Generally speaking, it makes the prototyping and troubleshooting of the PCB more difficult.
- Striplines can not decouple easily.
- Moreover, proper matching leads to low impedance.
Which One Should You Select? Stripline Vs. Microstrip
Each transmission line of a PCB comes with its own advantages and disadvantages. Most PCBs with high frequency and high-speed needs high-density circuits. Therefore, you may end up using both of them in your application.
Modern printed circuit board tools aid in simplifying the routing configuration of stripline and microstrip. Moreover, the impedance calculators for PCBs also greatly help in determining the perfect layer configuration and width of the trace. Whereas the stack-up editors also facilitate using the right material and width of the board.
The combination of these tools aids you in choosing the best microstrip and stripline routing approach and configuration of layers with the routing layers.
Conclusion
Both microstrips and strip lines possess a slight structural distinction that changes their nature and properties greatly. However, every transmission line has certain properties that may tend you to use both in your high-speed and high-frequency circuit board to reduce losses. RayPcb hopes this clears all your doubts, yet if you still have any queries, then reach out to us.
