Why is It so Difficult to Design RF and Microwave PCB

There are many problems in the design process and can have a serious impact on quality and productivity. For example, when embedding a designer's RF circuitry into other designers' PCBs, efficiency is bound to be compromised because they often use different design formats. In addition, designers are often forced to make changes in their designs to work with RF circuits. Since simulations are often performed in RF circuits, rather than in the context of the entire PCB, the significant impact of the board on the RF circuitry may be missed, and vice versa.

 

As RF content continues to increase, PCB designers and engineers realize that to improve productivity and product quality, it is best for them to address their own RF design challenges within their own design tools. Unfortunately, most desktop PCB design tools don't help them simplify this task.

 

For example, after modeling a circuit using an RF simulator, once the desired electrical performance is achieved, the simulator produces the copper foil shape of the circuit (usually in DXF format) for import into the PCB design tool. This process often causes some confusion for the designer, for example, the DXF file cannot be converted correctly and cannot be converted into a copper foil shape. In this case, the designer needs to manually import the DXF file, which may cause human error and error in the shape and size, resulting in failure of the RF circuit.

 

The challenges faced by PCB designers or engineers in trying to design Layouts for RF and microwave circuits are far more than just the above. However, fortunately, there are small solutions in your design tools that can play an important role in resolving these challenges. This white paper will introduce you to six tips to help you simplify any RF PCB design tasks and reduce stress!

 

1. Maintain a good, accurate RF shape

 

Some serious errors like the one described above can cause poor circuit performance or even work. To minimize errors, simplify RF design tasks, and increase productivity, PCB design tools provide import control for complex copper foil shapes. For example, you can create a usable copper foil shape by controlling the layers in the DXF file and re-imaging them into the CAD electrical system layer (Figure 1).

 

Maintain a good, accurate RF shape

 

Design tools that allow users to control the DXF import process will help reduce human error and errors, such as when imported files cannot be converted to copper foil shapes due to high complexity.

 

2. Keep the corner shape (CORNERS SHARP)

 

When designing copper foil shapes for RF and microwave, an important aspect is the ability to create Gerber files with sharp corners. Excellent PCB design tools can simplify this process. For example, drawing a shape with a 50 mm line tends to have a smaller radius than a 50 mm circular aperture drawing. When designing a Gerber file, the design tool can obtain a sharp corner by correctly converting the line width automatically (Figure 2).

 

 Keep the corner shape (CORNERS SHARP)

 

Figure 2: An effective PCB design tool automatically considers the line shape used to draw shapes to calculate the exact line width, helping you easily create sharp corners.

 

3. Automatic chamfering (CHAMFERED CORNERS)

 

Chamfering is often used in RF and microwave circuits to reduce the segmentation discontinuity impedance between the supply line and the capacitor, thereby improving the frequency performance of the MMIC. The distance between the 90o corner and the chamfer is crucial. Therefore, designers need to adopt an automated approach to specify the chamfer ratio that needs to be generated based on the design. If the PCB design tool can automatically enforce the required chamfer ratio based on the design rules, designers and engineers will benefit from it, saving time and improving design quality (Figure 3).

 

Automatic chamfering (CHAMFERED CORNERS)

 

Figure 3: The ability to set chamfering rules simplifies the design process and saves time.

 

4. Use automation to help arrange COPLANAR and CHANNEL WAVEGUIDES

 

Coplanar waveguides and channel waveguides are also common in RF and microwave designs. When set up manually, this task can be time consuming and error prone. Designers need to control the specific distance between the trace and via, and the distance between one via and the other via to ensure that the circuit has the performance required to meet the design requirements. Design tools can also help in this area by reducing the complexity and quality by providing via usage control and automatic use of vias (Figure 4).

 

Use automation to help arrange COPLANAR and CHANNEL WAVEGUIDES

 

Figure 4: If the PCB design tool can control the establishment of coplanar and wave-guide vias, it will help to significantly reduce design errors and shorten design time.

 

5. Use automated STITCHING VIAS

 

Another important aspect of RF design is ensuring that vias are properly masked to specific areas. Although this task can be done manually by the designer, this process is extremely time consuming. If the PCB design tool automates this process, it will shorten the design cycle time and ensure that all your design rules are met. With such tools, designers can specify via mode to generate specific rules and leave the rest of the work to the PCB design tool.

 

6. Use design rules to ensure that “design is correct”

 

PCB design tools that support RF design typically allow multiple design rules to be set: via type for different copper areas; via type to which via itself needs to be connected; distance from the edge of the copper foil area to via; a via to The distance of the next via; the via mode type; and whether the Faraday cage can be created simply by adding via to the outer edge of the copper foil area (Fig. 5).

 

 Use design rules to ensure that “design is correct”

 

Figure 5: Using PCB design tools that support RF design, you can set design rules for generating via mode and automatically enforce these rules in your design, saving you time and ensuring that all your design rules are met .

 

In conclusion

 

Today PCB designers and PCB engineers face increasing design challenges, so it is necessary to have a PCB design tool that efficiently supports RF and microwave designs. Manually creating complex copper foil shapes, chamfers, and via modes is a time consuming and error prone process. By using effective design tools to increase the ability to operate RF and microwave elements, designers can focus on implementing more features and reducing device size while maintaining high product quality.