How to Optimize Your Rigid Flex PCB Stackup Design

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Rigid-Flex PCB stackups are a mainstay in many PCB designs today. They are among the most popular design team options, surpassing single-sided and double-sided boards. Rigid flex PCB stackups help manufacturers reduce costs, increase packaging yield and improve their overall bottom line. The key to successfully designing these types of boards is to avoid errors when balancing mechanical and electrical parameters.

By carefully optimizing the rigid flex PCB stackup design, you can promptly meet your manufacturability and performance requirements. This article overviews how to optimize your rigid flex PCB stackup design.

rigid flex design guide

Ways to Achieve an Optimal Rigid Flex PCB Stackup

Keep Connectors in Mind

The connectors on a rigid flex board can impact the final product's performance and reliability. Connectors ensure that signals are adequately transmitted from one component to another when you are designing a board that has high frequencies and power levels, it is essential to consider these factors when placing connectors.

For example, if you are designing a board with high frequencies, you may want to consider using surface mount (SMT) connectors instead of through-hole (TH) connections. SMT connections are more reliable at higher frequencies because they have better shielding and can handle higher currents than TH connections.

Pay Attention to the Panels

The panels are the layers of copper that make up the rigid flex PCB stackup. When designing a PCB stackup, you want to ensure that each panel is optimized for its purpose. That way, you can achieve the best results from your design.

Here are some tips on how to optimize each panel:

Top Copper (Top Side) – This is the top layer of copper that goes through all of your vias and connects to your PCB bottom side. It should be made with single-sided FR4 material so it will be flexible enough to allow for flexing during use without being too thin or brittle. The thickness of this copper also needs to be thick enough, so there are no issues with signal integrity when flexing occurs during use.

Bottom Copper (Bottom Side) – This is the bottom layer of copper that connects directly to the top side via connections and provides electrical connections between components on both sides of the PCB during use. It should be made with double-sided FR4 material to provide good mechanical strength and rigidity during operation without being too costly or difficult to manufacture due to its thickness requirements (1 oz per square foot minimum).

Consider a Prepreg Instead of a Laminate

Many PCB designers are not aware that there is a difference between a laminate and prepreg. There are several benefits of using prepreg over a laminate in your design process:

  • Prepreg allows for more control over the mechanical properties of your RF circuit board.
  • The mechanical properties are more consistent than with laminates.
  • You can use higher copper weights without sacrificing strength or stiffness.
  • You can produce thinner boards that transmit better signals at higher frequencies without compromising strength or stiffness in the board itself.

Place Vias Strategically

Vias allow you to route signals between two layers without having to run them along the entire length of a trace. This reduces inductance, which helps optimize signal integrity. In addition, using vias allows you to route traces on different layers without adding extra copper to the board for routing purposes.

When placed strategically, vias also help reduce impedance mismatches caused by trace lengths that are too long or short due to impedance effects such as skin and proximity effects.

Layer the Correct Number of Layers

By layering the correct number of layers, you can reduce costs, improve yield, and speed up production. There are several factors that go into determining the optimum layer stackup for a rigid flex PCB. The first is the end product itself. If it is a high-performance component with stringent thermal management requirements, you might want to add more layers for better dissipation. If it is a consumer product sold in large quantities, you might want to keep costs down by using fewer layers.

Another factor is the complexity of your design. For example, if your rigid flex board contains an analog circuit with many different paths, then you should consider adding extra layers so that each path can have its dedicated plane. This ensures optimal signal integrity and reduces crosstalk between signals.

Finally, other considerations, such as manufacturing capacity and tool availability, will influence how many layers are used in your design. Generally, the more layers you have in your rigid flex stackup, the more time it will take to optimize your design and test for electrical integrity — not to mention increased fabrication costs due to extra masking steps required for each additional layer added above two.

Consider the Thermal Threats in Your Product

When designing a PCB stackup for a rigid flex product, it is essential that designers understand how these factors affect the design and what can be done to optimize thermal performance.

Thermal management issues in the rigid portion of your product can impact other components. For example, if you have a large heat sink on one side of your product, it may cause the flex portion of your board to flex too much when used. If the flex portion of your board flexes too much, it can cause damage to other components, such as connectors or other components mounted on the board.

The following are some tips for optimizing rigid-flex PCB stackups for high-temperature applications:

Thermal Analysis - There are many software tools available to perform thermal analysis on any given design. These tools allow you to model the temperature distribution over time and determine where hotspots may occur within your product. You can also run simulations to see how different materials behave under various conditions.

Thermal Testing - Thermal testing is another crucial part of the design process for any electronic device. It is important to understand how different materials respond at specific temperatures to determine what type of material best suits your product's needs.

Conclusion

We hope you have learned a lot about how to optimize your rigid flex PCB stackups and a pretty good starting point for the design of your next rigid flex PCB stackup. Rigid-flex technology opens up an entirely new realm of design freedom, so the possibilities are endless. If you are interested in learning more about rigid flex PCB, check out Hemeixin's website.

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