Rigid-Flex PCBs and Flex PCBs: Materials, DFM and Cost Impacts

Flex and rigid-flex printed circuit boards (PCBs) offer a range of advantages over rigid PCBs, including flexibility, lightweight materials, and durability. Flex PCBs and rigid-flex PCBs can bend and twist, making them ideal for small and lightweight electronic products that require space and weight optimization. However, these types of PCBs are generally more expensive than rigid PCBs. To reduce costs, there are several strategies you can use. First, it's important to understand the basics of rigid, flex, and rigid-flex PCB materials and their associated costs. Additionally, there are important design-for-manufacturing (DFM) considerations that can impact PCB costs. By taking these factors into account, you can design cost-effective flex and rigid-flex PCBs without sacrificing performance or reliability.What Are Flex and Rigid-Flex PCBs?Flex PCBs, also known as flex circuits, are made by laminating a layer of transparent polyester film, such as polyamide, to a thin sheet of copper, which is then etched away to leave the specific PCB pattern in place. These circuits can be fully bent to a specific shape. Rigid-flex PCBs combine rigid PCB materials with flexible circuits, providing the advantages of both. While flex and rigid-flex PCBs are generally more expensive than rigid PCBs, they can help reduce costs in other ways. These boards require less material and offer quicker assembly, as well as a range of design flexibility advantages.Cost Drivers for Rigid-Flex PCBs and Flexible PCBsThe cost of manufacturing a printed circuit board (PCB) can be heavily influenced by the number of manufacturing steps required and the materials used. Therefore, it is important to understand where the biggest costs come from so that you can design a more economical board that still meets your performance and cost requirements. By optimizing your design and considering factors such as the number of layers, board size, and the complexity of the circuitry, you can help reduce manufacturing costs without compromising on quality or functionality. Additionally, choosing cost-effective materials and finding a reputable PCB manufacturer who can offer competitive pricing can also help bring down the overall cost of production.Least InfluentialTo keep your PCB manufacturing costs low, there are some factors that have only a minor impact on your PCB's cost. These include:

2. Routing: More complex routing will increase the cost of manufacturing since it requires more precision.
4. Panel thickness: Going with thinner, more common panel sizes generally saves you money.
6. Via plugging: Completely filling in vias with resin or solder mask requires an extra step in the manufacturing process. If you can limit instances of via plugging, you can save on costs.
8. Strain relief: Limiting the need for strain relief and its associated materials can help you save money.
10. Adhesive: PCBs can use adhesive or adhesiveless cores to bond the stiffener to the board. The most affordable adhesive material will vary depending on your stiffener, but adhesiveless materials are the more expensive option overall.

More InfluentialTo maintain the structure and keep costs down, here are some factors to consider for your flex or rigid-flex PCB:

• Aspect ratio: A larger aspect ratio between the thickness of the PCB and the diameter of a drilled hole can increase the cost of plating the inside of the holes. Keeping the drilled holes to a larger size or reducing the size of the PCB can help find a good ratio for plating.
• Number and size of drilled holes: Excessive drill holes or smaller holes require additional labor and precision, which can add to the cost of the PCB.
• Trace and space size: Tight trace/spaces can increase the complexity and price of the PCB.
• Stiffeners: Using stiffeners or rigidizers can increase costs due to additional material requirements. Choosing FR4 as a material can be a more cost-effective option than polyimide, aluminum, or stainless steel.
• Button or selective plating: Any kind of button or selective plating will increase the price of a PCB due to its added complexity.
• Controlled impedance: Opting for controlled impedance can increase the cost due to additional checks and coupons that require more labor and materials.
• Annular rings: Choosing an appropriate size for annular rings to create a reliable connection with the via can help avoid paying more for oversized rings.

Most InfluentialFinally, the following factors significantly affect the cost of your PCB:

2. Advanced technologies: Choosing advanced technologies for your PCB will increase the cost.
4. Buried vias: Incorporating buried vias requires more drilling, plating, and lamination, which can raise the cost. Additionally, they may require more expensive materials.
6. High layer count: A higher number of layers in your flex PCB will increase the cost due to the increased complexity of lamination, requiring more time, materials, and expertise.
8. Panel utilization: The most important cost driver is panel utilization, as manufacturers typically charge by the panel. Maximizing the number of components per panel can help reduce costs.
10. Selective plating: The process of selective plating is time-consuming and results in material waste, which can increase the cost of your PCB.
12. Dual surface finish: Using multiple surface finishes adds complexity to the process and can increase the cost of your PCB.

Trade-Offs in Cost for Flex and Rigid-Flex PCBsThe previous factors we discussed are important in driving up the cost of PCB design, but it is important to consider the trade-offs that come with lower-cost designs. When considering the affordability of your PCB design, you should keep in mind the following factors: Production panel placement: It is essential to consider how your PCBs will integrate into the production panel. Proper placement can help maximize material utilization and minimize waste. Adhesiveness and reliability: Although adhesive boards are generally cheaper, the addition of acrylic resin in the via stack can impact the reliability of the board, especially in high-temperature or high-stress environments. Line width and spacing: Before adding more layers, consider if you can reduce the width and space of the traces. This can allow you to pack more lines into one layer, minimizing the price. However, consider how these changes may affect the final product and if it may negatively impact performance. Overall, reducing the cost of your flex or rigid-flex PCB design can be achieved by minimizing layers, reducing material thickness, and carefully selecting materials. However, it is important to consider the trade-offs and potential impacts on the performance and reliability of the final product.Learn More About Flex and Rigid-Flex PCBsFlex and rigid-flex PCBs offer unique design options that can benefit many projects. By considering the factors that drive up their costs and making design choices that prioritize efficiency and reliability, you can create high-quality PCBs while keeping costs down. If you have any questions about designing flex or rigid-flex PCBs, the team at Sprintpcb can help. As an ISO 9001-certified company, we offer a range of high-quality bare PCBs, including flex and rigid-flex designs. Explore our selection today to learn more about how we can support your project.