Flex Circuit Support High-Speed Signals
Whether it is for high-speed data transmission or high power distribution, signal integrity is crucial to the performance of electronic devices. Poor signal integrity can result in signal corruption, delays, or even system failures. Therefore, maintaining high-speed signal integrity requires careful design considerations and simulation, as well as specialized testing equipment. Sierra Circuits has the capabilities to meet flex and rigid-flex PCB signal integrity requirements.
High-speed signals require a specific type of conductor known as a differential pair. A differential pair consists of two transmission lines with equal and opposite polarity signals, closely timed to each other. Compared to single-ended traces, differential pairs deliver more precise control of transmission line noise and distortions, especially in high-speed signal applications. In addition, differential pairs reduce crosstalk between adjacent signals by straddling the empty diamond-shaped cross hatches that separate each single-ended transmission line.
While rigid PCBs can be fabricated using various materials, the dielectric constants of the substrate play a significant role in signal integrity. Fortunately, flex circuit have superior dielectric constants, which significantly improve signal transmission and reliability.
How Does a Flex Circuit Support High-Speed Signals?
However, a number of factors can still impact signal integrity in flex circuits. For example, mechanical stress during manufacturing and assembly can bend the circuits, resulting in skewed traces and impedance mismatches. To minimize the risk of mechanical stress, manufacturers must ensure strict process controls in material preparation, imaging, etching, and lamination. The process should also maintain tight tolerances for trace widths and spacing, ensuring consistent impedance.
In addition, traces on flex circuits must be routed around the bend areas with special care. Vias and pins should be avoided at these regions, as they are prone to damage and short circuits. Furthermore, routing a flex circuit near a bend area is more challenging than routing it on a rigid PCB because of the layer architecture. In order to avoid these issues, designers should stagger the traces and stack layers with a minimum distance of 8 mil between them.
Another important factor for high-speed signal integrity is the reference plane and EMI/RFI shielding. Flex and rigid-flex circuits often use mesh ground planes to reduce noise. These grids are often made from a combination of solid copper layers and silver inks, or specialized films. The latter are more flexible and offer better shielding, but their higher thickness may compromise controlled impedance values.
The key to maintaining high-speed signal integrity in a flex or rigid-flex circuit is understanding the manufacturing processes and implementing best practices during the design phase. By working with a trusted and experienced CM, you can minimize the effects of stress on your flex circuit and ensure that it will perform as expected.