What is the role of impedance control in flex PCB design?
Technologyrole of impedance control in flex PCB design
Printed circuit boards carry electric signals between connecting components in electronic devices. However, these signals don’t travel freely along signal traces; they take time to reach their destination and this delay is measured in impedance. Controlling impedance on a flex pcb is important because it can limit interference between high-speed signal paths. It can also improve performance and protect data integrity.
During a PCB’s design phase, the board’s mechanical engineers will have to consider how a rigid-flex or flexible circuit board will bend. The bending location, radius and axis will need to be carefully planned so that the copper conductors do not break or crack during deformation. This is a challenging task because it requires careful consideration of the physical properties of the material, its dielectric constant and layer thickness. It is important to consult with the flex pcb design and layout experts early in the process to ensure that these requirements are met.
As the PCB layout moves forward, the designer will often need to change a component’s location to avoid overlapping traces. It is also critical to avoid putting too much pressure on the copper conductors because this can cause them to fracture during bending. For this reason, it is essential to route traces perpendicular to the bend line to eliminate stress concentration points and prevent breakage.
What is the role of impedance control in flex PCB design?
A PCB’s surface finish is another factor that can impact impedance. For example, a thicker cover layer can affect the dielectric constant, while a thinner one can improve the flexibility of the flex circuit.
The choice of materials can have a significant impact on the final price of a flex or rigid-flex circuit board. For instance, thicker cores will increase cost but may be necessary to achieve the desired performance. It is important to select a material with the right dielectric constant and layer thickness to minimize costs while still meeting the mechanical demands of the application.
It is also a good idea to include power planes on each of the signal layers to help maintain controlled impedance. These planes will supply a return path for the signals and reduce signal loss. However, the power planes should be dispersed throughout the stack to avoid creating a dead zone near the signal layers that can negatively affect performance.
When designing a flex or rigid-flex circuit, it is important to be clear when specifying impedance. Vague specifications can lead to fabricator confusion and delays. For example, if a specification calls for a specific copper weight but does not include details on trace width, the fabricator will need to ask the designers to clarify what is being requested.
When the target impedance for a flex or rigid-flex circuit is too close to the manufacturing capability limits, it is important to ask for impedance control. This will allow the manufacturer to work towards the target value rather than trying to hit it on their first attempt and then needing to make costly adjustments.