best material for PCB flex rigid
The driving need for PCB flex rigid is often linked to harsh environments, and the reliability of these circuits depends on material selection. The choice of material can affect how well a board will resist temperature, moisture, chemicals, shock and vibration, among other factors.
Rigid-flex circuit boards are fabricated from a combination of traditional rigid-board materials, including glass fiber and epoxy. They are also typically layered with thin flexible PI or PET films and polyimide coverlay, which functions as solder mask.
PCB flex rigid manufacturers should be aware of the specialized properties and limitations of these materials to avoid defects in the final product. For instance, a PCB made from PI is less brittle than normal copper foil but it has a lower tensile strength, which means that it can stretch more easily but not as tightly as the traditional rigid-board substrate. It is also more susceptible to thermal expansion, which can result in cracks at vias.
What is the best material for PCB flex rigid?
Another consideration when designing a pcb flex rigid is the thickness and impedance requirements of each layer in the stack-up. These factors can have a significant impact on the performance of a rigid-flex circuit, so it is important to choose the best materials to ensure your product’s reliability and functionality.
To reduce flex-rigid PCB failures, RUSH PCB UK Ltd recommends that designers follow IPC guidelines for laying out flex and rigid-flex circuits. Ensure that the transition region between the flex and rigid sections is free of discontinuities like vias, cut-outs, slits, or holes. This will prevent stress from developing in the area around the bend, which can cause traces to break or malfunction. It is also helpful to stagger traces along the length of the bend, as this can minimize I-beaming and stress points that can damage the copper.
Conductor traces on a flex-rigid circuit should be routed perpendicular to the bend radius, rather than parallel. This will reduce stress on the copper, which can damage it or cause it to rip and tear. It is also helpful to minimize stress points by using stiffeners in areas that are susceptible to excessive pressures. In addition, anchors and spurs encapsulated with coverlay should be used to prevent trace lifting and pad peeling.
Drill-to-copper distance is another factor that should be considered when designing a flex-rigid circuit. Because flex materials are more likely to move and compress during manufacturing, it is important to ensure that there is at least 8 mils between the drill and the copper. Choosing the correct drilling method is also important, as some options may have different benefits for your project.
Depending on your flex-rigid PCB design, you should also consider whether or not to use panel plating or pad-only plating (button plating). Panel plating is more cost-effective but does not provide the flexibility that button plating offers. With this method, copper is deposited only on the pads and vias, which can improve etch yields in small etch patterns. This can also help support controlled impedance designs.
