panelization optimize Rigid flex pcb
Rigid flex pcbs combine rigid and flexible circuit board technology to provide the best of both worlds: the structural stability and component mounting of a rigid PCB with the flexibility needed to bend and twist for signal routing in a small footprint. These high-reliability pcbs are used in avionics, aerospace and military equipment where the weight and size of components is important. But the process of creating a rigid flex is complex, and the cost can be prohibitive for low-volume production runs. To reduce cost, a design-for-manufacturability (DFM) assessment must be done early in the development cycle to make sure that a design can meet fabrication costs and tolerance requirements.
Taking these requirements into account at the beginning of the design process reduces manufacturing change requests and increases product success in the field. This approach is referred to as panelization and involves creating an array of PCBs that optimize material usage and improve manufacturing yield rates.
To ensure that a rigid-flex PCB can handle the bending and twisting required for assembly, it must have adequate support at points of motion. This is achieved with the use of stiffeners, or extra layers of FR-4 or polyimide to prevent warping. The stiffener layers also serve to protect the flex circuit from damage and deformities caused by mechanical stress.
How does panelization optimize Rigid flex pcb processes?
Another consideration when designing rigid flex circuit boards is how to connect the rigid and flexible sections of the board together. Using rigid-flex PCBs eliminates the need for bulky cable harnesses, reducing manufacturing cost and assembly time. But the transition between rigid and flex sections can cause problems if not designed carefully, with signal integrity and EMI issues being major concerns. The rigid-flex PCB must be fabricated from materials with similar thermal expansion coefficients, and careful planning is required to place connectors in locations that will maintain signal continuity and avoid mechanical stress.
The flex layer of the PCB is connected to the rigid layers with either an adhesive or a photo-imageable solder mask. A photo-imageable solder mask is preferred for flex because it can be printed on the surface and allows for easy visual inspection of solder connections, eliminating the need for costly rework or repair. For the rigid section, it is a good idea to keep the copper layer thickness as thin as possible for a smaller footprint and more reliable connection. It is also important to use a low-flow prepreg so that the resin will not flow out onto the flex layer and distort it during reflow soldering.
Using a panelization approach allows for the most efficient production of a rigid flex PCB, minimizing both materials and manufacturing costs. In order to take full advantage of this, it is important that the fabricator be involved in the design process as soon as possible. This will allow the fabricator to provide a fabric-specific template that ensures all data is available to the design team and will help them optimize the rigid-flex design for manufacture. To further streamline this workflow, IPC-2581 provides a vendor-neutral XML format that facilitates the smooth exchange of design data between designers and manufacturers, including layer stack-up, drill details and other specifications. With this standardization, collaboration is streamlined and the risk of miscommunication is minimized.
