PCB Circuit Boards
The versatility of a pcb circuit board allows engineers and designers greater adjustability, which can reduce overall product costs, increase airflow to keep temperatures low, and provide a better ability to withstand stress and vibration. However, the flexibility of a PCB also comes with a few challenges, particularly as the design process moves closer to fabrication. It’s important to follow design for manufacturing (DFM) guidelines to prevent a flexible circuit board from becoming damaged during production.
During the front-end engineering stage, the shape of a flex pcb circuit board is determined as well as the component locations and traces. This is the phase where ECAD software converts schematic diagrams into electronic drawings that define how components connect to one another. It’s important to consider the bending requirements of a flex circuit board at this stage to ensure that it can withstand a lifetime of bending.
Once the component locations and traces are set, routing tools in the ECAD software are used to set their geometry. This is where it’s important to pay close attention to impedance, which refers to how much and how quickly electricity travels down a trace. Having a flat impedance vs frequency curve is essential to avoid signal distortion, especially for high-speed signals.
How PCB Circuit Boards Improve Design Flexibility
At this point, the designer is ready to move onto the next step of designing the circuit board’s electrical connections. This is where it’s crucial to review the flex PCB’s reference plane layers and shielding to make sure they’re positioned appropriately for impedance control and signal integrity.
As the EE and mechanical engineer review the layout of the flex circuit board, it’s important to make sure the flex sections are designed with proper bend radius restrictions to avoid a crimp at the solder joints. It’s also important to consider removing slits, slots, or inside corners that could tear and cause failure. Alternatively, these areas can be replaced with tear-relief holes or tangent curves with a minimum of 1.5mm radius.
Once the EE and mechanical engineer have finalized their layout, they can then send the design to the fabrication house for manufacture. At this point, the fabricator will offer helpful feedback on the stiffness and bend requirements as well as any keepout regions or specific material considerations. The fabricator may also provide information on a suggested layer stackup, based on their experience with the type of flexible circuit board being manufactured.
When the flex PCB is ready for assembly, it will be cut and drilled to create holes that are plated with copper. These holes are called vias, and they allow vertical interconnect access between the different conductive layers of the circuit board. When a flex circuit board is made with multiple layers, it can be difficult to determine which ones will need vias, because they are often arranged unevenly and have differing thicknesses. It’s important to plan these out as early in the design process as possible to prevent rework and redesign during production. The fab house can also add stiffeners to the flex section of the circuit board to help improve its handling and durability. This can help protect the circuit board from mishandling, which can rip away copper from the surface and void the solder joints.