How to Minimize the Risk of Component Damage During Rigid Flex Circuits

Risk of Component Damage During Rigid Flex Circuits

Rigid flex circuits are designed to combine the benefits of rigid PCBs with flexible components. The result is a highly reliable hybrid design that minimizes material fatigue and stress during dynamic operations. While these flexible circuits provide a host of benefits, they can also present challenges during the design process. How do you minimize the risk of component damage during the rigid flex manufacturing process? The answer lies in a careful evaluation of the design and operating circumstances. This approach reduces the risk of costly production delays and product failure, while ensuring that your customers receive a high-quality, durable product.

Rigid-flex PCBs are complex structures that require a highly experienced CM to fabricate them reliably. Some of the most common DFM mistakes include improper material selection and routing, unoptimized stack-up, excessive bend angles, neglecting pad supports and stiffeners, and insufficient clearances and overlapping traces. These mistakes can lead to significant problems during the assembly and testing phases of the rigid-flex board, resulting in failures or malfunctions.

Unoptimized Stack-Up: The layer arrangement on a rigid flex circuit plays a crucial role in its overall performance characteristics. Careful planning and arranging of the layers can improve impedance control, signal integrity, thermal management, and mechanical robustness.

The thickness and copper weight of the PCB play a critical role in its ability to handle high-speed signals. It is important to evaluate the manufacturer’s capabilities in this area, as well as the available surface finish options and their solderability.

Uneven Trace Widths: The uneven width of traces on a rigid flex circuits can be a significant source of stress and failure during the bending operation. This type of stress concentration is commonly referred to as “bend reliability issues.” To avoid this issue, the designer should use uniform trace widths across the flex region and utilize a teardrop configuration to prevent abrupt changes in trace width.

How to Minimize the Risk of Component Damage During Rigid Flex Circuits

Improper Impedance Control: The rigid-flex PCB’s impedance should be optimized to ensure signal integrity and prevent reflections. This is especially important for high-speed signals that traverse multiple layers of the PCB. The CM should use impedance matching techniques to ensure consistent impedance throughout the flex and rigid sections of the circuit board.

Transition Zones: The region where the flex and rigid sections of the circuit meet is a common source of defects during production. The flex-to-rigid transition zones are prone to adhesive squeeze-out, protruding dielectric materials, and crazing. These defects can cause conductor paths to decouple, resulting in failures and poor performance.

To address these issues, the CM should use a low-flow preform and less adhesive for the flex-to-rigid transition zone. The flex-to-rigid segment should also be laminated with a thin layer of insulating material to mitigate stress concentrations.

These simple DFM steps can greatly reduce the risk of defect during the rigid-flex manufacturing process. By evaluating the manufacturer’s process and implementing these measures, you can rest assured that your rigid-flex circuit will meet or exceed your expectations for quality and performance. Optimize trace routing by keeping traces perpendicular to the bend lines to minimize stress. Use teardrop shapes at the junctions of traces and pads to reduce stress concentration points.

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