rigid flex boards
Rigid flex circuit boards have unique design and manufacturing challenges. These can lead to a number of failure modes that can compromise the quality and reliability of the board. Understanding the common failure modes associated with rigid flex circuit boards can help engineers and manufacturers develop high-quality products.
Thermomechanical stresses in the material of a rigid-flex PCB are caused by changes in temperature, humidity and mechanical shock. These stress can cause cracking, delamination or solder joint degradation that can affect electrical performance. To minimize these stresses, proper engineering of the flex and rigid areas is important, as is the use of conformal coatings or encapsulation to protect the board from environmental factors.
The most significant issue with rigid flex board is the risk of thermal induced delamination. This occurs when the different layers of the board separate from one another due to poor bonding, temperature cycling or mechanical stress. This can result in electrical shorts, opens and reduced board reliability. Minimizing this risk is key, and can be achieved by selecting high-quality bonding materials, controlling lamination parameters and allowing adequate curing time.
What are the common failure modes associated with rigid flex boards?
Connectors and solder joints are critical interfaces in any electronic product, and this is particularly true for rigid-flex circuit boards. These components can fail due to mechanical stress, temperature cycling, or improper soldering techniques. To reduce the risk of these failures, engineers should select high-quality components, ensure proper alignment and fit, and follow recommended soldering guidelines.
During the fabrication process, a flexible circuit may experience deformation, which can cause the copper traces to bend or fracture. To avoid this, designers should design the flex portion of the circuit with a minimum bend radius that is based on the IPC-2223B design standard. They should also be careful when placing solder and PTH holes in the flex area so that they are not close to the bend point, as this can create a stress concentrator.
Rigid-flex circuit boards are often exposed to harsh environments that can contribute to corrosion, oxidation, or other degradation of the components in the board. These failures can be caused by exposure to moisture, chemicals or contaminants that can damage insulation and dielectric materials. To minimize these risks, strict quality control measures should be implemented by the manufacturer and encapsulation or potting should be used to protect the circuit board from environmental factors.
The region where the flex and rigid sections of a circuit board meet is prone to transition zone defects such as adhesive squeeze-out, protruding of dielectric materials, crazing and haloing. These problems can cause conductor paths to be damaged, and are usually caused by a lack of space between the flex and rigid sections. To mitigate these problems, designers should ensure the flex layer extends into the rigid section to provide a seamless transition. They should also ensure that there is sufficient clearance between the rigid and flex sections to prevent inadvertent damage during assembly or operation.