Prevent Flexing Fatigue in PCB Assembly
When it comes to the PCB assembly process, there are numerous steps that need to be taken into consideration. The assembly requires expertise, precision, and adherence to industry standards. The assembly process includes mounting components, soldering the joints, and testing the circuit boards to verify that they meet the required specifications.
One of the biggest concerns for pcb assemblers is flexing fatigue, which can damage components and cause the board to fail. This problem is prevented by using stiffeners that help to reinforce flex circuits and prevent them from flexing excessively. Stiffeners are typically made from rigid materials such as FR-4, polyimide, or aluminum and can be customized in thickness to suit the desired application.
Stiffeners are necessary for flex circuits to ensure that the conductive copper traces remain intact and do not crack under repeated bending stress. These stiffeners also provide structure and rigidity to the flex circuit, which facilitates component mounting and handling. Stiffeners can be used for a variety of applications, from consumer electronics to aerospace products.
How Stiffeners Prevent Flexing Fatigue in PCB Assembly
To avoid flexing fatigue, a pcb assembler must use stiffeners that are properly placed and anchored. This can be done by using a stencil to map out the stiffener locations and then applying a bead of epoxy, acrylic, or hot-melt glue to the top side of the flex circuit. This step adds to the assembly time, and it must be carefully coordinated with the fabrication and assembly teams. It is also recommended to use a flexible substrate and adhesive that are designed for dynamic flexing.
For example, when a flex circuit bends, the stress on the copper is transmitted through the film substrate and coverlay to the stiffener. This causes work-hardening and fatigue fractures, which are difficult to detect by visual inspection. To avoid this, pcb assemblers must keep the track widths as consistent as possible. It is also best to route flex circuits with arc corner modes rather than hard right-angles.
A pcb assembler must also take care not to put too many stiffeners on a flex circuit, as this can compromise the design and lead to signal loss. The stiffeners must be the proper size and shape to fit the area of the flex circuit that needs reinforcement. They should also be anchored securely to the substrate with adhesive or mechanical anchoring. Finally, they should be able to withstand the thermal expansion of the flex circuit and avoid outgassing chemicals that can contaminate the components and the flex circuit.
Another way to reduce flexing fatigue is to eliminate vias that are placed on a flex circuit, unless they are essential for the function of the circuit. It is also best to limit flexing immediately over plated through holes and vias, which can crack soldiers. It is also a good idea to use blind and buried vias, which offer better signal performance over through-hole vias.
A pcb assembler should test the flex circuit for defects and failures, such as de-wetting, which occurs when solder fails to make a solid connection with the solder pad. This problem is usually caused by contamination, overheating, or mishandling, and it can be remedied with thorough cleaning and inspection procedures.