How Are Flex PCB Made?

Flex PCB Made

The flex pcb is an electronic circuit board that can be bent without damaging the copper layers. Its unique ability to withstand dynamic bending, a requirement in many industrial applications, makes it ideal for automobiles, medical devices, mobile phones and portable electronics. Moreover, the flex pcb can be used in places where space is restricted and offers advantages such as better thermal performance, improved signal transmission, and resistance to corrosion and radiation.

The manufacturing process of a flex pcb starts with the design of the layout using computer-aided design (CAD) software. During the design process, the expected mechanical and electrical requirements are considered and the placement of components and the routing of traces are determined. Once the design is complete, output files are generated which can be used to create the conductive layers in the flex pcb. The copper layers are then designed with the correct impedance to ensure that the flex circuit will function properly under both static and dynamic conditions.

Once the conductive layers have been designed, they are etched in order to remove the protective layer and expose the copper. The copper is then chemically plated and metalized. The plated copper is then cleaned and dried before being cut to the desired shape. This process is often called blanking and can be done by hand or using a hydraulic punch and die set for high volume production. For low-volume production, a blanking knife is typically used.

How Are Flex PCB Made?

For a flex PCB, the coverlay layers are often laminated with an adhesive to add strength and rigidity to the overall structure. These coverlays are also used to protect the surface of the flex circuit from contaminants during handling and assembly. In addition, the coverlay layers may be printed with a photo-imageable solder mask to help maintain proper conductivity and solder joint integrity.

During the fabrication of a flex pcb, copper foil is added either by laminating it to the polyimide film or by chemical plating directly on to the seed layer. The resulting structure is known as a Copper-Clad Laminate (CCL). The need for adhesives in CCL production has been largely eliminated by the development of processes that provide a much stronger bond between the copper foil and the underlying layers, reducing manufacturing costs.

To connect the plated through-holes and copper traces on a flex circuit, it is common to use teardrop or annular rings. These connectors are smaller and more rounded than square or round holes, which helps reduce stress concentration spots. In addition, it is a good idea to keep the area around the expected flex bend radius free of discontinuities like vias and cut-outs/slits, as these can increase the risk of failure due to stress and cracking.

Lastly, a final layer of protective polyimide or PTFE is applied to the finished product in order to prevent contamination and moisture damage. This layer can be a transparent or opaque coating and is typically used for single-sided flex circuits.

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