Flex Circuit Boards Manufactured

Unlike rigid PCBs, flex circuits allow for dynamic bending and movement within the product. They also enable lower material costs. As a result, these boards are ideal for high-density applications that need to be able to accommodate varying environmental conditions. While flex circuits provide many advantages, they are still expensive to produce. Knowing how flex circuits are manufactured can help you determine if they are the right option for your project.

The primary materials of a flex circuit board are flexible copper and polyimide, a plastic-like film used as a base. The conductive copper is plated onto the film with either an adhesive or by chemical plating. The copper layers are usually between 0.0001 and 0.010 inches thick, with the dielectric layer being a thin polyester (Mylar), polyimide (Kapton), or fluoropolymer (PTFE) film. The flex substrate is also typically resistant to humidity and tears.

In addition to the basic materials of a flex PCB, a flex circuit must be designed with a structure that can support dynamic bending and movement. This requires a special design that reduces the thickness of the tracks and pads. This allows them to withstand the stresses of daily use and repeated flexing. The final design must also comply with smaller design rules than a rigid circuit, which can make the creation of a flex-circuit more difficult and time-consuming.

How Are Flex Circuit Boards Manufactured?

Before a flex-circuit is fabricated, it must pass an inspection to verify that it meets industry standards and specifications. It must also undergo optimization for production, which can reduce its size and weight while increasing the density of components on it. Once the design is ready, the fabrication process begins with a single or double-sided flex-circuit stackup. This is followed by the etching, drilling, and plated-through holes of both the rigid and the flex sections of the PCB.

Fabrication of a flex-circuit can involve one or two flex sections inserted between a few rigid panels or a full multilayer rigid-flex PCB. It’s also common for a flex-circuit to include stiffeners, which are pieces of FR-4 fiberglass that stabilize the ends of the flex-circuit. These stiffeners allow the flex-circuit to attach to zero insertion force (ZIF) connectors.

After the flex-circuit is laminated and cured, the coverlay is applied, which is a printed image similar to a sticker. The coverlay can be a photo-printed conductive or non-conductive pattern. Next, the flex-circuit is drilled for top-to-bottom plated-through holes. Blind vias can also be laser-drilled at this stage.

Once the flex-circuit is etched, it is then laminated with its final copper foil layer. This is then drilled for plated-through holes, blind vias, and any additional features. The flex-circuit is then tin-finished or soft gold covered, depending on the performance requirements of the product it will be used in. The tin finishing prevents corrosion, while the soft gold coating improves conductivity and signal timing. The flex-circuit is then ready to be packaged for shipping and use in the end product. The last step in the process is to cut out the finished flex-circuit, which can be done with a hydraulic punch and die set or by using a blanking knife.

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