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Trouble in Your Tank: Working With Flexible Circuits

Flexible circuits were first introduced as a replacement for wire harnesses. The earliest versions date back to World War II. Today, flex and rigid-flex circuits are filling an important role across multiple industries, including applications in the medical, automotive, and telecommunications fields.

Even though they are a smaller part of the circuit board industry, flex and rigid-flex circuits have been growing in popularity over the last decade, and for good reasons. These circuits are made to be thin, flexible, and durable. However, in addition to the opportunities that come with flex and rigid-flex circuits, there are also challenges. Generally, these occur with the processing part of the technology.

Characteristics of Flex and Rigid-flex Circuits

Flex and rigid-flex circuits have become a go-to solution for a variety of applications because they offer capabilities that simply aren’t available from alternatives. They can be manufactured to very thin specifications, and they will survive bending and folding without error.

These circuits can be run over long distances to make a connection. For example, some users have designed 14–18-foot flexible cables.

Some of the most sought-after features of flex and rigid-flex circuits include the following:

• Thin-core capability
• Improved dielectric constant
• Low dielectric constant (Dk) and dissipation factor (Df) critical concerns
• Ultra-fine line capable (L/S decreasing to less than 15 microns)
• Shorter interconnect distances

Flexible circuits have the same capabilities of their rigid counterparts, including repeatability, reliability, and high density. In addition, they have characteristics that make them more versatile than rigid circuits. For example, they are flexible, of course, and can resist vibration more effectively. One of the most popular features of flexible circuits is that they can be designed into three-dimensional configurations.

Rigid-flex circuits combine the best features of flexible and rigid circuits to meet a variety of needs. The rigid areas make it possible to mount stationary components while the flexible areas can be custom configured and serve as protection against vibration.

Despite the fact that flex boards can be extremely thin, they are remarkably durable. These circuits are capable of repeating the same bends through millions of cycles without interruption. This is a critical point when it comes to applications that face intense vibration and/or acceleration.

To read the full article, which appeared in the September 2019 issue of PCB007 Magazine, click here.