Flex Circuits: The What, Where & Why

Flex circuits are known by many names including flex boards, flex PCBs, flexible circuit boards, flexible printed circuit boards and, more officially, flexible electronics. You may think of flex circuits as a product that you buy—which is true. But more formally the term flex circuit refers to the type of technology which allows for the mounting of electronic devices and circuits on flexible substrates. Simply put, a flex circuit is a flexible computer board.

Flex circuits offer the same advantages of traditional PCBs including repeatability, reliability, and high density. Conversely, flex circuits offer flexibility and vibration resistance, both of which aren’t available on traditional PCBs. The most important attribute, however, is the capability of a flex circuit to undertake three-dimensional configurations, which is compelling designers and engineers alike to adopt flex circuit technology. Designing a flex circuit requires a slightly different approach when compared to traditional PCBs. While flex circuits may yield significant savings in manufacturing cost in addition to reduced space and less weight, their designs must be optimized for materials and applications.

Similar to how semiconductors are manufactured, flex circuits are made using a semiconductor-industry technology called photolithography. Photolithographic technology is the process of transferring geometric shapes on a mask to a substrate. The use of this tried-and-true technology results in the lamination of etched copper traces in between two layers of dielectric film. The two layers are then glued together using an adhesive which is thermosetting, meaning the glue is activated using heat. Just like any other PCB, a flex circuit can be a single or multi-layer product, and can be made in an infinite number of shapes. Additionally, flexible circuits can optionally be manufactured in conjunction with traditional PCBs. However, this hybrid technology carries its own unique name most commonly known as rigid flex circuits. Flex circuits can be designed to accommodate either surface-mount and/or through-hole devices of which can be either active and/or passive components.

Where Are They?

Flex circuits can be found in almost any of the hightech devices in our world today. One of the most up-and-coming markets is that of wearables for both professional and personal use. In the medical market, flex circuits can be found in wearable oxygen sensors used for monitoring the real-time oxygen levels of patients during surgery. Skin patch delivery devices, which are used for the delivery of drugs and insulin, also use flex circuit technology. And in the public domain, examples include many of the different personal training and athletic gadgets, such as the Nike FuelBand activity tracker.

Beyond wearables includes the ubiquitous market of cameras and smart phones which also employ flex circuit as do GPS units. The market of LED lighting, growing by leaps and bounds, uses flex circuits at its core for many applications—think LED lighting under kitchen cabinets. Solar panels are another growing industry that uses flex circuits, and with the ability to conform to virtually any shape, flex circuits are sure to expand into many more markets such as 3D Printers.

Flex circuits can also be found in both military and aerospace applications. For instance, satellites use flex circuits due to their thermal stability and chemical resistance properties. Radar systems take advantage of the interconnect cost savings and simplified assemblies. Night vision applications are an excellent product for using flex circuits since these specific applications require a printed circuit design to bend, fold, and to have both a component and simple assemblies. And laser gyroscope decided on flex circuit technology based on their interconnect dynamic bending and flexing properties.

Why Are They Popular?

Flex circuits have become most popular during the last decade largely due to the efforts of Japanese electronics packaging engineers who discovered new ways to use the technology. And today, flex circuits remain one of the fastest growing interconnect solutions available. There are many advantages of using flex circuits rather than traditional PCBs. The most obvious advantage is, as their name implies, their flexibility. Due to their ultra-thin material flex circuits can be bent and flexed millions of times; keep in mind these fully flexible circuits contain both electrical and mechanical devices. Other not-so-common advantages include:

• Flex circuits can be thinner than traditional PCBs.

• Flex circuits reduce weight and save space when compared to wire harnesses.

• Flex circuits dissipate heat better than other dielectric material.

• Flex circuits can influence the aesthetics of the final product.

• Flex circuits make installation and repair easier and more cost effective.

Flex circuits are similar, though not identical, to traditional PCBs in terms of design, functionality, and manufacturing. Flex circuits and traditional PCBs alike accept both surface-mount and through hole devices. However, the major difference, and advantage, of using flex circuits over traditional PCBs is their element of flexibility. This flexibility allows the boards to conform to three-dimension configurations which could have a significant influence on their mechanical enclosure for aesthetics, weight, space, assembly and cost. A well designed flex circuit can be lightweight, robust, easy to install, and suitable for a variety of applications such as wearable devices, LED lighting, 3D printers, solar, and military and space applications.

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