Flex Circuit Boards Impact System-Level Reliability

The materials and construction of flexible or rigid-flex circuits affect how well they perform in use. During the design phase, it’s important to select high-quality materials that will meet your application requirements, including mechanical strengths, temperature tolerances, and other critical factors. This will help you to avoid defects that could lead to product failure and minimize the risk of production issues that could impact reliability at a system-level.

The primary material in a flex circuit board is its base film, which provides most of its characteristic properties. It must be chosen to suit the application, especially if you’re using a rigid-flex board for a harsh environment. For example, if you’re designing a flex-rigid circuit for automotive products, the material must be able to withstand extreme temperatures. In addition, it must be able to withstand the stresses that can result from repeated bending.

PI and PET films are common in flex circuit board, as well as thin flexible-epoxy and glass-fiber substrates. Unlike many thermosetting resins that become rigid after heating, PI stays flexible, which makes it an excellent choice for the core of a flex circuit. It also resists humidity and tears better than many other flexible circuit core materials.

How Do Flex Circuit Boards Impact System-Level Reliability?

In order to maintain a high level of performance, flex circuits must be designed with proper signal integrity. To achieve this, it’s important to avoid overlapping traces and keep the drill-to-copper distance to 8 mil or more. This helps to prevent the stress and cracking that can result from bending the copper conductors, which can cause signal loss or even failure.

Another important consideration when selecting a flex-rigid circuit is the choice of plating method. Pad-only plating (button plating) uses less copper than panel plating, which improves etch yields and allows for smaller traces. However, it’s more difficult to use in harsh environments because the pads are exposed to moisture and corrosion.

Looking ahead, the evolution of flexible PCB technology shows no signs of slowing down. As demand for smaller, lighter, and more efficient electronic devices grows, so too does the need for increasingly sophisticated flexible interconnect solutions. Emerging trends such as flexible hybrid electronics (FHE), which integrate rigid components with flexible substrates, promise to unlock new possibilities in areas such as Internet of Things (IoT), healthcare, and smart manufacturing. With each advancement pushing the boundaries of what is possible, flexible PCBs remain at the forefront of technological innovation, poised to shape the electronics landscape for years to come.

Stiffeners are often required in flex and rigid-flex PCBs to relieve strain and support the structure. These stiffeners can be made from FR-4 fiberglass or a thin layer of pressure-sensitive adhesive (PSA). Often, single-layer flex PCBs have stiffeners on both ends to stabilize the end plates and provide support for zero insertion force (ZIF) connectors. Double-layer flex PCBs may require a stiffener in the center to add sturdiness to areas where components are mounted or terminated.