Flexible Circuit Boards
Whether you’re building a heads-up display for an aerospace pilot or a minuscule device to help manage hearing loss, a flexible circuit board can safely bend into a range of shapes and absorb shock and vibration. They also support different connectors and components that are less bulky than traditional wiring harnesses and ribbon connectors, allowing for more features to fit in the same space. In fact, some designers have reported that flex PCBs save up to 75% of space which increases stability and allows for better heat dissipation.
flex circuit board are made of thin substrates and are capable of supporting complex electronics with a high level of flexibility, tensile strength and bendability. Their durability comes from a combination of their materials and construction. They also offer resistance to a variety of substances, such as acids, oils and gases.
They also have good electrical conductivity and are suitable for use in environments with temperature variations. To make a flex PCB, manufacturers start with a conductive copper layer combined with a dielectric material. This can be a polyimide or other thermally stable materials. The conductive copper layer is then bonded with an adhesive or etch-back and vapour deposition to the substrate. This is a key step that helps to ensure that the copper is robustly attached and can endure the stresses of bending.
Are Flexible Circuit Boards Durable?
Most flex PCBs feature a rigid section, called a stiffener, to prevent breakage in areas that are expected to be bended frequently. The stiffener is made of FR-4 fiberglass or pressure sensitive adhesives, depending on the design requirements. To reduce the risk of cracks in other areas, manufacturers may fortify these rigid sections with additional layers of FR-4 or a specialized, durable version of polyimide, called adhesiveless PI.
Then, a coverlay or other protective material is applied. Depending on the design, this can include epoxy, acrylic or PSA (Pressure Sensitive Adhesive). If a solder mask is required for assembly, it can be applied as an epoxy or solvent-based coating. Lastly, the copper is surface-mounted using different types of solder.
Because a flex circuit board is more susceptible to movement and contraction, it’s important that the drill-to-copper distance is kept as low as possible. For this reason, it is recommended to use a pad-only plating technique, which involves depositing copper only on the vias and pads, rather than across the entire panel.
Finally, insulators are used to separate the conductors and avoid shorting out. Common insulators are polyester, polyimide and solder mask. These also provide protection from humidity and tear resistance. In addition, a flex circuit board must be designed with a large enough bend radius to avoid stress on the copper and to minimize damage during bending. In order to do this, designers should consider a gradual and curved bending angle, as well as avoiding 90o bends which can cause strain. The design should also be based on the intended manufacturing process, as different methods require a specific thickness of copper.