The Benefits of Flexible PCBs
Flex PCBs are used to create circuit boards that can withstand extreme environments. Their elasticity and durability make them ideal for mobile devices, wearable technology, and minuscule medical equipment.
Several innovations have helped refine flexible circuit board manufacturing, including laser direct imaging and roll-to-roll lamination. However, a few rules must be followed to ensure that flex circuits are designed correctly and can resist damage during handling.
Flexibility
As the electronics industry evolves, it is becoming increasingly important to find ways to improve device performance and functionality while shrinking size and weight. Flexible PCBs are an ideal choice to help achieve these goals as they provide significant design flexibility.
As a result, they are ideally suited for applications where a small form factor is necessary for improved usability and ergonomics. For example, wearable devices such as health trackers can be curved to accommodate wrists and other body shapes while providing users with convenient access to data. In addition, foldable smartphones and tablets can utilize flexible circuitry to enable a compact, user-friendly design without sacrificing display size or battery life.
During fabrication, the copper on a flexible PCB is subjected to an intense annealing process that dramatically enhances its flexibility and springiness. Once the copper is cured, it is then laminated onto multiple layers of insulating materials and coated with organic coatings to protect the copper until bonding occurs. The coatings can then be removed to expose the copper for surface finishing. Metals like nickel gold, tin and silver are then applied to the surface of the copper, and the board is etched using chemicals such as ferric chloride to reveal the desired circuit patterns.
Once the etching is complete, the finished flexible circuit is then cut to the desired shape and then undergoes inspection and packaging before shipping to the Flexible PCB end-user. To ensure accurate and consistent manufacturing, it is critical that the flex PCB designer uses an open, vendor-neutral XML format such as IPC-2581 for smooth exchanges of design data between designers and manufacturers.
Durability
Many of the devices that form the Internet of Things use flexible PCBs. This technology allows for circuits that are able to adapt to the interior of various applications, making them more ergonomic and user-friendly. It also helps them resist vibration and shock, which can otherwise damage electronic components.
In addition, flexible PCBs are lighter than their rigid counterparts, a benefit for many product designers. This lower weight translates into reduced shipping and handling costs and lower manufacturing costs overall.
A flex PCB is made from a specialized base material called polyimide. This material is highly flexible and tough, allowing it to bend and twist without breaking. It is also tolerant of solder reflow cycles and capable of withstanding high temperatures. It’s ideal for a variety of product assembly processes, including wire bonding and etching.
Because of this durability, flex PCBs can be used in a wide range of products. For example, a leading smartphone manufacturer integrated flex PCBs into a foldable device that provides users with a dual-screen experience while remaining compact when folded. They’ve also been incorporated into wearable devices like fitness trackers, which use curved displays to optimize for wrist contours.
To ensure that a flex circuit board is durable, manufacturers must implement strict inspection and verification processes throughout the fabrication process. This includes evaluating the thickness and properties of both rigid and flexible materials, as well as the adhesives used in the layer stack. Comprehensive electrical testing is also performed to verify that the flex circuits meet the design requirements. This includes flex endurance testing to simulate repeated bending, thermal cycling to assess temperature resilience, and moisture resistance testing.
Lightweight
Using flexible circuits can drastically cut down the weight of an application. Compared to rigid PCBs, the weight of flexible circuits can be reduced by up to 75%. This is because flex circuits are made of ultra-thin substrates. The primary material used in flex circuits is polyimide, also known as Kapton. This material is incredibly thin, and has already been used in multiple space missions.
It is possible to make a flexible PCB with as little as four layers. However, the thickness of the copper must be taken into account. Too much copper can increase the board’s weight, Flexible PCB manufacturer which can reduce its flexibility. The optimal thickness depends on the design and end use case of the circuit board.
In addition, traces should be staggered on a flex circuit to avoid stress points. This will help prevent the copper from cracking in the areas of expected bending. It is also recommended to avoid discontinuities like vias, cut-outs, and slits in the bend area. These can cause the circuit to break or fail.
Another way to increase the flexibility of a PCB is to add stiffeners. These are sections of rigid material that are laminated to a flex circuit, and they provide support for the circuit in areas where it may be subjected to stress. Stiffeners are usually made of materials like FR4, aluminum, or stainless steel.
Easy to Assemble
Flexible PCBs are much easier to assemble than rigid ones, although they may require some additional processing. For example, they can be laminated to a stiffener or other rigid layer to increase their thickness. This will help them withstand vibration and thermal expansion. In addition, they are less likely to bend out of shape due to gravity sag. This makes them a good choice for high-density applications.
A flexible PCB can be manufactured with a variety of materials and finishes. However, it is important to choose a manufacturer that produces flex circuit boards on a regular basis. This will ensure that your board is delivered quickly and with the quality that you expect.
Another tip to consider is using thinner copper traces in the areas that are expected to be bended. This will minimize the stress on them, which can cause the copper to break. A gradual change in width between wide and thin traces is also desirable to avoid sharp transitions that can cause soldering problems.
In addition, it is important to understand whether a panel plating or pad-only plating (button plating) process is best for a flex circuit. The panel plating process requires more copper than the pad-only option, but it also allows for better impedance control and etch yields.
