What Is a Flex Circuit Manufacturer?
A flex circuit manufacturer uses a polyimide material cladded with rolled copper that is more flexible than the rigid PCB materials used in rigid boards. Photolithography exposes and develops the desired mask pattern, and copper is chemically etched to create circuit traces.
This material is very thin and fragile, so it takes longer to fabricate than rigid boards. It is important to note the grain direction on your fabrication drawing.
Flexible Circuits
A flexible circuit, also known as a flex PCB, is comprised of components and printed circuit board circuitry that utilizes flexible materials. Unlike rigid circuit boards, a flex PCB can bend and fold without losing functionality. This allows them to fit into smaller spaces and reduces weight and package size. The flexibility of a flex circuit makes it possible for designers to create more complex configurations that would be impractical with traditional rigid boards.
Flex circuits are available in a variety of thicknesses and conductor types, making them suitable for almost any application. Using a flexible circuit allows manufacturers to design in a third dimension, increasing the amount of space they can use and improving airflow within an electronic product. They also offer a higher density of devices compared to rigid boards, resulting in a lighter and more compact design.
The base material of a flex circuit is typically a flexible polymer film. The base material provides most of the primary physical and electrical properties of the flex circuit. A flex circuit can be made from a single conductor layer on a flexible dielectric film or a multi-layer circuit that uses different metal layers separated by printed insulating layers. A double access flex, also known as a back-bared flex, features a single conductor layer but offers the ability to access selected features of the conductor pattern from both sides of the substrate.
Flex PCBs
Flex PCBs are printed circuit boards that can bend, fold, and conform to almost any shape or thickness, opening up unprecedented design flexibility for electronics. This enables the use of smaller and lighter components, improving performance and thermal efficiency while reducing assembly and handling costs.
The conductor layers of a flexible PCB are etched onto a thin film of polyimide or polyester-based material. The layers flex circuit manufacturer are then coated with a coverlay to protect the traces from moisture and contaminants. Typically, copper is the most common conductor choice due to its good balance of price and physical attributes. Other options include ED or rolled annealed copper, Constantan, silver ink, and even gold.
Single-Sided Flexible Circuits are the most popular type of flex PCB, found in calculators and similar devices. Double-sided flex circuits can also be produced and offer greater power-handling capability, though they are more expensive to produce.
Multi-Layer Flexible Circuits can have three or more layers of conductors and are often found in aerospace and military applications that can justify the increased cost. Rigid-Flex Circuits combine the best of rigid and flex PCBs, offering a hybrid that incorporates components mounted to a traditional rigid board with a network of flexible substrates connecting them together.
The main difference between a rigid and flex PCB is the number of steps and materials involved in manufacturing them. A webinar by Epec Engineered Technologies on Youtube compared the manufacturing process of a rigid PCB to that of a flex PCB and concluded that the more complex flex circuit is about 17 times more costly to produce than a rigid one.
Flex PCB Design
When you are working on a flex PCB, you need to pay attention to details such as the thickness-to-bend radius and pad-in-pad. You should also use pad fillets to improve etch yields. You should also avoid sharp corners that can cause stress and failure in the flexible area of your PCB. A tear-guard is a good solution for this, although it will increase the cost of your PCB.
The PCB manufacturing process is a complex and delicate one that requires expertise and experience. It starts with the creation of a base material substrate, which is usually made from FR4 or Rogers 4003 polyimide. A photoresist is then used to overlay the circuit artwork patterns onto the surface of the board.
Copper plating is next, followed by the application of a coverlay. This layer protects the traces and pads from damage during the drilling and soldering processes. A stiffener can be added to rigidize the flex PCB for assembly and insertion at high speeds.
Once the bare circuit board is finished, it is subjected to electrical testing. This ensures that the circuit board is free of internal faults and will function properly when assembled. The flex PCB can also be coated with adhesive tape to make it more durable and easier to handle. It is important to choose the right material for this, as it will affect the price of your final product.
Flex PCB Manufacturing
Flex PCB manufacturing combines processes adapted from rigid PCB fabrication with innovations that enable the flex circuit use of thin, heat-resistant flexible materials. The complex 2D and 3D structures they support make them an ideal choice for mobile, wearable and internet-connected products. Understanding their design considerations, specialized assembly methods and testing procedures is essential to achieving quality results.
To create a flex circuit board, engineers start with a copper-plated substrate. A photosensitive etch resist is coated onto the surface, with the desired mask pattern exposed and developed. Chemicals are then used to etch away the unexposed areas of copper foil, leaving behind the circuit pattern and conductors.
The resulting pattern is then laminated to a polyimide film. Conductive layers are then deposited on the top and bottom, with plated through holes used to interconnect them. Finally, a cover layer is applied to protect the circuit and provide electrical insulation.
Unlike traditional rigid circuit boards, flex PCBs can withstand repeated bending without damage or loss of function. They also have a lower mass and ductility, allowing them to be more easily formed to the desired shape of an electronic device.
When assembling the components on a flex circuit, SMT (Surface Mounted Technology) methods are commonly used. The resulting boards are then tested for electrical and mechanical performance. Electrical tests check conductivity, insulation and dielectric breakdown. Mechanical tests include dynamic bending, twist and torsion. Environmental and reliability tests evaluate performance in varying temperatures, humidity and operating environments.