Flex Circuit Board Fabrication – How to Select the Appropriate PCB Board Materials?

Flexible or flex printed circuit boards are popular PCB type designed to fulfill the needs of flexible electronic circuits. Flex circuit boards are the fastest replacement for traditional wire harnesses as they can be easily shaped to fit into various complex circuit designs. Additionally, these circuit boards provide freedom of designing while maintaining their performance and density. The performance of the flex circuit board entirely relies on primary materials. Selecting the optimum materials is essential to the success of a flex circuit board fabrications. There are different varieties of materials, and configurations are available to fulfill the needs of modern design applications. This post will guide you to find out different aspects of materials used in the flex circuit board fabrication.

Flex Circuit Board

Types of Flexible Core or Substrate Materials Used in Flex Circuit Board Fabrication

The core materials of flex circuit boards are made of adhesive as well as non-adhesive materials. Both are supplied with a range of polyimide core thicknesses.
  • Adhesive-based Flex Materials: Adhesive-based materials are a mainstay of the flexible circuit materials and commonly used in single- and double-sided circuit board designs. As its name implies, they make use either epoxy- or acrylic-based adhesives to glue the copper to the flex core. Adhesive-based flex materials offer a wide range of benefits including higher copper peel strength, reduction of material costs, and more.
  • Non-adhesive Flex Materials: This type of flex core materials are manufactured as either sputtered copper on dielectric film or cast dielectric on copper. They are commonly used when the design is a rigid or higher layer count flex construction. In both situations, non-adhesive flex core offers superior quality and reliability. Non-adhesive materials are widely used for several reasons. One major advantage of this material is the elimination of the adhesive layers, which results in flexible and thin construction. Other benefits of non-adhesive flex materials include tighter possible minimum bend radius, higher potential temperature ratings, and many more.

Conductor Materials Used in Flex Circuit Board Fabrication

It is possible to achieve high-level flex circuit board fabrication using the thin, fine-grained, low profile copper foils. Mainly, there are two types of copper foils available in both flex material configurations: electro-deposited (abbreviated as ED) and rolled annealed (abbreviated as RA). Both adhesive-based and non-adhesive start as electro-deposited copper; however, during the rolled annealing process the grain structure transforms from the vertical ED to horizontal RA copper.

Coupled with a relatively lower cost, ED copper foil has gained immense popularity in the market. RA foil is quite expensive but comes with improved bend capabilities. Additionally, RA foil is a standard material required for dynamic flex applications.

Coverlay and Flexible Soldermask Materials for Flex Circuit Board Fabrication

Flex printed circuit boards consist of external layer circuitry enclosed with either a flexible soldermask, coverlay, or a combination of both. PCB manufacturers previously used adhesives to glue the layers, which reduced the reliability of the circuit boards to some extent. To resolve such issues, most of them now prefer coverlays owing to their improved reliability and flexibility. Coverlay features a solid layer of polyimide with either an acrylic or epoxy adhesive. Similarly, flexible soldermask is a preferred material for rigidized component areas with high-density Surface Mount Technology (SMT) components. A good design practice utilizes both soldermask in component areas and coverlay in flex areas to make the best use of their capabilities.

The flex circuit board has gained immense popularity over the years and find large applications with complex circuitry. It is important to choose the correct flexible PCB materials as this will not only affect the board performance but the overall cost of the circuit board. If you still have any doubts, do contact one of the leading industry experts who can help you find the best possible solution for your electronic application. Rigiflex Technology is a reliable industry player specializing in single-layer, double-layer, multilayer, flexible, and rigid-flex PCBs.

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