How To Select the Appropriate Board Materials for Flexible PCB Fabrication?

How To Select the Appropriate Board Materials for Flexible PCB Fabrication?

Sep 16,2020


Flexible or flex printed circuit boards (PCBs) are one of the popular circuit board types that fulfil the needs of flexible electronic circuits. Designed as a replacement for traditional wire harnesses, flexible PCBs can be easily shaped to fit into several complicated electronic designs. Also, these boards provide design freedom while maintaining density and performance. Although the performance of a flexible PCB depends on various factors, primary materials play a key role in it. The selection of optimum materials is important to the success of a flexible PCB assembly. Today, there are varieties of materials available in different configurations fulfil the needs of modern applications. This post highlights different aspects of materials used in the flexible PCB fabrication. So, stay tuned to know more.

Commonly Used Flexible Core or Substrate Materials in Flexible PCB Fabrication

A flex circuit board requires adhesive and adhesiveless material for its layers to attach. Both the materials are supplied with a range of polyimide core thicknesses.

  • Adhesive Flex Materials:

    These types of materials are a mainstay of the flexible circuit board materials. As the name implies, they either use acrylic or epoxy-based adhesives to glue the copper to the flex core. Some important benefits of adhesive flex cores include greater copper peel strength, reduction of material costs, and many more. Adhesive-based materials are commonly used in single-sided and double-sided flex circuit board designs.

  • Adhesiveless Flex Materials:

    As its name implies, these types of flex core materials have copper directly attached to the core without any adhesives. They are manufactured either as cast dielectric on copper or sputtered copper on a dielectric film. They are commonly preferred for flex boards with a high number of layers. Several reasons have contributed to the popularity of adhesiveless materials including the elimination of flex thickness, improved flexibility, tighter possible minimum bend radius, higher potential temperature ratings, improved controlled impedance signal characteristics, and more.

Conductor Materials for Flexible PCBs

Copper is the most preferred and easily available conductor material for flexible PCB assembly. The material is used owing to its beneficial features including good electrical characteristics, high workability and more. There are two types of copper foils available in flex material configuration- rolled annealed (abbreviated as RA) and electro-deposited (abbreviated as ED). These foil forms are available in various weights and thickness. The foils are subjected to surface treatment before the board assembly. Combined with a relatively low cost, electro-deposited copper foil became popular in the market. Unlike ED copper foil, RA is quite expensive but comes with enhanced capabilities.

Flexible Soldermask Materials and Coverlay for Flexible PCB Fabrication

Flexible PCBs comprise external layer circuitry bounded with either a coverlay, soldermask or combination of both. Earlier, OEMs used adhesives to glue the layers to the core. However, this method reduced the reliability of the circuit board. To solve this issue, they now prefer coverlays owing to their improved flexibility and reliability. Coverlay has a solid layer of polyimide with either an epoxy or acrylic adhesive. Likewise, soldermask is a commonly used material for rigidized component areas with high-density SMT components. A good design practice encompasses the use of both coverlays in flex areas and soldermask in component areas to explore their capabilities.

In recent times, flexible PCBs have gained immense popularity and found a large application in complex circuitry. Thus, it is important to choose the appropriate flexible PCB materials for the efficient performance of circuit boards. If you have any doubts, do contact an experienced industry player who can help you find the best possible solution for your application. Creative Hi-Tech is a trustworthy player specializing in flexible PCBs.

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