Flexible or flexible printed circuit boards (PCBs) are one of the popular types of circuit boards that meet the needs of flexible electronic circuits. Designed to replace traditional wiring harnesses, flexible PCBs can be easily formed to fit various complex electronic designs. Moreover, these boards provide design freedom while maintaining density and performance. Although the performance of flexible PCBs depends on multiple factors, the main materials play a crucial role. Choosing the best material is crucial for the success of flexible PCB components. Nowadays, there are various materials available in different configurations to meet the needs of modern applications. This article focuses on the different aspects of materials used in the manufacturing of flexible PCBs. Therefore, please continue to follow for more information.
Flexible core or substrate materials commonly used in flexible PCB manufacturing
Flexible circuit boards require adhesive and adhesive free materials to attach their layers. Both materials provide a range of polyimide core thicknesses.
Flexible adhesive material:
These types of materials are the main body of flexible circuit board materials. As the name suggests, they use acrylic or epoxy based adhesives to attach copper adhesive to flexible cores. Some important advantages of adhesive flexible cores include higher copper peel strength, reduced material costs, and so on. Adhesive based materials are commonly used in the design of single sided and double-sided flexible circuit boards.
Non adhesive flexible materials:
As the name suggests, copper from these types of flexible core materials is directly connected to the core without any adhesive. They can either cast dielectrics on copper or sputter copper on dielectric films. Usually, they are preferred for flexible plates with a large number of layers. There are several reasons for the popularity of adhesive free materials, including eliminating bending thickness, improving flexibility, possibly tightening the minimum bending radius, potential higher temperature ratings, improved controlled impedance signal characteristics, and so on.
Conductor materials for flexible PCBs
Copper is the most preferred and easily obtainable conductor material for flexible PCB assembly. The use of this material is due to its beneficial properties, including good electrical properties and high processability. There are two types of copper foil with flexible material configurations: rolling annealing (abbreviated as RA) and electrodeposition (abbreviated as ED). These foils come in various weights and thicknesses. Perform surface treatment on the foil before assembling the board. Combined with relatively low costs, electrodeposited copper foil has become very popular in the market. Unlike ED copper foil, RA is quite expensive but has enhanced functionality.
Flexible solder resist materials and coatings for flexible PCB manufacturing
A flexible PCB includes a cover layer, solder mask layer, or a combination of both outer circuits. In the early days, OEM manufacturers used adhesives to bond layers to the core. However, this method reduces the reliability of the circuit board. To address this issue, they now prefer overlay layers due to their higher flexibility and reliability. Coverlay has a polyimide solid layer with an epoxy or acrylic adhesive. Similarly, the solder mask layer is a commonly used material for rigid component areas with high-density SMT components. Good design practices include using overlay layers in flexible areas and using solder mask layers in component areas to explore their functionality.