Keywords: Flexible PCB, Flex Circuits Board

Flex circuit cores are made of a flexible polymer, unlike the majority of conventional PCBs, which have a fiberglass or metal basis. The substrate for most Flexible PCB is a polyimide (PI) film. Although it remains flexible after thermosetting, PI film does not soften when heated. When heated, many thermosetting resins, including PI, become stiff, making PI a better material for flex PCB assembly. Standard PI film is not well resistant to moisture and rips, however, upgrading PI film reduces these problems.

For the layers of a flex PCB to adhere, it also needs an adhesive or unique base material. Before now, manufacturers exclusively utilized adhesives, however, this practice decreased the PCB's dependability. They created adhesiveness PI, which adheres to copper without the need for an adhesive, to address these problems. Thinner designs are possible with less chance of through fracture because of this material. Manufacturers utilize a coverlay film also made with PI to cover and shield flex circuits instead of a solder mask. The manufacturer may laminate a stiffer to that piece of the flex PCB if you want it to be firm, but the signal cannot pass through both the flex and the stiffer.

Due to its outstanding benefits, such as its flexible construction, small volume, and lightweight, suitable with the trend toward downsizing in electronics development, flexible PCB is growing and receiving a wide variety of applications. In addition to dynamic flexibility, curling, and folding, flexible PCB may also incorporate static flexibility. Flexible PCBs increase the degree of freedom in mechanical and circuit design by expanding into three dimensions. Additionally, by tracing on X, Y, and Z surfaces with fewer connections, machine work, and assembly mistakes may be reduced, and the reliability and stability of the entire system used by electronic devices can be significantly increased. Flexible PCBs are used extensively in a variety of industries, including computers, communication devices, instruments, medical equipment, aerospace, and the military. Additionally, new application areas for flexible PCB such as wireless floating heads, repeaters, digital cameras, mobile phones, flat panel displays, and HDI PCB have significantly fueled the growth of flexible PCB and increased its share of the overall PCB market.

• The Flexible PCB's structure

Flexible PCBs can be divided into the following groups based on structural types:

1. Single-side flexible PCB, which is readily fabric table and has a straightforward construction.

1. Double-sided flexible PCB, which has a more complex structure than single-sided flexible PCB and is more difficult to regulate.

1. Multi-layer flexible PCB, which has a more intricate structure than 2-layer flexible PCB and is more challenging to fabricate with consistent quality.

Rigid-flexible PCB with a single side

PCB with a double-side rigid-flexion

PCB with several rigid-flex layers

The first three varieties of flexible PCBs—single-side, double-side, and multi-layer rigid-flex—are more challenging to construct because they have significantly more intricate architectures.

Flexible PCB Material.

According to the flexible PCB's construction, the insulating substrate material, adhesive, metal conductor layer (copper foil), and cover layer are the ingredients that make up the flexible PCB. The flexible insulating film, which serves as a carrier and has great mechanical and electrical performance, must be the primary component of the Flex Circuits Board. Polyester and polyimide film are common materials, with the latter being used more frequently.

Rigid-flexible PCB with a single side

PCB with a double-side rigid-flexion

PCB with several rigid-flex layers

The first three varieties of flexible PCBs—single-side, double-side, and multi-layer rigid-flex—are more challenging to construct because they have significantly more intricate architectures.

Flexible PCB Material

According to the flexible PCB's construction, the insulating substrate material, adhesive, metal conductor layer (copper foil), and cover layer are the ingredients that make up the flexible PCB. The flexible insulating film, which serves as a carrier and has great mechanical and electrical performance, must be the primary component of flexible PCBs. Polyester and polyimide film are common materials, with the latter being used more frequently. Flexible PCB assembly is focused on the three main factors that play a significant influence on the final product's quality: flatness, positioning precision, and board carrier consistency.

Lower Density

The bulk of flexible PCBs is now only used for connections between modules with various functionalities due to product cost concerns, as flexible PCBs are more expensive than rigid PCBs. As a result, flexible PCBs have a low assembly density and a comparatively low number of components that are ready for assembly. In general, there are between 50 and 100 components per board, while some just have two connections.

d. There Are a Lot of Panels

To reduce the size of a single board, flexible PCB is mostly utilized in electronic items that have been downsized, including mobile phones and digital cameras. Additionally, there aren't many components integrated on a single board, therefore panels are typically used for assembly before being punched apart to increase assembly efficiency.

Widespread Use of Accessory Fixtures During the Assembly Process

Due to the deformation and damage characteristics of flexible PCBs, several auxiliary fixtures, such as flexible PCB baking fixtures, board carrying trays, electrical test fixtures, function test fixtures, and cutting fixtures are used during flexible PCB assembly.

High Standards for Product Quality

Components constructed on flexible PCB must be able to fulfill the requirements of their application environment since flexible PCBs are typically used in environments that necessitate repetitive bending and control precision. Flexible PCB hence has higher requirements than rigid PCB in terms of cleanliness, anti-static measures, and soldering dependability. In addition, flexible PCB assembly faces various technological difficulties as a result of the popularity and acceptance of lead-free manufacturing techniques.

f. Expensive Assembly

Flexible PCB assembly is more expensive overall than rigid PCB assembly, which is particularly true in the early stages due to the wide range of fixture applications, lengthy manufacturing process, low equipment utilization rate, higher demands for accessories and staff, and higher standards for the manufacturing environment and product quality.

As electronic goods advance and flexible PCB assembly technology continuously advances and becomes optimized with a steady decrease in production and assembly costs, the application range expands. This will ultimately cause flexible PCB to advance into a wider variety of applications.