Which Flexible Circuit Board Material Is Used in Fabrication of Your Flex PCB?

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Printed circuit boards are an evolving line of technology in the electronics industry. They have allowed humans to invent increasingly complex and small appliances with unparalleled accuracy. There are stark differences between traditional circuit boards and their printed counterparts. In fact, some companies specifically specialize in manufacturing printed circuit boards.

Subsequently, a certain category of PCBs has recently been growing in popularity. It refers to flexible circuit boards. Flex circuit boards are considered one of the most innovative design models for a good number of reasons. They are mainly responsible for allowing a size reduction in new consumer products.

This article will discuss flex circuit boards and the types of material used in flex PCB fabrication.

Flex Circuit Boards

Flexible PCBs are made using flexible material, which allows them to be bent, looped, or flexed. This ability helps flex circuit boards fit into an electrical design, making their utility more versatile than traditional circuit boards.

As a result, flex circuit boards have become very popular in applications concerning limited space as well as consumer electronics, medical appliances, and foldable electronic devices. They have the following benefits:

  1. Flexibility

Flexibility is the most noticeable benefit of flex circuit boards. This trait allows designers the chance for more creative freedom and limits compromises on the device design over product assembly.

  1. Connectivity

Correctly designed flex boards can be bent for an indefinite number of cycles which is why dynamic flex applications are particularly popular. It also increases the range of connectivity between electrical components, the user interface, and the device.

  • Reduced Weight

In order for efficient performance, flex circuit boards are designed using very thin sheets and circuitry, which makes them lightweight. Their reduced weight makes them more reliable for use in lightweight products and grants them better shock absorption as well.

 

Types of Material Used in Flex circuit Fabrication

PCB fabrication refers to the process of building a circuit board from scratch. A flex PCB is built in a different way than its rigid counterpart. At least one flex circuit board component is different from a rigid board. We will discuss the reasons later on.

Flex Circuit Board

Rigid Circuit Board

1.       Core

1.       Core

2.       Conductor

2.       Conductor

3.       Coverlay

3.       Solder mask

 

Core

The base core of a flex circuit board has to be made using a flexible material. While traditional PCBs use an epoxy-based film, flex boards mainly use a polyimide (PI) film for increased flexibility. Epoxy and fiberglass are prone to breakage, while polyimide is a polymer that can be subjected to a great deal of stress. Furthermore, polyimide can retain its flexibility after thermosetting, but other core materials cannot withstand high temperatures or become rigid after cooling down.

Similarly, another common material is polyester, but it cannot tolerate high temperatures. Therefore, it is mostly used in low-cost electronics and can only work with printed circuits and lamination. It cannot and should not be subjected to soldering.

Flex circuit boards have cores that used to require adhesives for connecting to the layers, but adhesiveless technology has also been developed now!

Adhesive vs. Adhesiveless Cores

Adhesive based cores require epoxy or acrylic adhesives to attach the flex PCB layers. Although adhesive cores increase the copper peel strength, they also increase the thickness of the final design, which defeats the purpose of flex boards. Increased thickness also results in reduced flexibility.

On the flip side, newer adhesiveless options resolve this issue and use a PI substrate that directly attaches to the copper circuitry. This minimizes the risk of breakage and allows for a thinner design. Adhesiveless cores can withstand higher temperatures and offer more flexibility based on their thin designs.

Coverlay Film

Instead of using a solder mask which increases rigidity, manufacturers use a coverlay film to mask the outer surface of conductors in the circuit. Commonly used materials for coverlay films are also polyimide and polyester. Sometimes, flexible solder mask ink is also used, but polyimide is more common. The reason is again for increased flexibility and because PI and PET film thickness is less than that of glass fiber and epoxy films.

The purpose of a coverlay film is to insulate the conductor and protect it from corrosion and damage. It is just as important as the core for the continued performance of an electrical device.

Conductor

One of the most popular types of material used in flex PCB fabrication is the conductor, copper. Cheap electronics can use printed conductors such as carbon films or silver-based inks, but copper has always been the conductor of choice in the circuit board industry.

Different types of copper conductors are used depending on the nature of the application. Common copper layers include the following types.

         i.            Rolled Annealed (RA)

Higher grade rolled-annealed foils are used when an application involves repetitive creasing, such as dynamic flex applications. Annealed copper can stretch more, unlike standard copper, which is infamous for fatigue cracking. It also has increased flexibility.

       ii.            Electro-Deposited (ED)

This is a low-cost alternative to standard copper. It is the flexible circuit board material of choice when a circuit is being used to eliminate connectors and increase flexibility, while conductivity is not the main target.

      iii.            Copper-Clad Laminate

Copper-clad laminate is used in applications where conductors are exposed to high temperatures where standard copper would become prone to increased resistance to conductivity. It prevents board failure and retains its flexibility, making it a popular choice.

 

Conclusion

To summarize, there are many types of material used in flex PCB fabrication. Each kind depends on the nature of the application they will be used in. It is important to consult professional PCB manufacturers like Hemeixin Electronics for all your design needs. Their products are rigorously tested, and they use the best quality materials for client satisfaction. They also provide several options for flexible circuit board material.

In addition to their design guidelines, they can offer better advice by considering your budget, the nature of your application, and even your specific product design requirements. So, visit them today and get a quote for a satisfactory experience!

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