FLEXIBLE CIRCUIT BOARDS & STIFFENERS

Flexible printed circuit boards are a type of printed circuit board (PCB) that has been designed to be more flexible than traditional rigid printed circuit boards. They offer many advantages, including greater design flexibility, improved reliability, and reduced cost. Below we will discuss the benefits of flexible PCBs and how they are used in a variety of applications.

Advantages of FPC
The biggest advantage of flexible circuit boards is their flexibility. Traditional PCBs are rigid and limited in size, shape, and design options. Flexible PCBs can be designed to fit into tight spaces or can be shaped to follow curves or contours for better ergonomics or aesthetics. This allows for more creative designs which can help increase the efficiency of products or make them easier to use.
Flexible PCBs also have higher reliability than rigid PCBs due to their improved mechanical properties. The flexible substrate material is able to absorb shock and vibration better than traditional rigid circuit board materials, leading to improved product lifetimes and fewer failures during operation. Additionally, flexible PCBs also have improved electrical performance due to reduced signal loss associated with bending or flexing the board during operation. This leads to higher signal integrity and faster data rates compared to traditional PCBs.

Types of Stiffeners
Stiffeners are additional components that are attached to a flexible PCB in order to enhance its rigidity or strength. They are typically made of metal but can also be made from other materials such as plastic or carbon fiber depending on the application requirements. Stiffeners provide support for components mounted on the board as well as provide a more stable platform for soldering connections.
There are two main types of stiffeners: adhesive-backed and rigid. Adhesive-backed stiffeners are typically made of thin metal sheets that have an adhesive backing applied during the manufacturing process so they can be easily attached to the PCB surface. This type of stiffener is most commonly used when a high degree of flexibility is required or where there is limited space available for mounting components. Rigid stiffeners on the other hand provide greater rigidity but require more space for installation and may not be suitable for applications requiring flexibility. The material used for rigid stiffener depends on the application requirements, but it usually consists of thick metal foil or metal plates with cutouts designed specifically for mounting components onto them.

Benefits of Stiffeners
Using flex or rigid stiffener provides several benefits, including improved durability, better performance in extreme conditions, increased rigidity which helps prevent warping when subjected to thermal cycling (heating and cooling), increased shock and vibration resistance which leads to fewer failures due to mechanical stress, improved electrical performance by preventing electrical shorts between layers caused by movement and bending and finally improved electromagnetic interference (EMI) shielding effectiveness by providing an additional shield against external radio frequency (RF) waves entering into the system and causing disruption/interference with other nearby devices/components connected within it.
Stiffeners can also provide rigidity and support to component areas to prevent bending of flex in component areas and potential solder joint damage. Stiffeners are typically made from metal or plastic and are used in combination with components to strengthen specific areas. For example, stiffeners might be used along the edges of a circuit board where components have been soldered onto it. The stiffener provides additional support so that when the board is handled or pressure is applied, the solder joints remain intact. In addition, they can also be placed on top of components to prevent them from shifting during assembly or use.

Stiffener Materials
FR4 is a fiberglass-reinforced epoxy laminate material that is widely used as a stiffener material. It is composed of a woven glass fabric that is impregnated with epoxy resin to create a composite material. It is a rigid material and has good insulation properties. It is used in a variety of applications including circuit boards, microelectronics, and structural components. The material is also flame-retardant, making it a good choice for high-temperature environments.
Polyimide is a type of high-temperature, thermally and chemically resistant polymer that is often used as a stiffener material. It is a highly durable material that is extremely resistant to chemical solvents, acids and bases, and other harsh environmental conditions. It is also resistant to temperatures up to 250°C and can be used in both high and low temperatures. Polyimide is a great choice for stiffeners in applications such as automotive parts, medical components, and aerospace components.
Stainless steel is a type of metal alloy that is composed of iron and at least 10.5% chromium. It is a strong and durable material that is resistant to corrosion, rust, and other environmental conditions. Stainless steel is often used as a stiffener material due to its strength and durability. It is often used in applications such as medical instruments, aerospace components, and automotive parts.
Aluminum is a lightweight metal that is often used as a stiffener material due to its strength and durability. It is a non-magnetic, corrosion-resistant material that is resistant to most environmental conditions. It is also a good thermal conductor, making it a great choice for applications that require heat transfer. It is often used in applications such as aerospace components, automotive parts, and medical instruments.

Summary
Flexible circuit boards need stiffeners to help with shock and vibration resistance, improved electrical performance, and improved EMI shielding effectiveness. Stiffeners are typically made of metals such as FR4, polyimide, stainless steel, or aluminum, and the selection of the material should be based on the application requirements. Adhesive-backed stiffeners are typically used when a high degree of flexibility is needed, while rigid stiffeners are used when maximum rigidity is desired.