The Main Materials of FPC PI Circuit Board

What is Pi in FPC?

PI stands for polyimide. It is a type of organic polymer material that is both flexible and heat resistant. This is the primary material used to make FPC circuit boards. The material is known to have many properties, including excellent resistance to wear and heat, and is also ideal for insulating devices. PI is typically a yellow color, but it can also be black, white, or transparent. PI is essential to FPC circuit boards because it improves repeatability and flexibility.

The Pi in FPC is a component that depends on polyimide (PI). PI is an organic compound that gives flex circuit boards their flexibility. The exPlus Flex PCB has a line width of 2.75 mils. It is widely essential in mobile phones, as well as in other industrial settings. The flexible material allows for the easy connection of buttons, batteries, and microphones. In addition, the led light and engine control sensors are also essential in the automotive industry.

An FPC is a printed circuit board, a flex circuit, or a soft board. The PI material is very flexible and allows for bending and folding. It also allows for better heat dissipation than a traditional PCB, which can help extend the life of electronics. In addition, its flexibility makes it possible for electronics manufacturers to bend and shape it at will; they are even considering this in future smartphones.

FPC PI Materials


There are various types of PI. Single-layer PI is very thin and has many properties. It is heat-resistant and offers excellent insulation. It is often helpful as a protective film for gold fingers. Gold finger connectors must fit into the board, and the ordinary cover film is long and easily damaged. A single-layer PI circuit board offers excellent temperature and wear resistance.

RA copper foil

RA copper foil is the main material of the flexible PCB. This type of copper foil comes from an alloy of copper and epoxies. The conductor layer consists of a thin film of copper that resists bending. There are two types of copper foil: ED copper foil and RA copper foil. ED copper foil is more flexible and is available in smaller thicknesses, while RA foil is thicker and requires a higher-precision manufacturing process.

After etching, we coat the copper foil with an adhesive. Then we place the covering layer on top of it. Next,  we evenly coat the adhesive on the copper foil and the FPCB base layer. Once the adhesive dries, the FPCB is ready for installation. RA copper foil is essential in a wide variety of circuits.

FR4 stiffener

When designing an FPC PI circuit board, you must choose between FR4 and PI materials for the stiffener. FR4 is the most popular choice because of its high bond strength and solder resistance. However, PI is preferred for use on the backside of insertion gold fingers because it can be picked up from the flexible printed circuit connector body and inserted into the ZIF socket. It also provides flat support during reflow and pick-and-place processes.

FR4 is a glass-fiber laminate impregnated with epoxy resin. It is commonly helpful in FPC PI circuit boards because it is cheaper than stainless steel. Polyimide is another common material used in PCB stiffeners because it has good solder resistance and bond strength. PI is more conductive than polyimide, making it a good choice for high-performance flexible circuit boards.

PI stiffener

flex pcb

A PCB stiffener helps to make circuit boards rigid. This is ideal for several reasons. First, we place some stiffeners on one side of the board. Then, other stiffeners are placed on both sides to increase rigidity. However, this option can be more expensive and requires several lamination cycles. We add this type of stiffener in plated-through holes. They help to provide flat support during pick-and-place and reflow processes.

There are two main types of circuit board stiffeners: molded and conductive. Molded stiffeners help in rigid-flex circuits. They are also essential in battery-operated units and cellular phones. The stiffeners must be lightweight and strong enough to prevent the PCB from deforming while they are in use.

Conductive silver paste

The main material of the FPC PI circuit board is a conductive silver paste, which is highly conductive by nature. This paste is helpful mainly in industrial applications and research, producing it using an eco-friendly chemical blend. The main use for this paste is to create a conductive surface on an otherwise insulating surface. The electrical conductivity of the slurry varies according to the silver powder’s concentration, usually around 80 to 90%. Below 60 percent, the slurry becomes unstable.

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