**Introduction to FPC**
FPC stands for Flexible Printed Circuit, which in Chinese is translated as **柔性印刷电路板** and is commonly referred to as a **软板**. It is created by using light imaging pattern transfer and etching processes on a flexible substrate to form conductor circuit patterns. The surface and inner layers of double-sided and multi-layer circuit boards are electrically connected through metallized holes. The circuit pattern’s surface is protected and insulated by a PI layer and adhesive.
FPC is mainly categorized into single-sided boards, double-sided boards, multi-layer boards, hollow boards, and rigid-flex boards.
**PCB** stands for Printed Circuit Board, which in Chinese translates to **硬质印刷电路板** or simply **硬板**.
**Features of Flexible Circuit Boards**
1. **Short**: Reduced assembly time as all connections are pre-configured, eliminating the need for additional cable connections.
2. **Small**: Smaller volume compared to PCB (hard board), effectively reducing product size and enhancing portability.
3. **Light**: Lighter than PCB (hard board), contributing to a reduction in the final product’s weight.
4. Thin: The thickness is less than that of traditional PCB (hard boards), which enhances flexibility and supports assembly in constrained three-dimensional spaces.
**Advantages of Flexible Circuit Boards**
Flexible printed circuit boards are constructed from flexible insulating substrates, offering several advantages over rigid printed circuit boards:
1. They can be bent, wound, and folded freely, allowing for arrangement according to spatial layout requirements. This flexibility enables movement and expansion in three-dimensional spaces, facilitating the integration of component assembly and wire connections.
2. Utilizing FPCs significantly reduces the volume and weight of electronic products, making them ideal for the development of high-density, miniaturized, and highly reliable electronic devices. Consequently, FPCs are widely used in aerospace, military, mobile communications, laptops, computer peripherals, PDAs, digital cameras, and other fields.
3. FPCs offer benefits such as improved heat dissipation, solderability, ease of assembly, and lower overall costs. Additionally, the combination of flexible and rigid elements partially compensates for the slight limitations of flexible substrates in terms of component support.
**Main Raw FPC Materials**
The primary raw materials include: 1. Substrate, 2. Cover film, 3. Reinforcement, 4. Other auxiliary materials.
1. **Substrate**
1.1 **Adhesive Substrate**
Adhesive substrates consist of three components: copper foil, adhesive, and PI (polyimide). These are available in single-sided and double-sided types. Single-sided substrates have copper foil on only one side, while double-sided substrates feature copper foil on both sides.
1.2 **Non-Adhesive Substrate**
Non-adhesive substrates lack the adhesive layer found in traditional adhesive substrates. Comprising only copper foil and PI, these substrates are thinner, offer better dimensional stability, higher heat resistance, greater bending resistance, and improved chemical resistance. They are now widely used.
**Copper Foil:** Commonly used copper foil thicknesses include 1 OZ, 1/2 OZ, and 1/3 OZ. Recently, a thinner copper foil with a thickness of 1/4 OZ has been introduced, primarily used in China for ultra-fine lines (with line widths and spacings of 0.05 mm and below). As customer demands increase, this specification will likely see broader application in the future.
2. **Cover Film**
The cover film consists of three components: release paper, adhesive, and PI. Only the adhesive and PI remain on the product after production; the release paper is discarded and serves only to protect the adhesive during manufacturing.
3. **Reinforcement**
Reinforcement materials are specifically used in FPCs to enhance support strength and compensate for the “soft” nature of flexible substrates. Common reinforcement materials include:
– **FR4 Reinforcement:** Made of glass fiber cloth and epoxy resin, similar to FR4 used in PCBs.
– **Steel Sheet Reinforcement:** Composed of steel, offering high hardness and support strength.
– **PI Reinforcement:** Similar to the cover film, but with a thicker PI layer, available in thicknesses from 2 MIL to 9 MIL.
4. **Other Auxiliary Materials**
– **Pure Glue:** A heat-curing acrylic adhesive film with protective paper/release film, used for bonding in layered boards, flexible and rigid boards, and FR-4/steel sheet reinforcement boards.
– **Electromagnetic Protective Film:** Applied to the board surface for shielding.
– **Pure Copper Foil:** Composed solely of copper foil, mainly used for hollow board production.
**Types of FPC**
FPCs can be classified into six types:
A. **Single-Sided Panel:** Wiring is present on only one side.
B. **Double-Sided Panel:** Wiring is present on both sides.
C. **Hollow Board:** Also known as a window board, featuring an opening on one surface.
D. **Layered Board:** A two-sided circuit with separate layers.
E. **Multilayer Board:** Consists of more than two layers.
F. **Rigid-Flex Board:** A combination of flexible and rigid boards.
**Future Trends in FPC Development**
FPCs are expected to evolve in three main areas:
1. **Thickness:** Future FPCs must be even thinner and more flexible.
2. **Folding Resistance:** Enhanced folding resistance will be a key feature for future FPCs.
3. **Process Level:** To meet diverse requirements, FPC processes will need upgrading, with tighter specifications for minimum aperture and line width/spacing.
FPC stands for Flexible Printed Circuit, which in Chinese is translated as **柔性印刷电路板** and is commonly referred to as a **软板**. It is created by using light imaging pattern transfer and etching processes on a flexible substrate to form conductor circuit patterns. The surface and inner layers of double-sided and multi-layer circuit boards are electrically connected through metallized holes. The circuit pattern’s surface is protected and insulated by a PI layer and adhesive.
FPC is mainly categorized into single-sided boards, double-sided boards, multi-layer boards, hollow boards, and rigid-flex boards.
**PCB** stands for Printed Circuit Board, which in Chinese translates to **硬质印刷电路板** or simply **硬板**.
**Features of Flexible Circuit Boards**
1. **Short**: Reduced assembly time as all connections are pre-configured, eliminating the need for additional cable connections.
2. **Small**: Smaller volume compared to PCB (hard board), effectively reducing product size and enhancing portability.
3. **Light**: Lighter than PCB (hard board), contributing to a reduction in the final product’s weight.
4. Thin: The thickness is less than that of traditional PCB (hard boards), which enhances flexibility and supports assembly in constrained three-dimensional spaces.
**Advantages of Flexible Circuit Boards**
Flexible printed circuit boards are constructed from flexible insulating substrates, offering several advantages over rigid printed circuit boards:
1. They can be bent, wound, and folded freely, allowing for arrangement according to spatial layout requirements. This flexibility enables movement and expansion in three-dimensional spaces, facilitating the integration of component assembly and wire connections.
2. Utilizing FPCs significantly reduces the volume and weight of electronic products, making them ideal for the development of high-density, miniaturized, and highly reliable electronic devices. Consequently, FPCs are widely used in aerospace, military, mobile communications, laptops, computer peripherals, PDAs, digital cameras, and other fields.
3. FPCs offer benefits such as improved heat dissipation, solderability, ease of assembly, and lower overall costs. Additionally, the combination of flexible and rigid elements partially compensates for the slight limitations of flexible substrates in terms of component support.
**Main Raw FPC Materials**
The primary raw materials include: 1. Substrate, 2. Cover film, 3. Reinforcement, 4. Other auxiliary materials.
1. **Substrate**
1.1 **Adhesive Substrate**
Adhesive substrates consist of three components: copper foil, adhesive, and PI (polyimide). These are available in single-sided and double-sided types. Single-sided substrates have copper foil on only one side, while double-sided substrates feature copper foil on both sides.
1.2 **Non-Adhesive Substrate**
Non-adhesive substrates lack the adhesive layer found in traditional adhesive substrates. Comprising only copper foil and PI, these substrates are thinner, offer better dimensional stability, higher heat resistance, greater bending resistance, and improved chemical resistance. They are now widely used.
**Copper Foil:** Commonly used copper foil thicknesses include 1 OZ, 1/2 OZ, and 1/3 OZ. Recently, a thinner copper foil with a thickness of 1/4 OZ has been introduced, primarily used in China for ultra-fine lines (with line widths and spacings of 0.05 mm and below). As customer demands increase, this specification will likely see broader application in the future.
2. **Cover Film**
The cover film consists of three components: release paper, adhesive, and PI. Only the adhesive and PI remain on the product after production; the release paper is discarded and serves only to protect the adhesive during manufacturing.
3. **Reinforcement**
Reinforcement materials are specifically used in FPCs to enhance support strength and compensate for the “soft” nature of flexible substrates. Common reinforcement materials include:
– **FR4 Reinforcement:** Made of glass fiber cloth and epoxy resin, similar to FR4 used in PCBs.
– **Steel Sheet Reinforcement:** Composed of steel, offering high hardness and support strength.
– **PI Reinforcement:** Similar to the cover film, but with a thicker PI layer, available in thicknesses from 2 MIL to 9 MIL.
4. **Other Auxiliary Materials**
– **Pure Glue:** A heat-curing acrylic adhesive film with protective paper/release film, used for bonding in layered boards, flexible and rigid boards, and FR-4/steel sheet reinforcement boards.
– **Electromagnetic Protective Film:** Applied to the board surface for shielding.
– **Pure Copper Foil:** Composed solely of copper foil, mainly used for hollow board production.
**Types of FPC**
FPCs can be classified into six types:
A. **Single-Sided Panel:** Wiring is present on only one side.
B. **Double-Sided Panel:** Wiring is present on both sides.
C. **Hollow Board:** Also known as a window board, featuring an opening on one surface.
D. **Layered Board:** A two-sided circuit with separate layers.
E. **Multilayer Board:** Consists of more than two layers.
F. **Rigid-Flex Board:** A combination of flexible and rigid boards.
**Future Trends in FPC Development**
FPCs are expected to evolve in three main areas:
1. **Thickness:** Future FPCs must be even thinner and more flexible.
2. **Folding Resistance:** Enhanced folding resistance will be a key feature for future FPCs.
3. **Process Level:** To meet diverse requirements, FPC processes will need upgrading, with tighter specifications for minimum aperture and line width/spacing.
