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PCB/PCBA knowledge
FPC – what is it and how to design

FPC, Flexible Printed Circuit, is a highly reliable and excellent flexible printed circuit board made of polyimide or polyester film as the base material. It has the characteristics of high wiring density, light weight, thin thickness and good bendability. In this article, we mainly introduce the advantages and disadvantages, types, applications, structure composition and designs of FPC. Keep reading!

Table of Contents

What is FPC?

FPC is the abbreviation of Flexible Printed Circuit, also known as a flexible PCB.

FPC(Flexible Printed Circuit)
FPC(Flexible Printed Circuit)

FPC refers to the foldable printed circuit board formed on the copper foil with PET or PI as the base material, which can carry various active and passive components and accessories, and is widely used in the interconnection of modules in electronic products through proper assembly and design.

Features of FPC

FPC has some unique characteristics when compared with rigid PCB, such as:

  • Small size
  • Lightweight
  • Flex-for-installation
  • Dynamic flexibility

Advantages of FPC

(1) FPC can be bent, wound and folded freely, and can be arranged according to the space, and can be moved and stretched arbitrarily in three-dimensional space, so as to achieve the integration of component assembly and wire connection.

(2) The use of FPC can reduce the volume and weight of electronic products, which is suitable for the development of electronic products in the direction of high density, thinness, miniaturization and high reliability. Therefore, FPC is widely used in aerospace, military, mobile communications, notebook computers, PDA , digital cameras and other products.

(3) FPC also has the advantages of good heat dissipation and solderability, easy assembly, and low overall cost. The design of the combination of rigid and flex also makes up for the slight deficiency of the soft base material in the component’s bearing capacity to a certain extent.

Disadvantages of FPC

(1) High one-time initial cost
Since FPC is designed and manufactured for special applications, the cost of initial circuit design, wiring, negatives, and molds is relatively high.

(2) It is difficult to change and repair FPC

Once the FPC is made, it must be changed from the drawing of the film, so it is not easy to change. In terms of function, the short-circuit fault cannot be repaired compared with the rigid PCB board.

(3) FPC is easy to damage with improper operation

Improper operation by assemblers can easily cause damage to FPC, and its soldering and rework need to be operated by trained personnel.

Types of FPC

Various types of FPC
Various types of FPC

FPC has various types according to different classifications. Some common types are:

  • Single-sided FPC
  • Double-sided FPC
  • Multi-layer FPC
  • Rigid-flex FPC, etc.

Applications of FPC

Applications of FPC
Applications of FPC

FPC has wide applications, form little gadgets to large equipment, some common applications are:

  • Handset
  • Note-Book / Tablet
  • Net-Book/E-Reader
  • DCS
  • LCM/HDD
  • DVD/CD-ROM
  • Printer / Scanner
  • Auto-Mobile

FPC application considerations

1. Avoid folding, pressing, scratching, scratching, and it is best to use Tray for transfer and transportation FPC ;

2. Do not directly touch the product with your hands, especially your fingers or the PAD, to avoid grease pollution and cause solderability or conductivity problems;

3. Fingers and PAD parts should not be bent, so as not to cause the metal plating and copper surface to break. If other parts are bent, do not bend them deadly, so as not to cause line breaks or increase the resistance value;

4.Because the FPC is hygroscopic and has slightly poorer dimensional stability than the rigid PCBs, it is easy to cause expansion and contraction deformation due to poor external environment. Therefore, when it is not in use, please do not open the packaging bag and store it at a constant temperature and humidity space.

FPC structure composition

1, copper foil substrate CCL (Copper Clad Laminate)

It is composed of three layers of copper foil + glue + base material. In addition, there is also a non-adhesive base material, that is, a combination of two layers of copper foil + base material. Its price is relatively high, and it is suitable for products with a bending life requirement of more than 10W times.

1.1 Copper Foil

In terms of materials, it is divided into rolled copper and electrolytic copper. In terms of characteristics, rolled copper has better mechanical properties. When there is a requirement for flexibility, most of them use rolled copper. The thickness is divided into 1/3Oz, 1/2Oz, and 1Oz. , 2Oz and other four kinds.

1.2 Substrate

It is divided into PI Film and PET Film. The price of PI is higher, but its flame resistance is better. The price of PET is lower, but it is not heat-resistant. Therefore, if there is a welding demand, most of them use PI material. The thickness is generally 1/2mil, 1mil, 2mil.

1.3 Adhesive

There are generally two kinds of glue: Acrylic (acrylic glue) and Epoxy (epoxy resin glue). The most commonly used one is Epoxy glue. The thickness is 0.4-2mil, and 0.7mil thick glue is generally used.

2, Coverlay

The cover film is composed of substrate + glue, and its substrate is divided into two types: PI and PET. The thickness is from 0.5 to 1.4mil.

3, Reinforcing material stiffener

3.1 Function

In order to solder the parts on the flex board, reinforcement is added for installation, and the thickness of the flex board is compensated.

3.2 Material

PI/PET/FR4/SUS

Considerations in FPC design

FPC design
FPC design

A) FPC size determination: including the number of PINs, the number of layers (determining the thickness), the number of layers is determined by the width of the FPC, the number of PINs and the pitch of the PIN, etc., and the width of the FPC is generally determined by the size space;

B) The positioning of the FPC on the housing: assembly positioning and ensuring that the gap positioning is fixed;

C) FPC ground point design: add ground point, ESD requirements;

D) Fixation of the FPC connector in the Z-axis direction on the housing, and the fixation on the Z-axis is generally compressed with foam;

E) Determination of FPC hardening area (glue area) and non-hardening area;

F) Determination of the size of the reverse reinforcement plate after the connectors at both ends of the FPC are soldered;

G).emn file conversion.

FAQ

FPC is the abbreviation of Flexible Printed Circuit, also known as a flexible printed circuit board.

FPC refers to the foldable printed circuit board formed on copper foil with PET or PI as the base material, which can carry various active and passive components and accessories, and is widely used in the interconnection of modules in electronic products through proper assembly and design.

  • Small size
  • Lightweight
  • Flex-for-installation
  • Dynamic flexibility
  • Handset
  • Note-Book / Tablet
  • Net-Book/E-Reader
  • DCS
  • LCM/HDD
  • DVD/CD-ROM
  • Printer / Scanner
  • Auto-Mobile, etc
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Kerstin

Author

Kerstin

Hi, I am Kerstin, graduating from one of a well- known university in China and I has a master's degree in physics. I have more than 5 year's experience as a professional engineer in PCB industry and expertise in PCB design, PCB assembly, PCB manufacturing, etc. I am committed to offering services and solutions about PCB/PCBA for various industries for their projects with professional knowledge. During 5 years of engineering career, I have done different circuit designing projects for different companies such as electronics, industry and medical devices, winning a lot of reputation among many customers. Selected as an outstanding employee of IBE every year. I'm always here to provide you with fast, reliable, quality services about PCB/PCBA.

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