1. Introduction to FPC
FPC: English full spell Flexible Printed Circuit, its Chinese means flexible printed circuit board, referred to as soft board. It is made into conductor circuit patterns by using light imaging pattern transfer and etching processes on the surface of a flexible substrate. The surface and inner layers of double-sided and multilayer circuit boards are electrically connected to the inner and outer layers through metallized holes. , The surface of the circuit pattern is protected and insulated by PI and glue layer.
It is mainly divided into single-sided board, hollow board, double-sided board, multi-layer board, and rigid-flex board.
PCB: Printed Circuit Board in English, which means rigid printed circuit board in Chinese, abbreviated as hard board;
2. Development trend
The FPC industry first emerged in Japan in about 2002. The FPC industry outside Japan began to sprout in 2003, expanded rapidly in 2005, and declined in 2006. The FPC industry fell to the bottom in mid-2007 and began to recover in 2008.
In 2005, the FPC industry had low thresholds and high profits, which attracted a large number of enterprises to enter.
In 2006, competition has become increasingly fierce, and the phenomenon of oversupply is very serious. Many companies have to drop prices again and again in order to survive, or even lose money. At the same time, downstream customers of the FPC industry, such as large EMS manufacturers, added FPC departments and no longer outsourced FPC business, which made the FPC industry worse.
2007 was a precarious year for the FPC industry. The first is the sharp decline in profits. The soft board manufacturer M-FLEX’s net profit in fiscal year 2007 was only 3 million US dollars, while the net profit in 2006 fiscal year reached 40.4 million US dollars, and the net profit fell by 93%. Hong Kong-listed Giti Technology lost 29.8 million U.S. dollars in fiscal year 2007, while its 2006 fiscal year made a profit of 12.4 million U.S. dollars. The second is the decline in sales. Taiwan’s largest flexible board manufacturer Jialianyi had sales of 7.79 billion Taiwan dollars in 2004, and then declined for three consecutive years. In 2007, sales were 6.541 billion Taiwan dollars.
The gross profit margin fell again. In 2004, Jialianyi’s gross profit margin was 29%, which dropped to 12% in 2007. Young Poong, South Korea’s largest FPC company, divested the FPC business from the listed company to prevent investors from looking too ugly. Even if the big factory was like this, the small factory went bankrupt.
The numerous closures of small factories have brought opportunities to the FPC industry, which has been recovering since the beginning of 2008. However, the FPC industry is facing a new problem, which is the economic downturn. At the beginning of 2008, the global economy showed a downward trend, with soaring oil prices, subprime mortgage crisis, and soaring food prices. The global economy has entered a downward channel, especially in emerging countries. The decline in demand for FPCs stems from consumer electronics. When the economy is in a downward channel, the first hit is the demand for non-rigid consumer Electronic products: including mobile phones, notebook computers, flat-screen TVs, LCD monitors, digital cameras, DV and other products.
Three, the characteristics of flexible circuit boards
⒈ Short: short assembly time
All lines are configured, eliminating the need to connect redundant cables;
⒉ Small: smaller than PCB (hard board)
It can effectively reduce the product volume and increase the convenience of carrying;
⒊ Light: lighter than PCB (hard board)
Can reduce the weight of the final product;
4. Thin: thickness is thinner than PCB (hard board)
It can improve the softness and strengthen the three-dimensional assembly in a limited space.
Advantages of flexible circuit boards
Flexible printed circuit boards are printed circuits made of flexible insulating substrates, and have many advantages that rigid printed circuit boards do not have:
1. It can be bent, wound, and folded freely, can be arranged according to the space layout requirements, and can be moved and stretched in three-dimensional space, so as to achieve the integration of component assembly and wire connection;
2. The use of FPC can greatly reduce the volume and weight of electronic products, and is suitable for the development of electronic products in the direction of high density, miniaturization and high reliability. Therefore, FPC has been widely used in aerospace, military, mobile communications, laptop computers, computer peripherals, PDAs, digital cameras and other fields or products;
3. FPC also has the advantages of good heat dissipation and solderability, easy assembly and low overall cost, etc. The design of soft and hard combination also makes up for the slight deficiency of the flexible substrate in the component carrying capacity to a certain extent.
Disadvantages of flexible circuit boards
1. High one-time initial cost: Since the flexible PCB is designed and manufactured for special applications, the initial circuit design, wiring and photographic masters require higher costs. Unless there is a special need to apply a flexible PCB, it is usually best not to use it in a small amount of application;
2. It is difficult to modify and repair flexible PCBs: once a flexible PCB is made, it must be changed from the base map or the programmed light drawing program, so it is not easy to change. The surface is covered with a protective film, which must be removed before repairing and restored after repairing, which is a relatively difficult task;
3. Size is restricted: Flexible PCBs are usually manufactured by batch process when they are not yet common, so they cannot be made very long and wide due to the limitation of the size of the production equipment;
4. Improper operation and easy damage: Improper operation by the installation and connection personnel can easily cause damage to the flexible circuit, and its soldering and rework need to be operated by trained personnel.
Fourth, the main raw materials of FPC
The main raw materials are on the right: 1. Substrate, 2. Cover film, 3. Reinforcement, 4. Other auxiliary materials.
1.1 Adhesive substrate
Adhesive substrates are mainly composed of three parts: copper foil, adhesive, and PI. There are two types of single-sided substrates and double-sided substrates. The material with only one side of copper foil is a single-sided substrate, and the material with double-sided copper foil is Double-sided substrate.
1.2 Adhesive-free substrate
The non-adhesive substrate is the substrate without the adhesive layer. Compared with the ordinary adhesive substrate, the middle adhesive layer is missing. It is composed of only two parts: copper foil and PI, which is thinner than the adhesive substrate. , Better dimensional stability, higher heat resistance, higher bending resistance, better chemical resistance and other advantages, it has now been widely used.
Copper foil: At present, the commonly used copper foil thickness has the following specifications, 1OZ, 1/2OZ, 1/3OZ, and now a thinner copper foil with a thickness of 1/4OZ is introduced, but this material is already being used in China and is making ultra-fine roads. (Line width and line spacing are 0.05MM and below) products. With the increasing requirements of customers, materials of this specification will be widely used in the future.
2. Cover film
It is mainly composed of three parts: release paper, glue, and PI. Only the glue and PI remain on the product. The release paper will be torn off during the production process and will not be used again (its role is to protect the glue with foreign matter ).
It is a specific material used for FPC and is used in a specific part of the product to increase the support strength and make up for the “soft” characteristic of FPC.
At present, the commonly used reinforcement materials are as follows:
1) FR4 reinforcement: The main components are glass fiber cloth and epoxy resin glue, which are the same as the FR4 material used in PCB;
2) Steel sheet reinforcement: the composition is steel, which has strong hardness and support strength;
3) PI reinforcement: the same as the cover film, consisting of PI and release paper, except that the PI layer is thicker, and it can be produced from 2MIL to 9MIL.
4. Other auxiliary materials
1) Pure glue: This adhesive film is a heat-curing acrylic adhesive film composed of protective paper/release film and a layer of glue. It is mainly used for layered boards, flexible and rigid boards, and FR -4/Steel sheet reinforcement board, which plays a role of bonding.
2) Electromagnetic protective film: Pasted on the board surface for shielding.
3) Pure copper foil: only composed of copper foil, mainly used for hollow board production.
Five, the type of FPC
FPC types have the following 6 distinctions:
A. Single panel: Only one side has wiring.
B. Double panel: There are lines on both sides.
C. Hollow board: also known as window board (opening the window on the finger surface).
D. Layered board: two-sided circuit (separate).
E. Multilayer boards: circuits with more than two layers.
F. Rigid-flex board: a combination of soft board and hard board.
Six, FPC process flow