PCB Technical - FPC flexible circuit board composition process

The flexible circuit board is a highly reliable and excellent flexible printed circuit board made of polyimide or polyester film as the base material. Referred to as soft board or FPC, it has the characteristics of high wiring density, light weight and thin thickness.

Prenatal treatment

There must be a complete and reasonable production process to make a good-quality FPC board. From pre-processing before production to final shipment, every procedure must be strictly implemented. In the production process, in order to prevent excessive open and short circuits from causing too low yield or reduce the problem of FPC board scrap and replenishment caused by process problems such as drilling, calendering, and cutting, and to evaluate how to select materials to achieve customer use The best effect flexible circuit board. Pre-natal pretreatment is especially important.

Pre-natal pretreatment, there are three aspects that need to be dealt with, and all three aspects are completed by engineers. The first is the FPC board engineering evaluation, which is mainly to evaluate whether the customer's FPC board can be produced, whether the company's production capacity can meet the customer's board-making requirements and unit cost; if the engineering evaluation is passed, the next step is to prepare materials immediately to meet each production link Finally, the engineer processes the customer’s CAD structure drawing, gerber line data and other engineering documents to suit the production environment and production specifications of the production equipment, and then delegates the production drawings and MI (engineering process card) to the The production department, document control, purchasing and other departments enter the regular production process.

Production Process

Double panel system

Cutting - Drilling - PTH - Electroplating - Pre-treatment - Dry Film Pasting - Alignment - Exposure - Development - Graphic Plating - Stripping - Pretreatment - Dry Film Pasting - Alignment Exposure - Development - Etching - Stripping - Surface Treatment - Paste the cover film - Pressing - Curing - Immersion of nickel gold - Printing characters - Shearing - Electrical test - Punching - Final inspection - Packaging - Shipment

Single panel system

Cutting - Drilling - Pasting Dry Film - Aligning - Exposure - Developing - Etching - Stripping - Surface Treatment - Covering Film - Pressing - Curing - Surface Treatment - Immersion Nickel Gold - Printing Characters - Cutting - Electrical Measurement - Punching Cutting - final inspection - packaging - shipment

Production Process

Surface treatment: Immersion gold, anti-oxidation, gold plating, tin spray

Shape processing: manual shape, CNC (numerical control machine tool) cutting, laser cutting

Substrate copper thickness: 1/3 ounce, 1/2 ounce, 1 ounce, 2 ounces, 4 ounces

Detector

According to the characteristics of the material of the flexible circuit board and the wide application fields, in order to more effectively save the volume and achieve a certain degree of accuracy, the characteristics of the three-dimensional space and the thin thickness are better applied to digital products, mobile phones and notebook computers. The instrument used for flexible circuit board (FPC) testing is an optical image measuring instrument.

characteristic

⒈Short: short assembly time

All lines are configured, eliminating the need to connect extra cables

FPC circuit board

⒉ Small: smaller than PCB

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

Can improve flexibility. Strengthen the assembly of three-dimensional space in a limited space

basic structure

Copper Film

Copper foil: basically divided into electrolytic copper and rolled copper. The common thickness is 1oz 1/2oz and 1/3 oz

Substrate film: There are two common thicknesses: 1mil and 1/2mil.

Glue (adhesive): The thickness is determined according to customer requirements.

Cover Film

Cover film protection film: for surface insulation. Common thicknesses are 1mil and 1/2mil.

Glue (adhesive): The thickness is determined according to customer requirements.

Release paper: to prevent the adhesive from sticking to foreign matter before pressing; easy to work.

Stiffener Film (PI Stiffener Film)

Reinforcement board: Reinforce the mechanical strength of FPC, which is convenient for surface mounting operations. The common thickness is 3mil to 9mil.

Glue (adhesive): The thickness is determined according to customer requirements.

Release paper: to prevent the adhesive from sticking to foreign matter before pressing.

EMI: Electromagnetic shielding film to protect the circuit inside the circuit board from outside interference (strong electromagnetic area or susceptible to interference area).

Pros and cons

The advantages of multi-layer circuit boards: high assembly density, small size, light weight, because of high-density assembly, the connection between components (including parts) is reduced, thereby increasing reliability; it can increase the wiring layer, and then increase the design flexibility; The impedance of the circuit can also be formed, and a certain high-speed transmission circuit can be formed. The circuit and electromagnetic shielding layer can be set, and the metal core layer can also be installed to meet the functions and requirements of special thermal insulation. It is easy to install and has high reliability.

Disadvantages of multi-layer PCB boards (unqualified): high cost, long cycle; high reliability inspection methods are required. Multilayer printed circuit is the product of electronic technology, multi-function, high speed, small volume and large capacity. With the development of electronic technology, especially the wide application of large-scale and ultra-large-scale integrated circuits, the rapid, high-precision, high-number change directions of the multilayer printed circuit with higher density appear fine lines.

Prospects

Based on the vast FPC market in China, large companies from Japan, the United States, and Taiwanese countries and regions have all set up factories in China. By 2012, flexible circuit boards, like rigid circuit boards, have achieved great development. However, if a new product follows the rule of "start-development-climax-decline-elimination", FPC is now in the region between climax and decline. Before a product can replace the flexible board, the flexible board must continue to occupy the market share, We must innovate, and only innovation can make it jump out of this vicious circle.

So, in which aspects will FPC continue to innovate in the future? Mainly in four aspects:

1. Thickness. The thickness of FPC must be more flexible and must be thinner;

2. Folding resistance. The ability to bend is an inherent characteristic of FPC. In the future, FPC must be more resistant to bending, which must exceed 10,000 times. Of course, this requires a better substrate;

3. Price. At this stage, the price of FPC is much higher than that of PCB. If the price of FPC comes down, the market will be much broader again.

4. Technological level. In order to meet various requirements, the FPC process must be upgraded, and the minimum aperture and minimum line width/line spacing must meet higher requirements.

Therefore, the relevant innovation, development, and upgrade of FPC from these four aspects can make it usher in the second spring!