PCB News - Use Roll to Roll software to produce FPC fine circuit

With the vigorous development of electronic technology, the circuit pitch of flexible PCBs is constantly decreasing. When the conventional equipment mass-produces fine wire patterns with a line width/line distance of 0.05mm/0.05mm, the pass rate has not been improved due to strict control of the production conditions.

This article describes the Roll to Roll production process with high degree of automation, production efficiency and high pass rate in combination with the actual situation, and uses the Roll to Roll production process to develop fine lines.

One, the emergence of Roll to Roll production process

With the wide application of FPC products, the requirements for production technology of products are increasing day by day. Chip production technology can no longer meet the technical requirements of some products, especially when the conventional equipment mass produces fine wires with a line width/line distance of 0.05mm/0.05mm When it comes to graphics, its pass rate has not been improved due to strict control of production conditions. In view of the time-consuming, labor-intensive, labor-intensive, low-productivity, dimensional stability (heat and humidity) of chip production technology, it is difficult to guarantee, and the qualification rate of FPC for manufacturing high-density fine line width/line pitch is not high, and the quality is also difficult Guarantee, and the development of the continuous conveyor roller (Roll to Roll) production process has successfully solved the above problems.

2. The characteristics of Roll to Roll production process

RTR technology refers to the process technology in which flexible copper clad laminates are made by continuous rolls of FPC. The use of Roll-to-Roll production process can not only increase productivity, but more importantly, increase the degree of automation. This highly automated production significantly reduces human operation and management factors, and is less affected by environmental conditions (temperature, humidity, cleanliness, etc.), so it has a more uniform and stable dimensional deviation, which is also easy to correct and compensate. So it has a higher product qualification rate, quality and reliability.

3. Application of Roll to Roll production process

Due to the late start of FPC in China, RTR production technology is less applied. In order to meet the needs of the FPC product market and enhance market competitiveness, domestic flexible printed circuit board manufacturers have also put their sights on RTR production technology and began to conduct research on "RTR flexible circuit development and application". In order to achieve the high yield and low-cost process level of high-precision circuit production, our company also invested in the application and research of the Rol to Roll process to produce flexible printed boards in 2007, aiming to solve the problem of high-precision chip production The problem of low qualified rate of circuit opening and short circuit is serious, and the purpose of reducing labor cost is achieved at the same time. This article describes the "RTR" FPC development and application" through the company's technical transformation of the production of FPC boards in the RTR mode.

3.1 Process determination

The technical transformation of FPC produced by RTR method should first determine how to segment the entire process according to the performance of the RTR equipment and the needs of the type and characteristics of the FPC products actually produced by the enterprise, or the integration of development, etching, stripping, and post-processing, or development and etching, Stripping, post-processing separation. The function of the separation of development and etching is that after separation, the development line and the etching line can simultaneously produce FPC with different bottom copper thicknesses, and the parameters of the development line and the etching line can be independently adjusted for various production. Taking into account that our company's 1/2oz and 1oz bottom copper usage is very large, the segmented type (etching and developing separated) dual-row 250mm wide DES line is finally used.

3.2 Research on FPC produced by RTR process

After determining how to segment the RTR, the four factors of RTR positioning method, tension control, transmission control and prevention of material bending deformation become the key.

3.2.1 Material selection

In the production of high-precision circuits, the production method is very important, and the selection of the substrate is also very critical. According to the previous experience in the production of high-precision circuits, when the subtractive method is used to prepare fine circuits, the thinner the bottom copper thickness is, the easier it is to achieve the desired effect. The circuit can be prepared with low line width loss, large etching coefficient, and low side corrosion. In sheet production, when the thickness of the substrate is thin, in order to prevent the wrinkles caused by the operation before the cutting to the pressing, the conventional method is to paste the back glue on the substrate first, while the RTR equipment production does not have this problem without backing. glue.

3.2.2 Film

filming is the first step in the graphics transfer of flexible printed boards. The quality of the film directly affects the success or failure of the entire graphics transfer. The high-quality film not only eliminates the impurity of the board surface caused by the uncleanness of the copper surface and the dry film, but also requires the board surface to be smooth, free of bubbles, and wrinkles, and the adhesion of the dry film is up to standard and the degree of adhesion is high. For fully automatic roll production, the control of the parameters of the filming process is even more important. A little carelessness will cause huge waste and loss.

3.2.3 Exposure

Exposure is the beginning of the formation of flexible printed circuit boards. Accurate alignment and exposure energy are factors that require special attention in the exposure process. The alignment accuracy is particularly important in the RTR automatic exposure process. Once the alignment is deviated and reworked, it will cause the waste of resources such as the entire roll of dry film.

In recent years, there have been continuous inventions in spatial alignment. In our latest RTR parallel exposure machine, we have built-in edge finder to induce coil transfer and step controller to adjust the alignment accuracy to ensure the formation of the exposure process line. .

3.2.4 DES

After the exposure is completed, the graphics transfer of the flexible printed board enters the wet process stage. The DES process of the roll process and the sheet process has not changed much. The main difference is that in the roll process, because the thin substrate is not attached to the back glue, the roll material may cause a line surface during the DES transfer process. Wheel printing affects the appearance and performance of the conductor. In order to avoid the problem of line printing, the transfer roller of the DES line can be selectively replaced with a solid roller.

3.2.5 Comparison with chip production process

Compare the results of the production of 0.05/0.05mm line width/line spacing between sheet and roll processes.

The line width and etching coefficient of the circuit produced by the RTR process are equivalent to those of the chip. However, despite the strict control of production conditions and optimization of process parameters when the chip process produces 0.05/0.05mm circuits, a large number of open and short circuits still exist, making the product qualification rate low, and the best mass production qualification rate is only 75%. When the RTR production process is adopted, because it reduces human operation and management factors, it is less affected by environmental conditions, the open and short circuit problems are well controlled, and the mass production qualification rate reaches 90%.

Fourth, concluding remarks

At present, it is still a technical problem in the PCB industry to make 0.03mm/0.03mm line width/line spacing precision circuits using the subtractive method in China. Nevertheless, the emergence of the RTR production process has greatly improved the production efficiency of FPC and guaranteed the pass rate of fine line width/line pitch FPC. It can be applied not only to the production of FPC, but also to the subsequent packaging of FPC.