How to control the stability of FPC cost and size

FPC (Flexible Printed Circuit) refers to flexible circuit board, also known as flexible printed circuit board, flexible circuit board or flexible board. The circuit board has the advantages of high wiring density, light weight, thin thickness, etc. It is widely used in mobile phones, laptops, PDAs, digital video cameras, LCMs and many other products. In recent years, with the rapid development of PCB manufacturing process, the industry has put forward higher requirements for FPC. Precision PITCH is the main breakthrough direction of FPC in the future. The stability and delicacy of size also lead to the rise of FPC cost. How to control the contradiction between the two has become a major breakthrough in the production process. Let's briefly explain how to control and the key points of control.

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1、 Design

1. Line: FPC will expand due to temperature and pressure during ACF crimping, so the expansion rate of crimping finger shall be considered in the initial design of line for pre compensation;

2. Layout: The design products should be evenly and symmetrically distributed throughout the layout as far as possible. The minimum spacing between two PCS products should be more than 2 mm. The copper free part and the densely spaced via part should be staggered as far as possible. These two parts are two important aspects that will be affected by material inflation and shrinkage in the subsequent manufacturing process.

3. Material selection: The adhesive of the covering film should not be too thin than the thickness of the copper foil, so as to avoid product deformation due to insufficient filling of the adhesive during pressing. The thickness and even distribution of the adhesive are the main culprits for the rise and fall of FPC materials.

4. Process design: The covering film should cover all copper foil parts as much as possible, and it is not recommended to stick the covering film in strips to avoid uneven stress during pressing. The PI reinforcement bonding surface glue above 5 MIL should not be too large. If it cannot be avoided, the covering film should be pressed and baked before the PI reinforcement bonding and pressing.

2、 Material storage

I don't need to say much about the importance of material storage. It should be stored in strict accordance with the conditions provided by the material supplier. The refrigerated materials should be refrigerated.

3、 Manufacturing

1. Drilling: It is better to bake before drilling to reduce the increase in the expansion and contraction of the substrate during subsequent processing due to the high content of water in the substrate.

2. In electroplating: it shall be made of short side plywood, which can reduce the deformation caused by water stress generated by swinging. The swinging amplitude can be reduced as much as possible during electroplating. The number of plywood also has a certain relationship. The number of asymmetric plywood can be assisted by other leftovers; During electroplating, the plate shall be charged and lowered to avoid the impact of sudden high current on the plate, so as to avoid adverse effects on plate electroplating.

3. Pressing: The expansion and contraction of the traditional press is smaller than that of the fast press. The traditional press is thermostatically solidified, while the fast press is thermally solidified. Therefore, the change of the glue controlled by the traditional press should be stabilized. Of course, the laminating arrangement is also an important part.

4. Baking: For fast pressing products, baking is a very important part, and the baking conditions must be such that the adhesive can be completely cured, otherwise, it will cause endless trouble in subsequent production or use; The baking temperature curve is generally that the temperature is gradually increased to the temperature where the glue is completely melted, then the temperature is maintained until the glue is completely cured, and then the temperature is gradually lowered and cooled.

5. During the production process, try to maintain the stability of temperature and humidity in all work stations, and pay special attention to the product storage conditions for the transfer between work stations, especially those that need to be manufactured externally.

4、 Packaging

Of course, the completion of the product does not mean that everything is all right. It is necessary to ensure that the customer will not have any problems in the subsequent use. In terms of packaging, it is better to bake first, dry the moisture absorbed by the base material during the manufacturing process, and then use vacuum packaging to guide the customer how to preserve.

Therefore, to ensure the stable quality of such products, it is necessary to strictly follow the specific requirements from material preservation → process control → packaging → customer use.

5、 Concluding remarks

In the next few years, smaller, more complex and more expensive FPCs will require more novel methods of assembly, and hybrid FPCs will be added. The challenge for the flexible circuit industry is to use its technological advantages to keep pace with the computer, telecommunications, consumer demand and the active market. The PCB production and processing service department of Century Core has a group of high-level technical backbones and first-line operators, which provides a reliable guarantee for product quality (according to IPC-A-610CCLASS II and the company's standards), and the one-time acceptance rate of products has reached more than 99%.