FPC (Flexible Printed Circuit) refers to flexible circuit board, also known as flexible printed circuit board, flexible circuit board or flexible board. This circuit board has the advantages of high wiring density, light weight and thin thickness. Widely used in many products such as mobile phones, notebook computers, PDAs, digital video cameras, LCM and so on. In recent years, the PCB manufacturing process has developed rapidly, and the industry has put forward higher requirements for FPC. Precision PITCH is the main breakthrough direction of FPC in the future. The stability and exquisiteness of the size also caused the rise of the cost of FPC. How to control the contradiction between these two, in the production process, the control of the expansion and contraction of FPC materials has become the main breakthrough. Below we give a brief explanation of how to control and the main points of control.
1. Design
1. Circuit: Because the FPC will expand due to temperature and pressure during ACF crimping, the expansion rate of the crimping finger needs to be considered when pre-designing the circuit, and pre-compensation processing is required;
2. Typesetting: The design products are distributed as evenly and symmetrically as possible throughout the typesetting. The minimum interval between every two PCS products should be kept at least 2MM. The copper-free parts and the dense vias should be staggered as much as possible. These two parts are in the subsequent manufacturing process. There are two important aspects that are affected by material ups and downs.
3. Material selection: The adhesive of the cover film should not be too thin than the thickness of the copper foil, so as to avoid product deformation caused by insufficient adhesive filling during pressing, and the thickness and uniform distribution of the adhesive are the culprits of FPC material expansion and contraction.
4. In terms of process design: the cover film should cover all copper foil parts as much as possible. It is not recommended to stick the cover film to avoid uneven stress during pressing. The PI reinforced laminating surface glue above 5MIL should not be too large. After the cover film is pressed and baked, PI reinforcement and pressing are performed.
2. Material storage
I believe the importance of material storage needless to say. It should be stored strictly in accordance with the conditions provided by the material supplier.
3. Manufacturing
1. Drilling: It is best to add baking before drilling to reduce the increase and decrease of the substrate during subsequent processing due to the high water content in the substrate.
2. In electroplating: It should be made with short-edge splints, which can reduce the deformation caused by the water stress caused by the swing. The swing can be reduced as much as possible during electroplating. The number of splints also has a certain relationship. The number of asymmetric splints , Can be assisted by other side materials; during electroplating, the tank is charged to avoid the impact of sudden high current on the board, so as not to cause adverse effects on the board plating.
3. Pressing: The traditional pressing machine is smaller than the fast pressing machine. The traditional pressing machine is constant temperature curing, and the fast pressing machine is thermal curing. Therefore, the change of the control glue of the traditional pressing machine should be stabilized. Of course, the laminated panel is also Quite an important part.
4. Baking: For fast-pressing products, baking is a very important part. The baking conditions must be such that the glue is completely cured, otherwise it will cause endless problems in subsequent production or use; the baking temperature curve is generally gradually increased to The temperature at which the glue is completely melted. Continue this temperature until the glue is completely solidified, and then cool down gradually.
5. During the production process, try to maintain the stability of the temperature and humidity in all the stations, and the transfer between the stations, especially those that need to be sent out, the conditions of product storage need special attention.
4. Packaging
Of course, the completion of the product is not to say everything is fine. It is necessary to ensure that the customer does not have any problems in subsequent use. In terms of packaging, it is best to bake first and dry the moisture absorbed by the substrate during the manufacturing process before using it. Vacuum packaging, and guide customers how to save.
Therefore, to ensure the stable quality of such products, we must strictly follow the specific requirements from material preservation → control of each process → packaging → customers before use.
V. Conclusion
In the next few years, smaller, more complex and more expensive flexible circuits will require more novel methods of assembly and the need to add hybrid flexible circuits. The challenge for the flexible circuit industry is to use its technological advantages to keep pace with computers, telecommunications, consumer demand, and active markets. Century PCB's PCB production and processing service department has a group of high-level technical backbones and first-line operators, which provides a reliable guarantee for product quality (according to IPC-A-610CCLASSⅡ and company standards), and the production products are qualified for one-time inspection The rate reached more than 99%.