PCB Tech - FPC design and manufacturing

FPC (Flexible Printed Circuit) refers to flexible circuit boards, also known as flexible printed circuit boards, flexible circuit boards or soft boards. This kind of circuit board has the advantages of high wiring density, light weight and thin thickness.

FPC (Flexible Printed Circuit) refers to flexible circuit boards, also known as flexible printed circuit boards, flexible circuit boards or soft boards. This kind of circuit board has the advantages of high wiring density, light weight and thin thickness. It is widely used in mobile phones, notebook computers, PDAs, digital video cameras, LCMs and many other products. In recent years, PCB manufacturing technology has developed rapidly, and the industry has put forward higher requirements for FPC. Precision PITCH is the main breakthrough direction for FPC in the future. The stability and exquisiteness of dimensions have also led to the rise of FPC costs. How to control the contradiction between the two has become a major breakthrough in the control of the expansion and contraction of FPC materials during the production process. Below we give you a brief explanation on how to control and control the main points.

1. FPC design

1. In terms of wiring: As FPC will expand due to temperature and pressure during ACF crimping, the expansion rate of the crimping finger should be considered in the initial design of the circuit, and pre-compensation should be carried out;

2. Typesetting: The design products should be distributed evenly and symmetrically throughout the layout as much as possible. The minimum distance between every two PCS products should be kept above 2MM, and the copper-free parts and the dense via holes should be staggered as much as possible. These two parts are in the subsequent manufacturing process. Cause two important aspects that are affected by material expansion and contraction.

3. In terms of material selection: the glue of the cover film should not be too thinner than the thickness of the copper foil, so as to avoid insufficient glue filling during pressing and cause product deformation. The thickness of the glue and whether it is evenly distributed are the culprits for the expansion and contraction of FPC materials.

4. In terms of process design: the cover film should cover all the copper foil parts as much as possible. It is not recommended to stick the cover film to avoid uneven force during pressing. The PI reinforcement bonding surface glue above 5MIL should not be too large. If it is unavoidable, it needs to be After the cover film is pressed and baked, PI reinforcement is applied and pressed.

2. Material storage

I believe that the importance of material storage does not need to be said. It must be stored strictly in accordance with the conditions provided by the material supplier.

3. FPC manufacturing

1. Drilling: It is best to add baking before drilling to reduce the expansion and shrinkage of the substrate during subsequent processing due to the high content of moisture in the substrate.

2. During electroplating: it should be made of short-side splints, which can reduce the deformation caused by the water stress caused by the swing. During electroplating, the swing can be reduced to minimize the amplitude of the swing. The number of splints also has a certain relationship. The number of asymmetrical splints, Can be assisted by other side materials; during electroplating, go down the tank with electricity to avoid sudden high current impact on the board, so as to avoid adverse effects on the electroplating of the board.

3. Pressing: The traditional press is larger and smaller than the fast press. The traditional press is constant temperature curing, and the fast press is heat curing. Therefore, the change of the control glue of the traditional press should be stabilized. Of course, the laminated board is also Quite important part.

4. Baking: For fast pressing products, baking is a very important part. The baking conditions must be sufficient to fully cure the glue, otherwise there will be endless troubles in subsequent production or use; the baking temperature curve is generally to gradually increase the temperature to The temperature at which the glue is completely melted, continue this temperature until the glue is completely solidified, and then gradually cool down.

5. During the FPC production process, try to maintain the stability of temperature and humidity in all stations, transfer between stations, especially those that need to be made out, and the conditions for product storage should be paid special attention.