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Control of FPC PCB Material's Expansion and Shrinkage

Flexible printed circuit board has the advantages of high wiring density, light weight and thin thickness. It is widely used in in mobile phone, laptops, PDA, digital camera, LCM and many other products. In recent years, with the rapid development of PCB manufacturing technology, the industry puts forwards higher requirements for the flexible PCB. Precision Pitch is the main breakthrough direction of flexible PCB in the future. The stability and delicacy of size also lead to the rise of flexible PCB cost. How to control the contradiction between them becomes the main breakthrough in the process of production. Now we will give you a brief description of how to control the material's expansion and shrinkage, and the key points of control.

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Design of flex PCB

1. Circuit: Because the flexible PCB will expand due to the temperature and pressure during the ACF crimping. Therefore, the expansion rate of the compression fingers should be considered in advance and the pre-compensation process should be carried out.

2. Layout: The designed products should be evenly and symmetrically distributed in the whole layout as far as possible. The minimum interval between two PCs kept at least 2mm. The no copper parts and the dense part of the pore should be interlaced as much as possible. These two parts are two important aspects that cause the flex printed circuit board material to be affected by the expansion and shrinkage in the subsequent manufacturing process.

3. Material selection: The adhesive of the covering film should not be too thinner than the thickness of the copper foil so as to avoid the deformation of the product due to insufficient adhesive filling during lamination. The thickness and distribution of the adhesive are the main reason of the expansion and shrinkage of flexible PCB materials.

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

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