FPC (Flexible Printed Circuit) refers to flexible printed circuit boards, also known as flexible printed circuit boards, flexible circuit boards, or flexible boards. This type of circuit board has the advantages of high wiring density, light weight, and thin thickness. Widely used in many products such as mobile phones, laptops, PDAs, digital cameras, LCMs, etc. 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 future FPC. The stability and refinement of size have also led to an increase in the cost of FPC. How to control the contradiction between the two has become the main breakthrough point in controlling the expansion and contraction of FPC materials during the production process. Below, we will briefly explain how to control and the key points of control.

Control Method for Expansion and Shrinkage of FPC Materials

1、 Design aspect

1. In terms of wiring: Due to the expansion of FPC during ACF crimping due to temperature and pressure, it is necessary to consider the expansion rate of crimping fingers during the initial design of the wiring and perform pre compensation processing;

2. In terms of layout: Design products to be evenly and symmetrically distributed throughout the entire layout, with a minimum spacing of at least 2MM between every two PCS products. Try to stagger the copper free part and the dense through hole part, both of which are important aspects that are affected by material shrinkage during subsequent manufacturing processes.

3. Material selection: The adhesive used for covering the film should not be too thin than the thickness of the copper foil, in order to avoid insufficient filling of the adhesive during pressing and resulting in product deformation. The thickness and uniform distribution of the adhesive are the main culprits for the expansion and contraction of FPC materials.

4. In terms of 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 to avoid uneven stress during pressing. The PI reinforcement bonding surface adhesive above 5MIL should not be too large. If it cannot be avoided, the covering film should be pressed and baked before PI reinforcement bonding and pressing.

2、 Material storage

I don't need to say much about the importance of material storage. It is necessary to store materials strictly according to the conditions provided by the material supplier. Those that need to be refrigerated should be refrigerated and should not be careless.

3、 Manufacturing aspect

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

2. Electroplating: Short edge clamping plates should be used to reduce deformation caused by water stress caused by swinging. During electroplating, swinging can be minimized as much as possible to minimize the amplitude of swinging. The number of clamping plates also has a certain relationship. Asymmetric clamping plates can be supplemented by other edge materials; When electroplating, remove the battery from the slot to avoid sudden high current impact on the board and avoid adverse effects on the plating process.

3. Pressing: Traditional pressing machines have smaller shrinkage and swelling compared to fast pressing machines. Traditional pressing machines require constant temperature curing, while fast pressing machines require thermal curing. Therefore, traditional pressing machines need to stabilize the changes in adhesive control, and of course, the lamination arrangement is also a very important part.

4. Baking: For fast pressing products, baking is a very important part, and the baking conditions must achieve complete curing of the adhesive, otherwise there will be endless consequences in subsequent production or use; The baking temperature curve generally follows a gradual increase in temperature until the adhesive completely melts, followed by a continuous increase in temperature until the adhesive completely solidifies, and then a gradual cooling.

5. During the production process, it is necessary to maintain the stability of temperature and humidity within all workstations as much as possible. The transfer between workstations, especially for those that need to be outsourced, and the storage conditions of products need to be given special attention.