1. Production of special carrier board
According to the CAD file of the circuit board, read the hole positioning data of the FPC to manufacture a high-precision FPC positioning template and a special carrier plate, so that the diameter of the positioning pin and the positioning hole on the carrier plate and the aperture of the positioning hole on the FPC can be matched. Many FPCs are not the same thickness because they need to protect some lines or design. Some places are thick and some are thin and some have strengthened metal plates. Therefore, the combination of carrier and FPC needs to be pressed. The actual situation is processed and polished to ensure that the FPC is flat during printing and placement. The material of the carrier board is required to be light and thin, low heat absorption, fast heat dissipation, and small warpage after repeated thermal shock. Commonly used carrier materials are synthetic stone, aluminum plate, silica gel plate, special high temperature resistant magnetized steel plate and so on.
2. Solder paste printing of FPC:
FPC of solder paste composition is no special requirements, the size of the tin ball particles and metal content, will be subject to have FPC on fine pitch IC, but FPC high performance requirements of the solder paste printing, solder paste should be has good thixotropy, solder paste should be able to easily print demoulding and can firmly adhere to the surface of FPC, there will be no mold release bad block stencil hole leakage or produce the bad such as collapse after printing.
Because FPC is loaded on the load plate, and FPC is equipped with heat-resistant adhesive tape for positioning, which makes its plane inconsistent, so the printing surface of FPC cannot be as flat as PCB with the same thickness and hardness, so it is not suitable to use metal scraper, but the polyurethane scraper with hardness of 80-90 degrees. The solder paste printing machine should be equipped with optical positioning system, otherwise it will have a great impact on the printing quality. Although FPC is fixed on the load plate, there will always be some small gaps between FPC and the load plate, which is the biggest difference from PCB, so the setting of equipment parameters will have a great impact on the printing effect.
The printing station is also the key station to prevent FPC dirty, need to wear finger cover operation, at the same time to keep the station clean, frequently wipe steel mesh, prevent solder paste pollution of FPC gold finger and gold plated keys.
3.FPC patches:
According to the characteristics of the product, the number of components and the SMT efficiency, it can adopt the medium and high speed SMT mounting machine. Since each FPC has optical MARK MARK for positioning, SMD mounting on FPC is not much different from mounting on PCB. It should be noted that although FPC is fixed on the load plate, its surface cannot be as flat as PCB hard plate, and there will be local space between FPC and the load plate. Therefore, the drop height and blowing pressure of the suction nozzle should be set accurately, and the moving speed of the suction nozzle should be reduced. At the same time, the majority of FPC is joint plate, and the yield of FPC is relatively low, so it is normal for the whole PNL to contain some defective PCS, which requires the placement machine to have BAD MARK identification function, otherwise, the production efficiency will be greatly reduced when the production of such non-integral PNL is good plate.
4.FPC reflow welding:
Mandatory hot air convection infrared reflow welding furnace should be used, so that the temperature on the FPC can be more uniform change, reduce the generation of welding defects. If you use single side tape, because it can only fix the FPC's four sides, the middle part of the deformation in the state of hot air, the welding pad is prone to tilt, molten tin (liquid tin at high temperature) will flow and produce empty welding, continuous welding, tin bead, resulting in a high defect rate of the process.
