PCB Technical - What to pay attention to when processing FPC circuit board cover film

The FPC circuit board cover film needs to be processed with windows, but it cannot be processed immediately after being taken out of the refrigerator. Especially when the ambient temperature is high and the temperature difference is large, the surface will condense water drops. When the base film is polyimide, it is short. Moisture will also be absorbed within time, which will have an impact on subsequent processes. Therefore, the general roll cover film is sealed in a polyethylene plastic bag. The sealed bag should not be opened immediately after being taken out from the refrigerator, but should be placed in the bag for several hours. When the temperature reaches room temperature, it can be removed from the sealed bag. Take out the cover film for processing.

The cover film window uses a CNC drilling and milling machine or a punching machine, and the rotation speed of the CNC drilling and milling should not be too high. This kind of operation cost is high, and this method is generally not used in mass production. Lay 10-20 sheets of cover film with release paper together and fix them with upper and lower cover pads before processing. Semi-cured adhesive is easy to adhere to the drill bit, resulting in poor quality. Therefore, it should be inspected more frequently than when drilling copper foil plates, and the debris generated during drilling should be removed. A simple die can be used when processing the window of the cover film by the punching method, and the die is used for the processing of batch holes with a diameter of less than 3mm. When the hole of the window is large, use a punching die, and for small and medium batches of small holes, use CNC drilling and punching together for processing, and processing of the cover film

After removing the release film from the cover film with the opened window holes, paste it on the substrate with the etched circuit. Before lamination, the circuit surface must be cleaned to remove surface contamination and oxidation. Chemical methods for surface cleaning. After removing the release film, there are many holes of various shapes on the cover film, which completely becomes a film without a skeleton. It is particularly difficult to operate. It is not easy to use the positioning hole to overlap the position on the line.

At present, mass production plants still rely on manual alignment and stacking. The operator first accurately locates the cover film window hole and the connection plate and terminal of the circuit pattern, and temporarily fixes it after confirmation. In fact, if the size of either the flexible printed board or the cover film changes, it cannot be accurately positioned. If conditions permit, the cover film can be divided into several pieces before lamination positioning. If the covering film is forcibly stretched for alignment, the film will be more uneven and the size will change more. This is an important cause of wrinkles in the board.

Temporary fixing of the cover film can be done with an electric soldering iron or simple pressing. This is a process that relies entirely on manual operation. In order to improve production efficiency, various factories have thought of many methods.