One of the unique processes of the flexible printed board manufacturing process is the processing procedure of the cover layer. There are three types of processing methods for the covering layer, covering film, screen printing of the covering layer, and photocoating layer. Recently, newer technologies have been developed to expand the range of options.
The processing of FPC cover film is divided into three parts:
1. Screen printing of FPC overlay
2. FPC cover film
3. FPC photocoating layer
About Screen Printing of FPC Overlay:
The missing cover layer has worse mechanical properties than the laminated cover film, but the material cost and processing cost are lower. The most used are civilian products and flexible printed boards on automobiles that do not require repeated bending. The process and equipment used are basically the same as the printing of the solder mask on the rigid printed board, but the ink materials used are completely different. It is necessary to choose inks suitable for flexible printed boards.
There are UV curable and heat-curable inks in the market. The former has a short curing time and is convenient, but the general mechanical properties and chemical resistance properties are poor. If it is used for bending or under harsh chemical conditions, it is sometimes inappropriate. It is especially necessary to avoid electroless gold plating, because the plating solution will penetrate into the cover layer from the end of the window, and severely cause the cover layer to peel off. Since the curing of thermosetting inks requires 20-30 minutes, the drying tunnel for continuous curing is relatively long, and intermittent ovens are generally used.
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