PCB Technical - Yield improvement of FPC single-sided dual-contact board

When the length of the single-side double-contact FPC electrode is greater than 3.0mm and the width is less than 0.3mm, it is easy to cause deformation, distortion, and fracture of the electrode during the manufacturing process (etching, film removal, surface cleaning, and protective film), which seriously affects the quality of the product. Rate.

When the length of the single-side double-contact FPC electrode is greater than 3.0mm and the width is less than 0.3mm, it is easy to cause deformation, distortion, and fracture of the electrode during the manufacturing process (etching, film removal, surface cleaning, and protective film), which seriously affects the quality of the product. Rate. For example, FPC company received such an order before and made it according to the normal process. The yield rate was very low, only about 50%, and even the goods could not be delivered. After the process improvement, the yield rate has increased to between 90% and 95%. Below I will introduce how to improve the process:

1. Starting point for process improvement:

As shown in Figure 1, we assume that part B is the part that needs to be hollowed out in the process (after etching to the upper protective film pressing). When this part is hollowed out, there is no reinforced part to support the hollowed-out electrode, which is likely to cause the electrode to be twisted, deformed, and broken under the action of external forces (such as the spray pressure of the level machine, retracting, and transportation). Therefore, the key point of process improvement is to provide a support for the fragile electrode.

2. Selection of supports:

Since the support is used from before etching to the upper protective film, especially hot pressing is required. Therefore, we must choose materials that can withstand high temperatures. High-temperature tape can be used here. The tape requires that the glue does not transfer and can be heat-resistant (fast press) high temperature.

3. Process description:

The circuit is made with wet film, first silk-screen B-side, then silk-print A-side after baking, and then bake. Then carry out exposure and development. The point of attention in this step is that side B does not need to be exposed. If exposed, it will be difficult to remove the film. After development, tape on side B. It should be noted here that the high temperature tape should be flat, and when there is a reinforced alignment mark, the tape should not exceed the marking line as much as possible, because there will be a little mark at the position of the high temperature tape after pressing. If there is reinforcement, it can be covered. Hold the indentation; etching, developing, and surface cleaning are carried out in normal steps; the upper protective film is pressed together. At this time, the pressing parameters must be optimized. The optimization principle is to use the least time, minimum pressure and lower temperature for pressing. Because of high temperature, long time, and high pressure, it is easy to cause the transfer of high temperature glue and the difficulty of removing the wet film covered by the high temperature glue. Tear off the high-temperature tape, remove the film, and grind the plate to remove the ashing copper at the electrode; bake, and cure the upper protective film; the following procedures remain the same.

4. Later

The process of this method is a bit more troublesome, and additional high-temperature tape auxiliary materials are required. But I think it is still very suitable for the manufacture of single-side double-contact FPC with electrode length greater than 3.0mm and width less than 0.3mm, which is affirmative for the improvement of yield. You can try if you are interested, and weigh the pros and cons by yourself.