1. Flatten the warped board in time during the PCB manufacturing process

　　In the PCB manufacturing process, the board with relatively large warpage is picked out and leveled with a roller leveling machine, and then put into the next process. Many PCB manufacturers believe that this approach is effective in reducing the warpage ratio of the finished PCB board.

　　2. Warpage and leveling method of PCB finished board

　　For PCB boards that have been completed, the warpage is obviously too poor, and cannot be leveled by a roller leveling machine, some PCB factories put it into a small press (or similar fixture) to press the warped PCB board. After a few hours to ten hours for cold-pressing and leveling, the effect of this method is not very obvious from practical application. One is that the leveling effect is not large, and the other is that the flattened board is easy to rebound (ie, recover warpage).

　　There are also PCB factories that heat the small press to a certain temperature, and then hot-press and level the warped PCB board. The effect is better than cold pressing, but if the pressure is too high, the wire will be deformed; There will be defects such as discoloration of rosin, discoloration of the base, and so on. And whether it is cold-pressed leveling or hot-pressed leveling, it takes a long time (several hours to ten hours) to see the effect, and the rate of warpage and rebound of the leveled PCB board is also high. Is there a better leveling method?

　　3. Hot pressing and leveling method of bow-shaped mold for warped PCB board

　　According to the mechanical properties of polymer materials and years of work practice, this paper recommends the hot-pressing leveling method for bow-shaped molds. According to the area of the PCB board to be leveled, make several simple bow-shaped molds, and here are two leveling operation methods.

　　Place the warped surface of the warped PCB board against the curved surface of the mold bow, adjust the clamp screw, so that the PCB board is slightly deformed in the opposite direction of its warpage, and then put the mold with the PCB board into the oven that has been heated to a certain temperature. Bake for a while. Under the heating condition, the stress of the substrate gradually relaxes, so that the deformed PCB board returns to a flat state. But the baking temperature should not be too high to avoid discoloration of rosin or substrate yellowing. However, the temperature should not be too low. It takes a long time to completely relax the stress at a lower temperature.

　　Usually, the glass transition temperature of the substrate can be used as the reference temperature for baking, and the glass transition temperature is the phase transition point of the resin. At this temperature, the polymer segments can be rearranged and oriented, so that the substrate stress can be fully relaxed. Due to some leveling effect is obvious. The advantage of using a bow-shaped mold for leveling is that the investment is very small. Every PCB factory in the oven has it. The leveling operation is very simple. If the number of warped boards is relatively large, it is enough to make several more bow-shaped molds. There are several molds, and the baking time is relatively short (about tens of minutes), so the leveling work efficiency is relatively high.

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