The main material of FPC printed circuit board (soft board) is composed of polyimide resin. Due to the heat generated during drilling, it is easy to leave a large amount of resin slag in the hole, resulting in the copper plating layer on the hole wall and the inner The layers of the circuit are poorly connected, and even break and open circuits. At present, the industry mostly uses resin leavening agents and potassium permanganate liquids to remove slag in the holes.