1. Copper foil is excessively etched, and the electrolytic copper foil used in the market is generally single-sided galvanized (commonly known as ashed foil) and single-sided copper plated (commonly known as reddened foil). The common copper throwing is generally galvanized copper foil above 70um, while reddened foil and ashed foil below 18um have not undergone bulk copper throwing.

　　2. Local collisions occurred during the PCB process, causing the copper wire to detach from the substrate due to external mechanical forces. This defect manifests as poor positioning or directionality, where the detached copper wire will have obvious twisting or scratches/impact marks in the same direction. Peel off the defective copper wire and observe the rough surface of the copper foil. It can be seen that the color of the rough surface of the copper foil is normal, and there will be no side corrosion defects. The peeling strength of the copper foil is normal.

　　3. Unreasonable PCB circuit design, using thick copper foil to design overly fine circuits, can also cause excessive etching of the circuit and copper throwing.