1, copper foil etching is excessive, the electrolytic copper foil used on the market is generally single-sided galvanized (commonly known as ashing foil) and single-sided plated copper (commonly known as reddened foil), the common copper is generally more than 70um galvanized copper foil, reddening foil and 18um below the ashing foil basically have not appeared batch copper. When the customer line design is better than the etching line, if the copper foil specifications are changed and the etching parameters are not changed, the residence time of the copper foil in the etching solution is too long. Because zinc is originally a active metal, when the copper wire on the PCB is soaked in the etching liquid for a long time, it will lead to excessive side corrosion of the line, causing some fine line backing zinc layer to be completely reacted off and separated from the substrate, that is, the copper wire falls off. There is also a case that there is no problem with PCB etching parameters, but after etching, washing, and poor drying, resulting in the copper wire is also surrounded by the etching liquid remaining on the PCB surface, which is not treated for a long time, and it will also produce excessive side corrosion of the copper wire and throw copper. This situation is generally concentrated on the fine line, or in the wet weather period, the whole PCB will appear similar bad, strip the copper wire to see its contact surface with the base (the so-called coarser surface) color has changed, and the normal copper foil color is not the same, see the underlying original copper color, thick line copper foil stripping strength is also normal.

　　2. Local collision occurs in the PCB process, and the copper wire is separated from the substrate by external mechanical force. This poor performance is poor positioning or orientation, the lost copper wire will have obvious distortion, or scratches/impact marks in the same direction. Peel off the bad copper wire to see the copper foil surface, you can see that the color of the copper foil surface is normal, there is no bad side corrosion, and the copper foil peel strength is normal.