Explain the analysis of the reasons for copper rejection of PCB circuit boards?

Analysis of the reasons for copper rejection of PCB circuit boards

A local collision occurs in the PCB circuit board process, and the copper wire is separated from the base by external mechanical force. This phenomenon is poor positioning, and the falling copper wire will have obvious distortion, or scratches and impact marks in the same direction. Check the rough surface of the copper foil by looking at the copper wire in the defective part. It can be seen that the color of the rough surface of the copper foil is normal, there will be no bad side corrosion, and the peeling strength of the copper foil is normal.

The design of the PCB circuit board is unreasonable, and the design of too thin lines with thick copper foil will also cause excessive circuit etching and copper rejection.

The copper foil is over-etched. The electrolytic copper foils used in the market are generally single-sided galvanized (commonly known as ashing foil) and single-sided copper-plated (commonly known as reddish foil). Red foil and ashing foil below 18um basically do not have batch copper rejection. When the customer's circuit is designed to pass the etching line, if the copper foil specification is changed but the etching parameters remain unchanged, the copper foil will stay in the etching solution for too long. Because zinc is an active metal, when the copper wire on the PCB is immersed in the etching solution for a long time, it will inevitably lead to excessive side etching of the circuit, causing the backing zinc layer of some thin circuits to be completely reacted and separated from the substrate. That is, the copper wire falls off.

Another situation is that there is no problem with the PCB etching parameters, but after etching, the water washing and drying are not good, causing the copper wire to be surrounded by the etching solution left on the PCB board. And throw copper. This situation is generally concentrated on thin lines, or during humid weather, similar defects will appear on the entire PCB. Strip the copper wire to see that the color of the contact surface with the base layer (the so-called roughened surface) has changed. The color of the copper foil is different from that of the normal copper foil. The original copper color of the bottom layer is seen, and the peeling strength of the copper foil at the thick circuit is also normal.