1PCB process factors:
（1）. Excessive etching of copper foil. Generally, the electrolytic copper foil used in the market is single-sided galvanized (commonly known as ashing foil) and single-sided copper plating (commonly known as redding foil).
The design of customer's circuit is better than that of the etching line. If the specification of copper foil is changed and the etching parameters are not changed, the copper foil will stay in the etching solution for too long.As zinc is a kind of active metal, when the copper wire on the LED advertising screen PCB is immersed in the etching liquid for a long time, it will lead to excessive corrosion on the side of the line, causing the zinc backing layer of some fine lines to be completely reacted off the substrate, that is, the copper wire falls off.
Another case is that there is no problem with the etching parameters of PCB, but after the etching, washing and drying is not good, resulting in copper wire is also surrounded by the etching solution left on the surface of PCB, which has not been treated for a long time, resulting in excessive corrosion on the side of the copper wire and throwing copper.General performance of this kind of circumstance is concentrated in the fine lines, or the weather wet period, the entire PCB will appear similar adverse, remove the copper wire to see its and grassroots interface (so-called coarsening surface) color have change, unlike normal copper foil color, is to see the underlying original copper color, thick lines of copper foil peel strength also normal.
（2）. Local collision occurred during PCB process of LED advertising screen, and copper wire was separated from base material due to external mechanical force.This undesirable appearance is poor positioning or directional, shedding copper line will have obvious distortion, or to the same direction of the scratch/impact mark.When peeling the bad copper wire to see the copper foil wool surface, you can see that the color of the copper foil wool surface is normal, there will be no side corrosion defects, and the peeling strength of the copper foil is normal.
（3） Unreasonable design of LED advertising screen PCB circuit. If too thin circuit is designed with thick copper foil, it will cause excessive etching and throwing of copper.
2. Reasons for laminate manufacturing:
Under normal circumstances, as long as the high temperature section of the laminate is hot pressed for more than 30 minutes, the copper foil and semi-solidified sheet are basically combined. Therefore, the laminate generally does not affect the binding force of the copper foil and base material in the laminate.However, in the process of laminate stacking and stacking, if PP pollution, or damage to the copper foil's wool surface, the bonding strength of the copper foil and the substrate after lamination will be insufficient, resulting in positioning (only for the big board) or scattered copper wire falling off, but there will be no abnormality in the peeling strength of copper foil near the measured detachment.
3. Reasons for raw materials of laminate:
（1） LED advertising screen has mentioned above ordinary electrolytic copper foil MAO foil galvanized or copper plating the processed products, when MAO foil production peak is abnormal, or zinc/copper plating, coating the dendrite, the peel strength of the copper foil itself is not enough, caused by the bad foil after pressing sheet made PCB electronics factory plug-in, copper wire fall off by external shocks will occur.This kind of cast copper is not good enough to strip the copper wire to see the copper foil hair surface (that is, contact surface with the substrate), but the peeling strength of the whole copper foil will be very poor.
( 2） Poor adaptability of LED advertising screen copper foil and resin: some laminates with special properties, such as HTg plate, are used now. Due to different resin systems, curing agents are generally PN resin.When the laminate is produced, copper foil is used to mismatch the resin system, resulting in insufficient metal foil peeling strength of the sheet material.