Analysis of the Three Main Causes of PCB Copper Shedding

PCB copper trace shedding(also commonly known as copper shedding)is a problem with the laminate,often attributed to the PCB manufacturer by the PCB manufacturer,who is held liable for the resulting damage.Based on my years of experience handing customer complaints, the following are common causes of copper shedding:

1.Factors in the PCB manufacturer’s manufacturing process:

(1)Excessive copper foil etching.The electrolytic copper foil used in the market is generally single-sided copper-plated(commonly known as red foil).Common copper foil thicker than 70µm. Red foil and gray foil thinner than 18µm rarely experience widespread copper shedding. When a customer’s circuit design is being etched, if the copper foil specifications change while the etching parameters remain unchanged, the copper foil will remain in the etching solution for an extended period of time.

Because zinc is an inherently reactive metal.prolonged immersion of copper traces in the etching solution will inevitably lead to excessive undercutting of the traces.This can cause the zinc layer on some fine traces to completely react and separate from the substrate,resulting in copper shedding,Another situation is when the PCB etching parameters are correct,but post-etching washing and drying are inadequate.leaving the copper traces exposed to residual etching solution on the PCB surface.If left untreated for an extended period,excessive undercutting and copper shedding can occur,This condition typically manifests itself on thin traces,or during humid weather,can occur across the entire PCB.Peeling back the copper traces reveals a color change at the surface where they meet the base layer(the so-called roughened surface),differing from the normal copper foil color,The underlying copper color is visible,and the peel strength of the copper foil on the thick traces is normal.

(2).Localized impact during the PCB process can cause the copper traces to detach from the substrate due to external mechanical forces.This defect manifests as poor positioning or directionality,with noticeable twisting of the detached copper traces or scratches/impact marks in the same direction.Peeling back the traces at the defective area to examine the matte surface of the foil reveals normal color,no undercutting,and normal peel strength.

(3).Improper PCB circuit design,such as using thick copper foil for overly thin traces,can also lead to excessive etching and copper shedding.

2.Laminate Process Issues:

Under normal circumstances, once the laminate has been hot-pressed for at least 30 minutes, the copper foil and prepreg are essentially bonded. Therefore, lamination generally does not affect the bond between the copper foil and the substrate. However, during the lamination and stacking process, contamination of the polypropylene (PP) or damage to the rough surface of the copper foil can lead to insufficient adhesion between the copper foil and the substrate after lamination, resulting in positioning issues (only applies to large boards) or sporadic copper wire shedding. However, the peel strength of the copper foil near the shedding line will not be abnormal.

3.Laminate Raw Material Issues:

(1).As mentioned above,ordinary electrolytic copper foil is a raw foil that has been galvanized or copper-plated,If the raw foil has abnormal peak values during production,or if the galvanizing/copper plating process results in poor dendrite formation, the peel strength of the copper foil itself may be insufficient.After the poorly pressed foil is made into a PCB and then inserted into the electronic factory,the copper wires may fall out due to external force.This type of copper wire to view the matte surface of the copper foil (i.e., the surface in contact with the substrate), but the peel strength of the entire copper foil will be very poor.

(2)Poor compatibility between copper foil and resin: Certain specialized laminates currently in use, such as HTg laminates, utilize a different resin system. The curing agent is typically PN resin. This resin has a simple molecular chain structure and a low degree of crosslinking during curing, necessitating the use of a copper foil with a specific peak strength. When copper foil used in laminate production is incompatible with this resin system, the laminate’s peel strength is insufficient, and copper wire shedding can occur during insertion.