1. **Copper foil etching issues:** When copper foil etching is excessive, it’s important to consider that the electrolytic copper foil used in the market is generally single-sided galvanized (commonly known as ash foil) and single-sided copper plating (commonly known as red foil). Typically, copper foils with thicknesses greater than 70µm are galvanized, while red foil and ash foil with thicknesses below 18µm are less common. If the customer’s line design is better than the etching line and the copper foil specifications are changed without adjusting the etching parameters, the copper foil may remain in the etching solution for too long. Since zinc is an active metal, prolonged exposure to the etching solution can lead to excessive line erosion, causing some fine lines to lose their zinc layer and separate from the base material, resulting in copper wire detachment.
Another issue arises when there is no problem with the etching parameters but the etching solution is not adequately washed off and dried. This residual etching liquid can corrode the copper wire over time, leading to excessive copper loss. This problem is often observed in fine lines or during wet weather conditions, where the entire PCB may exhibit similar issues. When inspecting the copper wire, it may show a different color at the interface with the base material, indicating that the original copper color is exposed, while the peel strength of thicker copper foil remains normal.
2. **Mechanical damage during PCB processing:** In the PCB manufacturing process for LED advertising screens, local collisions can cause the copper wire to separate from the base material due to external mechanical forces. This issue usually manifests as misalignment or directional damage, with loose copper wires showing obvious distortion or scratches/impact marks in the same direction. Examining the damaged copper foil reveals that its surface color is normal, without any adverse side erosion, and the peel strength remains standard.
3. **Unreasonable PCB circuit design:** If the PCB circuit design for LED advertising screens is flawed, such as using thick copper foil for thin circuits, it can lead to excessive etching of the circuit and subsequent copper dumping.
**Laminate Process Reasons:**
Under normal conditions, pressing the laminate at a high temperature for over 30 minutes should ensure complete bonding between the copper foil and the semi-cured sheet. Therefore, pressing generally does not affect the binding force between the copper foil and the substrate. However, if there is PP contamination or damage to the copper foil surface during laminate stacking, it can result in insufficient bonding force between the copper foil and the base material, causing either localized (typically in large plates) or sporadic copper wire detachment. This will not affect the peel strength of the copper foil near the measured off-line areas.
**Laminate Raw Materials:**
1. **Copper foil quality issues:** For LED advertising screens, ordinary electrolytic copper foil (MAO foil), galvanized, or copper-plated products are used. If the MAO foil production peak is abnormal, or if zinc/copper plating results in dendrite formation, the peel strength of the copper foil may be insufficient. In such cases, poor-quality foil, after pressing, can lead to copper wire detachment due to external shocks. Inspecting the bad copper foil will reveal that the surface (the contact area with the base material) does not show significant side erosion, but the overall peel strength is very poor.
2. **Copper foil and resin adaptability:** Modern laminates often use special performance boards like HTg boards. Because the resin systems used, such as PN resin, have a simple molecular chain structure and low crosslinking degree, they require specific copper foils. When the copper foil and resin systems are incompatible, the metal foil coverage strength on the laminate is insufficient, leading to poor copper wire peel strength and detachment.
