PCB Tech - Second, the reason for the laminate process

PCB via hole copper leakage_three reasons why PCB copper sheet falls off
1. PCB factory process factors

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 plating (commonly known as red foil). The common thrown copper is generally more than 70um galvanized copper Foil, red foil and ash foil below 18um basically have no batch copper rejection.

When the customer circuit design is better than the etching line, if the copper foil specifications are changed but the etching parameters remain unchanged, the residence time of the copper foil in the etching solution is too long. Because zinc is originally a lively metal, when the copper wire on the LED advertising screen PCB is immersed in the etching solution for a long time, it will inevitably lead to excessive side corrosion of the circuit, causing some thin circuit backing zinc layer to be completely reacted and contact with the substrate. The material is detached, that is, the copper wire is detached.

Another situation is that there is no problem with the PCB etching parameters, but the copper wire is also surrounded by the remaining etching solution on the PCB surface after the etching, and the copper wire is also surrounded by the residual etching solution on the PCB surface. Throw the copper. This situation is generally manifested as concentrated on thin lines, or during periods of wet 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 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 line is also normal.

2. Part of the collision occurred in the PCB process of the LED advertising screen, and the copper wire was separated from the base material by external mechanical force. This poor performance is poor positioning or orientation, the copper wire will be obviously twisted, or scratches/impact marks in the same direction. If you peel off the copper wire at the defective part and look at the rough surface of the copper foil, you can see that the color of the rough surface of the copper foil is normal, there will be no side erosion, and the peeling strength of the copper foil is normal.

3. The PCB circuit design of the LED advertising screen is unreasonable. If a thick copper foil is used to design a circuit that is too thin, it will also cause the circuit to be over-etched and the copper will be thrown away.

Second, the reason for the laminate process

Under normal circumstances, the copper foil and the prepreg will be basically completely bonded as long as the high temperature section of the laminate is hot pressed for more than 30 minutes, so the pressing will generally not affect the bonding force of the copper foil and the substrate in the laminate. However, in the process of stacking and stacking laminates, if the PP is contaminated or the matte surface of the copper foil is damaged, it will also cause insufficient bonding force between the copper foil and the substrate after lamination, resulting in positioning (only for large plates) Words) or sporadic copper wires fall off, but the peel strength of the copper foil near the off-line is not abnormal.

3. Reasons for laminate raw materials

1. It is mentioned on the LED advertising screen that ordinary electrolytic copper foils are all products that have been galvanized or copper-plated on wool. If the peak value of the wool foil is abnormal during production, or when galvanizing/copper plating, the plating crystal branches are bad, resulting in copper. The peel strength of the foil itself is not enough. After the bad foil is pressed into a PCB and plug-in in the electronics factory, the copper wire will fall off due to the impact of external force. This kind of poor copper rejection will not cause obvious side corrosion after peeling the copper wire to see the rough surface of the copper foil (that is, the contact surface with the substrate), but the peeling strength of the entire copper foil will be very poor.

2. Poor adaptability of copper foil and resin for LED advertising screens: Some laminates with special properties, such as HTg sheets, are currently used because of different resin systems. The curing agent used is generally PN resin, and the resin molecular chain structure is simple., The degree of cross-linking is low during curing, and it is necessary to use copper foil with a special peak to match it. When producing laminates, the use of copper foil does not match the resin system, resulting in insufficient peeling strength of the sheet metal-clad metal foil, and poor copper wire shedding when inserting.