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Common Causes Of Copper On PCB Boards

There are several common causes of copper on PCB boards:

 First, PCB board factory process factors:


    1. Copper foil is excessively etched. The electrolytic copper foil used on the market is generally single-sided galvanized (commonly known as ash foil) and single-sided copper plating (commonly known as red foil). Common copper bismuth is generally galvanized copper of 70um or more. Foil, red foil and ash foil of 18um or less have basically no batch of beryllium copper. When the customer circuit is designed to pass through the etched line, if the copper foil specification is changed and the etching parameters are not changed, 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 PCB is immersed in the etching solution for a long time, it will lead to excessive side etching of the circuit board, causing some fine line backing zinc layer to be completely reacted and The material is detached, that is, the copper wire is detached. There is also a case where there is no problem with the etching parameters of the PCB, but the water is washed after etching, and the drying is poor, so that the copper wire is also surrounded by the etching liquid remaining on the surface of the PCB board. If it is left untreated for a long time, the copper side etching will also occur. Excessive and copper. This situation is generally manifested on the thin line, or in the wet weather period, the same PCB board will have similar defects, peeling off the copper line to see its contact with the base layer (the so-called rough surface) color has changed Unlike the normal copper foil color, the original copper color is seen, and the peeling strength of the copper foil at the thick line is also normal.


    2. Local collision occurs in the PCB board process, and the copper wire is separated from the substrate by external mechanical force. This bad performance is poor positioning or directional, and the detached copper wire will have obvious distortion or scratch/impact marks in the same direction. Peel off the copper wire at the bad place and look at the copper foil surface. It can be seen that the copper foil surface is normal in color, there will be no side erosion, and the copper foil peeling strength is normal.


    3, PCB board circuit design is unreasonable, the use of thick copper foil to design a thin line, will also cause excessive etching of the line and copper.


    Second, the laminate process reasons:


    Under normal circumstances, the copper foil and the prepreg are basically completely combined as long as the laminate is hot pressed for more than 30 minutes, so that the pressing generally does not affect the bonding force between the copper foil and the substrate in the laminate. However, in the process of stacking and stacking laminates, if PP contamination or damage to the copper foil surface is caused, the bonding strength of the copper foil to the substrate after lamination may be insufficient, resulting in positioning (only for large plates). Words) or sporadic copper wires fall off, but there is no abnormality in the peeling strength of the copper foil near the test strip.


    Third, the reasons for laminate raw materials:


    1. It is mentioned above that common electrolytic copper foils are galvanized or copper-plated products. If the peak of the wool foil is abnormal during production, or when galvanizing/copper plating, the plating crystal is poor, resulting in the copper foil itself. The peeling strength is not enough. When the bad foil pressed sheet is made into a PCB board and is inserted into the electronics factory, the copper wire will fall off when it is impacted by an external force. Such beryllium copper is poorly peeled off and the copper foil surface (ie, the contact surface with the substrate) does not have obvious side etching, but the peeling strength of the whole copper foil is very poor.


    2. Poor adaptability of copper foil and resin: Some special performance laminates, such as HTg sheets, are different because of the resin system. The curing agent used is generally PN resin. The resin molecular chain structure is simple and solidified. The degree of cross-linking is low and it is necessary to match the copper foil with a special peak. When the laminate is produced, the copper foil is not matched with the resin system, so that the peeling strength of the metal foil of the sheet is insufficient, and the copper wire may fall off poorly when the insert is inserted.

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