Causes of PCB copper shedding
When the copper wire of PCB falls off (also known as copper shedding), each PCB brand will say that it is a problem with the laminate and ask its production factory to bear the bad losses. Based on years of experience in handling customer complaints, the common reasons for PCB copper shedding are as follows:
1.PCB factory process factors:
(1)Excessive etching of copper foil.
The electrolytic copper foil used in the market is generally single-sided galvanized (commonly known as gray foil) and single-sided copper (commonly known as red foil). Common copper shedding is generally galvanized copper foil above 70um, and red foil and gray foil below 18um have basically not experienced batch copper shedding. When the circuit design is better than the etching line, if the copper foil specifications are changed but the etching parameters are not changed, this will cause the copper foil to stay in the etching solution for too long.
Because zinc is originally an active metal, when the copper wire on the PCB is immersed in the etching solution for a long time, it will cause excessive side etching of the circuit, causing the backing zinc layer of some fine circuits to be completely reacted and separated from the substrate, that is, the copper wire falls off. There is another situation that the PCB etching parameters are fine, but the washing and drying after etching are not good, causing the copper wire to be surrounded by the etching liquid remaining on the surface of the PCB. If it is not treated for a long time, the copper wire will be excessively etched and the copper will be thrown away. This situation is generally concentrated on fine lines, or in humid weather, similar defects will appear on the entire PCB. Peel off the copper wire to see that the color of the contact surface with the base layer (the so-called roughened surface) has changed, which is different from the normal copper foil color. What you see is the original copper color of the bottom layer, and the peeling strength of the copper foil at the thick line is also normal.
(2)There is a local collision in the PCB production process, and the copper wire is separated from the substrate by mechanical external force.
This defective performance has a problem with positioning, and the detached copper wire will have obvious distortion, or scratches or impact marks in the same direction. Peel off the copper wire at the defective part to 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 poor side etching, and the peeling strength of the copper foil is normal.
2.Laminate process reasons:
Under normal circumstances, as long as the laminate is hot-pressed for more than 30 minutes, the copper foil and the prepreg are basically fully combined, so the pressing generally does not affect the bonding strength between the copper foil and the substrate in the laminate. However, during the lamination and stacking process of the laminate, if the PP is contaminated or the rough surface of the copper foil is damaged, it will also lead to insufficient bonding between the copper foil and the substrate after lamination, resulting in positioning deviation (only for large boards) or sporadic copper wire shedding, but there will be no abnormality in the copper foil peeling strength near the shedding line.
3.Laminate raw material reasons:
(1)It is mentioned above that ordinary electrolytic copper foil is a product that has been treated with galvanized or copper-plated raw foil. If the peak value of the raw foil is abnormal during production, or the coating crystal dendrites are poor during galvanizing/copper plating, the peeling strength of the copper foil itself is insufficient. After the poor foil is pressed into the PCB, the copper wire will fall off due to external force when it is plugged into the electronics factory. This type of poor copper shedding will not show obvious side erosion when the copper foil rough surface (i.e. the surface in contact with the substrate) is peeled off, but the peeling strength of the entire copper foil will be very poor.
(2)Poor adaptability of copper foil and resin:
Some laminates with special properties currently used, such as HTG sheets, have different resin systems. The curing agent used is generally PN resin. The resin molecular chain structure is simple, and the degree of cross-linking is low during curing. It is necessary to use copper foil with a special peak value to match it. When the copper foil used in the production of laminates does not match the resin system, the peeling strength of the metal foil on the sheet is insufficient, and the copper wire will also fall off poorly during insertion.
