Abstract: Excess copper foil is etched. Electrolytic copper foil used in the market is generally galvanized on one side (commonly known as ash foil) and copper on one side (commonly known as red foil). Commonly used copper dripping is more than 70um galvanized. Copper foils, red foils, and ash foils below 18um have almost never exhibited mass rejection.
First, PCB factory process factors:
1. The copper foil is etched excessively. The electrolytic copper foil used in the market is generally unilateral galvanized (commonly known as ash foil) and single-sided copper (commonly known as red foil). Commonly used copper dripping is more than 70um galvanized copper. Foil, reddish foil, and ash foil below 18um did not show mass rejection of copper. When the customer circuit design is better than the etching line, if the specification of the copper foil is changed and the etching parameters do not change, the residence time of the copper foil in the etching solution is too long. Because zinc is a kind of active metal, when the copper wire on the PCB is immersed in the etching solution for a long time, it will lead to excessive corrosion on the side of the wire, causing some fine lines of the backing zinc layer to be completely reacted and detached from the substrate. That is, the copper wire falls off. In another case, there is no problem with the etching parameters of the PCB. However, after the etching, the water is washed and the drying is poor. As a result, the copper wire is also surrounded by the remaining etching solution on the PCB. If it is left untreated for a long time, excessive copper etching may occur. Throw copper. This situation generally appears to be concentrated on thin lines, or during periods of humid weather, similar defects appear on the entire PCB, and the copper lines are peeled off to see that the color of the contact surface with the substrate (the so-called rough surface) has changed. Unlike the normal color of the copper foil, the underlying copper color is seen, and the peel strength of the copper foil at the thick line is also normal.
2. Local collisions occur in the PCB process. The copper wire is separated from the substrate by external mechanical forces. This poor performance is poorly positioned or directional, and the shedding copper wire will have obvious distortions or scratches/impact marks in the same direction. Peel off the copper wire of the bad place and look at the matte side of the copper foil. You can see that the matte side of the copper foil is normal in color and there is no bad side corrosion. The peeling strength of the copper foil is normal.
3, PCB circuit design is not reasonable, with thick copper foil design too thin lines, it will cause the line to over-etch and throw copper.
Second, the laminate process causes:
Under normal circumstances, as long as the laminate is hot-pressed in the high temperature section for more than 30 minutes, the copper foil and the prepreg are basically completely bonded. Therefore, the press-fitting generally does not affect the bonding force between the copper foil and the substrate in the laminate. However, in the process of laminating and stacking laminates, if PP is contaminated or the copper matte surface is damaged, the bonding force between the laminated copper foil and the substrate may be insufficient, resulting in positioning (only for large panels and (Speaking) or sporadic copper wire falls off, but there is no abnormality in the peeling strength of the copper foil near the measured drop line.
Third, the reasons for the raw material of the laminate:
1. It was mentioned above that ordinary electrolytic copper foils are hair foil galvanized or copper plated products. If the peak value of wool foil production is abnormal, or when galvanized/copper plating is applied, the coating is poor in the coating, resulting in the copper foil itself. The peel strength is not enough. When the bad foil is pressed into the PCB and then plugged into the electronics factory, the copper wire will fall off under external force. If such copper spoils the copper wire, the copper matte surface (ie, the contact surface with the substrate) will not be significantly eroded, but the peel strength of the entire copper foil will be poor.
2. The poor adaptability of copper foil and resin: Some special properties of laminates, such as HTg sheets, are not the same as the resin system. The curing agent used is generally PN resin. The molecular structure of the resin is simple. The degree of cross-linking is relatively low, and it is necessary to use a special peak copper foil to match it. The use of copper foil when producing laminates does not match with the resin system, resulting in insufficient peel strength of the metal-clad sheet metal foils and poor copper wire drop-outs during the insertion.