What are the factors that lead to PCB copper-throwing?

Home » What are the factors that lead to PCB copper-throwing?

First, PCB factory process factors:

1, excessive copper etching, the market is generally used in electrolytic copper foil single-sided galvanized (commonly known as ash foil) and single-sided copper (commonly known as red foil), the common rejection of copper is generally 70um above the zinc-plated copper Foil, red foil and 18um the following basic ash foil did not appear batch rejection of copper.

Customer line design is better than the etching line, if the copper foil specifications change after etching parameters have not changed, resulting in the copper foil in the etching solution in the residence time is too long. Because zinc is already an active metal, when the copper on the PCB is immersed in the etchant for a long time, it will inevitably lead to overcorrection of the circuit, resulting in that some fine-line backed zinc layers are completely separated from the substrate, That is, copper wire falls off.

There is also a situation that there is no problem PCB etching parameters, but after washing water washing, and poor drying, resulting in copper PCB is also left in the surface of the etching solution surrounded by a long time untreated, copper overhang will also result in excessive Rejection of copper. This situation is generally manifested in the concentration of fine lines, or humid period, the entire PCB will appear similar to poor, peeled off the copper to see its interface with the grassroots level (the so-called rough surface) color has changed, With the normal color of copper is not the same, see the bottom of the original copper color, thick lines of copper foil peel strength is also normal.

2, partial collisions occurred in the PCB process, the copper wire is separated from the substrate by external mechanical force. The poor performance of the poor positioning or orientation, shedding copper there will be obvious distortion, or to the same direction of scratches / impact marks. Peel the bad copper wire to see the copper matte side, you can see the normal color copper matte side, there will be poor side-eroded, copper foil peel strength normal.

3, PCB circuit design is not reasonable, with thick copper foil design too thin lines, but also lead to excessive copper etching circuit rejection.

Second, the reasons for the laminate process:

Under normal circumstances, the laminate as long as the high temperature hot pressing more than 30min, the copper foil and prepreg basically complete, so the press will not affect the laminate copper foil and the substrate binding force. However, if the PP is contaminated or the surface of the copper foil is damaged during stacking and stacking of the laminates, the bonding force between the copper foil and the substrate after the laminating may be insufficient so as to cause positioning (only for the large plates Say) or sporadic copper off, but measured off-line copper foil peel strength will not be abnormal.

Third, the reasons for the original laminate material:

1, mentioned above are ordinary electrolytic copper foil foil or zinc plated copper treated products, if the peak when the production of foil is abnormal, or galvanized / copper plating, poor plating crystal branches, resulting in the copper foil itself Peel strength is not enough, the bad foil made of sheet metal PCB after the plug in the electronics factory, the impact of copper by external forces will fall off. Such poor rejection of copper strip copper wire to see the copper matte side (ie with the substrate contact surface) does not significantly after the side etching, but the entire surface of the peel strength of copper foil will be poor.

2, poor adaptability of copper foil and resin: Some special performance laminates used now, such as HTg sheet, because the resin system is not the same, the curing agent used is generally PN resin, the resin molecular chain structure is simple, when cured Low degree of cross-linking, it is bound to use a special peak of copper foil to match. When the production of laminates using copper foil and the resin system does not match, resulting in sheet metal foil foil peel strength is not enough, the plug will appear when the copper off bad.

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