Why does custom PCB copper plating surface bubble?

Why does custom PCB copper plating surface bubble?

Custom PCB surface bubbling is one of the more common quality defects in the production process of PCB. Because of the complexity of PCB production process and process maintenance, especially in the chemical wet treatment, it is difficult to prevent the bubbling defects on the board.

The bubbling on the PCB board is actually the problem of poor bonding force on the board, and by extension, the problem of surface quality on the board, which includes two aspects:

1. PCB surface cleanliness problem;

2. Micro roughness (or surface energy) of PCB surface; all the bubbling problems on the circuit board can be summarized as the above reasons. The binding force between the coating is poor or too low, in the subsequent production and processing process and assembly process is difficult to resist the production and processing process produced in the coating stress, mechanical stress and thermal stress, and so on, resulting in different degrees of separation between the coating phenomenon.

Some factors that cause poor surface quality in PCB production and processing are summarized as follows:

Custom PCB substrate — copper-clad plate process treatment problems; Especially for some thinner substrates (generally below 0.8 mm), because the substrate rigidity is poorer, unfavorable use brush brush plate machine, it may be unable to effectively remove the substrate in order to prevent the surface oxidation of copper foil in the process of production and processing and special processing layer, while the layer is thinner, brush plate is easy to remove, but the chemical processing is difficult, Therefore, it is important to pay attention to control in the production and processing, so as not to cause the problem of foaming caused by the poor binding force between the substrate copper foil and the chemical copper; when the thin inner layer is blackened, there will also be poor blackening and browning, uneven color, and poor local blackening.

PCB board surface in the process of machining (drilling, lamination, milling, etc.) caused by oil or other liquid dust pollution surface treatment is poor.

3. PCB copper sinking brush plate is poor: the pressure of the grinding plate before copper sinking is too large, resulting in hole deformation, and the copper foil fillet at the hole and even the base material leakage at the hole, which will cause bubble phenomenon at the hole in the process of copper sinking, plating, tin spraying and welding; ​even if the brush plate does not cause the leakage of the substrate, the excessive brush plate will increase the roughness of the copper hole, so in the process of micro-corrosion coarsening, the copper foil is easy to produce excessive coarsening phenomenon, there will also be a certain quality risk; ​therefore, attention should be paid to strengthening the control of the brush plate process, and the brush plate process parameters can be adjusted to the best through the wear mark test and water film test.

4. Washed PCB problem: because heavy copper electroplating processing should pass a lot of chemical liquid medicine processing, all kinds of acid-base the non-polar organic solvent such as drugs, board face wash not clean, especially heavy copper adjustment in addition to the agents, not only can cause cross-contamination, also will cause the board to face local processing bad or poor treatment effect, the defect of uneven, cause some of the binding force; therefore, attention should be paid to strengthening the control of washing, mainly including the control of the flow of cleaning water, water quality, washing time, and the dripping time of plate parts; ​especially in winter, the temperature is low, the effect of washing will be greatly reduced, more attention should be paid to the control of washing.