Why does the surface of the PCB board with copper plating experience bubbling

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Blistering on the PCB surface is one of the common quality defects in the production process of multi-layer circuit boards. Due to the complexity of the production process and maintenance of multi-layer circuit boards, especially in chemical wet treatment, it is difficult to prevent blistering defects on the board surface.
The bubbling on the PCB board surface is actually a problem of poor adhesion between the board surface, and by extension, it is a problem of surface quality of the board surface, which includes two aspects:

1. The issue of PCB surface cleanliness;
2. The issue of micro roughness (or surface energy) on the surface of PCB boards; The bubbling problem on all circuit boards can be summarized as the above reasons. The poor or low adhesion between the coatings makes it difficult to resist the coating stress, mechanical stress, thermal stress, etc. generated during the subsequent production and assembly processes, ultimately resulting in varying degrees of separation between the coatings.
The factors that cause poor board quality during PCB production and processing are summarized as follows:
1. The problem of PCB substrate - copper-clad laminate process treatment; Especially for some thinner substrates (generally below 0.8mm), due to the poor rigidity of the substrate, it is not suitable to use a brush machine to brush the board. This may not effectively remove the protective layer specially treated to prevent oxidation of the copper foil on the board surface during the production and processing of the substrate. Although this layer is thin and easy to remove by brushing, there are significant difficulties in using chemical treatment. Therefore, it is important to pay attention to control in production and processing to avoid the problem of foaming on the board surface caused by poor bonding between the copper foil and chemical copper on the board substrate; When blackening thin inner layers, there may also be issues such as poor blackening and browning, uneven color, and uneven blackening and browning in certain areas.