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How is the foaming of the PCB surface caused?


Published by: KEYOU PCB January 22,2024

The blistering of the board surface is actually a problem of poor bonding of the board surface. The extension is also the surface quality problem of the board surface. This includes two aspects:
1. The problem of board cleanliness;
2. The problem of surface micro-roughness (or surface energy).


                                How is the foaming of the PCB surface caused?


The problem of blistering on all boards can be summarized as the above reasons.
The bonding force between the plating layers is poor or too low, and it is difficult to resist the plating stress, mechanical stress and thermal stress generated during the production process and the assembly process, and finally cause different degrees of separation between the plating layers.


Some factors that may cause poor quality of the board during production and processing are summarized as follows:
1. Problems with substrate processing:
Especially for some thinner substrates (generally 0.8mm or less), it is not suitable to use a brushing machine to brush the board because of the poor rigidity of the substrate.
This may not effectively remove the protective layer that is specially treated to prevent oxidation of the copper foil on the board during the production process of the substrate. Although the layer is thin, the brush plate is easy to remove, but there is a great difficulty in chemical treatment, so in production Important attention control of processing, so as to avoid the problem of blistering of the board caused by poor bonding between the copper foil of the board surface and the chemical copper; this problem also occurs when the thin inner layer is blackened, there will also be blackening browning. Bad, uneven color, partial black browning and other problems.


2. The surface of the board is contaminated by oil or other liquids caused by machining (drilling, laminating, milling, etc.).


3. Bad copper brushing board:
The pressure of the pre-sinking plate is too large, causing the deformation of the orifice to brush out the copper foil round corners of the orifice or even the leakage of the substrate, so that the blistering phenomenon of the orifice will occur during the process of copper plating and tinning welding; The plate does not cause leakage of the substrate, but the excessively heavy brush plate will increase the roughness of the copper of the aperture. Therefore, during the process of micro-etching and coarsening, the copper foil is likely to be excessively roughened, and there will be a certain quality. Hidden dangers; therefore, it is necessary to pay attention to the control of the brushing process, and the process parameters of the brushing plate can be adjusted to the best through the wear scar test and the water film test;


4. Washing problem:
Because the copper plating treatment has to undergo a lot of chemical syrup treatment, all kinds of acid-base and non-polar organic solvents and other solvents are more, the board surface is not washed, especially the copper-adjusting degreaser will not only cause cross-contamination, but also cause Poor local treatment of the board surface or poor treatment effect, uneven defects, causing some problems in bonding; therefore, attention should be paid to strengthening the control of water washing, mainly including cleaning water flow, water quality, washing time, and dripping of plates. Time and other aspects of control; especially in winter, the temperature is lower, the washing effect will be greatly reduced, and more attention should be paid to the control of water washing;


5. The surface of the board is oxidized during production:
 If the copper plate is oxidized in the air, it may not only cause copper in the hole, the surface of the plate is rough, but also may cause foaming on the surface; the copper plate is stored in the acid for too long, and the surface of the plate is also oxidized, and Such an oxide film is difficult to remove; therefore, the copper plate should be thickened in time during the production process, and the storage time is not too long, and the copper plating is generally required to be thickened within 12 hours at the latest;

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