PCB News - What is the cause of blistering on the PCB board?

What is the cause of blistering on the PCB board?

1. PCB circuit board surface cleanliness problem;

2. The problem of surface micro-roughness (or surface energy).

The blistering problem on all circuit boards can be summarized as the above reasons.

The bonding force between the coatings is poor or too low, and it is difficult to resist the coating stress, mechanical stress and thermal stress generated during the production and processing in the subsequent PCB production and assembly process, which will eventually cause different degrees of separation between the coatings.

Now some factors that may cause poor board quality in the production and processing process are summarized as follows:

1. PCB substrate process processing issues:

Especially for some thinner substrates (generally less than 0.8mm), because the rigidity of the substrate is poor, it is not suitable to use a brushing machine to brush the plate.

This may not be able to effectively remove the protective layer specially treated to prevent the oxidation of the copper foil on the board surface during the production and processing of the substrate. Although the layer is thin and the brush is easier to remove, it is more difficult to use chemical treatment, so in production It is important to pay attention to control during processing, so as to avoid the problem of blistering on the board caused by the poor bonding between the copper foil of the board substrate and the chemical copper; this kind of problem will also cause blackening and browning when the thin inner layer is blackened. Poor, uneven color, partial black browning and other problems.

2. The phenomenon of poor surface treatment caused by oil stains or other liquids contaminated with dust during the machining (drilling, lamination, milling, etc.) process of the circuit board surface.

3. Poor rework of heavy copper:

Some reworked boards after copper sinking or pattern transfer are poorly plated during the rework process, incorrect rework methods or improper control of the micro-etching time during the rework process, etc., etc., or other reasons will cause the board surface to bubble; if the rework of the copper sink board is found online Poor copper sinking can be directly degreasing from the line after washing with water, then pickling and reworking without commissioning; it is best not to re-degreasing, micro-etching; for the plates that have been thickened by the board, the micro-etching tank should be deplated now, Pay attention to the time control. You can first use one or two plates to roughly calculate the deplating time to ensure the deplating effect; after the deplating is completed, apply a set of soft brushes and lightly brush the plate and then sink the copper according to the normal production process, but the corrosion is slight. The eclipse time should be halved or adjusted if necessary;

4. Washing problem:

Because the electroplating treatment of copper sinking has to go through a lot of chemical treatment, various kinds of acid, alkali, non-polar organic and other chemical solvents are too much, and the surface of the board is not clean with water, especially the copper sinking adjustment degreasing agent, which will not only cause cross-contamination, but also cause cross-contamination. Poor partial treatment of the board surface or poor treatment effect, uneven defects, causing some bonding problems; therefore, attention should be paid to strengthening the control of washing, mainly including the flow of washing water, water quality, washing time, and dripping of the plate. Time and other aspects of the control; especially in winter, the temperature is low, the washing effect will be greatly reduced, and more attention should be paid to the strong control of the washing;

5. The sinking copper brush plate is bad:

The pressure on the front grinding plate of the sinking copper is too large, causing the orifice to be deformed. The copper foil fillet of the orifice or even the orifice leaks the base material. This will cause the orifice to bubble during the process of electroplating, spraying and soldering of the sinking copper; even if it is brushed The board does not cause leakage of the substrate, but the heavy brushing board will increase the roughness of the hole copper, so during the process of microetching roughening, the copper foil at this place is very easy to produce excessive roughening, and there will also be a certain quality. Hidden dangers; therefore, pay attention to strengthening the control of the brushing process, and the brushing process parameters can be adjusted to the best through the wear scar test and the water film test;

6. The activity of the copper precipitation liquid is too strong:

The newly opened tank of the copper sinking solution or the high content of the three components in the bath, especially the high copper content, will cause the bath to be too active, the electroless copper deposition is rough, hydrogen, cuprous oxide, etc. are mixed in the chemical copper layer Excessively caused the defects of the quality of the coating's physical properties and poor bonding; the following methods can be appropriately adopted: reduce the copper content, (add pure water to the bath) including three major components, and appropriately increase the complexing agent and stabilizer Content, appropriately reduce the temperature of the bath liquid, etc.;

7. The board surface is oxidized during the production process:

If the immersion copper plate is oxidized in the air, it may not only cause no copper in the hole, the surface of the board is rough, but also may cause blistering of the plate; if the copper immersion plate is stored in the acid solution for too long, the plate surface will also be oxidized, and This kind of oxide film is difficult to remove; therefore, during the production process, the heavy copper plate should be thickened in time, and it should not be stored for too long. Generally, the thickened copper plating should be completed within 12 hours at the latest;

8. The micro-etching in the pre-treatment of copper sinking and the pre-treatment of pattern electroplating:

Excessive micro-etching will cause leakage of the substrate in the orifice, resulting in blistering around the orifice; insufficient micro-etching will also cause insufficient bonding force and cause blistering; therefore, it is necessary to strengthen the control of micro-etching; the general micro-etching of copper pretreatment The etching depth is 1.5-2 microns, and the micro-etching before the pattern plating is 0.3-1 microns. If possible, it is best to control the micro-etching thickness or the etching rate through chemical analysis and simple test weighing; in general, the micro-etched board The face is bright in color, uniform pink, no reflection; if the color is uneven or there is reflection, it means that there is a hidden quality problem in the pre-processing; pay attention to strengthen the inspection; in addition, the copper content of the micro-etching tank, the temperature of the tank, the load, and the micro-etching agent Content and so on are items to pay attention to;

9. Insufficient water washing after development during the graphics transfer process, too long storage time after development or too much dust in the workshop, etc., will cause poor cleanliness of the board surface, and slightly poor fiber processing effect, which may cause potential quality problems;

10. Organic pollution, especially oil pollution, is more likely to occur in the electroplating tank for automatic lines;

11. Pay attention to timely replacement of the acid bath before copper plating. Too much pollution in the bath or too high copper content will not only cause problems with the cleanliness of the board surface, but also cause defects such as rough board surface;

12.In addition, when the bath liquid is not heated in the production of some PCB factories in winter, it is necessary to pay special attention to the electrification of the plate during the production process, especially the plating tank with air agitation, such as copper-nickel; for the nickel tank winter PCB It is best to add a warm water washing tank before nickel plating (the water temperature is about 30-40 degrees) to ensure that the initial deposition of the nickel layer is dense and good.