Why does the PCB surface blisters? How to deal with it?

The blistering of the circuit board surface is actually a problem of poor bonding force of the board surface, and then it is the surface quality problem of the board surface, which contains two aspects:

1. The cleanliness of the board surface;

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

The blistering problem on all circuit boards can be summarized as the above-mentioned 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 in the production process during the subsequent production process and assembly process, which will eventually cause different degrees of separation between the coatings.

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

1. The problem of substrate processing:

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

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 difficult to use chemical treatment, so in the production process 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 substrate copper foil and chemical copper; this 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 board surface.

3. Poor sinking copper brush plate:

The pressure on the front grinding plate of the sinking copper is too high, causing the orifice to be deformed, brushing out the copper foil rounded corners of the orifice or even leaking the base material, which will cause the orifice to bubble during the process of electroplating and tinning welding 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 phenomenon, and there will also be a certain quality. Hidden hazards; therefore, attention should be paid 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;

4. Washing problem:

Because the electroplating treatment of copper sinking has to go through a lot of chemical treatments, there are many chemical solvents such as acid and alkali, electrodeless organic, etc., 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, it is necessary to strengthen 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. Micro-etching in the pre-treatment of copper sinking and the pre-treatment of pattern electroplating:

Excessive micro-etching will cause leakage of the base material in the orifice, causing 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; generally, the micro-etching process before copper deposits The etching depth is 1.5-2 microns, and the micro-etching before pattern plating is 0.3--1 microns. If possible, it is better to control the micro-etching thickness or the micro-etching rate through chemical analysis and simple test weighing method; in general, the micro-etching The surface of the etched board is bright in color, uniform pink, no reflection; if the color is not uniform, 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, and the load capacity , Microetching agent content, etc. are all items to be paid attention to;

6. Poor rework of sinking copper:

Some reworked boards with heavy copper or pattern transfer may cause blistering on the board surface due to poor fading, improper rework methods or improper control of the micro-etching time during the rework process or other reasons; if the rework of heavy copper boards is found online Poor copper sinking can be directly removed from the line after washing with water and then reworked directly without micro-etching after pickling; it is best not to re-degreas, micro-etching; for plates that have been thickened by electrical board, use the micro-etching bath to de-plating , Pay attention to the time control. You can first use one or two plates to roughly measure the deplating time to ensure the deplating effect; after the deplating is completed, use a brushing machine and a set of soft brushes to lightly brush and then sink the copper according to the normal production process. The micro-eclipse time should be halved or adjusted if necessary;

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 the plate surface to bubble; the immersion copper plate is stored in the acid for too long, and the plate surface will also be oxidized, and This kind of oxide film is difficult to remove; therefore, the heavy copper plate should be thickened in time during the production process, 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 activity of the copper sinking liquid is too strong:

The newly opened cylinder 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 solution to be too active, the chemical copper deposition is rough, hydrogen, cuprous oxide, etc. are mixed in the chemical copper layer Too much 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 components, and appropriately increase the complexing agent and stabilizer Content, appropriately reduce the temperature of the bath liquid, etc.;

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 a slightly poor pre-processing effect may cause potential quality problems;

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

11. Before copper plating, the pickling tank should be replaced in time. Too much pollution in the tank solution 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 some 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 and nickel; it is best for the nickel tank in winter. Add a warmed 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;

In the actual production process, there are many reasons for the blistering of the board. The author can only make a brief analysis. For different manufacturers' equipment and technical levels, there may be blistering caused by different reasons. The specific conditions should be analyzed in detail. ; The above-mentioned reason analysis does not distinguish between primary and secondary and importance. Basically, a brief analysis is made in accordance with the production process. This series is only to provide you with a problem-solving direction and a broader vision. I hope that everyone’s process production and problems In terms of solution, it can play a role in attracting new ideas!