PCB Tech - What is the cause of blistering on the PCB circuit board?

The blistering of PCB 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:

What is the cause of blistering on the circuit board surface 1. The problem of 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 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, and finally

Causes the phenomenon of different degrees of separation between the plating layers.

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

1. The problem of PCB process substrate processing:

Especially for some thin 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 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 poor bonding between the copper foil of the board substrate and the 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 large, causing the hole to be deformed, brushing out the copper foil rounded corners of the hole or even leaking the base material of the hole, which will cause the hole to bubble during the process of plating, spraying and soldering of the sinking copper; 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, 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 process of copper sinking has to go through a lot of chemical treatments, there are many chemical solvents such as acid, alkali, non-polar organic and so on. 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. 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 and cause 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; general micro-etching before copper The corrosion 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 thickness of the micro-etching or the corrosion rate through chemical analysis and simple test weighing method; in general, 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 copper-immersion or reworked boards after 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 the copper-immersed board is found online Poor copper sinking can be directly removed from the line after washing with water, and then reworked directly without corrosion after pickling; it is best not to re-degrease and micro-etch; for the plates that have been thickened by the board, the micro-etching tank should be deplated, Pay attention to time control. You can use one or two plates to roughly estimate 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;

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 immersion copper 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 activity of the copper sinking 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 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 process of graphics transfer, 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 fiber processing effect, which 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 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 warm water washing tank before nickel plating (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 do a brief analysis. For different PCB manufacturers' equipment technical levels, there may be blistering caused by different reasons. The specific conditions must be analyzed in detail, and cannot be generalized. The above reason analysis does not distinguish between primary and secondary and importance, and basically makes a brief analysis in accordance with the production process.