Causes of surface blistering in circuit board production

Board surface foaming is one of the common quality defects in the process of PCB production. Because of the complexity of PCB production process and process maintenance, especially in chemical wet treatment, it is difficult to prevent board surface foaming defects. Based on many years of practical production experience and service experience, the author now makes a brief analysis on the causes of blistering on the surface of copper plated circuit board, hoping to be helpful to peers in the industry!

The problem of blistering on the board surface of the circuit board is actually the problem of poor adhesion of the board surface, and then it is the problem of surface quality of the board surface, which includes two aspects:

1. Board surface cleanliness;

2. Surface micro roughness (or surface energy); All board surface blistering problems on circuit boards can be summarized as the above reasons. The adhesion between the coatings is poor or too low. It is difficult to resist the coating stress, mechanical stress and thermal stress generated in the production and processing process in the subsequent production and processing process and assembly process, resulting in the separation of coatings to varying degrees.

Some factors that may cause poor plate surface quality during production and processing are summarized as follows:

1. Problems of substrate process treatment; Especially for some thin substrates (generally less than 0.8mm), due to the poor rigidity of the substrate, it is not suitable to brush the plate with a brush machine, which may not effectively remove the protective layer specially treated to prevent the oxidation of copper foil on the plate surface during the production and processing of the substrate. Although the layer is thin and the brush plate is easy to remove, it is difficult to adopt chemical treatment, Therefore, it is important to pay attention to control in production and processing, so as to avoid the foaming problem caused by the poor adhesion between the substrate copper foil and chemical copper; When blackening the thin inner layer, there will also be some problems, such as poor blackening and browning, uneven color, and poor local black browning.

2. Oil stain or other liquid contamination, dust pollution and poor surface treatment caused by plate surface machining (drilling, lamination, edge milling, etc.).

3. Poor copper deposition brush plate: the pressure of grinding plate before copper deposition is too high, resulting in the deformation of the orifice, brushing out the copper foil fillet of the orifice and even leaking the base material of the orifice, which will cause the foaming of the orifice in the process of copper deposition, electroplating, tin spraying and welding; Even if the brush plate does not leak the substrate, the heavy brush plate will increase the roughness of the copper at the orifice. Therefore, in the process of micro etching coarsening, the copper foil at this place is very easy to coarsen excessively, and there will be some quality hidden dangers; Therefore, attention should be paid to strengthening the control of the brush plate process. The brush plate process parameters can be adjusted to the best through wear mark test and water film test.

4. Water washing problem: because the copper deposition electroplating treatment needs a lot of chemical solution treatment, there are many kinds of acid-base, non-polar organic and other pharmaceutical solvents, and the plate surface is not washed cleanly. In particular, the adjustment of degreasing agent for copper deposition will not only cause cross pollution, but also lead to poor local treatment or poor treatment effect and uneven defects on the plate surface, resulting in some problems in adhesion; Therefore, attention should be paid to strengthening the control of water washing, mainly including the control of cleaning water flow, water quality, water washing time, plate dripping time and so on; Especially in winter, when the temperature is low, the washing effect will be greatly reduced. More attention should be paid to the strong control of washing.

5. Micro corrosion in copper deposition pretreatment and pattern electroplating pretreatment; Excessive micro etching will cause leakage of substrate at the orifice and blistering around the orifice; Insufficient micro etching will also lead to insufficient bonding force and bubble phenomenon; Therefore, the control of micro etching should be strengthened; Generally, the micro etching depth of copper deposition pretreatment is 1.5-2 microns, and the micro etching depth of pattern electroplating pretreatment is 0.3-1 microns. If possible, it is best to control the micro etching thickness or etching rate through chemical analysis and simple test weighing method; Generally, the color of the slightly etched plate surface is bright, uniform pink, without reflection; If the color is uneven or reflective, it indicates that there is a potential quality hazard in the pre-processing of the manufacturing process; Pay attention to strengthening inspection; In addition, the copper content, bath temperature, load and micro etchant content of the micro etch tank should be paid attention to.

6. The activity of copper precipitation solution is too strong; The content of three major components in the newly opened cylinder or tank liquid of copper precipitation solution is too high, especially the copper content is too high, which will cause the defects of too strong activity of tank liquid, rough chemical copper deposition, excessive inclusion of hydrogen, cuprous oxide and so on in the chemical copper layer, resulting in the decline of physical property quality and poor adhesion of the coating; The following methods can be properly adopted: reduce the copper content, (supplement pure water into the tank liquid) including three components, appropriately increase the content of complexing agent and stabilizer, and appropriately reduce the temperature of the tank liquid.

7. Oxidation of plate surface during production; If the copper sinking plate is oxidized in the air, it may not only cause no copper in the hole and rough plate surface, but also cause blistering on the plate surface; If the copper plate is stored in the acid solution for a long time, the plate surface will also be oxidized, and this oxide film is difficult to remove; Therefore, in the production process, the copper plate should be thickened in time. It should not be stored for too long. Generally, the copper plating should be thickened within 12 hours at the latest.

8. Poor reworking of copper deposit; Some reworked plates after copper deposition or pattern conversion will cause blistering on the plate surface due to poor fading plating, wrong rework method, improper control of micro etching time in the rework process or other reasons; Rework of copper sinking plate if copper sinking defect is found on the line, it can be directly removed from the line after water washing, and then directly reworked without corrosion after pickling; It’s best not to remove oil again and slightly erode; For the plates that have been electrically thickened, the micro etching groove should be faded now. Pay attention to the time control. You can roughly calculate the fading time with one or two plates to ensure the fading effect; After the plating is removed, a group of soft grinding brushes behind the brush machine shall be used for light brushing, and then the copper shall be deposited according to the normal production process, but the etching and micro etching time shall be halved or adjusted as necessary.

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

10. Before copper plating, the pickling tank shall be replaced in time. Too much pollution in the tank liquid or too high copper content will not only cause the problem of plate surface cleanliness, but also cause defects such as plate surface roughness.

11. Organic pollution, especially oil pollution, occurs in the electroplating tank, which is more likely to occur for the automatic line.

12. In addition, in winter, when the bath solution in some factories is not heated, special attention should be paid to the charged feeding of plates into the bath in the production process, especially the plating bath with air stirring, such as copper and nickel; For the nickel cylinder, it is best to add a warm water washing tank before nickel plating in winter (the water temperature is about 30-40 ℃) to ensure the compactness and good initial deposition of nickel layer.

In the actual production process, there are many reasons for blistering on the board surface. The author can only make a brief analysis. For the technical level of equipment of different manufacturers, there may be blistering caused by different reasons. The specific situation should be analyzed in detail, which can not be generalized and copied mechanically; The above reason analysis, regardless of primary and secondary importance, basically makes a brief analysis according to the production process. This series only provides you with a problem-solving direction and a broader vision. I hope it can play a role in throwing bricks and attracting jade for your process production and problem-solving!