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A Brief Discussion on the Causes of Bubbling on the Surface of Copper Electroplated Printed Circuit Board

Bubbling on the board surface is one of the common quality defects in the production process of printed circuit boards, due to the complexity of the production process and process maintenance, especially in chemical wet treatment, making it difficult to prevent blistering defects on the board surface. Based on years of practical production and service experience, the author provides a brief analysis of the causes of blistering on the surface of copper plated circuit boards, hoping to be helpful to industry peers!

The blistering on the surface of a circuit board is actually a problem of poor adhesion between the board and the surface, which can be further extended to include two aspects: 1. The cleanliness of the board surface; 2. The issue of surface micro roughness (or surface energy); The blistering problem on all circuit boards can be summarized as the above reasons. Poor or too low adhesion between coatings makes it difficult to resist the coating stress, mechanical stress, and thermal stress generated during subsequent production and assembly processes, ultimately resulting in varying degrees of separation between coatings.

The factors that may cause poor surface quality during the production and processing process are summarized as follows,

1. Issues related to substrate processing technology; Especially for some thinner substrates (generally below 0.8mm), due to poor substrate rigidity, it is not advisable to use a brush machine to brush the board. This may not effectively remove the protective layer specially treated to prevent copper foil oxidation during substrate production and processing. Although this layer is thin and easy to remove, chemical treatment poses significant difficulties. Therefore, it is important to pay attention to control during production and processing to avoid foaming problems caused by poor bonding between the substrate copper foil and chemical copper; When blackening is carried out on thin inner layers, there may also be problems such as poor blackening and browning, uneven color, and poor local blackening and browning

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

3. Poor copper plating brush plate: Excessive pressure on the grinding plate before copper plating causes deformation of the hole opening, resulting in copper foil rounded corners or even substrate leakage at the hole opening. This can cause bubbling at the hole opening during processes such as copper plating, tin spraying, and welding; Even if the brush plate does not cause substrate leakage, an excessively heavy brush plate will increase the roughness of the copper at the hole opening. Therefore, during the micro etching and coarsening process, the copper foil at this area is prone to excessive coarsening, which also poses certain quality risks; 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 abrasion tests and water film tests;

4. Water washing problem: Due to the need for a large amount of chemical solution treatment for copper plating, there are many types of acid, alkali, and organic solvents, which make it difficult to clean the board surface with water. Especially when adjusting the oil removal agent for copper plating, it not only causes cross contamination, but also leads to poor local treatment or uneven treatment effect, resulting in some bonding problems; Therefore, attention should be paid to strengthening the control of water washing, mainly including controlling the flow rate, water quality, washing time, and dripping time of the cleaning water; Especially in winter when the temperature is low, the washing effect will be greatly reduced, and it is even more important to pay attention to controlling the washing process;

5. Micro corrosion in the pre-treatment of copper deposition and pattern electroplating; Excessive micro etching can cause substrate leakage at the pore opening, resulting in foaming around the pore opening; Insufficient micro etching can also cause insufficient bonding force, leading to foaming phenomenon; Therefore, it is necessary to strengthen the control of micro erosion; The micro etching depth for general copper deposition pre-treatment is 1.5-2 microns, and the micro etching depth for pattern electroplating pre-treatment is 0.3-1 microns. If conditions permit, it is best to control the micro etching thickness or rate through chemical analysis and simple experimental weighing methods; In general, the color of the slightly corroded board surface is bright, uniform pink, and without reflection; If the color is uneven or there is reflection, it indicates that there is a quality hazard in the pre-treatment of the process; Pay attention to strengthening inspections; In addition, the copper content of the micro etching tank, the temperature of the tank liquid, the load capacity, and the content of the micro etching agent are all items that need to be paid attention to;

6. The activity of copper precipitation solution is too strong; The content of the three major components in the newly opened cylinder or tank of copper sinking liquid is relatively high, especially the copper content is too high

High concentration can cause excessive activity of the bath solution, rough deposition of chemical copper, excessive inclusion of hydrogen gas, cuprous oxides, etc. in the chemical copper layer, resulting in a decrease in the physical properties and poor adhesion of the coating; The following methods can be taken appropriately: reducing the copper content, (adding pure water to the tank liquid) including the three major components, increasing the content of complexing agents and stabilizers appropriately, and lowering the temperature of the tank liquid appropriately;

7. The board surface undergoes oxidation during the production process; If the copper plate undergoes oxidation in the air, it may not only result in no copper in the holes and rough surface, but also cause blistering on the surface; If the copper plate is stored in acid for too long, the surface of the plate will also undergo oxidation, and this oxide film is difficult to remove; Therefore, during the production process, the copper plate should be thickened in a timely manner and should not be stored for too long. Generally, the thickened copper plating should be completed within 12 hours at the latest;

8. Poor copper sinking rework; Some reworked boards that have undergone copper deposition or graphic transformation may experience surface blistering during the rework process due to poor plating, incorrect rework methods, or improper control of micro etching time during the rework process, among other reasons; If poor copper deposition is found online during the rework of copper plate sinking, it can be directly removed from the line through water washing, acid washing, and rework without corrosion; It is best not to re degrease or slightly corrode; For boards that have already been thickened by electroplating, the plating should be removed from the micro etching groove now, and attention should be paid to time control. One or two boards can be used to roughly calculate the plating time to ensure the plating effect; After the stripping process is completed, a set of soft grinding brushes should be used on the brush plate machine to lightly brush, and then copper should be deposited according to the normal production process, but the etching time should be reduced by half or necessary adjustments should be made;

9. Insufficient washing after development, prolonged storage time after development, or excessive dust in the workshop during the graphic transfer process can lead to poor surface cleanliness and slightly poor fiber treatment, which may cause potential quality problems;

10. Before copper plating, the pickling tank should be replaced in a timely manner. If there is too much pollution in the tank solution or the copper content is too high, it will not only cause problems with the cleanliness of the board surface, but also cause defects such as rough board surface;

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

In addition, in winter, some factories should pay special attention to the electrification of the production process when the tank liquid is not heated, especially for plating tanks with air stirring, such as copper and nickel; For nickel cylinders in winter, it is best to add warm water to wash the tank before nickel plating (with a water temperature of around 30-40 degrees) to ensure that the initial nickel layer deposits tightly and well;

In the actual production process, there are many reasons that can cause blistering on the board surface. The author can only make a brief analysis. For different manufacturers with different equipment and technical levels, blistering may occur due to different reasons. The specific situation needs to be analyzed in detail, and cannot be generalized and mechanically applied; The above analysis of reasons does not distinguish between primary and secondary importance, and is mainly based on the production process flow for a brief analysis. This series only provides a direction for problem-solving and a broader perspective, hoping to play a role in throwing bricks and attracting jade in everyone's process production and problem-solving!