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

The bubbling on the circuit board surface is actually a problem of poor bonding between the board surface and, by extension, the surface quality of the board surface. This includes two aspects:

1. The issue of board cleanliness;

2. The issue of surface micro roughness (or surface energy); The bubbling problem on all circuit boards can be summarized as the above reasons The poor or low adhesion between the coatings makes it difficult to resist the coating stress, mechanical stress, thermal stress, etc. generated during the subsequent production and assembly processes, ultimately resulting in varying degrees of separation between the coatings.

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

01 Issues with substrate processing technology; Especially for some thinner substrates (generally below 0.8mm), due to the poor rigidity of the substrate, it is not suitable to use a brush machine to brush the board. This may not effectively remove the protective layer specially treated to prevent oxidation of the copper foil on the board surface during the production and processing of the substrate. Although this layer is thin and easy to remove by brushing, there are significant difficulties in using chemical treatment. Therefore, it is important to pay attention to control in production and processing to avoid the problem of foaming on the board surface caused by poor bonding between the copper foil and chemical copper on the board substrate; When blackening thin inner layers, there may also be issues such as poor blackening and browning, uneven color, and uneven blackening and browning in certain areas.

The phenomenon of poor surface treatment caused by oil or other liquid contamination and dust pollution during machining (drilling, lamination, milling, etc.) of the 02 board surface.

03 Poor copper plating brush plate: Excessive pressure on the grinding plate before copper plating causes deformation of the hole, resulting in copper foil fillets and even leakage of the substrate at the hole. This can cause bubbling at the hole during processes such as copper plating, tin spraying, and welding; Even if brushing does not cause substrate leakage, excessive brushing will increase the roughness of the copper holes, making it easy for the copper foil in this area to undergo excessive roughening during the micro etching process, which also poses a certain quality hazard; 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;

04 Water washing issue: Due to the extensive chemical treatment required for copper electroplating, various acidic, alkaline, non-polar organic and other chemical solvents are abundant, resulting in incomplete water washing of the board surface. Especially when adjusting the degreaser for copper plating, it not only causes cross contamination but also leads to poor local treatment or uneven treatment effects, resulting in some bonding problems; Therefore, attention should be paid to strengthening the control of water washing, mainly including the control of cleaning water flow rate, water quality, washing time, and board drip time; Especially in winter when the temperature is low, the washing effect will be greatly reduced, so it is important to pay more attention to controlling the washing process;

Micro corrosion in pre-treatment of 05 copper deposition and pre-treatment of pattern electroplating; Excessive micro etching can cause substrate leakage at the hole opening, resulting in bubbling around the hole opening; Insufficient micro corrosion can also cause insufficient bonding force, leading to foaming phenomenon; Therefore, it is necessary to strengthen the control of micro corrosion; The micro etching depth for general copper deposition pretreatment is 1.5-2 microns, and for graphic electroplating pretreatment it is 0.3-1 microns. If possible, it is best to control the micro etching thickness or etching rate through chemical analysis and simple experimental weighing methods; In general, the surface of the board after slight erosion has a bright color, uniform pink, and no reflection; If the color is uneven or there is reflection, it indicates that there is a quality hazard in the pre-treatment process; Pay attention to strengthening inspections; In addition, the copper content, bath temperature, load capacity, and micro etching agent content of the micro etching groove are all important factors to consider;

The activity of 06 copper immersion solution is too strong; The high content of the three major components, especially copper, in the newly opened cylinder or tank solution of the copper deposition solution can cause excessive activity of the tank solution, rough chemical copper deposition, excessive inclusion of hydrogen gas, cuprous oxide, 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 adopted appropriately: reducing the copper content (adding pure water to the tank solution), including the three major components, increasing the content of chelating agents and stabilizers appropriately, and lowering the temperature of the tank solution appropriately;

The 07 board surface undergoes oxidation during the production process; If the copper plate oxidizes in the air, it may not only result in no copper in the holes and rough surface, but also cause bubbling on the surface; If the copper plate is stored in acid solution for too long, the surface of the plate will also oxidize, 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 copper plating should be thickened and completed within 12 hours at the latest;

08 Copper sinking rework defects; Some reworked boards with copper deposition or graphic conversion may experience blistering on the surface due to poor plating, incorrect rework methods, improper control of micro etching time during rework, or other reasons; If copper deposition defects are found online during the rework of copper plates, they can be directly removed from the line by washing with water, followed by acid washing without corrosion, and reworked directly; It is best not to remove the oil again, as it may cause slight corrosion; For plates that have already been thickened by electroplating, they should be stripped in micro etching grooves now. Pay attention to time control, and use one or two plates to roughly calculate the stripping time to ensure the stripping effect; After the plating is completed, a set of soft grinding brushes should be lightly brushed with a brush plate machine, and then copper should be deposited according to the normal production process, but the micro corrosion time should be halved or adjusted as necessary;

Insufficient washing after development, prolonged storage time after development, or excessive dust in the workshop during the process of transferring 09 graphics can all cause poor cleanliness of the board surface. If the fiber processing effect is slightly poor, it may lead to potential quality problems;

Before copper plating, it is important to replace the immersion tank in a timely manner. If there is too much contamination or high copper content in the tank solution, it will not only cause problems with the cleanliness of the board surface, but also lead to defects such as rough board surface;

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

In addition, in winter, when the tank solution is not heated during production in some factories, special attention should be paid to the charging of the plates into the tank during the production process, especially for plating tanks with air agitation, such as copper and nickel; For nickel tanks in winter, it is best to add a warm water bath (with a water temperature of around 30-40 degrees) before nickel plating to ensure that the initial nickel layer is deposited densely and well;

In the actual production process, there are many reasons that can cause bubbling on the board surface. The author can only provide a brief analysis. Different manufacturers' equipment technology levels may lead to bubbling phenomena caused by different reasons. The specific situation needs to be analyzed specifically, and cannot be generalized or blindly applied; The above analysis of reasons is not divided into priority and importance, and is basically based on the production process for a brief analysis. This series is just to provide a direction for solving problems and a broader perspective. We hope that it can play a role in guiding everyone's process production and problem-solving!