PCB News - Talking about the Causes of Blistering on the Surface of the Electroplated Copper Plate of the Circuit Board

Talking about the Causes of Blistering on the Surface of the Electroplated Copper Plate of the Circuit Board

PCB surface blistering is one of the more common quality defects in the circuit board production process, because the complexity of the circuit board production process and the complexity of the process maintenance, especially in the chemical wet treatment, make the prevention of the board surface blistering defect more difficult. Based on many years of actual production experience and service experience, the author now makes a brief analysis of the cause of blistering on the surface of the copper plating of the circuit board, hoping to help the industry colleagues!

The blistering of the circuit board surface is actually the problem of poor bonding force of the board surface, and then the surface quality problem of the board surface, which includes two aspects: 1. The cleanliness of the board surface; 2. The surface micro-roughness (Or surface energy) problem; all the blistering problems on the circuit board can be summarized as the above reasons. The adhesion between the plating layers is poor or too low, and it is difficult to resist the production process in the subsequent production process and assembly process The coating stress, mechanical stress, thermal stress, etc. produced in the process will eventually cause different degrees of separation between the coatings.

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

1. The problem of substrate processing; especially for some thinner substrates, (usually below 0.8mm), because the substrate has poor rigidity, it is not suitable to use a brushing machine to brush the board, which may not be able to effectively remove the substrate production and processing In the process, the protective layer specially treated to prevent the oxidation of the copper foil on the board surface. Although the layer is thin and easy to remove by brushing, it is more difficult to use chemical treatment. Therefore, it is important to pay attention to control in the PCB production and processing to avoid causing the board. The blistering problem of the board surface caused by the poor bonding between the copper foil of the surface base material and the chemical copper; this problem will also have poor blackening and browning, uneven color, and partial black when the thin inner layer is blackened. The problem of browning is not superior;

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

3. Poor sinking copper brush plate: the pressure of the sinking copper front grinding plate is too large, causing the hole to be deformed, brushing out the hole copper foil rounded corners or even the hole leaking the substrate, which will cause the sinking copper electroplating, spraying and soldering, etc. Foaming phenomenon at the orifice; even if the brush plate does not cause leakage of the substrate, the excessively heavy brush plate will increase the roughness of the orifice copper, so the copper foil at this place is likely to be over-roughened during the micro-etching roughening process, There will also be certain quality hidden dangers; therefore, it is necessary to strengthen 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. Water washing problem: Because the electroplating treatment of copper sinking has to go through a lot of chemical treatment, various kinds of acid, alkali, non-polar organic and other pharmaceutical solvents are more, the surface of the board is not clean with water, especially the sinking copper adjustment degreasing agent, which will not only cause cross-contamination At the same time, it will also cause poor partial treatment of the board surface or poor treatment effect, uneven defects, and cause some bonding problems; therefore, attention should be paid to strengthening the control of washing, mainly including the flow of washing water, water quality, and washing time., And the control of the dripping time of the panel; 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 plating; excessive micro-etching will cause the hole to leak the substrate 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; generally the depth of micro-etching before copper sinking is 1.5-2 microns, and the micro-etching before pattern electroplating is 0.3--1 microns. If possible, it is best to pass chemical analysis and simple The test weighing method controls the thickness of the micro-etching or the corrosion rate; under normal circumstances, the surface of the micro-etched board is bright, uniform pink, without reflection; if the color is uneven, or there is reflection, it means that there is a hidden quality risk in the pre-processing; note; Strengthen the inspection; in addition, the copper content of the micro-etching tank, the temperature of the bath, the load, the content of the micro-etching agent, etc. are all items to be paid attention to;

6. The activity of the copper sinking liquid is too strong; the newly opened tank of the copper sinking liquid or the content of the three major components in the bath is too high, especially if the copper content is too high, it will cause the bath liquid to be too active, the electroless copper deposition is rough, hydrogen, and submerged. Copper oxides and other excessive inclusions in the chemical copper layer cause the deterioration of the physical quality of the coating and the defects of poor bonding; the following methods can be appropriately adopted: reduce the copper content, (add pure water to the bath), including three groups Properly increase the content of complexing agent and stabilizer, appropriately reduce the temperature of the bath, etc.;

7. The surface of the board is oxidized during the production process; if the copper sink 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 surface of the board to foam; the storage time of the copper sink in the acid solution If it is too long, the surface of the board will also be oxidized, and this oxide film is difficult to remove; therefore, the copper plate should be thickened in time during the production process, and it is not appropriate to store it for too long. Generally, the copper plating should be thickened within 12 hours at the latest. complete;

8. Poor rework of the heavy copper; some heavy copper or reworked boards after the pattern transfer are poorly plated during the rework process, the rework method is incorrect, or the micro-etching time during the rework process is not properly controlled, etc., or other reasons will cause the board surface to blisters; Shen If copper plate rework is found to be bad on the line, it can be directly deoiled from the line after washing with water, then pickled and reworked directly without corrosion; it is best not to re-degrease or micro-etch; for plates that have already been thickened, they should be reworked. Now that the micro-etching tank is deplating, 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, apply a set of soft brushes and lightly brush the plate and then press the normal production. Process copper immersion, but the time of etching and micro-etching should be halved or adjusted if necessary;

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 slightly poor fiber processing effect, which may cause potential quality problems;

10. 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;

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

12. In addition, when the bath liquid is not heated in some factories in the 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 priority and importance. Basically, a brief analysis is made in accordance with the production process flow. In this series, it only provides you with a problem-solving direction and a broader vision. I hope that everyone's process production and production In terms of problem solving, it can play a role in attracting ideas!