PCB Tech - Common problems of copper plating technology in PCB process?

PCB copper electroplating is the most common pre-coating used to improve the adhesion of the coating. The copper coating is the key to safety protection, the composition of the decorative art coating copper/nickel/chromium management system, flexibility and porosity The low copper coating plays a key role in improving the adhesion and corrosion resistance between the coatings. The copper coating is also used as part of the waterproof layer carbon, the printed circuit board hole metallization, and as the surface layer of the packaging printing roller. After organic chemistry, the colorful copper layer is coated with organic chemical film, which can also be used for decoration. In the article, people will introduce in detail the difficult problems encountered in the PCB processing technology of electroplating copper technology and their solutions.

1. Difficult problems of acid copper electroplating process

The copper sulfate electroplating process occupies an extremely important influence in the PCB electroplating process. The pros and cons of the acid copper electroplating process immediately endanger the quality of the electroplated copper layer and related physical properties, and cause certain hazards to the subsequent production and processing, so how to handle the acid The quality of the copper electroplating process is a key part of the PCB electroplating process, and it is one of the processes that are difficult to manipulate in many large factories.

1. The electroplating process is not smooth

Generally, the corners of the board are not smooth, and most of them are caused by a slightly larger current in the electroplating process. It can reduce the current and use the card meter to check whether the current display information is abnormal; the whole board is not smooth, which is generally not easy to appear, but the editor is in the customer I encountered it once, and when I checked it out, the average temperature in winter was slightly lower, and the water content of the polish was not enough; sometimes the surface of the reworked fading board was not clean and the similar situation occurred.

2. Copper particles on the surface of the electroplating process

There are many factors that cause surface copper particles. From the process of copper sinking to pattern migration, copper electroplating itself will often occur. I encountered copper particles on the surface caused by copper sinking in a large state-owned enterprise.

The surface copper particles caused by the copper immersion process will be caused by all the copper immersion solutions. Partial alkali degreasing in the water body has high strength and more smoke and dust from the rotating hole (very double-sided board has not been de-smeared). When the filter is not good, not only the surface will not be smooth, but also the hole wall will not be smooth; but it is generally always The hole wall is not smooth, and the slight spot-like waste on the surface can be removed by micro-etching; there are several key conditions for the micro-etching: the selected micro-etching agent hydrogen peroxide or hydrochloric acid is of poor quality or ammonium persulfate (sodium) contains too much residue. High, it is generally recommended that it should be at least CP level. Industrial type will also cause other common quality failures; excessively high copper water content in the micro-etching tank or slightly lower average temperature causes the slow dissolution of copper sulfate crystals; the tank liquid is turbid and the environment Pollution. Most of the activation fluid is caused by environmental pollution or poor maintenance. For example, the filter pump leaks steam, the bath liquid ratio is slightly lower, and the copper water content is too high (the active cylinder has been used for too long, about 3 years), and it will be in the bath liquid. Suspended solids or residual colloidal solutions are caused to be absorbed on the surface or edge of the hole, which will be accompanied by the unevenness of the hole wall. Debonding or speeding up: The bath solution is turbid after being used for too long. Since most of the solution solutions are now equipped with fluoroboric acid, it will attack the glass fiber in FR-4, resulting in silicate and calcium salts in the bath. In addition, the increase of the water content of copper in the bath and the amount of dissolved tin in the lifting solution will cause the formation of copper particles on the surface. The key to the copper sinking tank itself is that the tank liquid is too specific, the gas is mixed with dust, and there are more solid floating small particles in the tank liquid. The main parameters of the processing process can be adjusted to upgrade or remove the air purification filter. Reasonable treatment such as trough filter. The dilute acid tank for temporarily storing the copper coins after sinking, the tank liquid should be kept clean, and the tank liquid should be dismantled and replaced immediately when it is turbid. The storage time of heavy copper coins is not suitable for too long, otherwise the surface is very easy to be oxidized by air, even in acid and alkaline aqueous solutions, it will be air oxidized, and the air oxide film is more difficult to solve after air oxidation, so that the surface will also cause copper particles. It is often said that the surface copper particles deposited by the copper immersion process, except for the surface air oxidation, are generally spread on the surface relatively uniformly, with strong periodicity, and the environmental pollution caused here is no matter whether it is conductive or not. Leading to the copper particles on the surface of the electroplated copper, some small test boards can be used to solve the comparison and judgment independently. The common failure boards on the spot can be handled with a soft brush and light brush; the pattern migration process: developing! Glue (extra-thin residual film can also be plated and coated during the electroplating process), or the cleaning after development is not tidy, or the parts are placed for too long after the pattern migration, resulting in different levels of air oxidation on the surface, It is especially when the surface is not cleaned well or when the environmental pollution in the storage and production workshop is heavy. The solution means to improve hand washing, improve the progress of plan allocation, and improve the compressive strength of acid and alkali degreasing.

3. Electroplating process dents

The process flow caused by this shortcoming is also more, from sinking copper, pattern migration, to solving before the electroplating process, barrel plating and tin electroplating. The key to copper sinking is the poor long-term cleaning of the sinking copper basket. During microetching, the environmental pollution liquid with palladium-copper drips from the basket on the surface, causing environmental pollution and causing spots after the copper sinking and electricity. Missing plating is also called dents. The key to the pattern migration process is the poor maintenance and management of equipment and the development and cleaning. There are many reasons: the brushing machine, the brush roller, the moisture absorption stick, environmental pollution, glue stains, the internal organs of the centrifugal fan of the air knife during the drying and drying section, and the oil stains, soot, etc. Poor ash removal before printing on the surface film or packaging, incomplete development by the developing machine, poor hand washing after development, and environmental pollution of the surface with silicone defoamers containing silicon. Solve before the electroplating process, because whether it is acid-alkaline degreasing agent, micro-etching, pre-dipping, the key component of the bath liquid often contains hydrochloric acid, so when the water strength is high, it will appear turbid and the environment will pollute the surface; in addition, some enterprises hang bags Poor plastic, after a long time, it will be found that the plastic coating melts and diffuses in the tank at night, and the environment pollutes the tank liquid; this kind of non-conductivity particles are absorbed on the surface of the part, and the subsequent electroplating process will often lead to a different level of electroplating Process dents.

2. Conclusion

Some common problems in the PCB processing technology of acid-base barrel plating. In addition, the acid-alkaline barrel plating process has simple and clear basic components of the aqueous solution, stable aqueous solution, and high current efficiency. Adding a moderate brightener can obtain a coating with high gloss, high flatness, and high throwing power, so it is universal The use of. The pros and cons of acid-base barrel plating also depend on the selection and application of acid copper brightener. Therefore, it is expected that many workers can accumulate work experience in their daily work, not only can find and solve difficulties, but also can improve the level of PCB technology through independent innovation.