Electroplated copper is the most widely used pre-plating layer to improve the adhesion of the coating. The copper coating is an important part of the protective decorative coating copper / nickel / chromium system. The flexible and low porosity copper coating is The adhesion and corrosion resistance between the plating layers play an important role. Copper plating is also used for partial carburization, metallization of printed board holes, and as a surface layer of printing rollers. The colored copper layer after chemical treatment, coated with organic film, can also be used for decoration. In this article, we will introduce the common problems encountered by the electroplated copper technology in the PCB process and their solutions.

I. Common problems of acid copper plating

Copper sulfate electroplating occupies an extremely important position in PCB electroplating. The quality of acid copper electroplating directly affects the quality and related mechanical properties of the copper electroplating layer, and has a certain impact on subsequent processing. An important part of PCB electroplating is also one of the more difficult processes in many large factories. The common problems of acid copper plating mainly include the following: 1. Rough plating; 2. Electroplating (board surface) copper particles; 3. Plating pits; 4. The board surface is whitish or uneven in color. In view of the above problems, some summaries are made, and some brief analysis, solution and preventive measures are carried out.

1. Rough plating

Generally, the corners of the board are rough, and most of them are caused by the large plating current. You can lower the current and use the card meter to check whether the current shows abnormality; the whole board is rough and generally does not appear, but the author has encountered it once at the customer. At the time of tomorrow, the temperature was low in winter and the content of light agent was insufficient; there were also times when some reworked membranes were not cleanly treated.

2. Copper particles on the plated surface

There are many factors that cause the generation of copper particles on the surface of the board. From the sinking copper to the entire process of pattern transfer, copper electroplating itself is possible. I have met in a large state-owned factory, the copper grain on the surface of the board caused by sinking copper.

The copper particles on the board surface caused by the copper sinking process may be caused by any copper sinking process. Alkaline degreasing will not only cause roughness of the board surface but also roughness in the holes when the water hardness is high and the drilling dust is large (especially the double-sided board is not removed by the glue residue). The inside is rough, and the slight pitting micro-etching of the board surface can also be removed; there are several cases of micro-etching: the micro-etching agent used is hydrogen peroxide or sulfuric acid is of poor quality or ammonium persulfate (sodium) contains too high impurities, generally It is recommended that it should be at least CP grade. In addition to industrial grade, it will also cause other quality failures; the excessively high copper content of the micro-etching tank or the low temperature will cause the slow precipitation of copper sulfate crystals; the tank liquid is turbid and polluted. Most of the activation liquid is caused by pollution or improper maintenance, such as filter pump leakage, low specific gravity of the bath liquid, and high copper content (the activation cylinder is used for too long, more than 3 years), which will cause particulate suspension in the bath liquid Or impurity colloid, adsorbed on the surface of the board or the wall of the hole, at this time, it will be accompanied by the roughness in the hole.

Degumming or accelerating: The bath solution is too long to appear turbid, because most of the degumming solution is prepared with fluoroboric acid, so that it will attack the glass fiber in FR-4, causing the silicate and calcium salts in the bath to rise. High, in addition, the increase of copper content and dissolved tin in the bath will cause the generation of copper particles on the board surface. The copper sink itself is mainly caused by the excessive activity of the bath liquid, the air is stirred with dust, and there are many small particles suspended in the solid in the bath liquid. You can increase or replace the air filter element and the whole tank filter by adjusting the process parameters. Effectively solved. After sinking the copper, temporarily store the dilute acid tank of the sinking copper plate. The bath liquid should be kept clean, and it should be replaced in time when the bath liquid is turbid. Immersion copper plate should not be stored for too long, otherwise the surface of the plate is easy to oxidize, and it will oxidize even in acidic solution, and the oxide film is more difficult to deal with after oxidation, so that copper particles will also be generated on the plate surface. The copper particles on the surface of the board deposited by the copper sinking process mentioned above, except for the oxidation of the board surface, are generally distributed evenly on the board surface and have a strong regularity. The pollution generated here will cause no matter whether it is conductive or not For the generation of copper particles on the surface of the electroplated copper plate, some small test boards can be processed separately for comparison and judgment. For the on-site faulty board, you can use a soft brush to lightly solve it; graphics transfer process: there is residual glue (very thin residual film) during development It can also be plated and coated during electroplating), or it is not cleaned after development, or the plate is placed for too long after the pattern is transferred, causing different degrees of oxidation on the board surface, especially under poor cleaning conditions or storage When the air pollution in the workshop is heavy. The solution is to strengthen water washing, strengthen the schedule and schedule, and strengthen the acid degreasing intensity.

The acid copper plating tank itself, at this time, its pre-treatment generally does not cause copper particles on the surface of the board, because non-conductive particles at most cause leakage or pitting on the surface of the board. The reasons for the copper particles on the surface of the copper cylinder can be summarized into several aspects: maintenance of bath parameters, production operations, materials and process maintenance. The maintenance of bath parameters includes too high sulfuric acid content, too low copper content, low or too high bath temperature, especially for factories without temperature-controlled cooling systems, which will cause the current density range of bath liquid to decrease. According to the normal production process Operation, copper powder may be generated in the bath and mixed into the bath;

In the production operation, the current is too large, the plywood is bad, the empty pinch point, the plate in the tank is dissolved by the anode, etc. will also cause part of the plate current to be too large, producing copper powder, falling into the bath, and gradually causing copper particle failure ; The material is mainly the problem of phosphorus content and uniformity of phosphorus distribution; the production and maintenance are mainly large processing, and the copper angle is dropped into the tank when it is added, mainly during large processing, anode cleaning and anode bag cleaning, many factories They are not handled well and there are some hidden dangers. In the large-scale treatment of copper balls, the surface should be cleaned, and the fresh copper surface should be slightly etched with hydrogen peroxide. The anode bag should be immersed in sulfuric acid hydrogen peroxide and alkaline solution successively, especially the anode bag should use a 5-10 micron gap PP filter bag .

3. Plating pits

There are many processes caused by this defect, from copper sinking, pattern transfer, to pre-plating treatment, copper plating and tin plating. The main cause of sinking copper is poor long-term cleaning of the sinking copper hanging basket. During the micro-etching, the contaminant solution containing palladium and copper will drip from the hanging basket on the surface of the board, forming pollution, which will cause spot leakage plating after the sinking copper board is charged. Pit. The graphics transfer process is mainly caused by poor equipment maintenance and development and cleaning, and there are many reasons: the brush roller suction roller of the plate brush machine contaminates the glue stains, the internal parts of the air knife fan in the drying and drying section, and oil dust, etc. Improper, developing machine is not clean, poor water washing after development, silicon-containing defoamer contaminates the board surface, etc. Pre-plating treatment, because no matter it is acidic degreaser, micro-etching, prepreg, the main component of the bath liquid has sulfuric acid, so when the water hardness is high, it will appear turbid and pollute the surface of the board; in addition, some companies have poor encapsulation For a long time, it will be found that the encapsulation dissolves and diffuses in the tank night and pollutes the bath liquid; these non-conductive particles are adsorbed on the surface of the board, which may cause different degrees of plating pits for subsequent plating.

4. The board surface is white or uneven in color

The acid copper electroplating tank itself may have the following aspects: the blower tube deviates from the original position, and the air is not stirred uniformly; the filter pump leaks or the liquid inlet is close to the blower tube to suck air, generating fine air bubbles, which are adsorbed on the board surface or line side, Especially at the lateral edges and at the corners of the lines; there may also be the use of inferior cotton cores, which are not completely treated. The anti-static treatment agent used in the cotton core manufacturing process contaminates the bath liquid, resulting in missed plating. This situation can be added Breathing, just clean the liquid surface foam in time. After the cotton core is soaked with acid and alkali, the color of the board surface is white or uneven in color: it is mainly a light agent or maintenance problem, and sometimes it may be a cleaning problem after acid degreasing. Micro-erosion problem. The copper cylinder light agent is out of adjustment, the organic pollution is serious, and the bath temperature may be too high. Acidic degreasing generally does not have cleaning problems, but if the pH of the water is slightly acidic and there are many organics, especially recycled water, it may cause poor cleaning and uneven micro-etching; micro-etching mainly considers the content of micro-etching agent. Low, the copper content in the micro-etching liquid is high, the bath temperature is low, etc., it will also cause uneven micro-etching on the surface of the board; in addition, the quality of the cleaning water is poor, the washing time is slightly longer or the pre-immersion acid is contaminated, and the surface may be There will be slight oxidation. When the copper bath is electroplated, because the acid is oxidized and the board is charged into the tank, the oxide is difficult to remove, and it will also cause uneven color of the board surface; in addition, the board surface touches the anode bag, and the anode conductivity is uneven , Anode passivation and other conditions will also cause such defects.

II. Conclusion

This article summarizes some common problems in the acid copper plating process. At the same time, the acid copper plating process has a simple composition, stable solution, and high current efficiency. Adding an appropriate brightener can obtain a plating layer with high brightness, high leveling, and high average plating ability, which is widely used. The key to the quality of acid copper plating is also the choice and application of acid copper brightener. Therefore, it is hoped that the majority of staff can accumulate experience in their daily work, not only to find and solve problems, but also to innovate and fundamentally improve the process level.