I. Common problems of acid copper platingCopper 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 platingGenerally, 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;