Advantages of copper plating technology in PCB process

Electroplating copper is a pre-coating that is widely used to improve the adhesion of the coating. The copper coating is an important part of the copper/nickel/chromium system of the protective and decorative coating. The adhesion and corrosion resistance between the coatings play an important role. Copper plating is also used for partial anti-carburization, metallization of printed board holes, and as the outer surface of printing rolls. The colorful 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 in the PCB process of electroplating copper skills and their solutions.

1. Common problems of acid copper electroplating

    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 electroplated copper layer, and has a certain impact on subsequent processing. Therefore, how to control the quality of acid copper electroplating is An important part of PCB electroplating is also one of the most difficult processes to control in many large factories. The common problems of acid copper electroplating mainly include the following: 1. Plating rough; 2. Electroplating (board surface) copper particles; 3. Electroplating pits; 4. The board surface is whitish or the color is unequal. In response to the above problems, some summaries are made, and some brief analysis solutions and preventive measures are carried out.

1. Rough electroplating

    Generally, the board corners are rough, and most of them are caused by the large electroplating current. You can reduce the current and use a card meter to check whether the current is abnormal; the whole board is rough and generally does not appear. It was found that the temperature in winter was low at that time, and the content of light agent was insufficient; and sometimes some reworked and delaminated boards were not cleanly treated, and a similar situation would occur.

2. Copper particles on the electroplated board

    There are many factors that cause the occurrence of copper particles on the board surface, from the copper sinking, the whole process of pattern handling, and the electroplating copper itself. The author has encountered in a large public factory, the copper particles on the board composed of sinking copper.

    The copper particles on the board caused by the copper immersion process may be caused by any of the copper immersion processing steps. Alkaline degreasing has higher water hardness and more drilling dust (especially double-sided panels ).When the filtration is not good, it will not only cause roughness of the board surface, but also cause roughness in the hole; but generally it will only cause roughness in the hole, and micro-etching of fine point-like dirt on the board surface can also be removed; micro-etching is mainly There are several situations: the quality of the selected micro-etching agent hydrogen peroxide or sulfuric acid is too poor or the ammonium persulfate (sodium) contains too high impurities, it is generally recommended that it should be at least CP grade, in addition to industrial grade, it will also cause other quality Faults; the copper content of the micro-etching tank is too high or the temperature is too low to form the slow precipitation of copper sulfate crystals; the tank liquid is turbid and polluted. Most of the activation solution is composed of pollution or improper protection, such as air leakage from the filter pump, low specific gravity of the tank liquid, and high copper content (the activation time of the activation cylinder is too long, more than 3 years), which will cause particle suspension in the tank liquid. The material or impurity colloid is adsorbed on the plate surface or the hole wall, which will be accompanied by the occurrence of roughness in the hole. Degumming or speeding up: the bath solution is turbid after being used for too long. Because most degumming solutions are prepared with fluoroboric acid, it will attack the glass fibers in FR-4 and form the increase of silicate and calcium salts in the bath. If it is too high, the increase of copper content and dissolved tin in other baths will cause the occurrence of copper particles on the board. The copper sinking tank itself is mainly composed of excessive activity of the tank liquid, dust in the air mixing, and many small particles suspended in the tank liquid. The process parameters can be adjusted to increase or replace the air filter element, the whole tank filtration, etc. to solve it effectively. After the copper sinking, the dilute acid tank of the copper sinking plate should be temporarily stored. The tank liquid should be kept clean. When the tank liquid is cloudy, it should be replaced in time. The storage time of the copper immersion board should not be too long, otherwise the board surface will be easily oxidized, even in an acidic solution, and the oxide film will be more difficult to deal with after oxidation, so that copper particles will also occur on the board surface. The copper particles on the board surface deposited by the above-mentioned copper sinking process are generally distributed evenly on the board surface, except for the oxidation of the board surface, and the regularity is strong, and the pollution that occurs here is conductive or not. For the occurrence of copper particles on the surface of the electroplated copper plate, some small experimental boards can be used for step-by-step control and judgment. For on-site faulty boards, it can be solved with a soft brush. It can also be plated and covered during electroplating), or the cleaning after development is not clean, or the board is placed for too long after the pattern is transported, resulting in different degrees of oxidation of the board surface, especially in the case of poor cleaning of the board surface or storage. When the air pollution in the workshop is heavy. The solution is to strengthen water washing, strengthen planning and progress, and strengthen the strength of acid degreasing.

    The acid copper electroplating tank itself, at this time its pretreatment, generally does not form copper particles on the board surface, because the non-conductive particles Z mostly constitute the board surface leakage plating or pits. The reasons why the copper cylinder forms the copper particles on the board surface can be roughly summarized into several aspects: the protection of bath parameters, the production and operation, the material and the process protection. In terms of bath parameter protection, the sulfuric acid content is too high, the copper content is too low, the bath temperature is too low or too high, especially in factories without a temperature-controlled cooling system. At this time, the current density range of the bath will be reduced. According to the normal production process During operation, copper powder may be generated in the bath and mixed into the bath;

    In terms of production operation, the current is too large, the splint is bad, the empty pinch point, the falling board in the tank is dissolved against the anode, etc., which will also cause the current of some boards to be too large, resulting in copper powder, falling into the tank, and gradually causing copper particle failure. ;Material is mainly about the phosphorus content of phosphor copper corners and the uniformity of phosphorus distribution; production protection is mainly about large-scale processing, when the copper corners increase and fall into the tank, mainly when large-scale processing, anode cleaning and anode bag cleaning, many factories It is not handled well, and there are some dangers. For large copper ball treatment, the surface should be cleaned and the fresh copper surface should be slightly etched with hydrogen peroxide. The anode bag should be soaked with sulfuric acid hydrogen peroxide and lye to clean it, especially the anode bag should be PP filter bag with a gap of 5-10 microns. .

3. Electroplating pits

    There are also many processes caused by this disadvantage, from copper sinking, pattern handling, to pre-plating, copper plating and tin plating. Immersion copper is mainly composed of poor long-term cleaning of the immersion copper hanging basket. During micro-etching, the contamination solution containing palladium and copper will drip from the hanging basket on the board surface, causing pollution. pits. The graphics handling process is mainly composed of equipment protection and poor development and cleaning. There are many reasons: the brush roller of the brushing machine is contaminated with glue stains, the air knife fan in the drying section is dirty, and there is oil dust, etc., and the board is covered with film or dust before printing. Inappropriate, the developing machine is not clean, the washing is not good after development, and the silicon-containing defoamer contaminates the board surface, etc. In the pre-plating treatment, whether it is acid degreaser, micro-etching, pre-dipping, or the main component of the bath liquid is sulfuric acid, when the water hardness is high, it will appear turbid and pollute the board surface; If it is not good, it will be found that the encapsulation will dissolve and spread in the tank for a long time, contaminating the tank liquid; these non-conductive particles are adsorbed on the surface of the board, which may form electroplating pits to different degrees for subsequent electroplating.

4. The board surface is whitish or the color is uneven

    The acid copper electroplating tank itself may have the following aspects: the air blowing pipe is contrary to the original position, and the air mixing is uneven; the filter pump leaks or the liquid inlet is close to the air blowing pipe to inhale air, and fine air bubbles are generated, which are adsorbed on the board surface or the edge of the line. Especially the horizontal edge and the corner of the line; another point may be the use of inferior cotton wick, the treatment is not complete, the anti-static treatment agent used in the production process of the cotton wick contaminates the bath liquid, resulting in leakage plating, this situation You can increase the aeration and 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: mainly due to the problem of polishing agent or protection, and sometimes it may be cleaning after acid degreasing. problem, micro-etching problem. The copper cylinder polisher is out of balance, the organic pollution is serious, and the bath temperature is too high. Acid degreasing generally does not have cleaning problems, but if the pH value of the water is too acidic and there are many organic substances, especially the recycled water washing, it may cause poor cleaning and uneven micro-etching; micro-etching mainly considers the excessive content of micro-etching agents. Low, the copper content in the micro-etching solution is too high, and the temperature of the bath solution is one level lower, which will also cause uneven micro-etching on the board surface; in addition, the cleaning water quality is poor, the washing time is slightly longer or the pre-soak acid solution is polluted, and the board surface is treated after treatment. There may be slight oxidation. When the copper tank is electroplated, because it is acid oxidation and the board is charged into the tank, the oxide is difficult to remove, and the color of the board surface will also be uneven; other board surfaces contact the anode bag, the anode Uneven conduction, anode passivation and other conditions can also constitute such disadvantages.