What are the common problems of copper plating technology in PCB process? The solution is...

Electroplating copper is the most widely used pre-coating to improve the bonding force of the coating. The copper coating is an important part of the copper/nickel/chromium system of the protective decorative coating. The adhesion and corrosion resistance between the coatings play an important role. Copper plating is also used for local anti-carburization, metallization of printed board holes, and as a surface layer for printing rolls. 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 in the PCB process of electroplating copper technology 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, it is also one of the difficult processes for many large factories to control the process. The common problems of acid copper electroplating mainly include the following: 1. Rough electroplating; 2. Electroplating (board surface) copper particles; 3. Electroplating pits; 4. The board surface is white or uneven in color. In response to the above problems, some summaries are made, and some brief analysis solutions and preventive measures are carried out.

(1) Rough plating

Generally, the board corners are rough, most of which are caused by the large electroplating current. You can reduce the current and use a card meter to check whether the current display is abnormal; In the Ming Dynasty, the temperature was low in winter, and the content of light agent was insufficient; and sometimes some reworked and delaminated boards were not cleaned properly, and similar situations would occur.

(2) Copper grains on the electroplated board

There are many factors that cause copper particles on the board, from copper sinking to the whole process of pattern transfer, and electroplating copper itself is possible. The author has encountered copper particles on the board surface caused by sinking copper in a large state-owned factory.

The copper particles on the board surface caused by the copper immersion process may be caused by any one of the copper immersion processing steps. Alkaline degreasing will not only cause roughness on the board surface, but also roughness in the hole when the water hardness is high and there is a lot of drilling dust (especially the double-sided panel without de-smear). The inner roughness and the slight point-like dirt on the board surface can also be removed by micro-etching; there are mainly several cases of micro-etching: the quality of the micro-etching agent hydrogen peroxide or sulfuric acid is too poor, or the ammonium persulfate (sodium) contains too high impurities, generally It is suggested that it should be at least CP grade, in addition to industrial grade, other quality failures will be caused; the copper content of the micro-etching tank is too high or the temperature is low, causing the slow precipitation of copper sulfate crystals; the tank liquid is turbid and polluted. Most of the activation solution is caused by pollution or improper maintenance, 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 produce particulate suspended matter in the tank liquid Or impurity colloids are adsorbed on the plate surface or the hole wall, which will be accompanied by the generation of roughness in the hole. Degumming or acceleration: the bath solution is cloudy after being used for too long, because most degumming solutions are now prepared with fluoroboric acid, so that it will attack the glass fibers in FR-4, resulting in the increase of silicate and calcium salts in the bath. In addition, the increase of copper content and dissolved tin in the bath will cause the generation of copper particles on the board.

The copper sinking tank itself is mainly caused by the excessive activity of the tank liquid, dust in the air stirring, and many small particles suspended in the tank liquid. effective solution. After the copper is deposited, the dilute acid tank of the copper plate should be temporarily stored. The tank liquid should be kept clean, and the tank liquid should be replaced in time when it is cloudy. 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 be generated 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 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 used for step-by-step control and judgment. For the on-site faulty board, it can be solved with a soft brush. It can also be plated and coated during electroplating), or the cleaning after development is not clean, or the board is placed for too long after the pattern transfer, resulting in different degrees of oxidation of the board surface, especially if the board surface is poorly cleaned or stored. When the air pollution in the workshop is heavy. The solution is to strengthen the washing, strengthen the planning and schedule, and strengthen the strength of acid degreasing.

The acid copper electroplating tank itself, and its pretreatment at this time, generally will not cause copper particles on the board surface, because the non-conductive particles cause the most leakage plating or pits on the board surface. The reasons why the copper cylinder causes copper particles on the board surface can be roughly summarized into several aspects: maintenance of bath parameters, production operation, material and process maintenance. The maintenance of bath parameters includes high sulfuric acid content, too low copper content, and low or high bath temperature, especially in factories without temperature-controlled cooling systems. At this time, the current density range of the bath will decrease. According to the normal production process operation, copper powder may be produced 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 plate 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 producing copper particles failure. ;Material is mainly about the phosphorus content of phosphor copper corners and the uniformity of phosphorus distribution; production and maintenance are mainly about large-scale processing, when copper corners are added into the tank, mainly when large-scale processing, anode cleaning and anode bag cleaning, many factories If it is not handled well, there are some hidden dangers. For large copper ball treatment, the surface should be cleaned, and the fresh copper surface should be etched slightly with hydrogen peroxide. The anode bag should be soaked with sulfuric acid hydrogen peroxide and lye, and cleaned, 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 defect, from copper sinking, pattern transfer, to pre-plating, copper plating and tin plating. The main cause of copper sinking is the poor cleaning of the sinking copper hanging basket for a long time. During micro-etching, the contamination solution containing palladium and copper will drip from the hanging basket on the board surface, causing pollution and causing spot leakage after the copper sinking board is electrified. pits. The graphic transfer process is mainly caused by equipment maintenance 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. Improper, the developing machine is not clean, the washing is not good after development, and the silicon-containing defoamer contaminates the board surface, etc. Pre-treatment of electroplating, because no matter it is acid degreaser, micro-etching, pre-dipping, the main component of bath liquid is sulfuric acid, so when the water hardness is high, it will appear turbid and pollute the board surface; in addition, some companies have poor glue encapsulation , for a long time, it will be found that the encapsulation will dissolve and diffuse in the tank night, contaminating the tank liquid; these non-conductive particles are adsorbed on the surface of the board, which may cause different degrees of electroplating pits 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 deviates from the original position, and the air is not evenly stirred; the filter pump leaks or the liquid inlet is close to the air blowing pipe to inhale air, resulting in fine air bubbles, which are adsorbed on the board surface or the edge of the line. Especially at the horizontal edge and corner of the line; there may be another point that the use of inferior cotton core, the treatment is not thorough, the anti-static treatment agent used in the cotton core manufacturing process contaminates the bath liquid, resulting in leakage plating, this situation can be increased Blow air 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 maintenance, and sometimes it may be the problem of cleaning after acid degreasing. Micro-etching problem. The copper cylinder polishing agent is out of balance, the organic pollution is serious, and the bath temperature is too high. Acid degreasing generally does not cause cleaning problems, but if the pH value of the water is too acidic and there are many organic substances, especially recycling and circulating 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 low, etc., which will also cause uneven micro-etching of 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 may be treated after treatment. There will 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, which will also cause uneven color on the board surface; in addition, the board surface contacts the anode bag, and the anode conducts unevenly. , anode passivation, etc. can also cause such defects.