Copper electroplating 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 and decorative coating copper/nickel/chromium system. The flexible copper coating with low porosity is about improving The adhesion and corrosion resistance between the coatings play an important role. Copper plating is also used for partial anti-carburization, printed board hole metallization, and as the surface layer of the printing roller. 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 technology and their solutions.
One, 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 of the electroplated copper layer and related mechanical properties, 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 difficult processes in many large factories. The common problems of acid copper electroplating mainly include the following: 1. Rough plating; 2. Plating (board surface) copper particles; 3. Electroplating pits; 4. The board surface is whitish or unequal in color. In response to the above problems, some conclusions were made, and some brief analysis solutions and preventive measures were carried out.
1, rough plating
Generally, the board angle is rough, mostly caused by the electroplating current is too large, you can reduce the current and check the current flash with the card meter; the whole board is rough, and it usually does not appear, but the author has encountered it once in the customer's place. At the time of the investigation, the temperature in winter was low and the content of brightener was insufficient; and sometimes some reworked fading boards were not clean when the surface treatment was not clean.
2, plated copper particles
There are many factors that cause the generation of copper particles on the board. From the copper sinking to the entire process of pattern transfer, copper electroplating itself may be possible. The author met in a large publicly-owned factory, copper plates made of heavy copper.
The copper particles on the board surface caused by the copper immersion process may be caused by any copper immersion process. Alkaline degreasing has higher water hardness and more drilling dust (especially if the double-sided board is not de-smeared). When the filtration is not good, it will not only cause the board surface to be rough, but also the roughness of the hole; but generally only the hole is formed The internal roughness and the thin spots on the surface of the board can also be removed by micro-etching; there are mainly several situations for micro-etching: the selected micro-etching agent hydrogen peroxide or sulfuric acid is of poor quality or ammonium persulfate (sodium) contains too much impurities, generally It is recommended that it should be at least CP grade. In addition to industrial grade, other quality defects will be caused; excessively high copper content or low temperature in the micro-etching bath constitutes a slow separation of copper sulfate crystals; the bath liquid is turbid and polluted. The activation solution is mostly polluted or improperly maintained. For example, the filter pump leaks, the bath liquid has a low specific gravity, and the copper content is too high (the activation tank has been used for too long, more than 3 years), which will produce particulate suspended solids in the bath. Or impurity colloid, adsorbed on the board surface or hole wall, at this moment will be accompanied by the generation of roughness in the hole. Dissolving or accelerating: the tank solution is too long to be turbid, because most of the dissolving solutions are made of fluoroboric acid, so that it will infringe the glass fiber in FR-4 and constitute the silicate and calcium salt in the tank. High, the addition of the copper content and the amount of dissolved tin in other baths will form the production of copper particles on the plate surface. The copper sink itself is mainly composed of excessive activity of the bath liquid, dust in the air mixing, and more small particles suspended in the bath liquid. The process parameters can be adjusted, and the air filter element can be added or replaced, and the whole tank can be filtered. Come to a useful solution. After the copper is deposited, the dilute acid tank for temporarily storing the copper plate should be kept clean. If the tank liquid is turbid, it should be replaced in time. The storage time of the copper immersion plate should not be too long, otherwise the surface of the plate will simply oxidize, even in an acid solution, and the oxide film will be more difficult to deal with after oxidation, so that copper particles will also be generated on the surface of the plate. The copper particles on the plate surface caused by the copper sinking process mentioned above are generally evenly distributed on the plate surface, with strong regularity, except for the plate surface oxidation. The pollution generated here will constitute whether it is conductive or not. For the production of copper particles on the surface of the electroplated copper plate, some small test boards can be used to process separately for comparison and determination. The on-site defective board can be solved with a soft brush and light brush; the graphic transfer process: there is excess glue in the development (extremely thin residual film It can also be plated and coated during electroplating), or it is not clean after development, or the plate is placed for too long after the pattern is transferred, which constitutes different degrees of oxidation on the plate surface, especially when the plate surface is poorly cleaned or stored When the air pollution in the workshop is heavy. The solution is to strengthen the water washing, strengthen the plan and arrange the progress, and strengthen the acid degreasing intensity.
The acid copper electroplating tank itself, at this moment, its pretreatment generally does not constitute the copper particles on the board surface, because the non-conductive particles at most constitute the board surface leakage or pits. The reasons why the copper cylinder constitutes the copper particles on the board surface can be summarized in several aspects: the maintenance of bath parameters, the production operation, the material and the process maintenance. The maintenance of bath parameters includes too high sulfuric acid content, too low copper content, low or high bath temperature, especially for factories without a temperature-controlled cooling system. At this moment, the current density range of the bath will be reduced, and the normal production process will be operated. , May produce copper powder in the bath, mixed into the bath;
In terms of production operation, excessive current, poor splint, empty pinch points, and plate falling in the tank against the anode to dissolve, etc. will also constitute part of the plate. Excessive current will be generated, copper powder will be dropped into the bath liquid, and copper particle defects will gradually occur. ; The material aspect is mainly the phosphorus content of the phosphor copper corner and the uniformity of the phosphorus distribution; the production and maintenance aspect is mainly the large processing. The copper corner is added to the tank when the copper corner is added. The first is the anode cleaning and anode bag cleaning during the large processing. They are not handled well, and there are some dangers. The copper ball treatment is to clean the surface, and use hydrogen peroxide to micro-etch the fresh copper surface. The anode bag should be soaked in sulfuric acid hydrogen peroxide and lye successively to clean and clean, especially the anode bag should use a 5-10 micron gap PP filter bag .
3, electroplating pit
There are many processes caused by this defect, from copper sinking, pattern transfer, to electroplating pretreatment, copper plating and tin plating. The main component of the sinking copper is that the sinking copper hanging basket is poorly cleaned for a long time. During microetching, the polluted liquid containing palladium copper will drip from the hanging basket on the surface of the board, causing pollution. Pits. The graphics transfer process is mainly composed of equipment maintenance and poor development and cleaning. There are many reasons: the brush roller of the brushing machine is contaminated with glue stains, the internal organs of the air knife fan in the drying section are dried, there is oily dust, etc., the board surface is filmed or dust is removed before printing. Improper, the developing machine is not clean, the washing after development is not good, the defoamer containing silicon contaminates the board surface, etc. Pretreatment for electroplating, because no matter it is acidic degreasing agent, micro-etching, prepreg, the main component of the bath liquid is sulfuric acid, so when the water hardness is high, it will appear turbid and contaminate the board surface; other parts of the company`s hangers are poorly encapsulated For a long time, it will be found that the encapsulation will dissolve and disperse in the tank at night, contaminating the tank liquid; these non-conductive particles are adsorbed on the surface of the board, and may form electroplating pits of different degrees for subsequent electroplating.
The acid copper electroplating tank itself may have the following aspects: the air blast tube violates the original position, and the air is not uniformly mixed; the filter pump leaks or the liquid inlet is close to the air blast tube to inhale air, generating fine air bubbles, which are adsorbed on the board surface or the edge of the line. Especially at the side of the horizontal line and the corner of the line; another point may be the use of inferior cotton core, which is not completely handled. The anti-static treatment agent used in the cotton core manufacturing process contaminates the bath liquid and constitutes a leakage plating. This situation can be added. Blow up, clean up the liquid surface foam in time. After the cotton core is soaked in acid and alkali, the color of the board surface is white or uneven: the first is the problem of polishing agent or maintenance, and sometimes it may be the problem of cleaning after acid degreasing. Micro-etching problem. Misalignment of the polisher of the copper cylinder, severe organic pollution, and excessively high bath temperature may all be caused. Acidic degreasing generally does not have cleaning problems, but if the water pH is relatively acid and there are more organic substances, especially the recycling water washing, it may cause poor cleaning and uneven micro-etching; the first consideration for micro-etching is that the content of the micro-etching agent is too high. Low, the copper content in the microetching solution is too high, and the bath temperature is one level lower, which will also cause uneven surface microetching; in addition, the cleaning water quality is poor, the washing time is slightly longer or the pre-soak acid solution is contaminated, and the surface of the board will be treated after treatment. There may be fine oxidation. During electroplating in the copper bath, because it is acidic oxidation and the plate is charged into the bath, the oxide is difficult to remove, which will also cause uneven color on the plate surface; other plate surfaces contact the anode bag, and the anode does not conduct electricity. In general, anode passivation and other conditions can also constitute such defects.
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