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 of the PCB board, and has a certain impact on subsequent processing. Therefore, how to control acid copper electroplating The quality of PCB is an important part of PCB electroplating, and it is also one of the difficult processes for many large factories to control the process. Based on years of experience in electroplating and technical services, the author initially summarizes the following, hoping to inspire the electroplating industry in the PCB industry.Common problems in acid copper electroplating mainly include the following:
1. Rough plating; 2. Plating (board surface) copper particles; 3. Electroplating pit; 4. The surface of the board is whitish or uneven in color.
In response to the above problems, some conclusions were made, and some brief analysis solutions and preventive measures were carried out.
Rough electroplating: Generally the board angle is rough, most of which are caused by the electroplating current is too large. You can reduce the current and check the current display with a card meter for abnormalities; the whole board is rough, usually not, but the author has encountered it once in the customer’s place. It was later discovered that the temperature in winter was low and the content of brightener was insufficient; and sometimes some reworked faded boards were not cleanly treated, and similar conditions occurred.
Plating copper particles on the board surface: There are many factors that cause the production of copper particles on the board surface. From the copper sinking to the whole process of pattern transfer, it is possible to electroplating copper on the PCB board itself.
Copper particles on the board surface caused by the copper immersion process may be caused by any copper immersion treatment step. Alkaline degreasing will not only cause roughness in the board surface but also roughness in the holes when the water hardness is high and the drilling dust is too much (especially the double-sided board is not de-smeared). The internal roughness and slight spot-like dirt on the board surface can also be removed; 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 much impurities, generally It is recommended that it should be at least CP grade. In addition to industrial grade, other quality failures may be caused; excessively high copper content in the micro-etching bath or low temperature may cause slow precipitation of copper sulfate crystals; and the bath liquid is turbid and polluted.
Most of the activation solution is caused by pollution or improper maintenance. 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 matter in the bath. Or impurity colloid, adsorbed on the plate surface or hole wall, this time will be accompanied by the roughness in the hole. Dissolving or accelerating: the bath solution is too long to appear turbid, because most of the dissolving solution is prepared with fluoroboric acid, so that it will attack the glass fiber in FR-4, causing the silicate and calcium salt in the bath to rise. In addition, the increase of the copper content and the amount of dissolved tin in the bath will cause the production of copper particles on the board surface. The copper sinking tank itself is mainly caused by the excessive activity of the tank liquid, the dust in the air stirring, and the large amount of suspended solid particles in the tank liquid. You can adjust the process parameters, increase or replace the air filter element, filter the whole tank, etc. Effective solution. The dilute acid tank for temporarily storing the copper plate after the copper is deposited, the tank liquid should be kept clean, and the tank liquid should be replaced in time when it is turbid.
The storage time of copper immersion board should not be too long, otherwise the board surface will be easily oxidized, even in acid solution, and the oxide film will be more difficult to dispose of after oxidation, so that copper particles will be produced on the board surface. The copper particles on the surface of the board caused by the copper sinking process mentioned above, except for the surface oxidation, are generally distributed on the board surface more uniformly and with strong regularity, and the pollution generated here will cause no matter whether it is conductive or not. When dealing with the production of copper particles on the surface of the electroplated copper plate of the PCB system, some small test boards can be used to process separately for comparison and judgment. For the on-site faulty board, a soft brush can be used to solve the problem; the graphics transfer process: there is excess glue in the development (very thin The residual film 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, resulting in varying degrees of oxidation on the plate surface, especially poor cleaning of the plate surface When the air pollution in the storage or storage workshop is heavy. The solution is to strengthen the water washing, strengthen the plan and arrange the schedule, and strengthen the acid degreasing intensity.
The acid copper electroplating tank itself, at this time, its pre-treatment generally does not cause copper particles on the board surface, because non-conductive particles can at most cause leakage or pits on the board surface. The reasons for the copper particles on the plate surface caused by the copper cylinder can be summarized into several aspects: the maintenance of bath parameters, the production and operation, the material and the process maintenance. The maintenance of bath parameters includes too high sulfuric acid content, too low copper content, low or too high bath temperature, especially in factories without temperature-controlled cooling systems, this will cause the current density range of the bath to 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, excessive current, poor splint, empty pinch points, and the plate dropped in the tank against the anode to dissolve, etc. will also cause excessive current in some plates, resulting in copper powder, falling into the tank liquid, and gradually causing copper particle failure ; The material aspect is mainly the phosphorus content of the phosphor copper angle and the uniformity of phosphorus distribution; the production and maintenance aspect is mainly the large-scale processing, and the copper angle falls into the tank when the copper angle is added, mainly during the large-scale processing, anode cleaning and anode bag cleaning, many factories They are not handled well, and there are some hidden dangers. For copper ball treatment, the surface should be cleaned, and the fresh copper surface should be micro-etched with hydrogen peroxide. The anode bag should be soaked with sulfuric acid hydrogen peroxide and lye successively to clean, especially the anode bag should use a 5-10 micron gap PP filter bag. .
Electroplating pits: This defect also causes many processes, from copper sinking, pattern transfer, to pre-treatment of electroplating, 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 microetching, the pollution 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 caused by poor equipment maintenance and developing cleaning. There are many reasons: the brush roller suction stick of the brushing machine contaminates the 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 the 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. Pre-treatment for electroplating, because the main component of the bath liquid is sulfuric acid, whether it is acidic degreasing agent, micro-etching, prepreg, and the bath solution. Therefore, when the water hardness is high, it will appear turbid and pollute the board surface; in addition, some companies have poor encapsulation of hangers. For a long time, it will be found that the encapsulation will dissolve and diffuse in the tank at night, contaminating the tank liquid; these non-conductive particles are adsorbed on the surface of the board, which may cause electroplating pits of different degrees for subsequent electroplating.
The acid copper electroplating tank itself may have the following aspects: the air blast tube deviates from the original position, and the air is agitated unevenly; 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 cores, and the treatment is not thorough. The anti-static treatment agent used in the cotton core manufacturing process contaminates the bath liquid and causes plating leakage. 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: mainly due to polishing agent or maintenance problems, and sometimes it may be cleaning problems after acid degreasing. Micro-etching problem.
Misalignment of the brightening agent in the copper cylinder, serious organic pollution, and excessive bath temperature may be caused. Acidic degreasing generally does not have cleaning problems, but if the water has a slightly acid pH value and more organic matter, especially the recycling water washing, it may cause poor cleaning and uneven micro-etching; micro-etching mainly considers excessive micro-etching agent content Low, high copper content in the micro-etching solution, low bath temperature, etc., 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 contaminated, and the board surface may be contaminated after treatment. There will be slight 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, and it will also cause uneven color of the plate surface; in addition, the plate surface is in contact with the anode bag, and the anode conduction is uneven. , Anode passivation and other conditions can also cause such defects.