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Copper sulfate plating process common problems and solutions
Electroplated copper is the most widely used preplating layer for improving the bond strength of the coating. The copper coating is an important component of the protective decorative coating copper/nickel/chromium system. The flexible and low porosity copper plating is The adhesion and corrosion resistance between the coatings play an important role. The copper plating is also used for localized carburization, metallization of the printed board holes, and as a surface layer of the printing roller. The chemically treated color copper layer, coated with an organic film, can also be used for decoration. In this article we will discuss the common problems encountered in the PCB process with electroplating copper and their solutions.


I. Acid copper plating FAQ

Copper sulfate electroplating occupies an extremely important position in PCB electroplating. The quality of electroplated copper plating directly affects the quality and relevant mechanical properties of the electroplated copper layer, and has a certain influence on subsequent processing. Therefore, how to control the quality of the electroplated copper plating is good. An important part of PCB electroplating is also one of the more difficult process controls for many manufacturers. Acid copper plating common problems, mainly in the following: 1, electroplating rough; 2, electroplating (plate surface) copper particles; 3, electroplating pits; 4, surface whitish or uneven color. In response to the above issues, some conclusions were made and some brief analysis, resolution, and preventive measures were carried out.


1, rough plating


The general board angle is rough, most of which are caused by the plating current is too large, you can turn down the current and check the current display with the card table for any abnormalities; the whole board is rough and generally does not appear, but the author also met once at the customer's office, and later checked At that time, when the temperature in winter was low, the amount of photo-agents was insufficient; sometimes there were similar situations where some of the reworked decals were not clean on the board surface.


2, electroplated copper plate


There are many factors that cause the production of copper particles on the board surface. From the process of sinking the copper and transferring the pattern, electroplating copper itself is possible. The author encountered a large state-owned factory, and the surface copper particles caused by sink copper.


Plating copper particles caused by the sinker copper process may be caused by any sinking copper processing step. Alkaline degreasing has higher hardness in water and more dust in drill holes (especially when the double-sided panel is not removed by the rubber slag). It will not only cause rough surface of the board, but also cause the hole to be rough; but generally it will only cause holes. Rough inner surface, slight point-like dirt micro-etching on the board surface can also be removed; there are several cases of micro-etching: the use of micro-etching agent hydrogen peroxide or sulfuric acid quality is too bad or ammonium persulfate (sodium) impurities are too high, generally It is recommended that it should be at least CP grade, and industrial grades in addition will cause other quality failures; the copper content in the microetching tank is too high or the temperature is too low to cause the slow precipitation of copper sulfate crystals; the bath fluid is turbid and polluted.


The majority of the activation fluid is caused by pollution or improper maintenance, such as leakage of the filter pump, low specific gravity of the bath, and high copper content (activation cylinder is used for more than 3 years). This will produce particulate suspended solids in the bath. Or impurities colloids, adsorbed on the surface of the board or hole, this time will be accompanied by the production of rough holes. Dissolving or accelerating: The turbidity of the bath is too long, because most of the solution is now formulated with fluoboric acid, so that it will attack the glass fibers in the FR-4, resulting in silicates and calcium salts in the bath. High, in addition to the increase in copper content in the bath and the amount of dissolved tin will cause the formation of copper particles on the surface.


The sink copper bath itself is mainly due to the strong activity of the bath liquid, the dust in the air, the small particles suspended in the bath liquid, etc., which can be adjusted by adding or replacing the air filter element, the entire tank filter, etc. Effective solution. After the sinking of copper, temporarily store the dilute acid tank of the copper plate, the bath must be kept clean, and the bath should be promptly replaced when it is cloudy. Immersion copper plate storage time should not be too long, otherwise the plate surface is easily oxidized, even in acidic solution will also be oxidized, and oxide film is more difficult to deal with, so that the board surface will also produce copper particles.


The above-mentioned copper deposits on the surface of the copper sinking process, in addition to the oxidation caused on the surface of the slab, are generally evenly distributed on the surface of the slab and have a strong regularity, and the pollution generated here is conductive regardless of conductivity. Electroplated copper plate surface copper particles, processing can be used when a small test plate step by step separately to determine the control, for the site of the fault board can be resolved with a soft brush light brush; graphics transfer process: the development of more than adhesive (a very thin residual film Plating can also be coated and coated), or the cleaning after cleaning is not clean, or the board is placed in the graphics transfer time is too long, resulting in different degrees of oxidation of the board surface, especially in the case of bad board cleaning or storage When the air pollution in the workshop is heavy. The solution is to intensify washing, strengthen the schedule of the plan, and strengthen the acid degreasing intensity.


Acid copper plating bath itself, at this time its pre-treatment, generally does not cause the board surface copper particles, because the non-conductive particles cause plate surface leakage plating or pits. Causes of the copper crock caused by the copper on the surface of the board can be summarized in several aspects: the maintenance of bath parameters, production operations, materials and process maintenance. The maintenance of bath parameters includes high sulfuric acid content, too low copper content, and low or high bath temperature. In particular, there is no factory with a temperature-controlled cooling system, which will cause the current density range of the bath fluid to fall, according to the normal production process. The operation may produce copper powder in the bath and mix in the bath.


In the production operation, when the current is high, the current is too large, the splint is bad, the empty pinch point, and the falling plate of the slot is dissolved by the anode. This also causes the current of some plates to be too large, resulting in copper powder, falling into the bath, and gradually producing copper particles. Material is mainly phosphorus copper phosphorus content and phosphorus distribution uniformity problems; production and maintenance is mainly a large deal, when the copper angle is dropped into the tank, mainly when large processing, anode cleaning and anode bag cleaning, many factories It is not handled well and there are some hidden dangers. The treatment of large copper balls is to clean the surface and microetch the fresh copper surface with hydrogen peroxide. The anode bag should be soaked with sulfuric acid hydrogen peroxide and caustic soda, cleaned, especially the anode bag should use 5-10 micron gap PP filter bag. .


3, electroplating pits


The process caused by this defect is also more, from sink copper, pattern transfer, to electroplating pretreatment, copper plating and tin plating. The main cause of sinking copper is the long-term cleaning of the sinking copper hanging basket. During the micro-etching, the pollution liquid containing palladium and copper will drip from the hanging basket onto the surface of the board to form pollution. After the sinking copper board is electrically charged, it will cause point-leakage plating. Pits. The pattern transfer process is mainly due to equipment maintenance and poor development and cleaning. There are many reasons: the brush roller's roller sucker sticks to contaminate the rubber stains, blow dry the air knife fan's internal organs, there are oil dust, etc., and remove dust on the board surface or before printing. Improper development of the developer is not clean, poor water washing after development, silicon defoamer contamination of the board surface and so on.


Pre-plating treatment, because whether it is acidic degreasing agent, micro-etching, pre-soaking, the main components of the bath have sulfuric acid, so the water hardness is high, there will be turbidity, contamination of the board; In addition, some companies hang bad rubber package For a long time, it will be found that the encapsulated plastic will dissolve and diffuse in the tank at night, contaminating the bath fluid; these non-conductive particles are adsorbed on the surface of the plate and may cause different levels of electroplating pits for subsequent electroplating.


4, the board surface or uneven color


Acid copper plating tank itself may be the following aspects: the air tube deviation from the original location, uneven air mixing; filter pump leakage or air inlet near the air intake tube to produce air, resulting in fine air bubbles, adsorbed on the board or line, In particular, horizontal lines or corners; another point may be the use of inferior wicks, which are not handled thoroughly. The antistatic agent used in the manufacturing process of the wicks contaminates the baths, resulting in leakage plating. This can be added. Drums, the liquid surface foam can be cleaned in time, the soaking of acid and alkali in the Wick, the board surface color white or uneven color: the main light or maintenance problems, and sometimes it may be acidic oil cleaning problems, Micro-etching problem. The copper cylinder is misaligned, organic pollution is serious, and bath temperature may be too high.


Acidic degreasing generally does not have cleaning problems, but if the pH of the water is acidic and the organic matter is relatively high, especially for recycling, it may cause poor cleaning and inhomogeneous micro-etching; the micro-etching mainly considers the content of the micro-etching agent. Low, high copper content in the microetching solution, low bath temperature, etc., can also cause uneven microetching on the board surface; in addition, poor cleaning water quality, slightly longer washing time, or contamination with pre-soaked acid, may occur after treatment. There will be a slight oxidation, in the copper plating, because it is acidic oxidation and the plate is charged into the groove, the oxide is difficult to remove, can also cause uneven board color; In addition the board surface contact with the anode bag, the anode conductive uneven , anode passivation and other conditions will also cause such defects.


Second, the conclusion

This article summarizes some of the common problems in acid copper plating processes. At the same time, the acidic copper plating process is widely used due to its simple basic composition, stable solution, and high current efficiency, and the addition of an appropriate brightener to obtain a coating with high brightness, high leveling, and high throwing power. The quality of the acidic copper plating layer also lies in the selection and application of acid copper brighteners. Therefore, it is hoped that the majority of staff can accumulate experience in their daily work, not only to find solutions to problems, but also to fundamentally improve the technological level of innovation.