Copper plating is the most widely used in order to improve the binding force of the coating and a pre-coating, copper plating is an important protective decorative coating copper/nickel/chromium system components, flexible and low porosity of copper plating, to improve the binding force and corrosion resistance between the coating plays an important role. Copper plating is also used for local carburizing, metallization of printed board holes, and as a surface layer for printing rollers. 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.
First, acid copper plating common problems
Copper sulfate plating plays a very important role in PCB plating, copper acid plating directly affects the quality of electroplated copper layer and related mechanical properties, and has a certain impact on subsequent processing, so how to control the quality of copper acid plating is an important part of PCB plating, and it is also one of the more difficult processes for many large factories to control the process. The common problems of copper acid plating are mainly as follows: 1. Rough plating; 2. Electroplating (plate surface) copper particles; 3. Plating pits; 4. The board is white or uneven in color. In view of the above problems, some summaries are made, and some brief analysis solutions and preventive measures are carried out.
1. rough plating
Generally, the plate Angle is rough, most of which is caused by the electroplating current. The current can be lowered and the card meter can be used to check whether the current is abnormal. The whole board is rough, generally will not appear, but the author also met once in the customer, and later found out that the winter temperature was low and the light content was insufficient; There are also sometimes some reworked film board surface treatment is not clean will also appear in a similar situation.
2. plating plate surface copper particles
There are many factors that cause the production of copper particles on the surface of the plate, from the whole process of sinking copper, pattern transfer, electroplating copper itself is possible. I have met in a state-owned factory, caused by sinking copper plate copper particles.
Surface copper particles caused by the copper sinking process may be caused by any of the copper sinking processing steps. Alkaline oil removal in the water quality hardness is higher, more drilling dust (especially the double panel without rubber removal slag) poor filtration, not only will cause rough surface, but also cause rough hole; However, generally it will only cause roughness in the hole, and the slight spot dirt micro-erosion on the plate surface can also be removed; There are mainly several cases of microcorrosion: the use of microcorrosion agent hydrogen peroxide or sulfuric acid quality is too poor or ammonium persulfate (sodium) impurities are too high, it is generally recommended that at least CP grade, industrial grade in addition to cause other quality failures; The high copper content or low temperature in the micro-etching chamber results in the slow precipitation of copper sulfate crystals. The tank liquid is cloudy and polluted. Most of the activation liquid is caused by pollution or improper maintenance, such as filter pump leakage, the specific gravity of the tank is low, and the copper content is high (the activation cylinder is used for too long, more than 3 years), which will produce granular suspension or impurity colloids in the tank, adsorbed on the surface or the wall of the hole, at this time, it will be accompanied by the production of rough in the hole. Degluing or acceleration: the use time of the tank liquid is too long and there is turbidity, because most of the degluing liquid is now formulated with fluoroboric acid, so that it will attack the glass fiber in FR-4, resulting in the rise of silicate and calcium salt in the tank, and the increase of copper content and soluble tin in the tank will cause the production of copper particles on the surface of the plate. The copper sink itself is mainly caused by the strong activity of the tank liquid, the dust stirred by the air, the small particles suspended in the tank liquid, etc., which can be effectively solved by adjusting the process parameters, adding or replacing the air filter element, and the whole tank filtration. The dilute acid tank temporarily storing the copper plate after copper sedimentation should be kept clean and replaced in time when the tank is cloudy. The storage time of the copper plate should not be too long, otherwise the surface is easy to oxidize, even in an acidic solution, and the oxide film is more difficult to dispose of after oxidation, so the surface will also produce copper particles. The copper particles on the surface of the plate, in addition to the oxidation of the surface, are generally distributed more evenly on the surface, with strong regularity, and the pollution generated here, whether conductive or not, will result in the production of copper particles on the surface of the electroplating copper plate. Some small test plates can be used for step by step treatment and control judgment, and the on-site fault plate can be solved with a soft brush. Graphic transfer process: development of excess glue (extremely thin residual film can also be plated and coated), or cleaning after development is not clean, or the board is placed for too long after the graphic transfer, resulting in different degrees of oxidation of the board, especially under poor cleaning conditions or storage workshop air pollution. The solution is to strengthen water washing, strengthen the plan to arrange the progress, and strengthen the acid degreasing strength.
The acid copper plating bath itself, at this time its pre-treatment, generally will not cause copper particles on the surface of the plate, because the non-conductive particles will at most cause plate plating or pits. The reasons for copper cylinder to cause copper particles on the plate surface can be summarized in several aspects: tank parameter maintenance, production operation, material and process maintenance. In terms of tank parameter maintenance, the content of sulfuric acid is too high, the content of copper is too low, the temperature of the tank is too low or too high, especially in the factory without temperature control cooling system, the current density of the tank will decrease. According to normal production process operation, copper powder may be produced in the tank and mixed into the tank.
In terms of production operation, the current is too large, the splint is bad, the empty pinch point, the plate in the groove dissolving against the anode, etc., will also cause the current of some plates to be too large, resulting in copper powder, falling into the groove liquid, and gradually resulting in copper particle failure; In terms of materials, the main problems are the content of phosphorus and the uniformity of phosphorus distribution. In terms of production and maintenance, it is mainly a large treatment, when the copper Angle is added, it falls into the slot, mainly during the large treatment, anode cleaning and anode bag cleaning, many factories are not handled well, there are some hidden dangers. The surface of the copper ball should be cleaned and the fresh copper surface should be eroded with hydrogen peroxide, and the anode bag should be soaked with hydrogen sulfate and lalkali, and cleaned, especially the anode bag should use a 5-10 micron gap PP filter bag.
3. plating pits
This defect also causes many processes, from copper sinking, pattern transfer, to pre-plating treatment, copper plating and tin plating. The main cause of copper sinking is that the copper sinking hanging basket is poorly cleaned for a long time, and the pollution liquid containing palladium copper will drop from the hanging basket on the surface of the plate during micro-corrosion, forming pollution, and causing spot leakage plating or pits after the copper sinking plate is electric. The graphics transfer process is mainly caused by poor equipment maintenance and development cleaning, and there are many reasons: the brush roller suction rod pollution glue stains, blow drying section of the air knife fan internal organs, oil dust, etc., the surface of the board film or improper dust removal before printing, the development of the developer is not clean, poor washing after development, and the anti-foaming agent containing silicon contaminate the surface. Pre-plating treatment, because whether it is acid degreasing agent, micro-corrosion, pre-leaching, the main component of the bath has sulfuric acid, so when the water hardness is high, there will be turbidity and pollution of the surface; In addition, some companies have poor adhesive packaging, and for a long time, the adhesive will be found to dissolve and spread at night in the tank, polluting the tank liquid; These non-conductive particles are adsorbed on the surface of the plate, which may cause different degrees of plating pits for subsequent electroplating.
4. The board is white or uneven in color
The copper acid plating bath itself may have the following aspects: the blowpipe deviates from the original position, and the air is stirred unevenly; Filter pump air leakage or liquid inlet near the air blast pipe suction air, produce a fine air bubble, adsorbed on the surface or line edge, especially the transverse line edge, line corner; In addition, there may be a point that the use of poor quality cotton core, the treatment is not thorough, the anti-static treatment agent used in the process of cotton core manufacturing polluted the tank liquid, resulting in leakage plating, this situation can increase the air, the liquid surface foam can be cleaned up in time, the cotton core after the application of acid and alkali soaking, the color of the board is white or uneven: It is mainly a light agent or maintenance problem, and sometimes it may be a cleaning problem after acidic oil removal, and a micro-corrosion problem. The imbalance of copper cylinder polish, serious organic pollution, and excessive bath temperature may cause it. Acid oil removal generally does not have cleaning problems, but if the PH value of the water is acidic and there are more organic matter, especially recycling water washing, it may cause poor cleaning and uneven micro-erosion; The main consideration of micro-corrosion is that the content of micro-corrosion agent is too low, the copper content in the micro-corrosion liquid is too high, and the temperature of the bath is low, which will also cause the micro-corrosion of the plate surface is not uniform; In addition, the quality of the cleaning water is poor, the washing time is a little longer or the pre-leaching acid pollution, the plate surface may be slightly oxidized after treatment, in the copper bath plating, because it is acidic oxidation and the plate is charged into the tank, the oxide is difficult to remove, but also cause the uneven color of the plate; In addition, the plate surface contact with the anode bag, uneven anode conduction, anode passivation and other conditions will also cause such defects.
Some common problems in acid copper plating process are summarized in this paper. At the same time, acidic copper plating process has been widely used because of its simple basic composition of solution, stable solution and high current efficiency, and the addition of appropriate brightener can obtain a coating with high brightness, high leveling and high uniform plating ability. The choice and application of copper acid brightener is also the key to the quality of acid copper plating. Therefore, it is hoped that the majority of staff can accumulate experience in daily work, not only to find solutions to problems, but also to innovate and fundamentally improve the level of technology.
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