Analysis and solution and preventive measures of copper fault in PCB plate plating

- Nov 17, 2018-

Analysis and solution and preventive measures of copper fault in PCB plate plating

Copper sulfate plating occupy very important position in PCB plating, acid copper plating quality directly affect the quality of the PCB board plating copper layer system and related mechanical properties, impact and the subsequent processing, so how to control the quality of the good acid copper electroplating is an important part of the PCB plating, also is one of many companies process control more difficult to process.Based on several years of experience in electroplating and technical services, the author summarizes the following preliminarily, hoping to enlighten the electroplating industry in PCB industry.The common problems of copper acid plating are as follows: 1.Rough plating;2.Electroplated (panel) copper particles;3.Electroplating pits;4.The board is white or uneven in color.In view of the above problems, some summaries were made, and some brief analysis and solutions and preventive measures were carried out.

Rough electroplating: generally rough plate Angle, most of which is caused by excessive electroplating current, can lower the current and check the current display with a card.The board is rough, which will not appear generally, but I have encountered it once in the customer's place. Later, it was found that the temperature was low in winter and the content of light agent was insufficient.There are also some rework of the surface of the laminated plate surface treatment is not clean can appear similar situation.

Plate copper granule: there are many factors causing the production of plate copper granule. It is possible for PCB plate to electroplate copper in the whole process of transferring from heavy copper to graphics.The author encountered in a state-owned large factory, caused by heavy copper plate copper grains.

The copper granules on the board caused by the copper precipitation process may be caused by any of the copper precipitation processing steps.When the alkaline oil removal is hard in the water quality, and the drilling dust is more (especially when the double panel does not go through the glue removal slag), the poor filtration will not only cause the surface of the board to be rough, but also cause the roughness in the hole.However, it can only cause rough hole, and slight spot corrosion on the surface can be removed.There are mainly several cases of microcorrosion: the quality of peroxide solution or sulfuric acid is too poor or the impurity of ammonium persulfate (sodium persulfate) is too high. It is generally recommended to be at least CP level. Besides, industrial level, other quality failures will be caused.The copper content in microetching groove is too high or the temperature is too low.The tank is turbid and polluted.Most of the activated liquid is caused by pollution or improper maintenance, such as leakage of the filter pump, low proportion of the tank and high content of copper (the activation cylinder has been used for a long time, more than 3 years). As a result, granular suspended material or impurity colloids will be generated in the tank, which will be absorbed on the surface of the board or hole wall.Dissolving or accelerating: the solution used for too long is turbid because most of the solution is made of fluoborate acid, which will attack the glass fiber in fr-4, resulting in increased silicate and calcium salts in the solution. In addition, increased copper content and tin dissolution in the solution of the solution will lead to the production of copper particles on the surface of the board.The copper sinking tank itself is mainly caused by the excessive activity of the tank fluid, dust stirring in the air, and more small particles suspended in the solid in the tank fluid. It can be effectively solved by adjusting the process parameters, adding or replacing the air filter core and the whole tank filtration.The dilute acid tank of the copper sheet shall be temporarily stored after the copper is sunk. The tank liquid shall be kept clean. When the tank liquid is cloudy, it shall be replaced in time.Copper sheet should not be stored for too long, otherwise the surface of the plate is easy to oxidize, even in acidic solution will be oxidized, and oxidation film is more difficult to deal with after oxidation, so the surface of the plate will also produce copper particles.Said above made sink sink copper process of copper plate, in addition to the board face caused by oxide, generally on the board face distribution more uniform, strong regularity, and pollution from here, conductive or not cause PCB board copper electroplating copper surface grain production system, can be used when processing a small test plate individually contrast judgement step by step, for field failure boards can be solved with a soft brush gently brush can;Figure transfer process: the development superglue (extremely thin residual film plating can also be plated and coated), or the cleaning is not clean after the development, or the board parts are placed for too long after the figure transfer, resulting in different degrees of oxidation of the board surface, especially under poor cleaning conditions or heavy air pollution in the storage workshop.The solution is to strengthen water washing, strengthen planning schedule, and strengthen the strength of acid oil removal.

The copper acid electroplating bath itself, at this time its pretreatment, generally will not cause the plate surface copper grains, because the non-conductive particles most cause the plate surface leakage or pit.The cause of the copper cylinder causing the copper particles on the surface of the plate can be summarized as follows: tank parameter maintenance, production operation, materials and process maintenance.The maintenance of tank liquid parameters includes too high sulfuric acid content, too low copper content, low or too high temperature of tank liquid, especially the factory without temperature control cooling system. At this time, the current density range of the tank liquid will drop. According to normal production process, copper powder may be produced in the tank liquid and mixed into the tank liquid.

In the production operation, the current is too large, the splint is not good, the empty clamping point, the plate falling in the groove and being dissolved by the anode, etc., will also lead to excessive current in some parts of the plate, producing copper powder, falling into the groove liquid, gradually causing copper grain failure.The content and distribution uniformity of phosphorus are the main problems in materials.The production and maintenance aspect is mainly the big treatment. When the copper Angle is added, it falls into the groove. When it is the big treatment, the anode cleaning and the anode bag are cleaned.For the large treatment of copper ball, the surface should be cleaned and the fresh copper surface should be slightly etched with hydrogen peroxide. The anode bag should be soaked successively with hydrogen peroxide and alkali solution, and cleaned, especially the anode bag should be filled with PP filter bag with a gap of 5-10 microns.

Electroplating potholes: this defect also causes a number of processes, from sinking copper, pattern transfer, to preplating, copper plating, and tin plating.The main cause of copper sinking is poor long-term cleaning of the copper sinking basket. During microerosion, the pollution liquid containing palladium copper will drop on the board surface from the basket, forming pollution.Graphics transfer process mainly due to equipment maintenance and developing the poor, the reason a lot: brush machine brush roll stick glue stains pollution water, dry drying period of air knife fan internal organs, such as greasy dust, board face sticker or improper cleaning before printing, not net developing machine development, enhancement after washing, containing silicon defoamer pollution board face, etc.Before electroplating, because sulfuric acid is the main component in acidic oil remover, microetching, presoaking and bath liquor. Therefore, when the water quality is higher in hardness, turbidity will appear and contaminate the board surface.In addition, some companies have poor adhesives for hanging, which will be found to be dissolved and diffused in the tank at night and contaminate the tank solution.These non-conductive particles are adsorbed on the surface of the plate, which may lead to different degrees of electroplating pits for subsequent electroplating.The copper acid electroplating bath itself may be the following aspects: the air tube deviates from the original position, and the air is not evenly stirred;The air leakage of the filter pump or the intake port is close to the air blower tube and the air bubble is generated, which is absorbed on the board surface or the line edge, especially the horizontal line edge and line Angle.Additionally there may be a little is used inferior cotton core, processing is not complete, cotton core used in the manufacturing process of anti-static treatment bath pollution, cause plating leakage, this kind of circumstance can increase the pep, foam liquid surface can be cleaned in time, after the sour alkali soak cotton core application, board face uneven color white or color: mostly light agent or maintenance issues, sometimes after acidic degreasing cleaning might be the problem, the corrosion problem.Copper cylinder photoagent imbalance, serious organic pollution, tank temperature may be too high.Acidic oil removal generally will not have cleaning problems, but if the water PH value is relatively acidic and there are more organic matters, especially recycling water washing, it may cause poor cleaning and uneven microerosion.Microcorrosion mainly considers that the content of microetching agent is too low, the content of copper in the microetching solution is too high, the temperature of the bath liquid is low and so on, which will also cause the non-uniform microetching on the surface.In addition, the quality of cleaning water is poor, the washing time is longer or the pre-soaking acid solution is polluted, and the board surface may have slight oxidation after treatment. When the copper bath is electroplated, the oxide is difficult to remove because of the acidic oxidation and the board parts are charged into the groove, which also leads to uneven color of the board surface.In addition, the plate contact with the anode bag, non-uniform conduction of the anode, and passivation of the anode will also cause such defects.