PCB Blog - Defects and Troubleshooting of Pattern Electroplating Copper in PCB Board

With the increasingly fierce competition in the industry, manufacturers of printed circuit boards continue to reduce costs to improve product quality, pursue zero defects, and win with high quality and low price.

1. Defect features and causes
2.1 Coating pitting
Pockmarks appear on the patterned copper electroplating, which are more prominent in the middle of the board. After the lead and tin are withdrawn, the copper surface is uneven and the appearance is not good. After the brush board is cleaned, the surface pitting still exists, but it is basically smoothed and not as obvious as after the tin is removed. After this phenomenon appeared, the problem of electroplating copper solution was first thought, because the solution was treated with activated carbon the day before the failure occurred. The steps are as follows:

1) Add 2 liters of H2O2 under stirring conditions;
2) After fully stirring, transfer the solution to a standby tank, add 4 kg of activated carbon fine powder, and add air to stir for 2 hours, then turn off the stirring and let the solution settle. It was found from the investigation that the production line transferred the solution from the standby tank back to the working tank that night considering the allegro the next day. Settling activated carbon without adequate filtration, while transferring solution without circulating filter pump (slow) directly returns from the output of the working tank (coarse pipe, fast). Because the off-duty time has passed after the solution is transferred back to the working tank, the electroplating personnel do not have low current density empty plating treatment of the anode. Due to the urgency of scheduling, the electroplating personnel did not operate according to the procedures of the process document, and the solution was not fully circulated and filtered, resulting in mechanical impurities in the solution affecting the quality of the coating. Another factor is that after the phosphor copper anode is cleaned, it does not work directly through electrolytic treatment, and there is no time to form a black and uniform "phosphorus film" on the surface of the anode, resulting in a large accumulation of Cu+, and Cu+ hydrolysis to produce copper powder, resulting in rough and pitted coating. The dissolution of metallic copper is restricted by the control steps, and Cu+ cannot be rapidly oxidized to Cu2+. While the anodic film is not formed, the reaction of Cu-e.Cu2+ continues to proceed in a fast manner, resulting in the accumulation of Cu+, while Cu+ is unstable, and is disproportionated by disproportionation. Reaction: 2Cu+.Cu2+Cu, which will be deposited on the coating by electrophoresis during the electroplating process, affecting the quality of the coating. The anode film formed after the anode undergoes low-current electrolysis treatment can effectively control the dissolution rate of Cu, so that the anode current efficiency is close to the cathode current efficiency, and the copper ions in the plating solution are kept in balance, preventing the generation of Cu+ and maintaining the normal operation of the plating solution. The defect of electroplating copper this time also exposed some problems: the operator sometimes ignores the production procedure due to the relationship between time, working hours and production volume, which affects the quality of the product. Therefore, the production operation should be carried out in strict accordance with the process documents, and the illegal operation should not be carried out because of the tight production task and the short cycle. Otherwise, it will be reworked or scrapped due to quality problems, which will affect the product qualification rate, thereby affecting the production cycle and reducing credibility.
Troubleshooting: After finding out the cause, replace the filter element of the patterned copper electroplating solution to strengthen the filtration; in addition, an experimental board 500mm * 500mm is prepared to electrolyze the anodes of the 6 electroplating tanks respectively. In this way, the printed circuit board produced the next day is completely normal except for the defect of the plating pitting of the allegro produced.

1.2 Coating bloom (dendritic)
The surface of the patterned copper electroplating is flowery, especially on a large area of the coating, which is like a branch, with long and short. However, the plating area is small, and the PCB board with pads or thin lines to be plated has almost zero defects after electroplating on the same day, so the phenomenon of coating blooming at the beginning did not attract enough attention, and the betrayal was an accidental factor: PCB board, substrate problems, or brush marks from the pumice plastering machine before pattern transfer after hole metallization. Later, with the increase of production volume, the number of PCB surface flowers became more and more, especially the printed circuit board with the drawing number MON?_1, the size is 265mm * 290mm, the plating area A surface area is 2.35dm2, B The surface area is 4.48 dm2, and almost half of the entire PCB surface needs to be patterned with copper plating, so the phenomenon of pattern plating blooming can be seen at a glance, which seriously affects the appearance of the printed circuit board. A large number of defective PCB boards appear, and it is imperative to analyze the characteristics to find out the reasons and eliminate the faults completely. For this reason, in order to achieve customer satisfaction, the quality department of our center will intercept all the PCB boards with defective coatings: whether it is a large area of coating blooming, or filamentous traces on the lines. Quality is the life of an enterprise. Our technical department will explore the problems of the coating:
1) First of all, according to past experience, it is judged that there is a large amount of organic matter in the weak corrosion and pre-dipping solution of pattern plating pretreatment. Because the spraying and washing after degreasing may not be sufficient, the organic matter in the degreasing solution is brought into the working tank behind and selected as secondary pollution, and the adsorption of organic matter on the pattern to be plated on the PCB surface will affect the adsorption on the cathode. Thus affecting the appearance of the coating. According to this, the weak corrosion and pre-dip liquid were re-opened, and the printing defects in the production were reduced, but the phenomenon of the PCB surface blooming did not completely disappear. It seems that the previous experience did not fully take effect in this troubleshooting, and then the focus shifted: Could it be that there is a problem with the oil removal? Caused by the aging of the degreasing fluid and the unclean degreasing? Check that its temperature and composition are within the normal range. In order to find out the root cause of the defect as soon as possible, the Hall cell test was carried out: a small copper piece was mechanically brushed with charcoal and then rinsed as cathode electroplating. Because the sample is not degreasing, but is degreasing mechanically, there are still branch patterns, so it can be seen that degreasing cannot be the culprit of this failure.
2) After troubleshooting in the small experiment, add CL- and brightener FDT-1 to the working tank according to the proportion, after sufficient air stirring and circulating filtration, wipe the two bare copper plates of 350mm*350mm size and then remove the oil? Washed? Weak corrosion? Washed? Pickling? The pattern is electroplated with copper, and the pattern is electroplated without any defects after the normal resident process. So the production line continued to electroplating, and the printed circuit board electroplated the next day was completely normal. It can be seen that there are many reasons for the blooming of the coating: degreasing solution, weak corrosion solution, pre-dip solution, chloride ion concentration in the pattern copper electroplating solution and brightener FDT-1 all affect the quality of the coating. The inaccuracy of the chloride ion concentration analysis directly affects the adjustment of the solution; and the addition standard of the brightener FDT-1 "measurement of the conductivity of the plating tank by current integration" can no longer be used. The addition of the daily brightener FDT-1 is mainly combined with the Hall cell. Experiment and adjust for the day's workload. Only with the synergy of chloride ions and additives can an ideal coating be obtained. Strictly controlling the process parameters is the key to producing qualified products, otherwise any parameter out of control will lead to coating defects.

1.3 Hydrosphere traces on the coating
There are a lot of water circles on the electroplated copper of the printed circuit board pattern with larger size, especially the water circles around the holes are more prominent.
1) This phenomenon first led our thinking to water spray. Because the spray water circuit of the pattern electroplating line and the hole metallization line share a set of water circuit system, the solenoid valve of the individual spray pipe has failed, and the water can only be sprayed continuously. In this way, when the two lines work at the same time and need to be sprayed at the same time, the Insufficient pressure will directly affect the spray effect. For this reason, the printed circuit board with two sides and three poles was tested, and it was produced according to the normal procedure, except that a water pipe was connected to strengthen the water washing during spraying, and the water circle still existed after the pattern was electroplated with copper. From the analysis of defect characteristics, the defects on the electroplated copper surface are consistent with the traces of water droplets. It should be a problem of water washing. However, it has nothing to do with the water washing of the pattern electroplating line. Is it caused by the poor development and washing after the pattern is transferred?
2) Trace back to the source and find the waterway of the graphic transfer. It turned out that a Diansheng exposure machine newly purchased by our center adopts the water circulation cooling method, and its waterway and the washing section of the developing machine use the same waterway. When the exposure machine and the developing machine work at the same time, the spray pressure of the washing section of the developing machine is small; and the size of the PCB board is large, especially the water sprayed from the upper spray is easy to accumulate on the PCB board surface, which is not conducive to the circulation of the solution. In this way, the residual liquid of the dry film or wet film development of the photoresist is not fully rinsed. After the drying section, the watermark of the mucous membrane is not easy to be found in the subsequent repair work (unlike the residual glue with obvious blue film) ); It is not easy to remove the pattern before electroplating. After one hour of electroplating copper, the traces of the watermark are clearly identifiable and have a certain depth, which is not easy to be polished off and affects the appearance of the PCB surface. In order to confirm this conclusion, 10 printed circuit boards with 460mm*420mm drawing number Y005 were transferred and developed, 5 pieces were air-dried and sent directly to the pattern electroplating line, and the other 5 pieces were sent to the cleaning machine for cleaning without drying. Post-feed graphic plating line. After the same pretreatment and copper electroplating comparison, no water circle was found on the 5 printed circuit boards that were fully washed, while the 5 printed circuit boards that were directly sent to the pattern electroplating line after development could clearly see the water circle.
3) Troubleshooting: Transform the water circuit of the exposure machine so that it is separated from the water washing section of the developing machine; in addition, 3 rows of upper and lower spray pipes are added after the water washing section of the developing machine. Moreover, the lost and deactivated spray pipes on the pattern plating line are replaced. After the repair and modification, the pattern copper electroplating is of good quality.

1.4 Rough coating
The slight roughness of the coating on the surface of the PCB board can be removed by mechanical friction of the brushing machine. Serious surface unevenness or even roughness in the hole causes the hole to be small, which affects the welding and electrical performance and can only be scrapped. The reasons for the roughness of the coating are easy to find, such as excessive cathode current density, insufficient additives, low copper ion content, wrong pattern area (too large) or serious uneven distribution of pattern area. According to the specific situation of the printed circuit board, it is not difficult to find the reason for the rough coating. For example, if the whole batch of PCB boards is rough, the composition of the solution should be checked, and the Hall cell test should be used to determine whether the brightener is insufficient and whether the ammeter is faulty. If the coating of individual PCB boards is rough, first check the production records: whether the input of the plating level is correct, whether the current is too large, whether the graphic area on the processing sheet is too large, and whether the machine is faulty (the current is suddenly increased due to the instability of the ammeter). There are many kinds of information introduced, and troubleshooting is not difficult, so I won't repeat them here. It is worth noting that due to the design of some printed circuit boards, the distribution of electroplating patterns is seriously uneven, and there are only isolated pads or a few thin lines in some parts, while the area of other parts is too large, or the area of A/B surface is very different. In this way, even if the electroplating solution is good and all parameters are normal, defective products are prone to occur. Experience can refer to: 1) The current halving time is doubled, but this will reduce the production efficiency. 2) Using the method of accompany plating, find some leftovers to be plated together to improve the current distribution. 3) The current can be controlled separately for the large difference in the area of A/B surface.

1.5 Plating
Pattern electroplating copper infiltration causes irregular lines, reduced line spacing, and even short circuits in severe cases. Due to insufficient cleaning of the PCB surface (with oil stains or oxidation) and poor bonding with the resist; or there are pits on the film roller, dirty spots on the exposure machine, poor local contrast or dust on the production negative, all of which constitute the hidden danger of graphic electroplating. . Therefore, the cleaning process of the brush board before filming should not be ignored: the sulfuric acid (10%) in the pickling section is updated in time, the pressure of the brush roller is suitable, the high-pressure water washing is circulated and clean, and the drying temperature is moderate to ensure that the PCB surface is clean and dry. In addition, when laminating the film, adjust the pressure of the roller according to the thickness of the sheet, and select the appropriate temperature and speed. The quality of the film produced, the cleaning and maintenance of the exposure machine, and the environment of the clean room must be strictly controlled. Prevention of bleeding must control the production operation of the pattern transfer process, the quality of the photoresist and various process parameters. Ensure that the resist is intact during electroplating operations and select an appropriate current density. In this way, the phenomenon of seepage can be effectively avoided.

1.6 Layering
Another defect of patterned copper electroplating is copper/copper delamination. The obvious delamination is clear at a glance. If the coating adhesion is poor, stick it tightly with tape and then pull it up with force, and the weakly bonded coating will be adhered to the tape. Due to the poor adhesion of the blistering and delamination of the coating, it will partially fall off when the front plate is blocked, causing a hidden danger of short circuit, or because the concave surface is uneven with other graphic parts after the local lines are layered, there is a color difference after printing the obstacle (the color of the concave surface is dark), such defects are not acceptable to users. There are many factors that cause coating delamination.

2. Conclusion
Pattern copper electroplating is an important process in the production of printed circuit boards, and the quality of electroplating directly affects the appearance of printed circuit boards.