PCB circuit board electroplating surface pit improvement

　　With the improvement of PCB circuit board circuit production, the open and short circuit problem in circuit production has become an important factor affecting the product qualification rate. Usually, the improvement of the circuit qualification rate will take into account the dry film adhesion, exposure energy and other factors. From the perspective of the production of the entire system, the flatness of the plate surface itself after electroplating is a fundamental and direct cause that affects the line yield.

　　For the hole-filling plate with vertical continuous electroplating, the pits on the board surface are the main problem. The pits in the pattern area will largely lead to the opening of the circuit. For example, the size of the poorly degreasing pit fluctuates up to 50um. It has little effect on the 4mil line, but the effect on the 3mil line will be prominent. This phenomenon is now attracting more and more attention from circuit board manufacturers. Therefore, this article starts from improving the surface pit defects of electroplating to improve the yield rate of the circuit production. Through the process improvement of the vertical continuous electroplating process, the adverse effect of the surface pits on the circuit production is solved.

　　There are many reasons for the pits on the PCB circuit board, such as anti-plating on the board, pinholes, scratches, etc. Through the collection and classification of defects, such as Table 1 and Chart 1, you can see the proportional distribution of different pits. .

　　PCB circuit board plating

　　PCB circuit board plating 1

　　According to the above defect ratio analysis, anti-plating is the main cause of pits. The initial improvement was mainly carried out for the obvious impurities on the surface, but there is still a relatively high proportion of pits. Further analysis shows that the most likely factor that causes the plate surface to resist plating is the organic matter pollution on the plate surface before electroplating, including the external introduction Grease (such as fingerprints), mineral grease (such as conductive oil), and organic substances absorbed on the board surface introduced by the previous process, and the contribution of these organic substances to the gap and disconnection of the circuit may be more concealed and larger . The most likely source is that the chemical inclusions in the PTH process are difficult to remove between the chemical copper.

　　"PTH copper bath solution contains complexing agent (EDTA), stabilizer (pyridine) and other substances. These substances all have a relatively strong force with copper ions, and it is difficult to remove them after being adsorbed on the surface of the board. Only in an alkaline environment can they have relatively high solubility.

　　Since the production of organic substances on the PCB board surface cannot be avoided, then we need to reduce the content of organic substances in the post-process processing. This also led to the idea of introducing an alkaline degreaser before electroplating.

　　1. Introduction of alkaline degreasing

　　Usually, acid degreasing system is basically used in electroplating pretreatment, because electroplating chemicals are all acid systems, and few people use alkaline degreasing. However, through analysis, it can be seen that compared with the acidic degreasing agent for VCP electroplating pretreatment, the alkaline degreasing and decontamination ability is better, and the PTH chemical residue and the contaminated oil stains in the circuit board handling process are stronger. The VCP line has hot water washing and acid immersion after degreasing, which can completely ensure that the alkaline degreasing can be completely cleaned before entering the electroplating bath, and will not pollute the bath. In addition, the alkaline degreasing will not be compared with the acid degreasing. The corrosion of PTH electroless copper is better to ensure the integrity of electroless copper, so alkaline degreasing is selected.

　　The composition and effect of the two are compared as shown in the table below:

　　PCB circuit board

　　2. Test test

　　2.1 Test process design

　　…→Upper plate→Degassing→Alkaline degreasing (acid degreasing)→DI washing→pickling→pre-plating→DI washing→micro-etching→DI washing→…

　　2.2 Test results

　　Two batches of test boards are used, Panel1 and Panel2 are respectively pre-treated with acid-base degreasing method, and then checked the yield rate of the circuit production, and the results in Chart 2 are obtained.

　　PCB circuit board 2

　　Panel1 and Panel2 have different wiring difficulties, so there is a significant difference in the number of defects between the two.

　　From the data shown in Chart 2, after using alkaline degreasing, the defect of broken wire gap is significantly improved. Compared with acid degreasing, alkaline degreasing can effectively reduce the defect rate by more than 70%.

　　In addition, the test also compared the defect rate of the board and circuit production under the state of degreasing concentration of 5% and 7.5%, which were 45% and 35%, respectively. It was found that the high concentration of degreasing liquid improved the reduction of defects.

　　3. Production application

　　Tried to use alkaline degreasing instead of acid degreasing on a vertical continuous electroplating line. At the same time, it also counted the defect rate of two-level line gap disconnection of an online production PCB circuit board from June to December.

　　Line gap broken wire defect rate

　　It can be seen from the change trend of the defect rate in Chart 3 and Chart 4 that since the beginning of the alkaline degreasing pre-treatment in August, the defect rate of the notch disconnection of this type of circuit board has decreased significantly.

　　Due to the success of replacing the pre-treatment liquid on the VCP1# line to improve the disconnection and gap, the alkaline degreasing agent was applied and extended to the pre-treatment of all vertical continuous electroplating lines.

　　4 Conclusion

　　The pits on the plate surface after electroplating will directly cause the disconnection gaps in the circuit production of the subsequent process, and the anti-plating is the main cause of the pits. Through analysis, the plate surface will adsorb grease and other organic substances in the previous process, and these organic impurities are in the original process. There are acidic degreasing agents that cannot be removed, causing the plate surface to resist plating. The use of alkaline degreasing agent can effectively dissolve the organic matter on the board surface. Experiments show that compared with acid degreasing, the use of alkaline degreasing agent can reduce the line defect rate by more than 70%. This pretreatment method is extended to the back of the production line. , Through SPC monitoring, it was found that the line manufacturing defects had a significant downward trend after the pre-processing method was changed. Alkaline degreasing has been promoted in all vertical continuous electroplating lines. In the future, we will continue to monitor the effect of circuit production after alkaline degreasing. This improvement measure is believed to be a shortcut to steadily improve the qualification rate of PCB circuit board products with increasingly refined circuit production.

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