Improve pits of PCB circuit board plating surface

As the PCB circuit board line production of fine line open circuit in the making problem become the important factor of affecting the product percent of pass, usually for line qualification rate of improvement action will consider the dry film adhesion, exposure energy etc, from the point of view of the whole system production, after plating board face itself is the flatness of influence line yield a fundamental and direct reasons. For filling orifice plate adopt vertical continuous plating, surface pit is the main problem point, potholes in the graphics area will lead to much line holes, such as bad degreasing pits size in 50 um fluctuates up and down. For 4 mil line impact is not big, but for the influence of 3 mil line will be highlighted. The phenomenon has become more and more cause the attention of the circuit board factory. Therefore, this article embarks from the improved pits of plating surface defects, in order to improve the line production percent of pass is focus, through process improvement, process for vertical continuous plating solution panel pits effects of line production. There are many reasons that cause the pits of PCB PCB board face, such as surface plating, pinhole, scratches, etc. , through collection and classification of defects, such as table 1 and chart 1, you can see the different proportion of defects in the pits of distribution. PCB circuit boards PCB PCB electroplating electroplating 1 according to the above defect ratio analysis, plating resistance is the main cause of depressions. Prior to improve surface is mainly for the obvious stuff, but still had a higher proportion of pit, further analysis that the current is the most likely cause of surface plating resistance before plating board face of organic matter pollution, including the introduction of fat ( The introduction of fingerprints, for example) And mineral oils ( Such as conductive oil) Is introduced, including fabrication process of the adsorption on the surface of organic material, and the organic matter contribution to line the gap of the break line may be hidden, and more. Is the most likely source of PTH process chemicals mixed between chemical copper is difficult to remove. PTH copper tank liquid contains complexing agent ( EDTA） And stabilizer ( Pyridine) Such as material. These substances are compared with copper ions have a strong reaction, adsorption removal is difficult, after the board face only in alkaline environment have a higher solubility. Since cannot avoid PCB board face organic material to produce, so we need to reduce the content of organic material in the working procedures. Also therefore had introduced the idea of alkaline except oil before plating. 1. The introduction of the alkaline degreasing treatment before plating basic usually use acidic degreasing system, because the electroplating potions are acidic system, few people use alkaline degreasing. But through the analysis shows that compared with VCP plating pretreatment acid in addition to oil, alkaline degreasing decontamination ability is better, the PTH chemical residues and contamination of oil removal in the process of PCB copy ability is stronger, and we have hot water to wash the VCP line behind the oil removal and acid leaching, this can ensure the alkaline degreasing before entering the plating bath liquid can completely clean, not pollution bath, in addition to the oil relative to acidic alkaline degreasing not chemical sink copper corrosion of PTH better chemical sink copper intact, so choose the alkaline degreasing. The composition and function of contrast in the following table: PCB circuit board 2. Test 2. To upper, degassing and alkaline degreasing ( Acidic degreasing) 2. 2 test results using two batches of test board, Panel1 and Panel2 after pretreatment with alkali degreasing ways to check the line production yield, get the result in the chart 2. Difficulty of PCB circuit board 2 Panel1 and Panel2 line is different, so the number of defects have obvious difference. Look from the data shown in chart 2, using alkaline degreasing, bolt hole defect improved significantly, compared with acidic degreasing, basic degreasing can effectively will be decreased by more than 70% defect rate. In addition, the test also compares the oil removal concentration 5% and 7. 5% state processing panel line defect rate, 45% and 35%, respectively, found that in addition to high concentrations of oil are improved with respect to the reduction of defects. Production application in a vertical continuous plating line try using alkaline degreasing instead of the original acid oil removal, and statistics the June to December, an online production of PCB circuit board two levels of the line gap break line defects. Line gap break line defect rate from table 3 and the trend of the defects of the chart 4 can see since August after alkaline degreasing before treatment, the type of circuit board gap break line defects have significant decline. Because VCP1 # line change before handling liquid to improve the disconnection, gap's success, therefore, the alkaline except oil application and promotion to all the vertical continuous plating line before processing. 4. Conclusion after plating board face pits will directly cause the process line break gap, and plating resistance is the main cause of depressions, through the analysis of the former process surface adsorption grease and other organic material, and the organic impurities in oil acid in addition to the original agent cannot clear, plating resistance of the plate. Use of alkaline agent can effectively dissolve in addition to the plate of organic matter, experiments show that compared with acidic degreasing, using alkaline except oil can line defect rate fell by more than 70%, after the pretreatment methods to the production line, through the SPC monitoring, line production defect found after pretreatment method changes obviously decline. Has been used widely in various vertical continuous plating line alkaline degreasing. After the follow-up will also continue to monitor the alkaline degreasing line production effect, this improvement initiatives believe is stable to improve line makes more refined PCB circuit board product percent of pass of a shortcut.

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