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78 PCB007 MAGAZINE I MARCH 2021 blame the etching operation for the condition shown in Figure 1? ere is further evidence in a section shown in Figure 2. As shown quite clearly in Figure 2, there was an issue related to the tin plating. ere is suffi- cient thickness of copper as the plating moves down the plated through-hole. When presented with this situation, the trou- bleshooting team should approach the prob- lem-solving exercise as follows: Available methodologies are the TQC PDCA process: Plan–Do–Check–Act; and the Six- Sigma DMAIC process: Define–Measure–An- alyze–Improve–Control. Both are used in for- mal problem-solving exercises. Many of you are also familiar with the General Scientific Method: • Define the question/make observations • Gather information and facts • Form hypothesis • Perform experiments and collect data • Analyze data • Interpret data and draw conclusions • Summarize results In a future column, I will present a more de- tailed discussion of problem-solving and meth- odology. For purposes of this month's column, a less formal approach is used. e engineers and operators determined the etching process was in control. Data supports that statement. Not all part numbers processed by the fabricator exhibited this condition. Looking back on the plating operation, samples of randomly selected part numbers not yet etched were checked for tin plat- ing thickness. While plat- ing thickness within the vias met minimum thick- ness requirements (0.30- 0.35 mils), there were pads showing considerably less tin (0.12-0.15 mils); and even thinner on the knees of some holes. Armed with this information, the team de- termined as a first approach to review the tin electroplating process as well as any issues in the control of the tin process. e information gathered provided the following: • Tin plating thickness was within specification in the holes • Tin plating thickness on some part numbers showed very thin tin on the surface (pads) but not within the vias • Electrical connections were checked to ensure that sufficient current was flowing from the power supplies to the cathodes (the boards) • Tin plating was non-uniform on the pads (in many cases) and very thin over the knee of some of the larger diameter vias (in most cases this occurred randomly) Now, as a point of further information, the fabricator was using a semi-bright tin plating process. is included controlling two separate organic addition agents. One of the additives is a grain refiner and wetting agent designed to insure a more even plating distribution across the panel. e second additive is used to im- prove throwing power, especially in small di- ameter vias. Upon further analysis, it was dis- covered that the ratio of the two additives were Figure 2: The tapering of the copper plating moves from the center of the hole to the knee and pad of the hole.