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February 2016 • The PCB Magazine 87 debris, or over plating? If it was over plating, was it caused by an incorrect plating program, incorrect plating square inch data, inaccurate copper thickness measurement or a tool? See where this is going…there are multiple permu- tations of each potential root cause that needs to be broken down and evaluated. When the quality group runs the monthly quality report, the defect Pareto will not be very effective if ge- neric, broad-based defect codes are used. Peel- ing back the onion, layer-by-layer, can be a long and tedious process, but it will be very difficult to attack the heavy-hitters by analyzing the symptoms and not the source. Tools There are many RCA tools available, includ- ing Ishikawa Cause & Effect Diagrams, Fault Trees, Brainstorming, Scatter Diagrams, DOE (design of experiment), and the 5 Whys tech- nique. The 5 Whys have become a very popular and highly effective RCA tool. The technique gained prominence when it became an integral part of the Toyota Production System in the 1970s. By continually asking "Why?" (5 times seems to be effective, but it could be four or it could be seven) you can quickly peel away the symp- toms and drive to the true root cause (Figure 1). While embroiled in the "why" game with your five-year-old, you probably never imagined that they were using an advanced root cause analysis technique on you! Ah, the wisdom of children. Three Types of Causes The basic premise of RCA is that it assumes that systems and events are interrelated. You have heard the maxim, "For every action there Figure 2: CSI-style root cause analysis. root Cause analysis: Csi for the pCb industry

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