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20 PCB007 MAGAZINE I DECEMBER 2019 manageable as possible. Begin to brainstorm on the linkages in the up- and downstream processes and potential effects of process variation in these process steps. Gather all pertinent information, including SPC charts, temperature logs, analysis records (including a record of calibration and analytical stan- dards), etc. Then, develop a cause-and-effect diagram. Fish-bone diagrams serve this pur- pose well. At the risk of having hundreds of factors to investigate, only the most likely causes should be investigated first. This will serve to weed out those processes that are not contributing to the defect. A process audit is a must in this sit- uation. Hopefully, you have a reliable suppli- er or suppliers who work with your company in close partnership. Ongoing process audits jointly and separately performed by your sup- plier and designated individuals in the fabrica- tor's facility should be the standard operating procedure. Process audits alert the manufac- turer if a process is "drifting" out of the control window. Once the team has set up its test plan based on a narrowing of potential causes, the divide- and-conquer approach will aid in the efforts. For example, if one suspects that thin plating of copper in the hole is caused by problems associated with the electrodeposition process, simply processing the pwb in the acid copper plating solution for the required time and cur- rent density should yield whether or not the copper plating process or the equipment (cop- per plating anodes, rectifier, electrical connec- tions, etc.) are the cause. If not, then one must examine the previous steps. Are there discon- tinuities in the electroless copper deposit or direct metalization process causing thin plat- ing? Are there voids one cannot see? These are just some of the questions to be asked. Only a systematic approach will help solve problems expeditiously. Soft Skills There are a few other soft skills that I see as being absent in many of the facilities I visit. Here are a few of these critical soft skills that you should know. Design of Experiments (DOE) Understand how to design an experiment. This requires brainstorming and certainly a team approach to solving the problem. DOE methods are for engineers to employ during ex- perimentations. Whether it is problem-solving or process development, the DOE experimental method provides the most efficient means of determining the correct answers and is critical for troubleshooting. It helps you understand those variables that are weighing more heavily on the issue and those that are of little conse- quence. Start with a brainstorming session and con- struct a fish-bone diagram or something simi- lar. This will help put into perspective the pos- sible causes of the problem you are seeing. Then select from there and focus on the most likely causes of the defect based on everyone's input. Then, design the experiment to investi- gate the most likely causes. Total Quality Control (TQC), Six Sigma, Statistics, and Curve Fitting TQC and Six Sigma is the philosophy of con- tinuous improvement through statistical tech- niques and a commitment to excellence. The plan-do-check-act (PCDA) process is a central theme using the nine basic tools: cause-effect, process flow, Pareto, scatter, histograms, pro- cess capability index, control charts, time se- ries, and check sheets. A useful book is the Sta- tistical Engineering Handbook available from NIST and free to everyone to download. A fun- damental place to start is how to "Select The Right Statistical Tools" (measurement system analysis, SPC, comparative methods, DOE). At the risk of having hundreds of factors to investigate, only the most likely causes should be investigated first.

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