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26 The PCB Magazine • April 2016 2. Establish whether operating procedures were followed and whether an assignable cause can be quickly identified as the reason behind the problem. • Only continue into more detailed analysis if the initial questions do not lead to an obvious answer • Even if the answer appears to be obvious, confirm the answer by operation of the process before closing the project 3. Develop a clear, concise problem state- ment that quantifies the problem whenever possible and reduces the scope of the investiga- tion to a manageable size. 4. Gather all pertinent data and facts. • Use SPC, historical data, records, logs, etc. • This includes temperature charts, analysis records, maintenance logs, etc. 5. Perform a causal analysis. • Producing out-of-specification parts requires immediate action (i.e., shut down the process) • Out-of-control processes require determination as to whether the process can continue to operate • Severe process variation requires evaluation of the severity and effect of the problem on the final product 6. Develop an action plan that includes the procedures for addressing products produced during out-of-specification or out-of-control conditions. The plan should also indicate who should make those decisions. These issues in- clude but are not limited to: • Disposition of the defective material (repair, scrap, replace, etc.) • Checking the effect on scheduled delivery • Informing the effect on scheduled delivery • Request for non-conformance authority or material review board (MRB) action • Establish a corrective action plan to reduce or eliminate the likelihood of recurrence 7. Conduct a measurement system evalua- tion, which is a means used to detect and iden- tify the problem. This includes not only the measuring apparatus, but also: • The sampling method • The operator (and his/her instructions) • Accuracy and calibration of equipment • Environmental factors (i.e., lighting, temperature, and relative humidity) 8. The variation inherent in the measure- ment of attribute data and responses that are subjective in nature can be addressed. The eval- uation is more complex in nature, but it is still an essential part of the analysis of the problem. IPC-9191 (General Guidelines for Implemen- tation of SPC) discusses this subject in greater detail. For further reading and learning on this subject, please review the IPC-9121, a new stan- dard for understanding and preventing printed circuit board defects. This handbook provides problems, causes and possible corrective actions related to PWB manufacturing processes. To keep this document current, readers are encour- aged to submit process problems with photos as well as proposed causes and solutions to the IPC 7-24 Printed Board Process Effects Handbook Subcommittee for consideration in future revi- sions of this document [1] : Finally, one should never assume that mak- ing one small change in a process (new mate- rial, photoresist, specialty cleaner, etc.) does not require validation. As an example, a fab- ricator made a switch to another acid cleaner on its pattern plating line. The thought pro- cess was that the new cleaner (similar to the present process) would provide additional residue solubilizing properties. The result of this change was that the new cleaner attacked the sidewalls of the exposed resist, creating plating defects including copper adhesion failures and pitting. In this case the fabricator neglected the cardinal rule for considering a process change: Performing the initial capabil- ity study. These capability studies are ideally done before the process is accepted for produc- tion. This means creating a match between a proCess engineer's guiDe to effeCtively troubleshooting pWb DefeCts