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20 The PCB Magazine • April 2016 well as to provide anchoring sites for subse- quent copper metalization. It is conceivable that the solvent swell (the first process step in the alkaline permanganate process) is not sufficiently weakening the polymer-polymer bonds in the resin. This will result in reduced resin removal and insufficient topography. First and foremost, the defect or issue must be properly identified in order to design a plan of attack. And again, I cannot stress enough the importance of up and downstream processing. Looking into methods to troubleshoot deeper, determine whether or not proper oper- ating procedures were followed. Did the process change in some way from the standard? Com- pare the defective product to a non-defective one. Was the process operating within the spec- ified parameters? Don't take anyone's word for it. Check this out thoroughly! On way too many occasions, significant loss has been incurred be- cause the process or processes were run out of spec. Famous last words: We checked every- thing an hour ago and all is good! Simple analysis or control procedures would have prevented such an occurrence. If the anal- ysis shows that the chemistry, dwell times, op- erating temperatures, etc., are not in control, then bring the operation to a halt until the cor- rections are made. Then run some tests to see of these corrections solve the problem. If this does not correct the problem, then the team must sit down to determine other possible causes for the defect. Possible Causes The rule of thumb here is to keep the trou- bleshooting project as 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. Gath- er all pertinent information including statistical process control (SPC) charts, temperature logs, analysis records (including record of calibration and analytical standards) and the like. Then develop a cause-and-effect diagram. Fish-bone diagrams serve this purpose 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 pro- cess audit is a must in this situation. Hopefully, you have a reliable supplier or suppliers who work with your company in close partnership. Ongoing process audits jointly and separately performed by your supplier and designated in- dividuals in the fabricator's facility should be standard operating procedure. Process audits alert the manufacturer 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 associ- ated with the electrodeposition process, simply processing the PWB in the acid copper plat- ing solution for the required time and current density should yield whether or not the copper plating process or the equipment (e.g., copper plating anodes, rectifier, electrical connections, etc.) are the cause. If not, then one must exam- ine the previous steps. Are there discontinuities in electroless copper deposit or direct metal- ization process causing thin plating? 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. Above all, after select- ing the processes and test procedures to be im- plemented, test these assumptions with vigor. Time is money. Hopefully, these actions will identify the suspect cause(s) of the defect. When the prob- lem is located, corrective action must be imple- mented. Determine what measures will be tak- en to ensure that the problem does not reoccur. Redefine the process control window. Set up a proCess engineer's guiDe to effeCtively troubleshooting pWb DefeCts " First and foremost, the defect or issue must be properly identified in order to design a plan of attack. "