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82 SMT Magazine • November 2016 sis of the study was to compare what is currently available in- dustry wide to ascertain which technique was better at predict- ing reliability. Mark Northrup, who is the primary researcher on this project, approached me and asked a couple of questions. The first question he asked was, "Do you know of any studies that show a correlation between the chromatography testing and any IPC electrical test?" To which I responded, "No, I wasn't aware of any." He followed up with a second question, which was, "Is one a better predictor of reliabil - ity?" To that I said, "I don't have an answer." Then he asked me if I'd be interested in partici- pating in a study to try and determine an answer and that' s how I got involved. Goldman: I take it you guys have worked on this for some time now? Russeau: Well, Mark and I have had numer- ous discussions about the limitations of circuit board cleanliness testing for the past few years. Mark motivated us a little over a year ago to ini- tiate this study, and we did the testing over a span of about six months. We looked at a to- tal of eight different groups of CAF coupons. The CAF coupons we used were the ones that the PCQR² document calls out. We looked at the ionic cleanliness of the coupons before they went into CAF using ion chromatography as a baseline. Subsequently, these tested coupons were submitted for CAF testing. Upon comple- tion of the CAF testing, coupons were retested via ion chromatography for cleanliness again. The idea was to compare residue levels before and after to determine what changes occurred and if the chromatography could predict a CAF failure. Our hypothesis was that we would see a correlation between the CAF and IC tests. We applied IEC Electronics ionic cleanliness limits to the ion chromatography test results and the current criteria used for the PCQR 2 test results to evaluate our hypothesis. We postulated that if there were residues that exceeded IEC Elec- tronics ionic cleanliness limits before the CAF test, that corresponding failures should occur in the CAF test re- sults. Of the eight groups, we had four groups that failed IC testing based on IEC Electronics ionic cleanliness limits and also failed CAF testing. The other four groups failed IEC Electron- ics ionic cleanliness limits, but passed CAF testing. Based on this data, we drew the conclusion that there wasn't a significant correlation between the two tests, and in addition to that, we could not say definitively that either one of the tests was a better reliability predic- tor. We are still in the process of reviewing our methodologies and the variables that we want to do to try to improve the testing. We're just here today to present our initial data, hopefully get other people interested in the topic, solicit input as well for other ideas, and start a discus- sion of how to improve risk prediction for mod- ern devices. Remember, this is just an initial test and is in no way definitive. Goldman: I understand you're presenting some early data; it sounds like there's much more to be done. Russeau: That's correct. We have a lot more test- ing to do. Within IPC, I am the chairman of the 7-11 Test Methods subcommittee. I also sit on other task groups related to chromatogra- phy and board cleanliness. We deal with these issues within those task groups all the time. We know there are limitations in the IPC test meth- ods and that industry demands improved test- ing methods as electronics continuously in- crease in density. We're working both from the standpoint of industry people who are com- ing together on their own to look for ways to make improvements, and then we're also sup- porting the IPC test methods committees (e.g., 7-11 subcommittee where we're starting to re- quire validation of methods). Ultimately, we're trying to make sure that IPC test methods cor- relate and have solid data to support their in- tended purpose, so we can get to better reliabil- ity predictors. INCREASING RELIABILITY THROUGH PREDICTIVE ANALYSIS Joe Russeau

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