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82 SMT007 MAGAZINE I JULY 2021 tively and accurately measured by the 4-point technique and by taking in to account the effect of temperature on film electrical resistance. e film temperature must be measured using a thermocouple with fine wires. e film elec- trical resistance corrected for temperature is inversely proportional to the film thickness remaining. e rate of decrease of remaining film thickness is the corrosion rate of the film and is used to characterize the corrosion pro- tection provided by the conformal coating. Test environmental conditions in a modified iNEMI flowers of sulfur chamber at 40°C are aggressive enough for the conformal coating testing. e advantage of not using too aggressive condi- tions is that the degradation mechanism in the test is the same as that in the field. SMT007 References 1. ASHRAE white paper, Particulate and Gaseous Contamination in Datacom Environments, 2 nd Edi- tion, ASHRAE, Atlanta, GA, USA. 2. R. Danilak, "Why energy is big and rapidly growing problem for data centers," https:/www. forbes.com, 15Dec 2017. 3. Airside economizers and ASHRAE standard 90.1-2013, Trane Engineers Newsletter, vol 44-2. 4. O. V. Geet, "A method for estimating poten- tial energy ad cost savings for cooling existing data centers," NREL, https://www.nrel.gov/docs/fy17osti/ 68218.pdf. 5. Cole M., L. Hedlund, G. Hutt, T. Kiraly, L. Klein, S. Nickel, P. Singh, T. Tofil, "Harsh Environment Impact on Resistor Corrosion," SMTA International Pro- ceedings, 2010 6. Lembke P., M. Cole, T. Tofil1, J. Porter, J. Wertz, J. Wilcox, M. Gaynes, M. Meilunas and H. Rubin, "Test- ing and Mitigating Silver Sulfide Corrosion," SMTA International, Rosemont, IL, Oct 2018. 7. Cole M., J. Porter, J. Wertz, M. Coq, M. Meilunas, J. Wilcox, "Effectiveness of Conformal Coatings In Preventing Resistor Silver Sulfide Corrosion," SMTA International, Rosemont, IL, Sept 2016. 8. Singh P., Characterization of conformal coat- ings, SMTA International, San Diego, Feb 2015. 9. Singh P., "Conformal Coating Characterization Using Stacked Thin Films," 2020 Pan Pacific Micro- electronics Symposium .10-13 Feb 2020. 10. Singh P., L. Palmer, Fu H., D. Lee, J. Lee, K. Guo, J. Liu, S. Lee. G. Tong, C. Xu, "Round Robin Eval- uation of the iNEMI Creep Corrosion Qualification Predicting field performance oen requires accelerated testing involving higher tempera- tures and harsher environments to shorten the test times to convenient durations. A down- side of harsher conditions is that they may unduly overstress the hardware thus chang- ing the failure mechanism from one occurring in the field. A better approach is to keep the test conditions close to or the same as the field conditions and to shorten the test time by improving the sensitivity of detection of the hardware degradation. e latter approach was taken in this paper by characterizing con- formal coatings based on the corrosion rates of coated thin films that can be measured with down to +/-1 nm sensitivity. As a result, there is no need to accelerate the test condi- tions. is and earlier studies indicate that the environmental conditions in a flowers of sulfur chamber at 40°C are adequate for test- ing conformal coatings [8,9] . In this study, the chamber air was not mechanically stirred. In future studies, we will study the role of gentle mechanical stirring of the air in the flowers of sulfur chamber. Conclusions e study provides additional evidence that conformal coatings can be evaluated by the degree of corrosion protection they provide to the coated copper and silver films. e corro- sion rates of metal thin films can be very effec- A downside of harsher conditions is that they may unduly overstress the hardware thus changing the failure mechanism from one occurring in the field.